JP4761817B2 - Interferometer, Fourier spectrometer - Google Patents

Description

  The present invention relates to an interferometer that divides incident light into two optical paths and then superimposes them again to generate interference light, and a Fourier spectroscopic device equipped with the interferometer, and in particular to adjustment errors of the components of the interferometer. The present invention relates to an interferometer and a Fourier spectroscopic device capable of reducing a reduction in interference efficiency and visibility (an index representing the clarity of interference light).

As a method for evaluating the optical properties or light absorption characteristics of a subject, the subject is irradiated with interference light generated by an interferometer or the like, and the interference light transmitted through the subject or reflected from the subject is monitored. In addition, a Fourier spectroscopic device is known that acquires spectrum information corresponding to the interference light by Fourier transforming the measured value (interferogram or the like).
As interferometers used in the Fourier spectrometer, two-beam interferometers such as Jaman interferometers, Michelson interferometers, and Rayleigh interferometers are well known.

Here, a schematic configuration of a conventional Fourier spectroscopic device Y including a Michelson interferometer B which is an example of a two-beam interferometer and an operation of the Michelson interferometer B will be described with reference to FIG. Here, an example in which interference light transmitted through the sample 20 (subject) in the Fourier spectrometer Y is detected will be described. FIG. 6 is a schematic configuration diagram showing a schematic configuration of the Fourier spectrometer Y.
As shown in FIG. 6, the Fourier spectroscopic device Y forms an image of Michelson interferometer B and interference light generated by the Michelson interferometer B at a predetermined point of the sample 20 (measurement point of the sample 20). (Condensed) objective lens 12, collimator lens 13 for converting divergent interference light (transmission interference light) transmitted through the sample 20 into parallel light, and detection for detecting the intensity of the collimated transmission interference light The transmission interference light detected by the detector 14 (an example of the transmission interference light detection means) and the transmission interference light detected by the detector 14 is sampled at a predetermined timing, and the measured value (interferogram data) is subjected to Fourier transform to obtain the transmission interference. And a computer 16 having a function of acquiring spectral information corresponding to light.
The Michelson interferometer B includes a light source 1, a collimator lens 2, a beam splitter 3 (an example of a light splitting unit and a photopolymerization unit), a moving mirror 4 (an example of a second reflecting unit and a moving reflecting unit), a fixed A mirror 5 (an example of first reflecting means and fixed reflecting means) and a piezo driving device 15 are provided.
In the Michelson interferometer B configured as described above, when light such as infrared light having a relatively long wavelength (wavelength of 1 μm or more) is generated and emitted from the light source 1, the light is emitted from the collimator lens. After being collimated into parallel light L 1 by 2, the parallel light L 1 enters the beam splitter 3.
The parallel light L1 incident on the beam splitter 3 is divided into two optical paths by the beam splitter 3, and one of the parallel lights L21 is moved to the movable mirror 4 which is controlled to move at a constant speed in the direction of arrow P in FIG. The other parallel light L22 reflected is transmitted through the beam splitter 3 and guided to the fixed mirror 5.
In the movable mirror 4, the parallel light L21 is reflected in the direction parallel to the incident direction, but the movable mirror 4 is moved at a constant speed in the direction of arrow P by the movement control of the piezo drive device 15. Therefore, the optical path length (phase) of the reflected parallel light L31 changes with the movement. On the other hand, the fixed mirror 5 reflects the parallel light L22 in a direction parallel to the incident direction. However, since the fixed mirror 5 is fixed, the optical path length does not change.
The reflected parallel lights L31 and L32 reflected by the movable mirror 4 and the fixed mirror 5 are incident on the beam splitter 3 again, and are superimposed by the beam splitter 3 to generate and output interference light L4.

On the other hand, in Patent Document 1, coherent laser light having good wavelength stability is supplied to the above-described two-beam interferometer, an interference pattern of laser light output from the interferometer is obtained, and obtained from this interference pattern. An interference efficiency measuring device that calculates interference efficiency based on the optical path difference (phase error) is disclosed. If the interference efficiency is obtained using this interference efficiency measuring apparatus, it is possible to identify the cause of the decrease in interference efficiency based on the optical path difference (phase error).
JP-A-10-170340

In the Michelson interferometer B or the interferometer of the interference efficiency measuring apparatus (Patent Document 1), the tilt adjustment of the reflecting surfaces of the components such as the beam splitter 3, the moving mirror 4, and the fixed mirror 5 is performed with high accuracy. Otherwise, good interference light cannot be obtained. For example, when the tilt of the reflecting surface is deviated from the reference tilt angle, an optical path length difference is generated between the interference light beams passing through the respective regions in the plane of the interference light L4 output from the beam splitter 3. become. Since this optical path length difference appears as a phase difference in each interference light passing through each of the above regions, the visibility, which is an index representing the interference efficiency and the clarity of the interference light (contrast), is reduced.
Further, even when the reflecting surfaces of the beam splitter 3, the movable mirror 4, and the fixed mirror 5 do not have high plane accuracy (flatness), the interference efficiency or visibility is reduced similarly to the above, and good interference light is obtained. I can't.
The cause of lowering the interference efficiency can be specified using the interference efficiency measuring apparatus described in Patent Document 1, but when the cause is specified, as an improvement method, reflection of each of the above constituent elements is possible. There is no choice but to perform adjustment work such as re-adjusting the inclination of the surface and the plane accuracy with high accuracy. However, there is a limit to the adjustment accuracy obtained by such adjustment work. For this reason, in the conventional interferometer, a certain decrease in interference efficiency and a decrease in visibility have to be allowed. Such a decrease in interference efficiency and visibility is undesirable because it affects the interferogram and spectral information measured by the Fourier spectrometer.
Furthermore, when infrared light having a relatively long wavelength is used as the outgoing light from the light source 1, the interference efficiency is greatly reduced because the optical path length difference is relatively smaller than the wavelength of the outgoing light. When light of a short wavelength region such as visible light (wavelength 400 to 700 nm) or ultraviolet light (wavelength 200 to 400 nm) having a wavelength much shorter than that of the infrared light is used as the emitted light The optical path length difference is relatively large with respect to the wavelength of light in the short wavelength region. Therefore, there arises a problem that the interference efficiency and visibility of the interference light generated by the beam splitter 3 are greatly reduced due to the optical path length difference.
Accordingly, the present invention has been made in view of the above circumstances, and the object of the present invention is to identify interference light that causes a reduction in interference efficiency or visibility, and to remove the identified interference light. It is an object of the present invention to provide an interferometer capable of reducing a decrease in interference efficiency or visibility and a Fourier spectrometer using the interferometer.

In order to achieve the above object, the present invention provides a light dividing means for dividing light emitted from a light source into at least two light paths, and a first light for reflecting one light divided by the light dividing means in its incident direction. Photo-polymerization for generating interference light by superimposing the reflected light from the first reflecting means and the second reflecting means, the second reflecting means for reflecting the other light in the incident direction, and the reflected light from the first reflecting means and the second reflecting means An interferometer having means,
An image pickup means for imaging a wavefront image of the generated interference light successively in time by the photopolymerization means,
A phase difference calculating means for calculating a phase difference of the interference light wave for each of a plurality of divided regions in the continuous wavefront image based on the continuous wavefront image continuously picked up in time by the image pickup means;
Phase synchronism determining means for determining the phase synchronism of the interference light wave for each of the plurality of divided regions based on the phase difference calculated by the phase difference calculating means;
Interference light transmission limiting means for transmitting only interference light of a predetermined phase generated by the photopolymerization means;
A transmission control means for controlling the interference light transmission limiting means so as to transmit only the interference light determined to be in phase by the phase synchronization determination means;
An interferometer comprising:
The phase synchronism determining means compares the complex deviation angle obtained by Fourier transforming the luminance waveform for each of the plurality of divided areas obtained from the continuous wavefront image with a predetermined reference complex deviation angle. The interferometer is configured to determine the phase synchronism of the interference light wave.
Here, as the first reflecting means, a fixed mirror fixed at a predetermined position can be considered, and as the second reflecting means, a movable mirror controlled to be movable in the light incident direction can be considered.
As a result, the interference light that causes the interference efficiency or visibility is identified, and the identified interference light is removed from the interference light generated and output by the photopolymerization means. Can be extracted and output. As a result, it is possible to reduce the degradation of interference efficiency and visibility.

  As a calculation method of the phase difference, a luminance waveform of interference light in each of the plurality of divided regions is obtained from the continuous wavefront image, and the phase difference of the interference light wave is calculated from the obtained luminance waveform and a predetermined reference waveform. It is conceivable to calculate.

Synchronization determination proposed method to which the present invention is employed, the complex argument obtained by the luminance waveform for each of the plurality of divided regions obtained by the upper Symbol phase calculation means for Fourier transform, and default reference complex argument it is obtained so as to determine the synchronization of the phase of the interference light waves by comparing.
As a result, it is possible to clearly determine the causal element (interfering light having different phases) that is reducing the interference efficiency or visibility.

Here, as the interference light transmission limiting means, a transmittance variable filter that freely changes the transmittance for each predetermined region on the incident surface of the interference light according to the input of a predetermined control signal, or the input of a predetermined control signal This includes a variable aperture that freely adjusts the opening position and / or opening area according to the above.
By using such a variable transmittance filter and variable aperture, the certainty of the output of only the coherent interference light is increased.
In view of the fact that the interference efficiency and visibility of interference light are significantly reduced when light in the short wavelength region such as visible light or ultraviolet light is used, the interferometer of the present invention has a short wavelength of less than 1 μm. It is suitable when using a light source that emits light that contains it.

In addition, the present invention is a Fourier spectrometer that includes the interferometer, measures the interference light generated by the interferometer, and obtains spectral information corresponding to the interference light by Fourier transforming the measured value. You may catch it. With such a Fourier spectrometer, the accuracy of the acquired spectrum information can be improved.
There are various methods for acquiring spectral information with the Fourier spectroscopic apparatus. For example, as one form, the intensity of transmitted interference light transmitted through the subject is detected by irradiating the subject with the interference light. It is conceivable that a transmission interference light detection means is provided and the spectral information is acquired based on the intensity of the transmission interference light detected by the transmission interference light detection means.
In addition, a probe laser beam irradiation unit that irradiates a subject that has generated heat by irradiation with the interference light, and a transmitted laser beam that has been irradiated by the probe laser beam irradiation unit and transmitted through the subject. Or a probe laser light detecting means for detecting the reflected laser light reflected by the subject, and the spectral information based on the phase change of the transmitted laser light or the reflected laser light detected by the probe laser light detecting means. May be obtained.
Of course, a Fourier spectroscopic apparatus provided with all the above means (transmission interference light detecting means, probe laser light irradiating means) that acquires spectral information by a plurality of methods is also an embodiment of the present invention.

  According to the present invention, the interference light that causes the interference efficiency or visibility is identified, and the identified interference light is removed from the interference light generated and output by the photopolymerization means, Since only interference light having substantially the same phase can be extracted and output, it is possible to reduce the degradation of interference efficiency and visibility.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
Here, FIG. 1 is a schematic configuration diagram showing a schematic configuration of a Fourier spectrometer X equipped with the Michelson interferometer A according to the embodiment of the present invention, and FIGS. 2 and 3 are measured by the Fourier spectrometer X. FIG. 4 is a graph showing an example of a luminance waveform, FIG. 4 is an image showing an example of a wavefront image of a captured interference light plane, and FIG. 5 is a characteristic diagram showing an example of transmission characteristics of a micro filter constituting a variable transmittance filter. 6 is a schematic configuration diagram showing a schematic configuration of a Fourier spectroscopic device Y provided with a conventional Michelson interferometer B. FIG.

As shown in FIG. 1, the Fourier spectrometer X generates a Michelson interferometer A that generates and outputs predetermined interference light, and converges the interference light output from the Michelson interferometer A to a sample 20 ( An objective lens 12 that collects light at a predetermined measurement point of a subject, a collimator lens 13 that converts divergent interference light transmitted through the sample 20 into parallel light, and interference that has been converted into parallel light by the collimator lens 13. It comprises a detector 14 for detecting light (an example of transmitted interference light detection means) and a computer 16 for obtaining spectral information according to the transmitted interference light detected by the detector 14 by calculation.
The computer 16 is connected to a display device and an input device (not shown). The computer 16 displays the brightness of the monitored interference light (appears as interference fringes) on the display device and receives a signal input from the input device. Is configured to do.

In the Fourier spectroscopic device X configured as described above, as is well known, first, by irradiating the sample 20 with interference light output from the Michelson interferometer A, interference light (transmission interference light) transmitted through the sample 20 is transmitted. ) Is detected by the detector 14. Then, the brightness of the detected interference light is monitored by the computer 16, and the measured value (interferogram data etc.) obtained by sampling at a predetermined timing is subjected to Fourier transform to obtain a spectrum corresponding to the transmitted interference light. Information is acquired. Hereinafter, the operation mode of the Fourier spectroscopic device X that acquires spectrum information as described above is referred to as a spectrum acquisition mode.
In this embodiment, the Fourier spectroscopic device X configured to detect the transmission interference light transmitted through the sample 20 by the detector 14 will be described as an example. However, the reflected light reflected from the sample 20 is detected. The present invention can also be applied to a so-called reflection type Fourier spectrometer.

Unlike the conventional spectrum acquisition mode, the Fourier spectrometer X has a phase different from a predetermined phase (reference phase) as a reference from the interference light generated and output from the Michelson interferometer A in addition to the spectrum acquisition mode. There is a calibration mode in which interference light is identified and removed (hereinafter referred to as “interference light calibration”).
As described above, when the phase difference occurs in the interference light due to the adjustment error of the components of the Michelson interferometer A, the interference efficiency and the visibility are lowered. In order to reduce a significant decrease in interference efficiency and visibility, the Fourier spectrometer X is provided with the calibration mode.
The calibration of the interference light in the calibration mode is automatically performed by the computer 16 at the time of manufacturing the Fourier spectroscopic apparatus X, at the time of delivery to the customer, or at predetermined intervals, for example. The operation mode and the calibration mode are switched by the computer 16 based on a switching signal input from an input device (not shown) by the operator. Alternatively, the calibration mode is automatically switched every time a certain period elapses.

  In the following, each component of the Fourier spectroscopic apparatus X will be described, and interference light calibration performed by the computer 16 in the calibration mode will be described. In this embodiment, an example using a Michelson interferometer A as an example of an interferometer will be described. However, this is merely an example. For example, an interferometer such as a Jaman interferometer or a Rayleigh interferometer (two It is also possible to use a light beam interferometer) or a multi-beam interferometer.

In the spectrum acquisition mode, the detector 14 irradiates the sample 20 with the interference light output from the Michelson interferometer A, and then images the transmitted interference light transmitted through the sample 20 at a predetermined sampling timing. It is. In the calibration mode, the wavefront image of the interference light output from the Michelson interferometer A is continuously captured every minute time. Needless to say, the transition of the wavefront of the interference light may be captured as a moving image (video data). That is, the detector 14 functions as an example of transmitted interference light detection means in the spectrum acquisition mode, and functions as an example of image capturing means in the calibration mode. Unlike the configuration of the present embodiment, for example, an image sensor that is an example of an image capturing unit that continuously captures interference light may be provided separately from the detector 14. Absent.
A specific example of the detector 14 includes an image sensor such as a CCD that captures a continuous image so that the luminance of the interference light changes. The interference light (continuous image of interference fringes) detected (imaged) by the detector 14 is transferred to the computer 16 for analysis.

The computer 16 is an electronic computer having a CPU, other control elements such as RAM and ROM.
The computer 16 is provided with a phase difference calculation function, a phase synchronism determination function, and a light transmission control function. Each of these functions is realized by executing processing according to a predetermined program by the CPU in the calibration mode. Each function (phase difference calculation function, phase synchronism determination function, control) When the function is activated, the computer 16 functions as a phase difference calculation means, a phase synchronism determination means, and a control means of the present invention. Each of the above functions will be described later.
In the present embodiment, an example in which the above functions (phase difference calculation function, phase synchronization determination function, control function) are realized by program processing by the computer 16 will be described. Instead of the program processing, for example, There may be an embodiment in which each function is achieved by hard logic using an IC or the like in which a circuit for executing processing corresponding to each function is incorporated.

  The Michelson interferometer A includes a light source 1, a collimator lens 2, a beam splitter 3 (an example of a light splitting means and a photopolymerization means), a moving mirror 4 (an example of a second reflecting means and a moving reflecting means), a fixed mirror 5 (Example of first reflecting means and fixed reflecting means), piezo driving device 15, and transmission limiting device 6 (an example of interference light transmission limiting means). The Michelson interferometer A is different from the conventional Michelson interferometer B (FIG. 6) in that the transmission limiting device 6 is provided.

Here, each component of the Michelson interferometer A will be described.
The light source 1 is, for example, a light source that generates white light and emits the generated white light. Conventionally, a light source that emits infrared light having a relatively long wavelength has been used as the light source 1. However, in the Michelson interferometer A, interference efficiency and visibility are improved by the transmission limiting device 6 as described later. Since interference light (interference light having a phase different from the reference phase) that causes a decrease is removed, white light including light in a short wavelength region with a wavelength of less than 1 μm, such as visible light and ultraviolet light, is used as outgoing light. It is also possible to use it. Of course, infrared light having a wavelength of 1 μm or more can be used as in the conventional case, or a light source that emits the visible light or ultraviolet light as a single light can be used.

  The collimator lens 2 is a lens that converts light emitted from the light source 1 into parallel light. Any optical system device that converts light from the light source 1 into parallel light may be used. The collimator lens 2 is provided between the light source 1 and the beam splitter 3 in order to make the light parallel light and enter the beam splitter 3. In the present embodiment, an example in which the light from the light source 1 is converted into parallel light and irradiated to the optical system device at the subsequent stage will be described. is not.

A beam splitter 3 is arranged on the collimator lens 2 on the parallel light traveling direction side.
This beam splitter 3 divides (branches) incident light into at least two optical paths, and includes, for example, a half mirror (semi-transparent mirror) having a transmittance of 50% on its reflection surface. The beam splitter 3 reflects one of the divided lights in a direction approximately 90 ° with respect to the incident direction and irradiates the movable mirror 4 substantially perpendicularly, and the other light transmitted through the beam splitter 3 is irradiated. It is arranged so that it goes straight as it is and irradiates the fixed mirror 5 substantially vertically.
The beam splitter 3 also generates interference light by superimposing the reflected light from the movable mirror 4 and the fixed mirror 5.
In this Michelson interferometer A, as described above, splitting of incident light and superposition (combination) of reflected light are carried out by one beam splitter 3, but the splitting and superposition are realized by separate optical system devices. It may be in form.

The movable mirror 4 and the fixed mirror 5 have reflecting surfaces 4a and 5a for reflecting incident analysis light in the incident direction.
The fixed mirror 5 is arranged on a linear extension line connecting the light source 1, the collimator lens 2 and the beam splitter 3, so that the beam splitter 3 is positioned between the fixed mirror 5 and the collimator lens 2. It is fixedly arranged.
The movable mirror 4 is disposed at a position where the light reflected by the beam splitter 3 enters substantially vertically. Unlike the fixed mirror 5, the movable mirror 4 is arranged so as to be movable in the light incident direction (the direction of arrow P in FIG. 1). When generating interference light, a known piezo drive device 15 is used. Constant speed movement control is performed.

The transmission limiting device 6 is a device that transmits only the interference light having a predetermined phase among the interference light generated by being superimposed by the beam splitter 3. In other words, the interference light having a phase different from the reference phase is blocked or attenuated from the generated interference light, and only the interference light having substantially the same phase as the reference phase is allowed to pass to the detector 14. .
The transmission limiting device 6 is disposed on the optical path of the interference light in the spectrum information acquisition mode, and is retracted from the optical path in the calibration mode.
As such a transmission limiting device 6, for example, in accordance with a predetermined control signal, which will be described later, output from the computer 16, a transmission capable of freely changing the transmittance for each predetermined region on the incident surface of the interference light. A variable aperture filter, a variable aperture having a mechanism capable of moving the opening position according to the predetermined control signal, or freely expanding and contracting the opening area, and the like are applicable.

The variable transmittance filter is, for example, a small filter (such as a band filter) whose wavelength band to be transmitted changes (shifts) according to the value of a supplied current (voltage) signal (corresponding to a control signal). A configuration in which a plurality of surfaces are arranged is conceivable. Moreover, the filter which consists of a liquid crystal in which these micro filters were arranged in the shape of a plurality of grids may be used.
As the fine filter, for example, as shown in the transmission characteristic diagram of FIG. 5, the transmission characteristic of the fine filter according to the supplied current value is the total wavelength component (for example, in FIG. 5). From the transmission characteristic 51 (solid line) that transmits only light in the wavelength band 51w including the shaded portion 53), only light in the wavelength band 52w that does not include all wavelength components included in the interference light is transmitted (that is, This corresponds to the transmission characteristic 52 (broken line) that does not transmit the interference light.
Note that the transmittance at a predetermined wavelength is changed by changing the wavelength band. Of course, not only the transmittance of the filter but also the refractive index or the like may be changed.
In addition, a plurality of minute interference filters are arranged on the incident light incident surface so as to be tiltable, and the inclination of the plurality of interference filters is determined by current (voltage) signals (corresponding to control signals) supplied to the respective interference filters. A configuration in which the corners are individually driven and controlled is conceivable. This utilizes the characteristic property of the interference filter, that is, the property that the transmitted wavelength band changes (shifts) in accordance with the inclination of the interference filter. Note that this minute interference filter also changes its transmission characteristic from the transmission characteristic 51 (solid line) to the transmission characteristic 52 (broken line) as shown in the transmission characteristic diagram of FIG. 5 according to the inclination of the filter. .
When the transmittance variable filter as described above is used, during calibration, which will be described later, a region where interference light having a phase different from the reference phase (interference light to be removed) passes, interference light having substantially the same phase as the reference phase is transmitted. Information indicating the passing area (interference light to be transmitted) or the position (coordinates) of these areas is acquired in advance. Based on these pieces of information, for example, the current wavelength band 51w (see FIG. 5) is applied only to the minute filter arranged in a region through which interference light having a phase different from the reference phase (interference light to be removed) passes. A signal to be changed to the wavelength band 52w is output. Thereby, the interference light having a phase different from the reference phase is attenuated by the transmittance variable filter, and the interference light having substantially the same phase as the reference phase is transmitted without being attenuated and guided to the detector 14.

The variable aperture includes, for example, a diaphragm mechanism made of a non-translucent member that freely expands and contracts an opening area provided in a camera and the like, and a driving unit such as a motor that is connected to the diaphragm mechanism and transmits a driving force. And a device for operating the diaphragm mechanism to expand and contract the size of the aperture by driving the driving means in accordance with a driving signal (corresponding to a control signal) from the computer 16, and for emitting interference light. A moving mechanism using a rail mechanism or the like that freely moves the diaphragm mechanism in a direction perpendicular to the direction, and a device that transmits a driving force to the diaphragm mechanism and moves the diaphragm mechanism to a predetermined position by the horizontal movement mechanism Etc. may also be configured.
Even when such a variable aperture is used, the above-described information is acquired in advance at the time of calibration described later. Based on these pieces of information, for example, the aperture of the diaphragm mechanism is changed so as to have the same size as a region through which interference light having substantially the same phase as the reference phase (interference light to be transmitted) passes. The aperture mechanism is moved so that the aperture center of the aperture mechanism coincides with the center of the interference light having substantially the same phase. As a result, interference light having substantially the same phase as the reference phase passes through the aperture of the diaphragm mechanism and is guided to the detector 14, and interference light having a different phase is blocked by the variable aperture.

In the Michelson interferometer A configured as described above, in the spectrum acquisition mode, the light emitted from the light source 1 is converted into parallel light by the collimator lens 2 and then incident on the beam splitter 3. The one light is reflected toward the movable mirror 4 and the other light is not reflected but passes through the beam splitter 3 and travels straight toward the fixed mirror 5.
The light traveling to the fixed mirror 5 is reflected by the reflecting surface 5a, and the light reflected by the moving mirror 4 is reflected by the reflecting surface 4a of the moving mirror 4. Then, the light reflected by the fixed mirror 5 and the movable mirror 4 returns to the beam splitter 3 and is superimposed by the beam splitter 3 to generate interference light.
Thereafter, only the interference light having a phase different from a predetermined reference phase is attenuated or blocked by the transmission limiting device 6 and only the interference light having a phase substantially in phase with the reference phase is detected by the transmission limiting device 6. 14 is output.

When the Fourier spectrometer X configured as described above is in the calibration mode, the interference output from the Michelson interferometer A is saved by removing or removing the transmission limiting device 6 from the optical path of the interference light. The light is guided to the detector 14 without changing its characteristics. When the variable aperture is used as the transmission limiting device 6, all the interference light may be guided to the detector 14 by widening the aperture of the diaphragm mechanism to the maximum.
Here, in the calibration mode, it is desirable to remove the sample 20 from the optical path of the interference light. However, since the phase of the interference light does not change even if it passes through the sample 20, it must be removed. is not.

The interference light guided to the detector 14 includes a plurality of optical path length differences caused by tilt errors of the reflecting surfaces of the beam splitter 3, the fixed mirror 5, and the movable mirror 4, and plane accuracy (distortion, etc.). Interference light is included.
When this interference light is incident on the detector 14, the wavefront image of the incident interference light is continuously captured in time by the detector 14, and then the captured continuous wavefront image is transferred to the computer 16. The
In the computer 16, the transferred continuous wavefront image is analyzed by the phase difference calculation function of the computer 16. By this analysis, the phase difference of each interference light passing through each of the divided areas (corresponding to the predetermined divided areas) obtained by dividing the continuous wavefront image into a plurality of parts is calculated (step S1).
Specifically, the scanning position of the movable mirror 4 that moves at a constant speed is indicated on the horizontal axis (the numerical value on the horizontal axis indicates the distance from the beam splitter 3), and the plurality of divided regions corresponding to the scanning position of the movable mirror is shown. The luminance waveform (interferogram waveform) shown in FIG. 2 and FIG. 3 expressed by plotting the average luminance [cd / mm ² ] of the interference light in each axis on the vertical axis is obtained, and this luminance waveform is determined in advance. A method of calculating the phase difference of the interference light wave from a predetermined reference waveform (described later) is conceivable. Of course, the phase difference can be obtained by applying other methods. Note that if the moving mirror 4 is controlled to move at a constant speed by the piezo drive device 15, the luminance waveform can be said to be a waveform in which the average luminance is plotted in the time series direction.
Here, FIG. 2 shows a luminance waveform Qα (solid line in the figure) of the interference light that has passed through each area when the continuous wavefront image is divided into three areas of divided areas α, β, and γ (see FIG. 4). FIG. 3 is a graph showing Qβ (broken line in the figure) and Qγ (dashed line in the figure), and FIG. 3 is a detailed graph in the vicinity of the position 610 of the movable mirror 4 having a large variation in average luminance in FIG. FIG. 4A shows an example of a wavefront image of the interference light at the position 611. FIG. 4B is a schematic diagram of FIG.
Originally, if there is no tilt error or plane distortion of the reflection surface of the optical system equipment such as the beam splitter 3, one luminance waveform can be obtained. However, depending on the tilt error or plane distortion of the optical system equipment, etc. When a plurality of interference lights having different optical path length differences are generated, a plurality of luminance waveforms Qα, Qβ, Qγ are obtained as shown in FIGS.
As the reference waveform, for example, reference waveform data stored in advance in the memory (storage medium) of the computer 16 may be used. More preferably, interference light having the largest area occupancy in the wavefront image (see FIG. 4). In the example shown, interference light passing through the region γ) may be used as a reference. Therefore, for example, when the luminance waveform Qγ of the interference light passing through the region γ is used as the reference waveform, the phase difference Δθ1 (see FIG. 3) between the waveform Qγ and the waveform Qα, and the phase difference between the waveform Qγ and the waveform Qβ. Δθ2 (see FIG. 3) is obtained by the computer 16.
In the following description, the luminance waveforms Qα, Qβ, Qγ will be described as an example. For convenience of explanation, an example in which the continuous wavefront image is divided into three divided regions α, β, and γ will be described. Needless to say, the embodiment is not limited to such a divided mode. It is desirable from the viewpoint of improving the resolution to divide into a large number of regions and obtain the phase difference of the interference light in each region.

At the time of the calibration, when the computer 16 obtains the phase differences Δθ1 and Δθ2 from the luminance waveforms Qα, Qβ, and Qγ shown in FIGS. 2 and 3, each luminance is subsequently determined based on the phase differences Δθ1 and Δθ2. Processing for determining the phase synchronism of the waveforms Qα, Qβ, Qγ is performed by the computer 16 (step S2).
In this determination, the phase synchronism is determined by comparing the calculated phase difference with a threshold value relating to a predetermined phase difference. Specifically, if the calculated phase difference Δθ1 is less than the threshold value, it is determined that the phase of the reference waveform Qα and the reference waveform (in this embodiment, the luminance waveform Qγ) are the same or substantially the same. That is, it is determined to be substantially in phase. If the phase difference Δθ1 is equal to or greater than the threshold value, it is determined that the phase is different. The phase synchronism is similarly determined for the phase difference Δθ2.
Further, a complex declination angle (an angle formed by a real part and an imaginary part) obtained by Fourier transforming the obtained luminance waveforms Qα, Qβ, and Qγ for each of the plurality of divided regions α, β, and γ is determined in advance. The phase synchronism of the interference light wave may be determined by comparing a reference complex deviation angle (corresponding to a predetermined reference complex deviation angle) as a reference. That is, it is determined that the complex declination obtained by Fourier transform is the same or substantially the same as the reference complex declination, and it is determined that the reference complex declination is out of phase if there is a gap more than a predetermined width. To do. Here, the reference complex declination means a complex declination of the interference light having the largest occupation ratio in the reference waveform data and the wavefront image.

If it is determined by the above-described synchronization determination that, for example, interference light other than the interference light passing through the region γ (FIG. 4) has no synchronization (that is, the phase is different from the interference light passing through the region γ), Thus, control of the transmission limiting device 6 by the computer 16 is executed. That is, the transmission limiting device 6 is controlled so as to transmit only the interference light determined to have the same phase (step S3). Thereby, the interference light irradiated to the sample in the spectrum acquisition mode is calibrated.
For example, when the above-described variable transmittance filter is used as the equal configuration limiting device 6, the light transmittance is increased by adjusting the inclination of the minute filter arranged at the position corresponding to the region γ. A current signal (control signal) is output to each microfilter so as to reduce the light transmittance by adjusting the inclination of the microfilter arranged at a position corresponding to the region.
When the variable aperture is used as the equal configuration limiting device 6, the driving means is controlled so that the aperture area of the aperture mechanism is the same size as the region γ, and the aperture center of the aperture mechanism is The diaphragm mechanism is controlled to move so as to coincide with the center of the region γ.

Thus, in the calibration mode of the Fourier spectrometer X, only the interference light having substantially the same phase is output from the Michelson interferometer A by performing the calibration described above. That is, interference light having no optical path length difference is output. Therefore, a decrease in interference efficiency and visibility of interference light irradiated on the sample 20 is reduced.
Further, since the spectral information obtained by the Fourier spectroscopic device X is obtained by irradiating the sample 20 with only substantially in-phase interference light, the accuracy of the spectral information is improved.

Needless to say, the Fourier spectrometer X described in the above embodiment is an example of an embodiment of the present invention. Therefore, the present invention can be applied to other various forms of Fourier spectroscopic apparatuses.
For example, a laser beam (corresponding to a probe laser beam) is irradiated on the sample 20 that has generated heat by being irradiated with the interference light output from the Michelson interferometer A, and thus the transmitted laser beam transmitted through the sample 20 or The reflected laser light reflected from the surface of the sample 20 is detected by a detector (an example of a probe laser light detecting means) having a CCD or the like, and the detected laser light is analyzed by the computer 16 to obtain spectral information. The Fourier spectroscopic apparatus of the embodiment, or the Fourier spectroscopic apparatus configured to obtain the spectral information by arranging the sample as the subject on the reflecting surface of the fixed mirror 5 or arranging the sample as the fixed mirror 5. The present invention can be applied.

The schematic block diagram which shows schematic structure of the Fourier spectrometer X provided with the Michelson interferometer A which concerns on embodiment of this invention. The graph which shows an example of the luminance waveform measured with the Fourier spectrometer X FIG. 3 is a detailed graph of a portion where the average luminance variation is large in FIG. 2. The image figure which shows an example of the wave surface image of the imaged interference light plane. The characteristic view which shows an example of the transmission characteristic of the micro filter which comprises a transmittance | permeability variable filter. The schematic block diagram which shows schematic structure of the Fourier spectrometer Y provided with the conventional Michelson interferometer B.

Explanation of symbols

X ... Fourier spectrometer A ... Michelson interferometer 1 ... light source 2 ... collimator lens 3 ... beam splitter 4 ... moving mirror 5 ... fixed mirror 6 ... transmission restriction device 12 ... objective lens 13 ... collimator lens 14 ... detector 15 ... piezo Drive device 16 ... computer 20 ... sample

Claims (8)

A light splitting means for splitting the light emitted from the light source into at least two light paths; a first reflecting means for reflecting one light split by the light splitting means in its incident direction; and the other light being made incident An interferometer comprising: a second reflecting means for reflecting in a direction; and a photopolymerization means for generating interference light by superimposing the reflected light from the first reflecting means and the second reflecting means,
An image pickup means for imaging a wavefront image of the generated interference light successively in time by the photopolymerization means,
A phase difference calculating means for calculating a phase difference of the interference light wave for each of a plurality of divided regions in the continuous wavefront image based on the continuous wavefront image continuously picked up in time by the image pickup means;
Phase synchronism determining means for determining the phase synchronism of the interference light wave for each of the plurality of divided regions based on the phase difference calculated by the phase difference calculating means;
Interference light transmission limiting means for transmitting only interference light of a predetermined phase generated by the photopolymerization means;
A transmission control means for controlling the interference light transmission limiting means so as to transmit only the interference light determined to be in phase by the phase synchronization determination means;
An interferometer comprising:
The phase synchronism determining means compares the complex deviation angle obtained by Fourier transforming the luminance waveform for each of the plurality of divided areas obtained from the continuous wavefront image with a predetermined reference complex deviation angle. An interferometer for determining the phase synchronism of the interference light wave.   The phase difference calculating means obtains a luminance waveform of interference light in each of the plurality of divided regions from the continuous wavefront image, and calculates a phase difference of the interference light wave from the obtained luminance waveform and a predetermined reference waveform. The interferometer according to claim 1.   The interference light transmission limiting means is a transmittance variable filter that freely changes the transmittance for each predetermined region on the incident surface of the interference light according to the input of a predetermined control signal, or according to the input of the predetermined control signal The interferometer according to claim 1, further comprising a variable aperture that freely adjusts an opening position and / or an opening area.   The interferometer according to claim 1, wherein the light source emits light including a short wavelength of less than 1 μm.   The first reflecting means is a fixed mirror fixed at a predetermined position, and the second reflecting means is a movable mirror controlled to be movable in the light incident direction. Interferometer.   The interferometer according to any one of claims 1 to 5 is provided, the interference light generated by the interferometer is measured, and spectral information corresponding to the interference light is obtained by performing Fourier transform on the measured value. Fourier spectroscopy equipment. A transmission interference light detecting means for detecting the intensity of the transmission interference light transmitted through the subject by irradiating the subject with the interference light,
The Fourier spectroscopic apparatus according to claim 6, wherein the spectrum information is acquired based on an intensity of the transmitted interference light detected by the transmitted interference light detection unit. A probe laser beam irradiation means for irradiating a probe laser beam to a subject that has generated heat by being irradiated with the interference light;
Probe laser light detection means for detecting transmitted laser light irradiated by the probe laser light irradiation means and transmitted through the subject or reflected laser light reflected by the subject;
8. The Fourier spectroscopic apparatus according to claim 6, wherein the spectral information is acquired based on a phase change of transmitted laser light or reflected laser light detected by the probe laser light detecting means.

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