JP3264450B2 - Method and apparatus for measuring electric field on photoreceptor surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measuring method, and more particularly to a method and an apparatus for measuring an electric field on a photosensitive member surface for measuring an electric field generated by an electrostatic field on the photosensitive member surface in an electrophotographic process.

[0002]

2. Description of the Related Art In an electrophotographic process, an image is based on an electrostatic latent image on the surface of a photoreceptor. This is important for evaluating, analyzing, and inspecting the photoconductor. However, since the electrostatic latent image on the photoreceptor is an electrostatic field having a high voltage, many problems need to be solved for direct measurement.

For example, in the manufacturing process of a photoreceptor, an appearance inspection of the surface of the photoreceptor is performed as a defect inspection of the photoreceptor. Appearance defects such as aggregation due to contamination have been examined. Such a defect on the photoconductor surface has been inspected visually or by performing image processing based on a luminance distribution of the photoconductor surface captured by a television camera. However, this defect detection method has a problem that the luminance distribution on the surface of the photoconductor does not always match the characteristics when an electrostatic latent image is recorded on the photoconductor.

In recent years, a method of forming an electrostatic latent image by fine dots is often used, as represented by a laser printer and a digital copying machine, and high gradation reproducibility is required for the image itself. Therefore, a method of measuring an electrostatic latent image having a high spatial resolution in consideration of a fine dot size is expected.

Therefore, in the related art, a DC amplification type measuring method has been widely used for measuring an electrostatic field formed by an electrostatic latent image on a photosensitive member. The basic configuration of this DC amplification type measurement circuit will be described with reference to FIG. In this case, the electric charge induced in the measuring electrode 1 by bringing the measuring electrode 1 close to the measuring object (photoconductor) 2 is converted into a voltage by the measuring capacitor 3 and amplified by the amplifier 4 having a high input impedance. Further, since the electric charge flowing from the outside is accumulated in the measuring capacitor 3, the discharging switch 5
As a result, the electric charge charged in the measuring capacitor 3 is discharged.

[0006]

However, in such a conventional system, it is necessary to reduce the size of the measuring electrode 1 in order to obtain a high spatial resolution. For example, 400
The electrostatic latent image of dpi has a dot pitch of about 60 μm,
In order to observe this dot shape, at least 10μ
A spatial resolution of about m is required, and an advanced processing technique is required to configure an electrode size that assumes this spatial resolution.

When the size of the measuring electrode 1 is reduced, the amount of electric charge induced in the measuring capacitor 3 is reduced. Therefore, in order to obtain a sufficient output voltage, the capacity of the measuring capacitor 3 must be reduced. If the capacitance of the measuring capacitor 3 is reduced, the measured voltage is likely to fluctuate due to the flow of a minute current from the outside or noise due to the minute measuring capacitance.

Further, in such a measurement of a DC amplification type electrostatic field, since a metal electrode is inserted into an electric field to be measured, the electrostatic field is disturbed, which is inconvenient for high precision measurement. In addition, since the electrostatic field of the photoconductor is directly measured, it is a direct method for inspecting the photoconductor for defects. When performing a defect inspection of the body surface, it is necessary to scan the measurement electrode 1 by any method in order to measure and observe a wide range.

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

According to the first aspect of the present invention, an electric field sensor is formed by depositing a light wave reflecting portion made of a dielectric on one surface of an electro-optic crystal having an electro-optic effect. The electric field sensor is disposed near the surface of the photoconductor to be measured so that an electric field due to a latent image charge charged in the body penetrates the inside of the electro-optic crystal, and the electric field sensor faces the light wave reflecting portion of the electric field sensor. Circularly polarized light having a predetermined polarization state is incident as probe light from the other surface of the electro-optic crystal, and the probe light passes through the electro-optic crystal and is reflected by the light wave reflecting portion to be reflected by the polarization splitter. The light is separated into two orthogonal polarization components, the light intensity of each of the separated polarization components is detected as an electric signal by a light receiving element, and each of the detected light intensity signals is input to a division operational amplifier. Detecting a change in the polarization state of the probe light on the basis of a division output signal of the division operation amplifier,
The electric field penetrating the electro-optic crystal was measured from the change in the polarization state of the probe light.

According to the second aspect of the present invention, an electric field sensor is formed by depositing a light wave reflecting portion made of a dielectric material on one surface of an electro-optic crystal having an electro-optic effect, and the latent image charged on the photosensitive member to be measured is formed. The electric field sensor is disposed in the vicinity of the surface of the photoconductor to be measured so that an electric field due to image charge passes through the inside of the electro-optic crystal, and the other of the electro-optic crystals facing the light wave reflecting portion of the electric field sensor. Circularly polarized light having a predetermined polarization state is incident from the surface as probe light, and the probe light passes through the electro-optic crystal and is reflected by the light wave reflection portion to be reflected by the polarization splitting element and each arm thereof by λ. /
Leading to a Michelson-type polarization interferometer having a four-wave plate,
The light intensity change of the interference signal output from the Michelson-type polarization interferometer is converted into an electric signal by a light receiving element, and a change in the polarization state of the probe light is detected based on the light intensity change of the electric signal. The electric field penetrating the electro-optic crystal was measured from the change in the polarization state of the probe light.

According to the third aspect of the present invention, an electric field sensor is formed by depositing a light wave reflecting portion made of a dielectric on one surface of an electro-optic crystal having an electro-optic effect, and the latent image charged on the photosensitive member to be measured is formed. The electric field sensor is disposed in the vicinity of the surface of the photoconductor to be measured so that an electric field due to image charge passes through the inside of the electro-optic crystal, and the other of the electro-optic crystals facing the light wave reflecting portion of the electric field sensor. The orthogonal two-frequency light generated by the orthogonal Zeeman laser is used as probe light from the surface so that the main axis of the refractive index ellipsoid in the plane of the electro-optic crystal orthogonal to the probe light coincides with the probe light. The reflected light passing through the crystal and being reflected by the light wave reflector is arranged on a polarization separation element and its respective arms by λ.
マ イ wavelength plate and a Michelson-type polarization interferometer, and the light intensity change of the interference signal output from the Michelson-type polarization interferometer is converted into an electric signal by a light receiving element.
The electric field penetrating the electro-optic crystal is measured by electrically detecting the phase change of the electric signal.

According to a fourth aspect of the present invention, an electric field sensor having an electro-optic crystal having an electro-optic effect and a light-wave reflecting portion made of a dielectric material deposited on one surface of the electro-optic crystal is provided with an electric field caused by a latent image charge charged on a photosensitive member to be measured. Is disposed in the vicinity of the surface of the photoreceptor to be measured so as to penetrate the inside of the electro-optic crystal, and enters as probe light from the other surface of the electro-optic crystal facing the light wave reflecting portion of the electric field sensor. Provided is a light source that emits circularly polarized light having a polarization state, and a polarization splitting element into which the reflected light reflected by the light wave reflecting portion is passed when the probe light emitted from the light source passes through the electro-optic crystal. A Michelson-type polarization interferometer having a λ / 4 wavelength plate on each arm is provided, and an interference signal output from the Michelson-type polarization interferometer is separated from the orthogonal polarization axis of the polarization separation element by 45 °. An imaging means having an observation surface for observing as a contour line of the surface potential of the photoreceptor to be measured through an angled polarizing plate was provided.

According to a fifth aspect of the present invention, an electric field sensor in which a light-wave reflecting portion made of a dielectric material is deposited on one surface of an electro-optic crystal having an electro-optic effect is used as an electric field due to a latent image charge charged on a photosensitive member to be measured. Is disposed in the vicinity of the surface of the photoconductor to be measured so as to penetrate the inside of the electro-optic crystal, and a predetermined light which enters as probe light from the other surface of the electro-optic crystal facing the light wave reflecting portion of the electric field sensor. Providing a light source that emits circularly polarized light having the polarization state of, a polarization separation element where the probe light emitted from the light source passes through the electro-optic crystal and the reflected light reflected by the light wave reflection unit enters, The λ /
A phase change of a total of one wavelength is provided at equal intervals to the wavelength λ of the light wave in a direction parallel to the optical axis of the light wave incident on the four-wavelength plate and the mirror, and the mirror of one arm of the polarization separation element. Is provided with a Twyman-Green interferometer having a minute displacement applying mechanism for moving the mirror by N steps at an interval of λ / (2N), and interfering signals output from the Twyman-Green interferometer to be orthogonally polarized by the polarization splitter It has an observation surface for observation through a polarizing plate at an angle of 45 ° with respect to the axis, and picks up N interference fringe images formed on this observation surface each time the mirror is moved in N stages by the minute displacement applying mechanism. Image pickup means for performing N
A / to convert one interference fringe image into a digital interference fringe image
D conversion means, and superimposition means for superimposing a signal variation between N pixels at each pixel of the interference fringe image digitally converted by the A / D conversion means with a sine signal forming one cycle between the N images. This superimposing means extracts only components having a sine signal as a fundamental wave from signal fluctuations between N pixels in each pixel of the interference fringe image on which the sine signal is superimposed, and converts the phase of the fundamental wave component to each of the interference fringe images. A phase calculating means for independently calculating the pixel, and a surface potential distribution calculating means for calculating a surface potential distribution of the measured photoreceptor based on a phase at each pixel of the interference fringe image calculated by the phase calculating means. Electric field measuring means provided.

According to a sixth aspect of the present invention, an electric field sensor in which a light-wave reflecting portion made of a dielectric material is deposited on one surface of an electro-optic crystal having an electro-optic effect is used to form an electric field caused by a latent image charge charged on a photosensitive member to be measured. Is disposed in the vicinity of the surface of the photoconductor to be measured so as to penetrate the inside of the electro-optic crystal, and a predetermined light which enters as probe light from the other surface of the electro-optic crystal facing the light wave reflecting portion of the electric field sensor. Providing a light source that emits circularly polarized light having the polarization state of, a polarization separation element where the probe light emitted from the light source passes through the electro-optic crystal and the reflected light reflected by the light wave reflection unit enters, The λ /
A Twyman-Green interferometer having a four-wavelength plate and a mirror, and a mirror minute angle tilting means for tilting the mirror of one arm of the polarization separation element by a small angle; By tilting the mirror of one arm by a small angle, a light wave that is incident on this mirror and reflected and returned to the polarization splitting element generates a linear phase delay in a plane orthogonal to the light wave traveling direction, and the Twyman Green A spatial carrier signal is generated in one direction of the interference signal output from the interferometer, and the interference signal carrying the spatial carrier signal is passed through a polarizing plate that forms an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. A two-dimensional or one-dimensional imaging device parallel to the direction in which a spatial carrier signal is generated for capturing an interference fringe image formed on the observation surface having an observation surface for observation. A / D conversion means for converting a two-dimensional or one-dimensional image captured by the imaging means into a digital interference fringe image, and a two-dimensional interference fringe image digitally converted by the A / D conversion means. In the case of an image, one for each scanning line parallel to the direction in which the spatial carrier signal is generated.
In the case of a two-dimensional image, the dividing means divides the signal sequence into a plurality of sections each having one cycle of the spatial carrier signal for each line output, and each section divided by the dividing means has the same spatial carrier signal frequency as the spatial carrier signal frequency. Superimposing means for superimposing a sine signal, and calculating a phase of an interference fringe image signal by extracting a fundamental component of a Fourier series having a spatial carrier signal as a fundamental wave for each of the sections where the sine signal is superimposed by the superimposing means. And an electric field measuring means for calculating a surface potential distribution of the photoreceptor to be measured based on the phase of the interference fringe image signal calculated by the phase calculating means.

According to a seventh aspect of the present invention, an electric field sensor in which a light-wave reflecting portion made of a dielectric material is deposited on one surface of an electro-optical crystal having an electro-optical effect is used to generate an electric field due to a latent image charge charged on a photosensitive member to be measured. A predetermined light source is provided near the surface of the photoreceptor to be measured so as to penetrate the inside of the electro-optic crystal, and is incident as probe light from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. A light source that emits circularly polarized light having a polarization state is provided, and a probe light emitted from the light source passes through the electro-optic crystal, and a reflected light reflected by the light wave reflection unit is incident thereon. Λ / 4 arranged on each arm of polarization splitting element
A Twyman-Green interferometer having a wave plate and a mirror, and a mirror minute angle tilting means for tilting the mirror of one arm of the polarization splitting element by a small angle is provided, and one of the polarization splitting elements is provided by the mirror minute angle tilting means. By tilting the mirror of the arm of the arm by a small angle, a light wave incident on the mirror, reflected and returned to the polarization separation element generates a linear phase delay in a plane orthogonal to the light wave traveling direction, thereby causing the Twyman-Green interference. A spatial carrier signal is generated in one direction of the interference signal output from the meter, and the interference signal carrying the spatial carrier signal is observed through a polarizing plate that forms an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. Two-dimensional or one-dimensional imaging means parallel to the direction in which the spatial carrier signal is generated for capturing an interference fringe image formed on the observation surface having an observation surface to be observed A / D conversion means for converting a two-dimensional or one-dimensional image captured by the imaging means into a digital interference fringe image, and an interference fringe image digitally converted by the A / D conversion means into a two-dimensional image In the case of, the Fourier transform in the spatial carrier distribution direction is obtained for each scanning line parallel to the spatial carrier signal generation direction, and in the case of a one-dimensional image, for each line output, and the line spectrum near the spatial carrier signal frequency is calculated as the spatial carrier signal frequency. Window function extracting means for extracting the spatial carrier signal frequency equivalent with a window function having a bandwidth with the center frequency as the center frequency, and the line spectrum extracted by the window function extracting means is shifted in the DC direction by the spatial carrier signal frequency. Phase calculation means for calculating the phase of the interference fringe image signal by performing an inverse Fourier transform on the interference fringe image signal, and interference calculated by the phase calculation means. An electric field measuring means having a surface potential distribution calculating means for calculating a surface potential distribution of the measured photoreceptor based on the phase of the fringe image signal.

[0025]

[0026]

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[0029]

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[0031]

[0032]

According to the first aspect of the present invention, since the polarization detection method using the division operational amplifier is used, the fluctuation of the light intensity of the probe light is canceled, and the electric field can be measured with high accuracy.

According to the second aspect of the present invention, according to coherent detection using a Michelson-type polarization interferometer,
Since the phase difference given to the probe light reciprocating in the electro-optic crystal by the electro-optic effect is converted into light intensity by the interference of the probe light itself, it becomes possible to generate interference fringes with high visibility, , It is possible to detect a signal having a high S / N ratio, and it is possible to follow a phase change on the order of wavelength, so that high measurement accuracy can be obtained.

According to the third aspect of the invention, by performing optical heterodyne-type polarization detection using an orthogonal Zeeman laser, the reading accuracy of the phase difference delayed by the electro-optic crystal of the electric field sensor is greatly improved, In particular, since the phase difference of the probe light is converted to an electrical signal, phase detection of about 2/100 of the phase can be detected by well-known phase detection technology, which enables high-precision and high-resolution electric field measurement. Becomes

According to the fourth aspect of the present invention, since the interference signal of the Michelson-type polarization interferometer is observed as the contour line of the surface potential of the photosensitive body to be measured by the imaging means, conventionally, a probe-like sensor is scanned. It is possible to perform two-dimensional measurement of the electric field while performing, enabling highly reliable multi-point parallel sensing, and visually monitor the measured field as an interference fringe image in real time Becomes

According to the fifth aspect of the present invention, the phase analysis of the interference fringe image is carried out, so that the phase conventionally obtained by visually counting the number of interference fringes can be quantitatively changed by 2π or less. Can be detected, and the spatial resolution is determined by the pixels of the imaging means such as a CCD camera.
By measuring the phase spatially and completely independently for each pixel, a measuring device with high accuracy, reliability, and reproduction can be constructed.

According to the sixth aspect of the present invention, the phase is analyzed from the interference fringe image into which the spatial carrier is introduced, so that the spatial resolution is disadvantageous as compared with the fifth aspect of the invention, but it is very small. Since a mirror minute displacement applying mechanism for displacing the mirror is not required, and its spatial phase distribution can be calculated from one interference fringe image,
The electric field can be measured efficiently in terms of processing time. In particular, since the arithmetic processing portion is an algorithm that can be easily implemented in hardware, it can be easily extended to real-time measurement at a video rate.

According to the seventh aspect of the present invention, the spatial resolution is substantially the same as that of the sixth aspect of the present invention. Since it occurs, it is possible to detect a signal having a gradual change in phase of 2π or less with a high S / N,
Further, since the smoothing effect depends on the width of the window function, the width of the window function can be tuned at the processing stage, so that a more optimal electric field measurement system can be constructed.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is to convert information contained in an electric field into an optical physical quantity using a substance having an electro-optical effect, and optically measure the electric field. Therefore, prior to the description of the embodiments of the present invention, the basic principle of electric field measurement will be described. The Pockels effect and the Kerr effect are generally known as an electro-optic effect for converting electric field information into an optical physical quantity. here,
The characteristic of the electric field measurement using the electro-optic effect is that the information exchange from the electric field to the light is performed inside the substance having the electro-optic effect, so that no special electric circuit or power supply for conversion is required. If the electro-optic effect of the measurement object itself is used, the electric field at the measurement point will not be disturbed at all. When a sensor is used, the measurement point is electrically insulated because the sensor portion can be formed only of a dielectric material, and the electric field at the measurement point is not significantly disturbed. Since the information transmission medium is light, it is resistant to electrically induced noise. In principle, response characteristics on the order of GHz can be expected. And five more.

Next, the electro-optical effect will be briefly described. When an electric field is externally applied to a certain substance, the polarization state of the substance changes, and as a result, the refractive index of light propagating through the substance may change. This is the electro-optic effect. The relationship between the refractive index n and the electric field E is as follows, where Pockels constant is a, and Kerr constant is b, n = n ₀ + aE + bE ² +... (1) The second term in equation (1) is the Pockels effect,
The term is the Kerr effect. The third and subsequent terms are minute and can usually be ignored. Further, the Pockels effect and the Kerr effect do not appear at the same time, and one of them remarkably appears depending on the symmetry of the crystal constituting the substance or the polarized molecular structure.

Here, a light wave E propagating through a substance is considered. The electric vector component of the light wave E can be a combination of two orthogonal linear polarization components Ex and Ey. Now, assuming that the orthogonal coordinates are x and y, each polarization component Ex and Ey
Is the propagation velocity in the material of the two orthogonal polarization components Ex,
Refractive indices n _x for each of the ey, is determined by n _y. At this time, the refractive index difference Δn is represented by Δn = n _x −n _y (2). When the refractive index difference Δn in the equation (2) is not zero, a difference in propagation velocity occurs between the two polarization components Ex and Ey, and the phase difference Δθ between the two orthogonal polarization components Ex and Ey after passing through the substance. Is generated. The phase difference Δθ is represented by A = (2π / λ) n ₀ ³ where λ is the lightwave wavelength, l is the length in the material propagation direction
· R _p · l, and B = 2πr _k · l, Pockels the r _p coefficient, car a r _k coefficient, and the Δθ ₀ and natural birefringence, Δθ = Δn (2πl / λ ) = Δθ 0 + AE + BE 2 .. ..… (3) Before the light wave E is incident on the substance, the polarization component E
If the phase difference Δθ between x and Ey is zero, the light wave E is linearly polarized. After the light wave E of the linearly polarized light passes through the substance, the polarization state becomes elliptically polarized light by generating the phase difference Δθ shown in the equation (3). When the substance has the Pockels effect, the phase difference Δθ changes linearly with respect to an electric field applied from outside to the substance. By measuring the change in the polarization state, an electric field penetrating through the substance can be optically measured.

According to the principle of the electric field measurement described above,
First Embodiment A first embodiment will be described with reference to FIGS. This embodiment relates to a method for measuring an electric field generated by a latent image charge on the surface of a photoconductor to be measured. FIG. 1 shows an electric field measuring system according to the present embodiment, in which a photoconductor (measured photoconductor) 8 having a photosensitive layer 7 applied on a substrate 6 is provided. The surface of the photosensitive layer 7 of the photosensitive member 8 is charged with a latent image charge 9 for forming an electrostatic latent image. In the vicinity of the surface of the photoconductor 8 (the surface of the photosensitive layer 7), an electro-optic crystal 10 having an electro-optic effect is formed. It is arranged to pass.

On one surface of the electro-optic crystal 10 facing the photoreceptor 8, a dielectric mirror 12 as a light wave reflecting portion is deposited, whereby the electric field sensor S
Are formed. The dielectric mirror 12 has a function of reflecting light that passes through the electro-optic crystal 10 and enters the other surface of the electro-optic crystal 10 facing the dielectric mirror 12.

On the other hand, a semiconductor laser (light source) 14 for emitting light having a predetermined polarization state via a beam splitter 13 is provided above the other surface of the electro-optic crystal 10 facing the dielectric mirror 12. It is arranged. As a result, the light having a predetermined polarization state emitted from the semiconductor laser 14 is used as probe light as the probe light through the beam splitter 13 for the electro-optic crystal 10 of the electric field sensor S.
, Passes through the inside of the electro-optic crystal 10, is reflected by the dielectric mirror 12, is again incident on the beam splitter 13, and is reflected by the beam splitter 13 in a direction perpendicular to the incident light. Is set to And on the optical path of the reflected light of the beam splitter 13,
A photo detector 15 as a light receiving element is provided. The output side of the photodetector 15 includes an amplifier 1
6 are connected.

In this embodiment, in the present embodiment, the dielectric mirror 1 of the electric field sensor S uses light having a predetermined polarization state emitted from the semiconductor laser 14 as probe light.
The probe light is made incident from the other surface of the electro-optic crystal 10 facing the electro-optic crystal 2, and as the probe light passes through the electro-optic crystal 10 and is reflected by the dielectric mirror 12,
The electric field penetrating the electro-optic crystal 10 is measured from the polarization state of light changed by the electro-optic effect of 0.

Here, the specific operation of this embodiment will be described with reference to FIGS. Only the p-polarized component of the light emitted from the semiconductor laser 14 reaches the electro-optic crystal 10 of the electric field sensor S by the beam splitter 13 and enters the electro-optic crystal 10 as linearly polarized light. At this time, the electric field 17 due to the latent image charges 9 of the photoconductor 8 is stored in the electro-optic crystal 10.
Exist, and the electric field 17 causes the electro-optic crystal 1
The main axis of the index ellipsoid at 0 changes. As a result, the light reflected by the dielectric mirror 12 and returned to the outside of the electro-optic crystal 10 causes a phase delay in the electric vector in a specific direction, and its polarization state changes slightly from linearly polarized light to elliptically polarized light.
That is, the probe light that has entered the electro-optic crystal 10 as linearly polarized light composed of the p-polarized component with respect to the beam splitter 13 passes through the electro-optic crystal 10, is reflected by the dielectric mirror 12, and enters the beam splitter 13 again. Sometimes s
That is, a polarized light component is generated. This s-polarized light component is reflected by the beam splitter 13 and
5 is incident. Then, the light intensity of the s-polarized light component is detected as an electric signal by the photodetector 15, and the electric signal is amplified by the amplifier 16 and output.

At this time, the light intensity detected by the photodetector 15 is a monovalent function of the phase delay due to the electro-optic effect. In particular, BSO, LiNb having the Pockels effect
In the case where the electro-optic crystal 10 made of a material such as O ₃ is used, the phase delay is one of the external electric fields 17 according to the equation (3).
It is expressed by the following function. Therefore, the value of the electric field 17 can be uniquely determined based on the light intensity detected by the photodetector 15.

In this case, the spatial resolution of the electric field 17 detected by the electric field sensor S in the horizontal direction (in-plane direction orthogonal to the probe light reciprocating in the electro-optic crystal 10 in FIG. 1) is within the electro-optic crystal 10. It is limited by the beam diameter of the reciprocating probe light. This is important for improving the spatial resolution when measuring the electric field on the surface of the photoconductor 8. In other words, it does not depend on the size of the electro-optic crystal 10, that is, it is not necessary to make the electro-optic crystal 10 minute. Rather, as shown in FIG. 2A, when the electro-optic crystal 10 is minute, the electric lines of force 11 formed by the latent image charges 9 are distorted due to the influence of the end face of the electro-optic crystal 10, and the electro-optic crystal 10 Since the internal electric field does not correspond to the surface charge distribution of the photoreceptor 8, as shown in FIG. 3B, the larger the electro-optic crystal 10 is compared with the spatial resolution to be measured, the more the probe light passes. In the vicinity of the electro-optic crystal 10, the disturbance of the electric flux lines 11 due to the influence of the end face of the electro-optic crystal 10 is advantageously eliminated.

As described above, in this embodiment, the electric field sensor S (probe) is constituted only by the dielectric mirror 12, so that the disturbance of the electrostatic field due to the measurement can be minimized. In addition, the spatial resolution of the measurement is determined by the beam diameter of the probe light, and the electro-optical crystal 10 does not disturb the field to be measured if it is somewhat larger than the spatial resolution to be measured in consideration of the influence of the end face on the field to be measured. This is advantageous from a viewpoint. Although a high voltage is generated on the surface of the photoreceptor 8, the electric field sensor S and the signal detecting unit (photodetector 1) are used for probing with light.
5) eliminates the metal part and enables wireless connection, and is not affected by external electromagnetic noise. Thus, the electric field 1 formed by the latent image charges 9 on the surface of the photoconductor 8
7 can be measured with high accuracy.

Next, a second embodiment will be described with reference to FIG. The same parts as those described in FIG. 1 are denoted by the same reference numerals. FIG. 3 shows a measurement system according to the present embodiment. As in the embodiment shown in FIG. The lines of electric force 11 from the electric charges 9 are arranged so as to pass through the inside of the electro-optic crystal 10. A light source 41 for emitting circularly polarized light having a predetermined polarization state is provided above the electric field sensor S in a direction perpendicular to the electric field sensor S.
Are arranged. As the light source 41, for example, a halogen lamp or a mercury lamp is used. The light source 41
A half mirror 43 is disposed on the optical path via a condenser lens 42. Thereby, the light source 41
Circularly polarized light emitted from the light enters the half mirror 43 as probe light via the condenser lens 42,
The light is reflected by the half mirror 43 to be incident on the electro-optic crystal 10 of the electric field sensor S, passes through the inside of the electro-optic crystal 10, and is reflected by the dielectric mirror 12 toward the half mirror 43. Is set to The half mirror 43, the polarizing plate (analyzer) 44, and the
An imaging lens 45 and an imaging camera (imaging means) 46 such as a CCD camera are sequentially arranged. However, the imaging camera 46 is set so that an image of the surface of the dielectric mirror 12 provided on the electric field sensor S is formed on the observation surface.

In such a configuration, the circularly polarized light emitted from the light source 41 enters the electro-optic crystal 10 of the electric field sensor S as probe light via the condenser lens 42 and the half mirror 43, and passes through the electro-optic crystal 10. Is reflected by the dielectric mirror 12 and again
0 and is reflected in the direction of the imaging camera 46. Here, the electric field 17 due to the latent image charges 9 is stored in the electro-optic crystal 10.
Exist, and the electric field 17 causes the electro-optic crystal 1
The main axis of the index ellipsoid at 0 changes. As a result, the light reflected by the dielectric mirror 12 and returned to the outside of the electro-optic crystal 10 causes a phase delay in an electric vector in a specific direction, and its polarization state changes slightly from circularly polarized light to elliptically polarized light. Here, since the polarizing plate 44 is provided on the entire observation surface of the imaging camera 46, only the linearly polarized light component in a specific direction is incident on the imaging camera 46 through the imaging lens 45.

At this time, the light intensity observed by the imaging camera 46 is a monovalent function of the phase delay due to the electro-optic effect. In particular, BS having the Pockels effect in the electro-optic crystal 10
When O, LiNbO ₃ or the like is used, the phase delay is expressed by a linear function of the external electric field according to the above equation (3), as in the embodiment shown in FIG. Therefore, the light intensity observed by the imaging camera 46 changes depending on the latent image charge 9 generated by the electrostatic latent image on the surface of the photoconductor 8, that is, the imaging output is the electrostatic image on the surface of the photoconductor 8. It will correspond to the latent image.

As described above, the density of the image picked up by the image pickup camera 46 as the light intensity corresponds to the electric field 17 generated by the latent image charges 9 formed on the surface of the photoconductor 8.
It is possible to directly image and observe the electrostatic latent image.
This makes it possible to observe the characteristics of the photoreceptor 8 and, for example, if a solid image or the like is written on the photoreceptor as an electrostatic latent image, an electrostatic defect on the surface of the photoreceptor 8 will occur. When it is present, it is possible to observe the defect existing on the surface of the photoconductor 8 as the density of the image. This is different from the conventional case where the luminance distribution on the surface of the photoconductor 8 is directly imaged and the defect is observed from the change in the density, and the reliability and the observation point are that the electric field 17 formed by the electrostatic latent image is directly observed. The accuracy will be even higher.

Next, a third embodiment will be described with reference to FIGS. The same parts as those described in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the electric field sensor S shown in FIG. 1 is inserted into an electrophotographic process development engine. That is, as shown in FIG. 4, the developing sleeve 18 of the developing engine held at the developing bias potential Vb and the photosensitive drum (photosensitive body to be measured)
An electric field sensor S is disposed between the electric field sensor S and the electric field sensor 19. As shown in FIG. 5, a prism 20 and a condensing lens 21 as a probe light guiding optical member into which probe light is incident are fixed on the upper surface of the electro-optic crystal 10 of the electric field sensor S, as shown in FIG.

Here, the gap between the developing sleeve 18 and the photosensitive drum 19 in the developing engine is generally several millimeters to 1 millimeter or less. Light is incident, and this probe light is collected by the condenser lens 21 and the prism 2.
By setting 0, the light is incident on the electro-optic crystal 10 from the normal direction of the surface of the photosensitive drum 19.
In practice, however, as shown in FIG. 6, the optical path between the beam splitter 13 and the condenser lens 21 is connected by a polarization maintaining optical fiber 22.

In such a configuration, the probe light reflected by the dielectric mirror 12 of the electric field sensor S enters the beam splitter 13 again via the prism 20, the condenser lens 21, and the polarization maintaining optical fiber 22, The light is reflected by the beam splitter 13 and received by the photodetector 15. The output signal of the photodetector 15 is amplified by the amplifier 16. By monitoring the output signal of the amplifier 16 outside the development engine, the electric field passing through the electro-optic crystal 10 is measured from the polarization state of the probe light changed by the electro-optic effect of the electro-optic crystal 10 of the electric field sensor S.

In this case, the lines of electric force 11 formed by the latent image charges 9 on the surface of the photosensitive drum 19 are drawn by the developing bias potential Vb of the developing sleeve 18 so as to penetrate through the inside of the electro-optic crystal 10, and are used during development. A developing electric field is formed. This makes it possible to measure the electric field on the surface of the photosensitive drum 19 which is close to the time of actual development.

In this embodiment, since the probing is performed by light, a wireless connection can be made between the electric field sensor S and the signal detection unit (photodetector 15), and actual measurement can be performed in the development engine. . Further, by guiding the probe light to the electro-optic crystal 10 by the polarization maintaining optical fiber 22, it is possible to measure the electric field on the surface of the photosensitive drum 19 even when the sensing position is other than the position that can be seen from the outside.

Referring to FIG. 1, in order to actually measure the spatial distribution of the surface potential of the photoconductor 8, an electric field at a position as close as possible and strictly as close as possible to the surface of the photoconductor 8 will be described. You need to know 17. However, since the electric field 17 to be measured is an electrostatic field generated by the latent image charges 9 due to the electrostatic latent image on the surface of the photoconductor 8, the electric field 17 is applied to the surface of the photoconductor 8 charged with the latent image charges 9. The sensor S cannot be brought into close contact. On the other hand, in general, the electric field near the charged body charged with a certain distribution of electric charges attracts each other depending on the distribution,
Due to the complex shape of repulsion, the charge distribution on the surface of the charged body and the electric field distribution formed by the charge distribution do not exactly coincide with each other except at a position close to the surface of the charged body.

Therefore, from such a viewpoint, the fourth reference implementation
An example will be described with reference to FIGS. The same parts as those described in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In the present embodiment, as shown in FIG. 7, a transparent electrode 23 is deposited on the surface of the electro-optic crystal 10 facing the dielectric mirror 12 in parallel with the surface of the photoreceptor 8 to form the electric field sensor S. Things. The transparent electrode 23 is maintained at a ground potential (ground) or a developing bias potential Vb in the developing engine. However, in the present embodiment, as shown in FIG. 7, the transparent electrode 23 is grounded.

In this case, since the transparent electrode 23 is grounded, the electric lines of force 1 generated by the latent image charges 9 on the surface of the photosensitive member 8
1 is attracted by the transparent electrode 23 and the electric field sensor S
Of the electro-optic crystal 10 of FIG. As a result, the transparent electrode 23 of the electro-optic crystal 10
In a cross section parallel to the above, the density of the lines of electric force 11 substantially matches the latent image charge distribution on the surface of the photoconductor 8.

FIG. 8 shows the relationship between the latent image charges 9 on the surface of the photoconductor 8 depending on the presence or absence of the transparent electrode 23 and the lines of electric force 11 passing through the inside of the electro-optic crystal 10 of the electric field sensor S. It is shown in a formula. FIG. 1A shows an electric field sensor S without the transparent electrode 23. Since the lines of electric force 11 are distorted by the latent image charge distribution, the transparent electrode 2 of the electro-optical crystal 10 is shown.
At some cross section parallel to 3, the electric field intensity distribution does not match the latent image charge distribution. However, as shown in FIG. 2B, when the transparent electrode 23 is grounded and is opposed to the dielectric mirror 12, the lines of electric force 11 generated from the latent image charges 9 become transparent electrodes 23.
To the transparent electrode 23 of the electro-optic crystal 10.
In a cross section parallel to, the electric field intensity distribution substantially matches the latent image charge distribution. As a result, a phase delay corresponding to the latent image charge distribution on the surface of the photoconductor 8 is given to the probe light that reciprocates inside the electro-optic crystal 10 of the electric field sensor S. Also,
If the potential of the transparent electrode 23 is set to the developing bias potential Vb, it becomes possible to measure an electric field intensity distribution close to that in an actual electrophotographic process developing engine.

As described above, when the transparent electrode 23 of the electric field sensor S is grounded, the latent image charge 9 on the surface of the photosensitive member 8 is
Line of electric force 11 generated by the electro-optic crystal 1 of the electric field sensor S
In order to efficiently draw the electric charges into the surface of the photoconductor 8, it is possible to form an electric field in the electro-optic crystal 10 more faithfully corresponding to the spatial distribution of the latent image charges 9 formed on the surface of the photoconductor 8. On the other hand, when the transparent electrode 23 is maintained at the developing bias potential Vb, it is possible to measure an electric field close to that in the actual developing engine. By controlling the state of the electric field in this way, highly accurate and highly reliable electric field measurement on the surface of the photoconductor 8 can be performed.

The fifth embodiment will be described with reference to FIGS. The same parts as those described in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, as shown in FIG. 9, the electric field sensor S was formed by depositing a transparent electrode 23 on the surface of the electro-optic crystal 10 facing the dielectric mirror 12 in parallel with the surface of the photoconductor 8. Things. The transparent electrode 23 is maintained at a ground potential (ground).

Also in this case, as shown in FIG. 8B, the lines of electric force 11 generated from the latent image charges 9 are
, The electric field intensity distribution substantially coincides with the latent image charge distribution in a certain cross section parallel to the transparent electrode 23 of the electro-optic crystal 10 as in the embodiment shown in FIG. As a result, a phase delay corresponding to the latent image charge distribution on the surface of the photoconductor 8 is given to the probe light reciprocating in the electro-optic crystal 10. In this way, the lines of electric force 11 generated by the latent image charges 9 on the surface of the photoreceptor 8 are
In order to draw the electric charges efficiently, it is possible to form an electric field in the electro-optic crystal 10 more faithfully corresponding to the spatial distribution of the latent image charges 9 formed on the surface of the photoconductor 8.

Next, a sixth embodiment will be described with reference to FIG. Note that the same portions as those described in FIG. 9 are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, as shown in FIG. 10, instead of grounding (holding at the ground potential) the transparent electrode 23 of the electric field sensor S as in the above-described embodiment shown in FIG. It is connected to a variable voltage regulator (variable potential setting means) 47 for setting a predetermined potential.

In this case, the transparent electrode 2 of the electro-optic crystal 10
By adjusting the potential of 3 with the variable voltage regulator 47,
Since the electric field created by the electrostatic latent image drawn by the potential of the transparent electrode 23 changes, the contrast of the visualized image can be adjusted.

Next, a seventh embodiment will be described with reference to FIG. The same parts as those described in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted.

[Outside 5] And the like. FIG. 11 (a)
As shown in the figure, the main axis of the electro-optic crystal 25 of the electric field sensor S is set to the z-axis, the z-axis coincides with the incident reflection direction of the probe light, and the xy plane corresponds to the transparent electrode 23 and the dielectric mirror. 12 is set in parallel.

[0069]

[Outside 6] The refractive index ellipsoid in the electro-optic crystal 25 belonging to 3 m is represented by the following equations (4) and (5), where x, y, and z are the principal axis coordinates of the electro-optic crystal 25. ^{_{B 11 x 2 + B 22 y}} 2 + B 33 z 2 + 2B 23 yz + 2B 31 zx + 2B 12 xy = 1 ..................... (4)

(Equation 1)

However, Ex, Ey, Ez shown in the equation (5)
Is an electric field vector penetrating the inside of the electro-optic crystal 25, T is an electro-optic constant tensor of the electro-optic crystal 25, n _x ,
_ny and _nz are the principal axis components of the refractive index of the electro-optic crystal 25 when no electric field is applied.

[Outside 7] The tensor T is represented by the following equation (6).

(Equation 2)

When light travels in the electro-optic crystal 25 of the electric field sensor S in parallel with the z-axis, the refractive index felt by this light is determined by the xy plane of the ellipsoid expressed by the equations (4) and (5). Is an ellipse represented by the cross section at. This ellipse is represented by _{^{n x ¯ 2 x 2 + n}} y ~ 2 y 2 + 2r 63 E z xy = 1 ............... (7). According to the equation (7), it is understood that the change in the refractive index of light propagating in the z-axis direction, which is the principal axis, in the electro-optic crystal 25 depends only on the z component Ez of the electric field in the electro-optic crystal 25. Therefore, as shown in FIG. 11B, the ellipse of equation (7) is coordinate-transformed into a new coordinate system α, β, z, which is rotated by 45 ° in the xy plane about the z-axis and described. Then, (7) cross term disappears in is represented by an ellipse comprising _{^{(n 0 ~ 2 -r 63 E}} z) α + (n 0 ~ 2 + r 63 E z) β = 1 ...... (8). However, it was the _{n x = n y = n 0} .
The length of the major axis and the minor axis of the ellipse shown by the equation (8), that is, the electro-optic crystal 25 in the z-axis direction in the new coordinate system (α, β, z).
Α, β components of the refractive index, nα,
N.beta _{is, nα = n 0 + n 0} 3 r 63 E z / 2 ................................. (9) nβ = n 0 -n 0 3 r 63 E z / 2 .................. ... (10) The phase difference φ between the α and β components of the polarization of the light wave after passing through the electro-optic crystal 25 in the z-axis direction caused by the refractive index difference of the expressions (9) and (10) is expressed by the following equation. the speed of light c _0, when the thickness of the electro-optic crystal 25 and d, phi = the _{^{ωn 0 3 r 63 E z d}} / c 0 ................................. (11). From this equation (11), it can be seen that the light wave traveling in the z-axis direction produces a phase difference φ between the α and β polarization components only by the z component Ez of the electric field in the electro-optic crystal 25. The polarization state changes due to the phase difference φ, and the electric field component Ez in the electro-optic crystal 25 can be detected by detecting the change in the polarization state.

That is, in this embodiment, the lines of electric force 11 generated by the latent image charges 9 on the surface of the photosensitive member 8 are drawn by the transparent electrode 23 as shown in FIG. An electric field in the z-axis direction corresponding to the latent image charge distribution on the surface of the photoconductor 8 is formed inside the crystal 25. Moreover, since the transparent electrode 23 of the electro-optic crystal 25 is grounded in the direction shown in FIG. 11A, a phase difference φ shown in the above equation (11) is generated in the probe light. By detecting a change in the polarization state due to the phase difference φ, the electro-optic crystal 25 is detected.
It is possible to detect the electric field component Ez inside.

In the present embodiment, the main axis of the electro-optic crystal 25 of the electric field sensor S is set to the z-axis, so that the component of the electric field to be probed is limited to only the component perpendicular to the surface of the photoconductor 8 opposed thereto. It is possible to limit to. This makes it possible to more accurately probe the latent image charge distribution on the surface of the photoconductor 8.

By the way, when a ground electrode is placed opposite to a charged body in which electric charges are distributed with a certain spatial distribution, a linear electric field in the charge distribution of the charged body is not completely reproduced on the surface of the ground electrode. . That is, when electric charges are distributed with a certain spatial frequency characteristic, it is known that the electric field on the ground electrode at a finite distance from the surface has a deteriorated spatial frequency characteristic compared to the electric field on the surface of the charged body. ing. In order to reduce this deterioration in measuring the high spatial resolution of the surface electric field of the charged body, it is desirable that the distance between the surface of the photoconductor 8 and the transparent electrode 23 be as short as possible. Therefore, the thickness of the electro-optic crystal 10 (the dielectric mirror 12 and the transparent electrode 23)
Are in the order of millimeters to sub-millimeters.

From such a viewpoint, the eighth reference implementation
An example will be described with reference to FIG. The same parts as those described in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, as shown in FIG. 12, the thickness d of the electro-optic crystal 10 of the electric field sensor S is set in the order of millimeters to sub-millimeters, and the electric field sensor S is provided with an optically isotropic transparent material. A glass support block 24 (support block) made of glass is supported and fixed so as to sandwich the transparent electrode 23.

In this case, in order to maintain a high spatial resolution when measuring the electric field on the surface of the photoconductor 8, the electro-optic crystal 10
Even if is set to a thickness of the order of millimeters to the order of submillimeters, the probe head that is easy to handle can be configured by supporting the electro-optic crystal 10 on the glass support block 24. In addition, the transparent electrode 23 is protected, and a highly reliable probe head can be manufactured.

[0077]

[Outside 8] 11, the main axis of the electro-optic crystal 25 of the electric field sensor S is set to the z-axis, and the z-axis coincides with the direction of the incident and reflected light of the probe light, and the xy plane Are set parallel to the transparent electrode 23 and the dielectric mirror 12.

Also in this case, as in the above-described embodiment shown in FIG. 12, the electro-optic crystal 25 of the electric field sensor S is set to a thickness of the order of millimeter to sub-millimeter and supported by the glass support block 24. In addition, it is possible to maintain a high spatial resolution when measuring the electric field on the surface of the photoconductor 8. Further, as in the embodiment shown in FIG. 11, the main axis of the electro-optic crystal 25 of the electric field sensor S is set to the z-axis so that the component of the electric field to be probed is perpendicular to the surface of the opposing photoconductor 8. By limiting to only the components, it is possible to more accurately probe the latent image charge distribution on the surface of the photoconductor 8.

Further, the transparent electrode of the electric field sensor S shown in FIG. 13 may be connected to a variable constant voltage regulator (variable potential setting means) 47 as in the embodiment shown in FIG. In this case, the contrast of the visualized image can be adjusted in addition to the functions described above.

Next, the principle of a method for detecting a phase from a change in the polarization state of light will be described. Here, assuming that the α component of the polarization of the light wave has a phase difference φ with respect to the β component, the case where the light whose polarization state has changed after passing through the electro-optic crystal is observed through an analyzer is observed. Assuming that the light intensity observed when the transmission axis of the analyzer is set parallel to the x-axis is Ix, and the light intensity observed when the transmission axis of the analyzer is set parallel to the y-axis is Iy, electro-optic The polarization components Eα and Eβ of α and β of the light that has passed through the crystal are as follows: Eα = A exp (−iφ)... (12) Eβ = A... (13) From these equations (12) and (13), the light intensity I
x and Iy are as follows: Ix = 2A ² sin ² (φ / 2) (14) Iy = 2A ² cos ² (φ / 2) (15) ). Then, the light intensity I shown in the equations (14) and (15)
If the division of x and Iy is taken, tan ² (φ / 2) = Ix / Iy (16), and therefore, the phase difference φ is expressed as φ = 2 tan from the equation (16). ~ ¹ √ (Ix / Iy)…… (Ix / Iy) (17) According to the equation (17), A, that is, (2π
/ Λ) The phase difference φ can be obtained without being affected by n ₀ ³ r _p l. That is, it is possible to cancel the fluctuation in the amount of light incident on the electro-optic crystal.

According to the principle described above, the present invention
The first embodiment will be described with reference to FIG. FIG.
The same parts as those described in are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, as shown in FIG. 14A, instead of the photodetector 15 and the amplifier 16 shown in FIG. 1, a polarized beam for separating the reflected light from the dielectric mirror 12 of the electro-optic crystal 10 into two. A splitter (polarization separation element) 26, photodetectors (light receiving elements) 27 and 28 for detecting the light intensity of each of the separated polarization components as electric signals, and photodetectors 27 and 2
And a division operational amplifier 29 to which each of the electric signals output from 8 is input. Further, instead of the semiconductor laser 14 shown in FIG. 1, a semiconductor laser (light source) 30 for emitting coherent circularly polarized light as probe light,
A polarizing plate 30a and a λ / 4 wavelength plate 30b are provided as analyzers. Further, the electric field sensor S is disposed near the photoconductor 8 so that the x-axis is perpendicular to the paper surface, the y-axis is horizontal, and the incident direction of the probe light is z-axis.

In such a configuration, the semiconductor laser 3
The light emitted from 0 is a polarizing plate 30a and a λ / 4 wavelength plate 30
b, the light becomes circularly polarized light, and this circularly polarized light enters the electro-optic crystal 10 of the electric field sensor S via the beam splitter 13 as probe light. At this time, an electric field 17 due to the latent image charges 9 is present in the electro-optic crystal 10, and the main axis of the refractive index ellipsoid in the electro-optic crystal 10 is changed by the electric field 17. As a result, the probe light reflected by the dielectric mirror 12 and returned to the outside of the electro-optic crystal 10 causes a phase delay in an electric vector in a specific direction, and its polarization state slightly changes. That is, a phase difference φ is generated between the α and β components. Thereafter, the probe light returned from the electro-optic crystal 10 again enters the beam splitter 13, is reflected by the beam splitter 13 in a direction perpendicular to the incident light, and enters the polarization beam splitter 26. Then, the probe light is split into two by the polarization beam splitter 26, and the separated probe lights are received by the photodetectors 27 and 28, respectively, and detected as light intensity.

At this time, the relationship between the directions of the beam splitter 13 and the polarization beam splitter 26 and the optical axis of the electro-optic crystal 10 is as shown in FIG. That is, FIG.
As shown in (a), the reflecting surface of the polarizing beam splitter 26 reflects the incident light perpendicularly to the paper. Further, a plane including a light beam incident on the polarization beam splitter 26 and reaching the photodetectors 27 and 28 and an orthogonal component (α, β component) including a phase delay of the probe light incident on the polarization beam splitter 26 are: An angle of 45 ° is formed as shown in FIG. Then, the intensity observed by the photodetector 27 is equal to I
The x component, the light intensity observed by the photodetector 28 is
This is the Iy component shown in equation (15). The output of each of these photodetectors 27 and 28 is divided by a division operational amplifier 29.
After the division operation is performed, the signal is amplified, and a signal from which the light intensity fluctuation term of the incident light (probe light) is removed is obtained as shown in Expression (16). At this time, if the phase change is smaller than the wavelength, equation (16) can be considered to change linearly with respect to the phase difference φ. If the phase change is large, the signal of equation (16) is calculated according to equation (17) to determine the phase difference φ.

The change in the polarization state of the probe light is detected from the phase difference φ thus obtained, and the electric field penetrating the electro-optic crystal 10 can be measured from the change in the polarization state. In this embodiment, the division operational amplifier 29
Is used, the fluctuation of the light intensity of the probe light is canceled, and the electric field on the surface of the photoconductor 8 can be measured with high accuracy.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same portions as those described in FIG. 14 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a coherent detection method using a Michelson-type polarization interferometer is performed. That is, as shown in FIG. 15A, the reflected light from the dielectric mirror 12 of the electro-optic crystal 10 is guided to the Michelson-type polarization interferometer 31 via the beam splitter 13, and the Michelson-type polarization interferometer 31 is used.
The interference signal, which is the output of, is converted to a polarizing plate (polarizing filter)
Incident on the photodetector (light receiving element) 32 through
The light intensity change of the interference signal is detected as an electric signal by the photodetector 32, and the electric signal output from the photodetector 32 is set to be input to the amplifier 33. Here, the Michelson-type polarization interferometer 31 includes a polarization beam splitter (polarization separation element) 34.
And λ / 4 wavelength plates 35, 36 arranged on the respective arms
And the mirrors 37 and 38. Also,
The polarizing plate 32a installed between the photodetector 32 and the polarizing beam splitter 34 is set to form an angle of 45 ° with respect to linearly polarized light beams orthogonal to each other from the polarizing beam splitter 34 to the photodetector 32. I have.

Further, the optical axis of the electro-optic crystal 10 forms an angle of 45 ° with the paper surface, the α axis is perpendicular to the paper surface, and β
The axis is set to be parallel to the paper surface. However,
As shown in FIG. 15B, these α and β axes are a new coordinate system rotated by 45 ° in the xy plane about the z axis.

In such a configuration, coherent circularly polarized light is incident as probe light from a semiconductor laser (not shown) on the electro-optic crystal 10 of the electric field sensor S. The α component and the β component of the circularly polarized light (probe light) are
The phase delay is caused by the electro-optic effect of zero. And
The probe light reflected by the dielectric mirror 12 and emitted from the electro-optic crystal 10 is reflected by the beam splitter 13 and enters the polarization beam splitter 34. Here, since the α-axis and β-axis of the electro-optic crystal 10 are set to be perpendicular and parallel to the paper surface, the α component of the probe light enters the polarization beam splitter 34 as the s-polarized light and the β component as the p-polarized light. .
The s-polarized light that has entered the polarization beam splitter 34 is reflected by the polarization beam splitter 34, and
5, the light becomes circularly polarized light, is reflected by the mirror 37, and enters the λ / 4 wavelength plate 35 again. The probe light that has passed through the λ / 4 wavelength plate 35 again becomes p linearly polarized light, passes through the polarization beam splitter 34, and reaches the photodetector 32 via the polarization plate 32a. Here, the λ / 4 wavelength plate 35 is set so that its polarization axis is at 45 ° with respect to the s-polarized light incident from the polarization beam splitter 34.

On the other hand, the p-polarized light incident on the polarizing beam splitter 34 passes through the polarizing beam splitter 34 and
The light passes through the quarter-wave plate 36, becomes circularly polarized light, is reflected by the mirror 38, and enters the λ / 4 wave plate 36 again. And
Light that has passed through the λ / 4 wavelength plate 36 again becomes s-linearly polarized light, is reflected by the polarization beam splitter 34, and reaches the photodetector 32 via the polarization plate 32a.

At this time, the polarizing plate 32a provided between the photodetector 32 and the polarizing beam splitter 34
Since it is set so as to form an angle of 45 ° with respect to the linearly polarized light orthogonal to each other from the polarization beam splitter 34 to the photodetector 32, the photodetector 32
In the position (1), the probe lights that have undergone phase delay due to the electro-optic effect of the electro-optic crystal 10 become linearly polarized lights in the same direction and interfere with each other. Therefore, the interference signal Iout observed by the photodetector 32 is equal to the above (12), (1)
Using the equation (3), Iout = | Eα + Eβ | ² = 2A + A ² cosφ (18) As shown in the equation (18), the change in the light intensity signal is a monovalent function of the phase difference φ, and is a monovalent function of the z-axis component Ez of the electric field according to the equation (11). This makes it possible to measure the electric field penetrating the electro-optic crystal 10.

As described above, if coherent detection is performed using the Michelson-type polarization interferometer 31, the phase difference φ delayed by the electro-optic effect is converted into light intensity by the interference of the probe light itself. It is possible to generate an interference fringe having high visibility, thereby enabling detection of a signal having a high S / N ratio. Moreover, it is possible to follow a phase change in the order of wavelength, and it is possible to obtain high measurement accuracy.

Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those described in FIG. 15 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, an optical heterodyne-type polarization detection method is implemented, and as shown in FIG. 16A, an orthogonal Zeeman laser 39 is used as a light source. The orthogonal Zeeman laser 39 has a polarization orthogonal to each other and is a well-known laser having a frequency difference between orthogonal polarization components. The orthogonal two-frequency coherent light emitted from the orthogonal Zeeman laser 39 is used as a probe. Mirror 4 as light
0, it is set to be incident on the electro-optic crystal 10 of the electric field sensor S via the beam splitter 13.

The probe light incident on the electro-optic crystal 10 of the electric field sensor S has a polarization component having an angular frequency ω ₁ parallel to the β-axis of the electro-optic crystal, as shown in FIG.
Polarization component of the angular frequency omega ₂ is set to be parallel to the α axis of the electro-optic crystal. However, these α and β axes are a new coordinate system rotated by 45 ° in the xy plane about the z axis as shown in FIG. 16B.

Here, the light exits the electro-optic crystal 10, is reflected by the beam splitter 13, and is polarized by the polarization beam splitter 34.
Consider the probe light incident on. The α component and β component of the probe light are applied to the polarization beam splitter 34 in the same manner as in the embodiment shown in FIG.
It is incident as a linearly polarized light component. These s linearly polarized light component and p linearly polarized light component interfere with each other at the position of the photodetector 32 through a process similar to that of the embodiment shown in FIG.
At this time, the polarizing beamsplitter 3
The two s-linear polarization components and p-linear polarization components that reach the photodetector 32 through the polarizing plate 32a after passing through the polarizer 32a have two angular frequencies ω ₁ and ω ₂ by the orthogonal Zeeman laser 39. That is, the photodetector 3
The two light waves Eα and Eβ that interfere with each other at the position 2 are (1)
Considering the time term in equations 2) and (13), Eα = A exp {−i (φ + ω ₂ t)} (19) Eβ = A exp (−iω ₁ t) ............ (20) Then, the light intensity Ih of the light waves Eα and Eβ of the equations (19) and (20) detected by the photodetector 32 is Ih = | Eα + Eβ | ² = 2A + A cos {φ + (ω ₂ −ω ₁ ) t}. ... (21) Generally, since the frequency difference of the orthogonal Zeeman laser 39 is about several MHz, the light intensity Ih shown in Expression (21) is obtained.
Is a frequency (ω ₁ −ω ₂ ) / 2 having an initial phase difference φ.
It is observed by the photodetector 32 as a time series signal of π. The phase can be measured with high accuracy by the phase meter based on the electric signal output from the photodetector 32.

As described above, the orthogonal Zeeman laser 39
The optical heterodyne-type polarization detection method according to the present invention significantly improves the reading accuracy of the phase difference delayed by the electro-optic crystal 10 of the electric field sensor S, and in particular, converts the phase difference of light into an electric signal. Because of this, the phase detection of about 2 / π of several hundreds is possible by the well-known phase detection technology,
It is possible to measure the electric field on the surface of the photoconductor 8 with high accuracy and high resolution.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. The same parts as those described in FIG. 15 are denoted by the same reference numerals, and description thereof will be omitted.
FIG. 17 shows a measurement system according to the present embodiment, in which imaging means (not shown) having an observation surface 50 is provided in place of the photodetector 32 and the amplifier 33 shown in FIG. A semiconductor laser 5 is used as a light source for emitting circularly polarized light.
1 is set so that the circularly polarized light emitted from the semiconductor laser 51 enters the electro-optic crystal 10 of the electric field sensor S as probe light via the imaging lens 52 and the beam splitter 13. However, a polarizing plate (polarizing filter) 32a installed between the polarization beam splitter 34 of the Michelson-type polarization interferometer 31 and the observation surface 50
Is set to have a polarization axis that is at 45 ° to the orthogonal polarization axis of the polarization beam splitter 34.

In such a configuration, the semiconductor laser 5
The circularly polarized light emitted from 1 is incident on the electro-optic crystal 10 of the electric field sensor S as probe light via the imaging lens 52 and the beam splitter 13. At this time, the electro-optic crystal 10
An electric field 17 due to the latent image charges 9 is present in the inside, and the electric field 17 changes the main axis of the refractive index ellipsoid in the electro-optic crystal 10, and as a result, is reflected by the dielectric mirror 12 and The light returning outside 10 causes a phase delay in a specific direction, and its polarization state changes slightly. That is,
A phase difference φ is generated between the α and β components. In this case, since the probe light is circularly polarized light, the light that has passed through the electro-optic crystal 10 becomes elliptically polarized light due to the phase difference φ generated between the α and β components. Then, the light returned from the electro-optic crystal 10 is reflected by the beam splitter 13 and enters the polarization beam splitter 34 of the Michelson-type polarization interferometer 31. Here, as shown in FIG. 17, the α axis, β
Because the axis is set perpendicular and parallel to the paper,
The α component of the probe light enters the polarization beam splitter 34 as s-polarized light and the β component as p-polarized light.

Thereafter, the two light waves of the s-polarized light and the p-polarized light pass through the same process as in the above-described embodiment shown in FIG. Observation surface 5 through plate 32a
Reach 0. Here, two light waves of p-polarized light and s-polarized light traveling from the polarization beam splitter 34 to the observation surface 50 are:
Since the polarization planes are orthogonal to each other, no interference fringes are observed in this state. Therefore, by passing these two light waves through a polarizing plate 32a having a polarization axis that forms an angle of 45 ° with the polarization axis of the polarization beam splitter 34, the observation surface 5
The light wave that reaches 0 becomes a projected component of two orthogonal linearly polarized lights to the polarization axis of the polarizing plate 32a, and their polarization planes coincide with each other.

As a result, an interference fringe corresponding to the phase difference φ between the α and β components of the light wave from the beam splitter 13 to the polarization beam splitter 34 is formed on the observation surface 50. As a result, the interference fringes are contour lines of the surface potential distribution of the photoconductor 8, and if this interference fringe image is observed by an imaging means such as a CCD camera, the two-dimensional distribution of the surface potential of the photoconductor 8 is directly obtained. Will be observed. FIG. 18 shows a schematic example showing the relationship between the observed interference fringes and the surface potential distribution of the photoconductor 8.

As described above, in this embodiment, since the interference signal of the Michelson-type polarization interferometer 31 is observed as the contour line of the surface potential of the photosensitive member 8 by the image pickup means, the conventional probe-like sensor is scanned. The electric field measurement that has been performed can be performed two-dimensionally, and highly reliable multi-point parallel sensing can be performed. In addition, the field to be measured can be visually monitored in real time as an interference fringe image.

Next, a fifth embodiment of the present invention will be described with reference to FIG. Note that the same portions as those described in FIG. 17 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 19 shows a measurement system according to this embodiment. In addition to the configuration of the Michelson-type polarization interferometer 31 shown in FIG. 18, a piezo element (a minute displacement applying mechanism) is attached to the mirror 38 on one arm of the polarization beam splitter 34. ) 53 to form a Twyman-Green interferometer 54. Here, the piezo element 53 has a function of slightly displacing the mirror 38 in a direction parallel to the optical axis. On the output side of the Twyman-Green interferometer 54, a two-dimensional (or one-dimensional) CC having an observation surface 50 is provided via a polarizing plate (polarizing filter) 32a.
A D camera (imaging means) 55 is provided. This CC
On the output side of the D camera 55, an A / D converter (A / D
D conversion means) 56, a frame memory 57, and a host computer 58 are connected to form an electric field measurement means 59. In addition, in the Hosutokon pin Yuta 58,
Algorithms such as superimposing means, phase calculating means, and surface potential distribution calculating means (not shown) are provided.

In such a configuration, the semiconductor laser 5
When the circularly polarized light emitted from 1 enters the electro-optic crystal 10 of the electric field sensor S as probe light via the imaging lens 52 and the beam splitter 13, the light passes through the inside of the electro-optic crystal 10 and is reflected by the dielectric mirror 12. The light that has been reflected and returned to the outside of the electro-optic crystal 10 again reaches the observation surface 50 through the same process as in the embodiment shown in FIG. 17, and forms interference fringes on the observation surface 50. Then, the mirror 38 is slightly displaced in the direction parallel to the optical axis of the light wave incident on the mirror 38 by the piezo element 53, that is, the phase of a total of one wavelength at equal intervals with respect to the wavelength λ of the light wave incident on the mirror 38. The mirror 38 is moved N steps at an interval of λ / (2N) so as to give a change, and N interference fringe images are captured by the CCD camera 55 at each position. Next, these captured N stripe interference images are converted into digital images by the A / D converter 56, and then stored in the frame memory 57.

Here, the superimposing means of the host computer 58 superimposes the signal fluctuations between the N pixels in each pixel of the interference fringe image with a sine signal forming one cycle between the N images, and this sine signal is superimposed. After extracting only the component having the sine signal as the fundamental wave from the signal fluctuations over N pixels at each pixel of the interference fringe image, the phase of this fundamental wave component is independently calculated at each pixel of the interference fringe image by the phase calculation means. calculate. That is, the interference fringe image is
n (x, y), where n = 1, 2, 3,... n, the phase difference φ (x, y) of the interference fringe at the pixel (x, y) is

(Equation 3) Is calculated. The operation shown in the expression (22) is performed by the host computer 58 by reading out image data from the frame memory 57. Therefore, it is possible to calculate the surface potential distribution of the photoconductor 8 by the surface potential distribution measuring means of the host computer 58 based on the phase difference φ (x, y) at each pixel calculated from the equation (22). .

As described above, in the present embodiment, the phase analysis of the interference fringe image is performed, so that the phase conventionally obtained by visually counting the number of interference fringes is quantitatively reduced to a phase of 2π or less. Changes can also be detected. Further, the spatial resolution is determined by the pixels of the CCD camera 55, and by measuring the phase spatially and independently for each pixel, an electric field measuring device with high accuracy, reliability and reproduction can be constructed. .

Next, a sixth embodiment of the present invention will be described with reference to FIGS. The same parts as those described in FIG. 19 are denoted by the same reference numerals, and description thereof will be omitted. The present embodiment relates to an electric field measuring apparatus on the surface of a photoreceptor in which spatial carriers are introduced into an interference fringe image observed on the observation surface 50 and the phase distribution is calculated. FIG. 20 shows a measurement system of the present embodiment. In place of the piezo element 53 installed on the mirror 38 of one arm of the polarization beam splitter 34 of the Twyman-Green interferometer 54 shown in FIG. A mirror slight angle tilting means (not shown) for tilting the mirror 38 by a small angle is provided. Further, as the electric field measuring means 59, the host computer 58 is provided with algorithms such as a dividing means (not shown), a superimposing means, a phase calculating means, and a surface potential distribution calculating means. Further, a two-dimensional CCD camera 55 (or a one-dimensional CCD line sensor parallel to the direction in which the spatial carrier signal is generated) such as a CCD area sensor is used as the CCD camera 55.

In such a configuration, for explanation, CC
The coordinates on the image captured by the observation surface 50 of the D camera 55 are taken as shown in FIG. 20, and the mirror 38 of the Twyman-Green interferometer 54 is shown by a virtual line in FIG. When installed at such a small angle, the interference fringe image picked up by the CCD camera 55 has spatial carriers in the x direction and becomes vertical stripe images running in the y direction, as shown in FIG. 21B. Here, FIG.
The image shown in FIG. 1 (b) represents an interference fringe image on which a spatial carrier signal is superimposed, and the image shown in FIG. 21 (a) represents an original (non-tilted mirror 38) interference fringe image.
Then, the interference fringe image on which the spatial carrier signal is superimposed as shown in FIG. After that, the interference fringe image picked up by the CCD camera 55 is converted into a digital image by an A / D converter 56 and then stored in a frame memory 57. Further, the stored image data is calculated by a host computer 58. Will be processed.

Here, the arithmetic processing performed by the host computer 58 will be described with reference to the flowchart of FIG. Since the mirror 38 is tilted as shown by the imaginary line in FIG. 20, the observed interference fringes are superimposed on the spatial carrier signal in the x-axis direction. Become. This interference pattern is subjected to a process of calculating a phase for each scanning line in the x-axis direction parallel to the spatial carrier signal generation direction (for each line sensor output when a one-dimensional CCD camera is used) by the phase calculation means.
Here, the image signal of the interference fringe image on one scanning line in the x-axis direction is phase-modulated by the phase distribution of the light wave to be measured by the sine signal which is a spatial carrier signal.
The interference fringe image signal I (x) is the spatial carrier frequency f _0, the phase distribution to be measured and phi, is represented by one-dimensional for simplicity, I (x) = a ( x) + b (x ) Cos {2πf ₀ x + φ (x)} (23) Where a (x) and b (x) in the equation (23) are
These are unnecessary and unknown terms such as visibility of interference fringe signals and background noise.

The interference fringe image signal I (x) shown in the equation (24) is divided into N columns d _i (i = 1,2,3, ... is divided into N), the superposition of the same sinusoidal signal with spatial carrier signal frequency for each interval d _i by the superimposing means. Here, the distribution of the phase phi (x) is a low-pass enough compared to the spatial carrier signal frequency, phi in a section d _i, a, b are if a constant, interference in the interval d _i fringe image signal I _i (x) _{is, I i (x) = a} i + b i cos (2πf 0 x + φ i) = a i + b i cos (2πf 0 x) cosφ i + b i sin (2πf 0 x) sinφ i ............ (24) The interference fringe image signal I shown in the equation (24)
_{Since i} (x) is digitized by the A / D converter 56, the interference fringe image signal I _i (x) of Expression (24) is extended to a discrete value sequence. Here, _assuming that x is sufficiently fine and discretized to x _n : (n = 0, 1, 2,... N−1) within the minute section d _i , I _i (x _n ) = a _{i + b i cos (2πf 0} x n) cosφ i + b i sin (2πf 0 x n) sinφ i ..................... becomes (25). Here, the spatial carrier signal in a section d _i extracts the fundamental wave component of the Fourier series of a fundamental wave to calculate the phase of the interference fringe image signal I _i (x _n). That is, from the equation (25), the phase φ _i becomes as shown in the equation (28) by calculating c _i and s _i as in the equations (26) and (27).

(Equation 4)

In this manner, the phase φ is calculated for each scanning line from one interference fringe image on which the spatial carrier signal is superimposed.
_{If i} is calculated and performed for all scan lines, N ×
The phase φ _i is obtained independently at (the number of scanning lines) points. That is, the two-dimensional distribution of the phase φ _i can be calculated. Then, the surface potential distribution of the photoconductor 8 is calculated by the surface potential distribution calculating means of the host computer 55 based on the two-dimensional distribution of the phase φ _i ,
The electric field can be measured.

As described above, in the present embodiment, the phase is analyzed from the interference fringe image in which the spatial carrier is introduced, so that it is disadvantageous in terms of the spatial resolution as compared with the embodiment shown in FIG. However, the piezo element 53 for slightly displacing the mirror 38 is not required, and the spatial phase distribution can be calculated from one interference fringe image. The measurement can be performed. In particular, since the arithmetic processing portion is an algorithm that can be easily implemented in hardware, it can be easily extended to real-time measurement at a video rate.

Next, a seventh embodiment of the present invention will be described with reference to FIGS. This embodiment has the same configuration as that of the embodiment shown in FIG. 20, and introduces a spatial carrier into the interference fringe image and detects an electric field on the surface of the photosensitive member so as to detect a phase by Fourier transform. It relates to a measuring device. In this embodiment, as the electric field measuring means 59, the host computer 58 is provided with an algorithm such as a window function extracting means, a phase calculating means, and a surface potential distribution calculating means (not shown).

In such a configuration, calculation processing until the phase distribution is calculated from the interference fringe image observed on the observation surface 50 will be described with reference to the flowchart of FIG.
First, introducing a spatial carrier,
The process up to the generation of the interference fringes as shown in FIG. 20B is the same as that of the embodiment shown in FIG. The generated interference fringe image signal I (x) is similarly expressed as in equation (23). Here, if equation (23) is expressed as an exponential function,

(Equation 5) Becomes However, c (x) in equation (29) is c (x) = (1/1)
2) b (x) exp {jφ (x)}, * is a complex conjugate. Then, assuming that the one-dimensional Fourier transform for x shown in the equation (29) is G (f), G (f) is

(Equation 6) It is represented by A (f), C shown in this equation (30)
(F) represents a spatial frequency spectrum of a (x) and c (x) shown in the equation (29), and A (f) represents a low-frequency spectrum caused by illuminance unevenness of a light wave in an interference fringe image. The background noise component, C (f), is the spectrum of the spatially modulated spatial carrier signal component. Here, assuming that the spatial carrier signal frequency f ₀ is sufficiently higher than the band of A (f), two components of A (f) and C (f) in the spatial frequency spectrum region are shown in FIG. Completely separated as shown. However, A shown in FIG.
The part and the C part correspond to A (f) and C (f) in the equation (30).

In such a spatial frequency spectrum region, as shown in FIG. 24, the window function 6 as a filter function, which is a window function extracting means of the host computer 58,
The 0, when cut only the portion C of the line spectrum of the spatial carrier signal frequency f ₀ near by filtering the spatial carrier signal frequency f ₀ as the center frequency, filtered spatial frequency spectrum G '(f) is, G' (F) = C (f−f ₀ ) ………………………… (31) The filter function is optimized so that distortion is reduced when a signal is returned to the spatial domain using a Hanning function, a Hamming function, a Blackman function, or the like in addition to the rectangular window function 60 shown in FIG. You can also. Here, since the cut-out width of the spectrum by the window function 60 affects the spatial resolution of the final signal detection result, it is better to increase the bandwidth of the window function 60 in order to suppress a decrease in the spatial resolution. . However, since signals other than the spatial carrier signal frequency f ₀ component are taken in the spectral domain, the final result S
/ N is reduced. Therefore, as shown in FIG. 24, the bandwidth of the window function 60 is changed to the spatial carrier signal frequency f _0.
, A good result can be obtained.

Subsequently, the line spectrum cut out by the window function 60 is shifted in the DC direction by the spatial carrier signal frequency f _{0 in the} frequency domain, and the spectrum peak is shifted to zero frequency, as shown in FIG. . By performing such an operation, the spatial frequency spectrum G ″ (f) of the equation (31) is obtained by using the following equation (31): G ″ (f) = C (f) ... (32) By performing an inverse Fourier transform of G ″ (f) in the equation (32), c (x) in the equation (29) is obtained. That, c (x) becomes ^{c (x) = F.T ~ 1} {G '' (f)} ................................. (33). However, FT- ¹ shown in the equation (33) is an inverse Fourier transform operator. At the stage of this equation (33), (29)
Unnecessary and unknown functions a (x) in the equation are eliminated. Further, c (x) is a complex number as shown in Expression (29), and the real part and the imaginary part of c (x) are respectively Re ｛c
(X)｝, Im ｛c (x)｝, the phase distribution function φ (x) to be detected is φ (x) = tan ~ ¹ [Im ｛c (x)｝ / Re ｛c (x )｝] (34) In this calculation process, the unnecessary and unknown function b (x) in the equation (29) is removed.

In this way, only the phase modulation component φ (x) can be extracted from the interference fringe image I (x) shown in the equation (23) including an unnecessary and unknown function term. Here, if E _z is a function E _z (x) of x in the above equation (11), the phase modulation component phi (x) _{is, φ (x) = n 0} 3 r 63 E z (x) d / C ₀ ... (35). The calculations of the equations (33) to (35) are performed by the phase calculation means of the host computer 58. In addition, the host computer 5
Be calculated electric field components E _z from the (35) surface potential distribution calculating means 8, it is possible to determine the surface potential distribution of the photoreceptor 8.

As described above, in this embodiment, the spatial resolution is almost the same as that of the embodiment shown in FIG. 20, but when the line spectrum is cut out by the window function 60 having a finite width,
Since a signal smoothing effect is generated, it is possible to detect a signal having a gradual change in phase of 2π or less with a high S / N. Further, since the smoothing effect depends on the width of the window function 60, the width of the window function 60 can be tuned at the processing stage, so that a more optimal electric field measurement system can be constructed.

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

Effects of the Invention According to the first aspect of the invention, the use of the polarization detection method division operation amplifier, in which the light intensity fluctuation of the probe light can measure the electric field of the canceled high-precision is there.

According to the second aspect of the present invention, the coherent detection by the Michelson-type polarization interferometer is used, and the phase difference given to the probe light reciprocating in the electro-optic crystal by the electro-optic effect is determined by the interference of the probe light itself. Since the light intensity is converted to light intensity, it is possible to generate interference fringes having high visibility, thereby increasing the S / S.
Since it is possible to detect an N-ratio signal and follow a phase change in the order of wavelength, high electric field measurement accuracy can be obtained.

According to the third aspect of the present invention, by performing optical heterodyne-type polarization detection using the orthogonal Zeeman laser, the reading accuracy of the phase difference delayed by the electro-optic crystal of the electric field sensor is greatly improved. And especially
Since the phase difference of the probe light is converted to an electric signal, it is possible to detect a phase of about 2π / hundredths by a well-known phase detection technology, and thus it is possible to measure an electric field with high accuracy and high resolution. You can do it.

According to the fourth aspect of the present invention, the interference signal of the Michelson-type polarization interferometer is observed by the imaging means as the contour line of the surface potential of the photoconductor to be measured. The two-dimensional measurement of the electric field that has been performed while scanning the object can be performed two-dimensionally, and highly reliable multi-point parallel sensing can be performed. In addition, the field to be measured can be visually recognized in real time as an interference fringe image. It can be monitored.

According to the fifth aspect of the present invention, by analyzing the phase of the interference fringe image, the phase conventionally obtained by counting the number of interference fringes by visual observation can be quantitatively reduced to a phase of 2π or less. Changes can also be detected, and the spatial resolution is determined by the pixels of the imaging means, such as a CCD camera. It is possible to construct a high electric field measuring device.

According to the sixth aspect of the present invention, the phase is analyzed from the interference fringe image into which the spatial carrier is introduced, which is disadvantageous in terms of the spatial resolution as compared with the fifth aspect of the present invention. However, since a mirror minute displacement applying mechanism for minutely displacing the mirror is not required, and the spatial phase distribution can be calculated from one interference fringe image, the electric field can be measured efficiently in terms of processing time. In particular, since the arithmetic processing portion is an algorithm that can be easily implemented in hardware, it can be easily extended to real-time measurement at a video rate.

According to the seventh aspect of the present invention, the spatial resolution is substantially the same as that of the sixth aspect of the invention, but when the line spectrum is cut out with a finite width window function, the signal is smoothed. Signal, the signal having a gradual change in phase of 2π or less can be detected with a high S / N.
In addition, since the smoothing effect depends on the width of the window function, the width of the window function can be tuned at the processing stage, so that a more optimal electric field measurement system can be constructed.

[Brief description of the drawings]

FIG. 1 is a front view showing a measurement system according to a first reference example of the present invention .

FIGS. 2A and 2B show the state of lines of electric force according to the size of an electro-optic crystal of an electric field sensor. FIG. 2A is a front view of a small-size electro-optic crystal, and FIG. FIG.

FIG. 3 is a front view showing a measurement system according to a second reference example of the present invention .

FIG. 4 is a front view showing a measurement system according to a third reference example of the present invention .

FIG. 5 is an enlarged partial front view showing the vicinity of the electric field sensor shown in FIG. 4;

6 is a partial front view showing an optical path of the probe light in FIG. 4 in an enlarged manner.

FIG. 7 is a front view showing a measurement system according to a fourth embodiment of the present invention .

FIGS. 8A and 8B show states of lines of electric force according to the presence or absence of a transparent electrode of the electric field sensor, wherein FIG. 8A is a front view of an electric field sensor without a transparent electrode, and FIG. It is.

FIG. 9 is a front view showing a measurement system according to a fifth reference example of the present invention .

FIG. 10 is a front view showing a measurement system according to a sixth reference example of the present invention .

11A and 11B show a measurement system according to a seventh embodiment of the present invention, wherein FIG. 11A is a front view, and FIG. 11B is a vector diagram.

FIG. 12 is a front view showing a measurement system according to an eighth embodiment of the present invention .

FIG. 13

[Outside 9] It is a front view showing a measuring system using a field sensor.

FIG. 14 shows a measurement system according to the first embodiment of the present invention .
(A) is a front view, (b) is a vector diagram.

FIG. 15 shows a measurement system according to a second embodiment of the present invention .
(A) is a front view, (b) is a vector diagram.

FIG. 16 shows a measurement system according to a third embodiment of the present invention .
(A) is a front view, (b) is a vector diagram.

FIG. 17 is a front view showing a measurement system according to a fourth embodiment of the present invention .

FIG. 18 is a schematic diagram illustrating a relationship between interference fringes formed on an observation surface and a surface potential of a photoconductor.

FIG. 19 is a front view showing a measurement system according to a fifth embodiment of the present invention including a partial block diagram.

FIG. 20 is a front view showing a measurement system according to a sixth embodiment of the present invention including a partial block diagram.

FIG. 21 shows interference fringes formed on the observation surface.
(A) is a schematic diagram showing an interference fringe without introducing a spatial carrier signal, and (b) is a schematic diagram showing an interference fringe on which a spatial carrier signal is superimposed.

FIG. 22 is a flowchart showing a procedure up to a phase calculation process for one scanning line.

FIG. 23 is a flowchart showing a seventh embodiment of the present invention .

FIG. 24 is a waveform chart showing a spatial frequency spectrum.

FIG. 25 is a waveform chart showing transition processing of a line spectrum cut out by a window function.

FIG. 26 is a circuit diagram showing a conventional example.

[Explanation of symbols]

8, 19 Photosensitive body to be measured 9 Latent image charge 10, 25 Electro-optic crystal 11 Line of electric force 12 Light wave reflecting portion 14, 30, 39, 41, 51 Light source 17 Electric field 18 Developing sleeve 20, 21, Probe light guide optical member 22 Polarized Wavefront maintaining optical fiber 23 Transparent electrode 24 Support block 26, 34 Polarization separating element 27, 28, 32 Light receiving element 29 Divide operational amplifier 31 Michelson-type polarization interferometer 32 a Polarizing plate 35, 36 λ / 4 wavelength plate 37, 38 Mirror 39 Orthogonal Zeeman laser 44 analyzer 45 imaging element 46, 55 imaging means 47 variable potential setting means 50 imaging surface 53 minute displacement applying mechanism 54 Twyman-Green interferometer 59 electric field measuring means S electric field sensor

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 29/12 G01R 15/00-17/22 G03G 15 / 00,21 / 00 G03G 13 / 08,15 / 08 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. An electric field sensor is formed by depositing a light-wave reflecting portion made of a dielectric on one surface of an electro-optic crystal having an electro-optic effect, and an electric field due to a latent image charge charged on a photosensitive member to be measured is formed. The electric field sensor is disposed near the surface of the photoconductor to be measured so as to penetrate the inside of the electro-optic crystal, and a predetermined polarization state is obtained from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. Is incident as probe light, and the probe light passes through the electro-optic crystal and separates the reflected light reflected by the light wave reflector into two orthogonal polarization components by a polarization separation element. The light intensity of each of the separated polarized light components is detected as an electric signal by a light receiving element, and each of the detected light intensity signals is input to a division operational amplifier, based on a division calculation force signal of the division operational amplifier. A method for measuring an electric field on a photoreceptor surface, wherein a change in the polarization state of the probe light is detected, and an electric field penetrating the electro-optic crystal is measured from the change in the polarization state of the probe light. 2. An electric field sensor is formed by depositing a light wave reflecting portion made of a dielectric on one surface of an electro-optic crystal having an electro-optic effect, and an electric field due to a latent image charge charged on a photosensitive body to be measured is formed. The electric field sensor is disposed near the surface of the photoconductor to be measured so as to penetrate the inside of the electro-optic crystal, and a predetermined polarization state is obtained from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. Is incident as probe light, and the probe light passes through the electro-optic crystal and is reflected by the light-wave reflecting portion to form a polarization separating element and a λ / 4 wavelength plate on each arm thereof. To a Michelson-type polarization interferometer, and converts the light intensity change of the interference signal output from the Michelson-type polarization interferometer into an electric signal by a light-receiving element. Detecting a change in the polarization state of light, electric field measurement method of the photoreceptor surface, characterized in that so as to measure the electric field penetrating the electro-optic crystal from the change in the polarization state of the probe light. 3. An electric field sensor is formed by depositing a light wave reflecting portion made of a dielectric on one surface of an electro-optic crystal having an electro-optic effect, and an electric field due to a latent image charge charged on a photosensitive body to be measured is formed. The electric field sensor is disposed in the vicinity of the surface of the photoconductor to be measured so as to penetrate the inside of the electro-optic crystal, and a perpendicular Zeeman laser is used from the other surface of the electro-optic crystal facing the light wave reflecting portion of the electric field sensor. Orthogonal two-frequency light is used as probe light, and the probe light is made incident so that the main axis of the refractive index ellipsoid in the plane of the electro-optic crystal is orthogonal to the probe light, and the probe light passes through the electro-optic crystal and The light reflected by the light wave reflector is guided to a Michelson-type polarization interferometer having a polarization separation element and a λ / 4 wavelength plate disposed on each arm thereof, and output from the Michelson-type polarization interferometer. A light intensity change of the interference signal is converted into an electric signal by a light receiving element, and an electric field penetrating the electro-optic crystal is measured by electrically detecting a phase change of the electric signal. Method of measuring electric field on body surface. 4. An electric field sensor having an electro-optic crystal having an electro-optic effect and a light-wave reflecting portion made of a dielectric material deposited on one surface of the electro-optic crystal. A circle having a predetermined polarization state, which is provided near the surface of the photoconductor to be measured so as to penetrate the inside thereof, and is incident as probe light from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. A light source that emits polarized light is provided, and the probe light emitted from the light source passes through the electro-optic crystal and the reflected light reflected by the light wave reflector is incident thereon.
A Michelson-type polarization interferometer having a 波長 wavelength plate is provided, and an interference signal output from the Michelson-type polarization interferometer is passed through a polarization plate at an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. An imaging means having an observation surface for observing the surface potential of the measured photoconductor as a contour line. 5. An electro-optic crystal having an electro-optic effect, wherein an electric field sensor formed by depositing a light-wave reflecting portion made of a dielectric material on one surface of the electro-optic crystal has an electric field caused by a latent image charge charged on a photoconductor to be measured. A circle having a predetermined polarization state, which is provided near the surface of the photoconductor to be measured so as to penetrate the inside thereof, and is incident as probe light from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. A light source that emits polarized light is provided, and a probe light emitted from the light source passes through the electro-optic crystal, and a reflected light reflected by the light wave reflection unit is incident thereon. A λ / 4 wavelength plate and a mirror arranged on the arm of
The mirror is set to λ / (so that a phase change of a total of one wavelength is given at equal intervals to the wavelength λ of the light wave in a direction parallel to the optical axis of the light wave incident on the mirror of one arm of the polarization separation element. 2N) A Twyman-Green interferometer having a micro-displacement applying mechanism that moves N steps at intervals is provided, and an interference signal output from this Twyman-Green interferometer is set at an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. An imaging means is provided which has an observation surface for observation through a polarizing plate, and which picks up N interference fringe images formed on the observation surface every N stages of movement of the mirror by the minute displacement applying mechanism. A / D conversion means for converting the N interference fringe images picked up by the imaging means into digital interference fringe images;
Superimposing means for superimposing a signal variation between N images at each pixel of the interference fringe image digitally converted by the D converting means with a sine signal which forms one cycle between the N images; A phase operation for extracting only a component having a sine signal as a fundamental wave from signal fluctuations between N pixels at each pixel of the obtained interference fringe image and independently calculating the phase of this fundamental wave component at each pixel of the interference fringe image Means, and a surface potential distribution calculating means for calculating a surface potential distribution of the measured photoreceptor based on the phase at each pixel of the interference fringe image calculated by the phase calculating means. An electric field measuring apparatus for a photoreceptor surface, characterized in that: 6. An electric field sensor having an electro-optic crystal having an electro-optic effect and a light-wave reflecting portion made of a dielectric material deposited on one surface of the electro-optic crystal. A circle having a predetermined polarization state, which is provided near the surface of the photoconductor to be measured so as to penetrate the inside thereof, and is incident as probe light from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. A light source that emits polarized light is provided, and a probe light emitted from the light source passes through the electro-optic crystal, and a reflected light reflected by the light wave reflection unit is incident thereon. A λ / 4 wavelength plate and a mirror arranged on the arm of
A Twyman-Green interferometer having a mirror minute angle tilting means for tilting the mirror of one arm of the polarization splitting element by a small angle, and the mirror of one arm of the polarization splitting element is tilted by the mirror minute angle tilting means. By tilting the mirror by a small angle, the light wave that enters the mirror, is reflected, and returns to the polarization splitter, generates a linear phase delay in a plane orthogonal to the light wave traveling direction, and causes interference output from the Twyman-Green interferometer. It has an observation surface for generating a spatial carrier signal in one direction of the signal and observing an interference signal carrying the spatial carrier signal via a polarizing plate that forms an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. A two-dimensional or one-dimensional imaging means parallel to the spatial carrier signal generation direction for imaging an interference fringe image formed on the observation surface of the lever; A / D conversion means for converting a two-dimensional or one-dimensional image taken by the camera into a digital interference fringe image, and a spatial carrier when the interference fringe image digitally converted by the A / D conversion means is a two-dimensional image. For each scanning line parallel to the signal generation direction, in the case of a one-dimensional image, for each line output, the signal sequence is divided into a plurality of sections each having one spatial carrier signal period, and the division is performed by the dividing unit. A superimposing means for superimposing a sine signal having the same spatial carrier signal frequency for each section, and a Fourier series fundamental wave having a spatial carrier signal as a fundamental wave for each section on which the sine signal is superimposed by the superimposing means. Phase calculating means for extracting a component to calculate the phase of the interference fringe image signal; and a surface potential of the photoreceptor to be measured based on the phase of the interference fringe image signal calculated by the phase calculating means. An electric field measuring device on the surface of a photoconductor, comprising an electric field measuring means having a surface potential distribution calculating means for calculating a distribution. 7. An electro-optic crystal having an electro-optic effect and an electric field sensor formed by depositing a light-wave reflecting portion made of a dielectric on one surface of the electro-optic crystal. A circle having a predetermined polarization state, which is provided near the surface of the photoconductor to be measured so as to penetrate the inside thereof, and is incident as probe light from the other surface of the electro-optic crystal facing the light wave reflection portion of the electric field sensor. A light source that emits polarized light is provided, and a probe light emitted from the light source passes through the electro-optic crystal, and a reflected light reflected by the light wave reflection unit is incident thereon. A λ / 4 wavelength plate and a mirror arranged on the arm of
A Twyman-Green interferometer having a mirror minute angle tilting means for tilting the mirror of one arm of the polarization splitting element by a small angle, and the mirror of one arm of the polarization splitting element is tilted by the mirror minute angle tilting means. By tilting the mirror by a small angle, the light wave that enters the mirror, is reflected, and returns to the polarization splitter, generates a linear phase delay in a plane orthogonal to the light wave traveling direction, and causes interference output from the Twyman-Green interferometer. It has an observation surface for generating a spatial carrier signal in one direction of the signal and observing an interference signal carrying the spatial carrier signal via a polarizing plate that forms an angle of 45 ° with the orthogonal polarization axis of the polarization separation element. A two-dimensional or one-dimensional imaging means parallel to the spatial carrier signal generation direction for imaging an interference fringe image formed on the observation surface of the lever; A / D conversion means for converting a two-dimensional or one-dimensional image taken by the camera into a digital interference fringe image, and a spatial carrier when the interference fringe image digitally converted by the A / D conversion means is a two-dimensional image. For each scanning line parallel to the signal generation direction, in the case of a one-dimensional image, a Fourier transform in the spatial carrier distribution direction is obtained for each line output, and a line spectrum near the spatial carrier signal frequency is determined using the spatial carrier signal frequency as a center frequency. A window function extracting means for extracting the spatial carrier signal frequency equivalent with a window function having a bandwidth, and the line spectrum extracted by the window function extracting means is shifted in the DC direction by the spatial carrier signal frequency and inverse Fourier transformed. Phase calculating means for calculating the phase of the interference fringe image signal by calculating the phase of the interference fringe image signal calculated by the phase calculating means. An electric field measuring means having a surface potential distribution calculating means for calculating a surface potential distribution of the photoreceptor to be measured.