CN117309330A - Method and device for measuring small-angle deflection precision based on cone light interference - Google Patents
Method and device for measuring small-angle deflection precision based on cone light interference Download PDFInfo
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Abstract
The invention discloses a method and a device for measuring small-angle deflection precision based on cone light interference. The method comprises the following steps: laser emitted by a laser light source sequentially passes through a deflector to be detected and a polarizer to obtain linearly polarized light; linearly polarized light is injected into the electro-optical crystal at a preset angle, o light and e light are obtained through decomposition, and phase delay is generated; the o light and the e light interfere after passing through the analyzer, and the generated interference light is received by the photoelectric detector; rotating the electro-optic crystal until the light spot intensity is maximum, and recording a first incident view field angle; the deflector to be tested scans with a scanning step length until the light spot intensity is 0, and a second incident view field angle is recorded; and counting the number of resolvable light spots received by the photoelectric detector in the process of changing the light spot intensity from the maximum to 0, and calculating to obtain the scanning precision of the deflection device to be detected according to the difference between the first incident view field angle and the second incident view field angle divided by the number of light spots. The method and the device have the advantages of simplicity in measurement and high measurement accuracy.
Description
Technical Field
The invention belongs to the technical field of photoelectrons and lasers, and particularly relates to a method and a device for measuring small-angle deflection precision based on cone light interference.
Background
The laser high-speed scanning system is widely applied in the technical fields of laser scribing, imaging, photoetching and the like, and the main laser high-speed scanning modes at present can be divided into two types, namely a mechanical scanner based on a reflecting mirror and mainly comprises a galvanometer scanning (galvo-mirrors) and a piezoelectric scanning (piezo mirrors); the second category is optical-based solid state deflectors, mainly including acousto-optic deflectors (AODs) and electro-optic deflectors (EODs).
The conventional mirror-based mechanical scanning approach suffers from accuracy and repeatability of beam positioning in high precision manufacturing due to mechanical movement and return error of the mirrors, and therefore its yaw angular velocity is substantially limited by inertia associated with the mass of the turning mirror and other moving parts. In contrast, the acousto-optic deflector and the electro-optic deflector do not contain any mechanical moving parts, so that the defects of abrasion, mechanical noise, drift and the like related to a mechanical scanner are avoided, the laser beam can be deflected with high precision without being influenced by mechanical inertia, and the acousto-optic deflector has the advantages of high scanning speed, high precision, short response time, random access scanning and the like, and is widely applied to laser direct writing systems.
In order to effectively evaluate the scanning accuracy of acousto-optic deflectors (AODs) and electro-optic deflectors (EODs), it is necessary to quantify them using a precise small angle measurement method. With the rapid development of laser industrial processing and photon imaging fields, the requirements on the scanning precision of an acousto-optic deflector (AOD) and an electro-optic deflector (EOD) are increasingly improved, so that the following problems exist in the traditional beam deflection angle precise measurement method, such as a direct measurement method based on a CCD, an auto-collimation method and a double-mirror reflection method: (1) The CCD-based direct measurement method has the advantages of complex operation, high measurement cost, easy influence of ambient stray light, limitation of the precision by the pixel size and the focal length of a camera lens, limitation, and difficulty in meeting the precision requirements of high-precision scanning devices such as an acousto-optic deflector (AOD), an electro-optic deflector (EOD) and the like; (2) The auto-collimation method has the advantages that an imaging light path is complex and difficult to adjust, the measurement distance is generally short, and in addition, the auto-collimation method usually needs to be accurately calibrated and adjusted in advance, so that the auto-collimation method is difficult to adapt to a dynamically-changed measurement scene; (3) The double-mirror reflection method has high requirements for the surface quality of the reflecting mirror, so that the manufacturing cost is high, in addition, the double-mirror reflection method needs accurate installation and debugging of the reflecting mirror to ensure that the positions and angles of the reflecting mirror and the light source are aligned accurately, so that the installation and debugging processes are relatively difficult, and the accuracy of the method is limited by the measuring distance and the angle range, so that the method has low practicability. (4) The measurement resolution is insufficient (> 2 mu rad) and cannot be matched with high scanning accuracy (.ltoreq.0.2 mu rad) of an acousto-optic deflector (AOD) and an electro-optic deflector (EOD).
Therefore, the small angle measuring method for the deflector in the prior art has the problems of complex operation, high measuring cost and lower measuring precision.
Disclosure of Invention
Aiming at the defects of the related art, the invention aims to provide a method and a device for measuring small-angle deflection precision based on cone light interference, and aims to solve the problems of complex operation, high measurement cost and lower measurement precision of a measuring method for a small angle of a deflector in the prior art.
To achieve the above object, in a first aspect, the present invention provides a method for measuring small-angle deflection accuracy based on cone light interference, including:
laser emitted by a laser light source sequentially passes through a deflector to be detected and a polarizer to obtain linearly polarized light;
the linearly polarized light is injected into the electro-optical crystal at a preset angle, o light and e light are obtained through decomposition, and phase delay is generated;
the o light and the e light obtained by decomposition interfere after passing through the analyzer, and the generated interference light is received by the photoelectric detector;
rotating the electro-optic crystal until the light spot intensity received by the photoelectric detector is maximum, and recording a first incident view field angle;
the deflector to be detected scans with a scanning step length until the light spot intensity received by the photoelectric detector is 0, and a second incident view field angle is recorded;
and counting the number of resolvable light spots received by the photoelectric detector in the process of changing the light spot intensity from the maximum to 0, and calculating to obtain the scanning precision of the deflection device to be detected according to the difference between the first incident view field angle and the second incident view field angle divided by the number of light spots.
Optionally, before the laser emitted by the laser light source sequentially passes through the deflector to be tested and the polarizer, the method further includes:
and the laser emitted by the laser light source is collimated by the collimating lens to obtain a reference beam.
Optionally, the preset angle is an included angle between the incident linearly polarized light and the optical axis of the electro-optic crystal, and the preset angle is 5 °.
Optionally, the phase delay is:
wherein L is the thickness of the electro-optic crystal,n o 、n e the main refractive index of o light and the main refractive index of e light are respectively, and omega is a preset angle.
Optionally, the light intensity of the interference light is:
wherein A1 is the amplitude of incident linearly polarized light, θ is the angle between the projection direction De of the e-light in the xy plane and the polarizing direction P1 of the polarizer, A o2 And A e2 The amplitudes of the o light and the e light after passing through the analyzer, respectively.
Optionally, when δ=2kpi, the interference fringe is a bright fringe, and the intensity of the light spot received by the photodetector is the largest;
when delta= (2k+1) pi, the interference fringes are dark fringes, and the intensity of a light spot received by the photoelectric detector is 0; where k represents the interference order, k=0, 1,2,3,4, … ….
Optionally, the to-be-detected deflector is an acousto-optic deflector or an electro-optic deflector, and if the to-be-detected deflector is the acousto-optic deflector, the reference beam coincides with the zero-order diffraction direction of the acousto-optic deflector.
In a second aspect, the present invention also provides an apparatus for small angle deflection accuracy measurement based on cone light interferometry, for performing the method according to any of the first aspects, comprising: the laser light source, the collimating lens, the deflector to be measured, the polarizer, the electro-optic crystal, the analyzer and the photoelectric detector are sequentially arranged along the light path;
the collimating lens is used for collimating laser emitted by the laser source to obtain a reference beam;
the deflector to be measured is used for deflecting the reference beam at a small angle;
the polarizer is used for converting an incident light beam into linearly polarized light;
the electro-optical crystal is used for decomposing incident linearly polarized light to obtain o light and e light and generating phase delay;
the analyzer is used for transmitting o light and e light in a preset direction and generating interference light;
the photodetector is used for receiving light spots generated by interference light.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. the method for measuring the small-angle deflection precision based on the cone light interference has the advantages that the adopted measuring device is simple in light path, easy to adjust and beneficial to practical application; the birefringence characteristic of the electro-optic crystal is utilized, so that deflection light is incident to the electro-optic crystal at different angles to generate different phase differences, and the photoelectric detector receives high-contrast light intensity, thereby measuring the accuracy of the deflection device; the measurement accuracy is not affected by the measurement range and the pixel resolution of the photoelectric detector, so that the high resolution can be ensured when the measurement range is large.
2. According to the method for measuring the small-angle deflection precision based on the cone light interference, the measurement precision of the system can be adjusted according to the measured scanning precision of the deflection device to be measured, so that the measurement precision of the system is matched with the scanning precision of the deflection device to be measured, and the practical feasibility is improved; the deflection device for measurement is an acousto-optic deflector or an electro-optic deflector, and the application range is wide.
3. The method for measuring the small-angle deflection precision based on the cone light interference has the advantages that the precision of the method is not limited by the measuring distance and the angle range, so that accurate installation and debugging are not needed, and only the angle of the electro-optic crystal is required to be adjusted to change the initial angle of view of deflection light entering the electro-optic crystal, and the method is simple to operate and high in practicability.
Drawings
FIG. 1 is a schematic flow chart of a method for measuring small-angle deflection accuracy based on cone light interference according to an embodiment of the present invention;
FIG. 2 is a diagram of an apparatus for interference of two beams of light in an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a device for measuring small-angle deflection accuracy based on cone light interference according to an embodiment of the present invention;
FIG. 4 is a graph showing the cone-shaped interference patterns of incident light at different angles of view when the incident light is incident on an electro-optic crystal and the intensity variation received by a corresponding photodetector according to an embodiment of the present invention;
FIG. 5 is a graph of angular spacing between adjacent bright-dark fringes versus angular field of view of incident light into an electro-optic crystal, provided by an embodiment of the present invention;
FIG. 6 is a graph showing the relationship between ultrasonic frequency and relative light intensity provided by an embodiment of the present invention;
FIG. 7 is a schematic structural diagram of another device for measuring small-angle deflection accuracy based on cone light interference according to an embodiment of the present invention;
FIG. 8 is a graph showing the relationship between the electric field intensity and the relative light intensity according to the embodiment of the present invention.
The same reference numbers are used throughout the drawings to reference like elements or structures, wherein: 1 is a laser light source; 2 is a collimating lens; 3 is an acousto-optic deflector (AOD); 4 is an electro-optic deflector (EOD); 5 is a polarizer; 6 is an electro-optic crystal; 7 is an analyzer; 8 is a photoelectric detector; 9 is o light; 10 is e light.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The description of the contents of the above embodiment will be given below in connection with a preferred embodiment.
Example 1
As shown in fig. 1, a method for measuring small-angle deflection accuracy based on cone light interference includes:
s1, laser emitted by a laser light source sequentially passes through a deflector to be detected and a polarizer to obtain linearly polarized light;
s2, the linearly polarized light is emitted into an electro-optical crystal at a preset angle, o light and e light are obtained through decomposition, and phase delay is generated;
s3, the o light and the e light obtained through decomposition interfere after passing through an analyzer, and the generated interference light is received by a photoelectric detector;
s4, rotating the electro-optic crystal until the light spot intensity received by the photoelectric detector is maximum, and recording a first incident view field angle;
s5, the deflector to be detected scans with a scanning step length until the light spot intensity received by the photoelectric detector is 0, and a second incident view field angle is recorded;
s6, counting the number of resolvable light spots received by the photoelectric detector in the process of changing the light spot intensity from the maximum to 0, and calculating to obtain the scanning precision of the deflection device to be detected according to the difference between the first incident view field angle and the second incident view field angle divided by the number of the light spots.
The method for measuring the small-angle deflection precision based on the cone light interference is applied to a device for measuring the small-angle deflection precision based on the cone light interference. As shown in fig. 2, the implementation device includes: a polarizer 5, an electro-optic crystal 6, and an analyzer 7 disposed along the optical path. First, the relevant reference coordinate system and direction in the present example are defined: the crystal main axis directions of the electro-optic crystal 6 are x and y directions, the crystal main axis directions x and y of the electro-optic crystal 6 are taken as a reference coordinate system, the light transmission directions of the polarizer 5 and the analyzer 7 are defined as P1, P2, P1 and P2 which are mutually orthogonal, and the included angle between the light transmission directions and the crystal main axis directions x and y of the electro-optic crystal 6 is 45 degrees. The angle between the polarization direction P1 of the polarizer 5 and the projection direction De of the electric displacement direction of the e-light 7 in the xy plane is θ, and the angle between the optical axis direction of the electro-optic crystal 6 and the laser light incident direction is ω.
The basic working principle is described as follows: normally, two linearly polarized lights whose vibration directions are perpendicular to each other are superimposed, and even if they have the same frequency, a fixed phase difference cannot produce interference. However, if the two light beams are passed through one polarizing plate, the vibration components of the two light beams in the transmission axis direction of the polarizing plate are in the same direction, and the two light beams can interfere. Fig. 2 is a diagram of an apparatus for realizing such two-beam light interference. As shown in fig. 2, the incident light becomes linearly polarized light after passing through the polarizer 5, and then is incident on the electro-optical crystal 6 at an angle of view ω, the crystal principal axis direction of the electro-optical crystal 6 is x, y direction, and the crystal principal axis direction x, y of the electro-optical crystal 6 is the reference coordinate system, and then the incident linearly polarized light is decomposed into o-light 9 and e-light 10 in the electro-optical crystal 6, and the projections of the electric displacement directions of the o-light 9 and e-light 10 in the xy plane are Do and De. After the o light 9 and the e light 10 are emitted through the electro-optical crystal 6, the o light 9 and the e light are synthesized into elliptical polarized light, and the elliptical polarized light can be also regarded as two linearly polarized light beams with a positioning phase difference, when the two linearly polarized light beams are emitted to the analyzer 7, only vibration components in the light transmission direction P2 of the analyzer 7 can pass through, so that the vibration of the two emitted light beams can interfere in the same direction. As shown in fig. 3, the device for measuring the small-angle deflection precision comprises a laser light source 1, a collimating lens 2, a deflector to be measured 3, a polarizer 5, an electro-optical crystal 6, an analyzer 7 and a photoelectric detector 8 which are sequentially arranged along a light path; the optical axis of the laser light source 1 coincides with the lens optical axis and with the direction of the output light of the deflector 3 to be measured. The interference light generated by the analyzer 7 is received by the photodetector 8 at the rear.
As can be seen from the interference condition, when δ=2kpi, the interference fringes are bright fringes, that is, the intensity of the light spot received by the photodetector 8 is maximum; when delta= (2k+1) pi, the interference fringes are dark fringes, namely the incident light is completely lost after passing through the measuring device, and the light spot intensity received by the photoelectric detector 8 is 0; where k=0, 1,2,3,4, … …, represents the interference order.
As shown in fig. 3, the electro-optical crystal 6 is rotated according to the light spot displayed by the photodetector 8 until the intensity of the light spot received by the photodetector 8 is maximum, at this time, the interference fringes are bright fringes, and a first incident view field angle is recorded; the electro-optical crystal 6 is kept still, the deflector 3 to be tested is started to scan with a scanning step length, the intensity of the light spot received on the photoelectric detector 8 is observed until the light spot intensity is 0 in the process that the deflector 3 to be tested steps one scanning step length, at the moment, the interference fringes are dark fringes, and the second incident view field angle is recorded. Along with the continuous scanning of the deflector 3 to be tested, the pattern of the light spot received by the photodetector 8 is shown in fig. 4, specifically, a cone light interference pattern when the incident light is incident on the electro-optical crystal at different angles of view and a corresponding light intensity variation curve received by the photodetector.
Specifically, when the incident light enters the electro-optical crystal 6 at different angles of view, the cone light interference pattern is periodic light and dark alternate stripes, the brightness degree of the stripes represents the loss of light intensity of the incident light after passing through a cone light interferometry system formed by the polarizer 5, the electro-optical crystal 6 and the analyzer 7, and the maximum value of the bright stripes represents no loss of the incident light after passing through the cone light interferometry system formed by the polarizer 5, the electro-optical crystal 6 and the analyzer 7, so that the light spot intensity received by the photoelectric detector 8 is maximum; the minimum value of the dark stripe represents that incident light is completely lost after passing through a cone optical interferometry system formed by the polarizer 5, the electro-optical crystal 6 and the analyzer 7, so that the intensity of a light spot received by the photoelectric detector 8 is 0; fig. 4 shows that the bright-dark fringes will vary periodically with the angle of incidence, and thus the intensity of the light spot received on the photodetector 8 will also vary periodically. In order to obtain enough measurement resolution, the difference between the incident field angles corresponding to the maximum value of the bright stripes and the minimum value of the dark stripes in the same period is selected as the measurement range of the method, so that the angular interval between the adjacent bright and dark stripes represents the measurement range of the method. Further, in order to obtain the angular spacing between the adjacent bright-dark fringes under different periods, the relationship between the angular spacing between the adjacent bright-dark fringes and the size of the angle of view of the incident light into the electro-optical crystal 6 needs to be studied.
In the present embodiment, P1 and P2 represent the directions of the transmission axes of the polarizer 5 and the analyzer 7, respectively, A1 is the amplitude of incident linearly polarized light, and the angle between the projection direction De of the e-ray 10 in the xy plane and the polarization direction P1 of the polarizer 5 is θ, so that the amplitudes of the o-ray 9 and e-ray 10 in the electro-optic crystal 6 are a o ＝A1sinθ，A e =a1cos θ. When o light 9 and e light 10 pass through the electro-optical crystal 6 and then pass through the light transmission direction P2 of the analyzer 7, only the components whose vibration directions are parallel to the light transmission direction P2 of the analyzer 7 can interfere with each other, and their amplitudes are equal:
A O2 ＝A O cosθ＝A 1 sinθcosθ
A e2 ＝A e sinθ＝A 1 sinθcosθ
according to the intensity formula of double-beam interference, the light intensity of the interference light of o light and e light is as follows:
wherein A1 is the amplitude of incident linearly polarized light, θ is the angle between the projection direction De of the e-light in the xy plane and the polarizing direction P1 of the polarizer, A o2 And A e2 The amplitudes of the o light and the e light after passing through the analyzer, respectively.
Delta is the phase difference generated by o light and e light after passing through the electro-optical crystal 6, and the phase delay is:
wherein L is the thickness of the electro-optic crystal,n o 、n e the principal refractive index of o light 9 and the principal refractive index of e light 10, respectively, ω being the angle between the incident light and the optical axis of the electro-optic crystal 6, i.e. the predetermined angle of incidence into the electro-optic crystal 6.
As can be seen from the above equation, the angular distance between adjacent bright and dark fringes can be written as:
as can be seen from the above equation, the angular distance between adjacent bright and dark fringes is related to the wavelength of the laser light source 1, the length of the electro-optic crystal 6, the crystal type, and the order of interference fringes, which is related to the angular size of the field of view of the output light incident on the electro-optic crystal, and thus the measurement range of the inventive method is related to the wavelength of the laser light source 1, the length of the electro-optic crystal 6, the crystal type, and the angular size of the field of view of the light incident on the electro-optic crystal 6.
As shown in fig. 5, the relationship between the angular interval between the adjacent bright-dark fringes and the size of the angle of view of the incident light entering the electro-optical crystal 6 is given, it can be seen that the angular interval between the adjacent bright-dark fringes will decrease with the increase of the angle of view of the incident light, and further, in order to match with the high scanning accuracy of the deflection device to be detected, the adjacent bright-dark fringes of a specific interference level need to be selected to obtain a sufficiently large measurement resolution, so that, in fig. 5, the light spot intensity change curve detected by the photodetector 8 is also given when the angle of view of the incident light entering the electro-optical crystal 6 is 5 ° and the angle of view of the incident light corresponds to the interference level, and the angle of view changes between the maximum value of the adjacent bright fringes and the minimum value of the dark fringes. It can be seen that when the incident field angle is 87.3mrad (5 °), the maximum value of the bright stripe corresponds; when the incident field angle was 87.2982mrad, the minimum value of dark fringes was corresponding. Therefore, when the preset angle of incidence is 5 degrees, the measurement range which can be achieved by the method is 1.7952urad. On the basis of the above embodiment, before the deflector 3 to be tested is tested, a preset angle of 5 ° is set, and the preset angle is the included angle between the incident linearly polarized light and the optical axis of the electro-optic crystal.
On the basis of the above embodiment, further, before step S1, the method further includes: and the laser emitted by the laser light source is collimated by the collimating lens to obtain a reference beam.
The collimating lens is used for reducing the divergence angle of the laser to obtain a parallel light path.
In the embodiment of the invention, linearly polarized light is decomposed by an electro-optical crystal to obtain o light and e light, phase delay is generated, the o light and the e light interfere after passing through an analyzer, and the generated interference light is received by a photoelectric detector; rotating the electro-optic crystal until the light spot intensity is maximum, and recording a first incident view field angle; the deflector to be tested scans with a scanning step length until the light spot intensity is 0, and a second incident view field angle is recorded; and counting the number of received light spots by the photoelectric detector in the process of changing the intensity between the bright stripes and the dark stripes from the maximum to 0, and dividing the difference of incident field angles by the number of the light spots to calculate and obtain the scanning precision of the deflection device to be detected. The invention utilizes the double refraction characteristic of the electro-optic crystal, makes the deflection light incident to the electro-optic crystal at different angles to generate different phase differences, makes the photoelectric detector receive the light intensity with high contrast, achieves the effect of the invention, solves the technical problems of complex operation, high measurement cost and lower measurement precision of the measurement method for the small angle of the deflector in the prior art, and realizes the beneficial effects of simple light path, wide application range, stable measurement precision and high resolution.
On the basis of the embodiment, the deflector to be tested is an acousto-optic deflector or an electro-optic deflector. Specific examples are given below showing the method of the invention for measuring the scanning accuracy of an acousto-optic deflector (AOD) and an electro-optic deflector (EOD), respectively.
If the measuring deflector 3 is an acousto-optic deflector, the reference beam coincides with the zero-order diffraction direction of the acousto-optic deflector.
As shown in fig. 3, a device for implementing measurement of scanning accuracy of an acousto-optic deflector includes: the laser light source 1 with the wavelength of 355nm, the collimating lens 2, the acousto-optic deflector (AOD) 3 and the polarizer 5 comprise a radio frequency driving power supply, an LN crystal serving as a piezoelectric transducer, a quartz crystal serving as an acousto-optic interaction medium, an antireflection film with high antireflection to the laser wavelength, a single-axis crystal as the crystal type of the electro-optic crystal 6, a 3mm crystal light-transmitting caliber of the electro-optic crystal 6, a 20mm crystal length of the electro-optic crystal 6, an analyzer 7 and a photoelectric detector 8. The optical axis of the laser light source 1 coincides with the collimator lens optical axis 2 and with the zero-order diffraction output light direction of the acousto-optic deflector 3. The crystal main axis directions of the electro-optic crystal 6 are x and y directions, the crystal main axis directions x and y of the electro-optic crystal 6 are taken as a reference coordinate system, the light transmission directions of the polarizer 5 and the analyzer 7 are defined as P1, P2, P1 and P2 which are mutually orthogonal, and the included angle between the light transmission directions and the crystal main axis directions x and y of the electro-optic crystal 6 is 45 degrees. Based on the above parameters, it can be calculated from the equation in the above that the measurement range achievable by the present measurement device is 1.7952urad when the positive first order bragg diffraction output light enters the electro-optic crystal 6 at an angle of view of 5 °.
As shown in fig. 3, when the acousto-optic deflector 3 is added to the sound field, the angle of the electro-optic crystal 6 is adjusted so that the angle of view of the positive first-order bragg diffraction output light entering the electro-optic crystal 6 is 5 degrees, and further, considering that errors may exist in the processing and assembly of the electro-optic crystal, the angle of the electro-optic crystal 6 needs to be finely adjusted until the light intensity of the light spot detected by the photodetector 8 reaches the maximum. When the sound field frequency is changed, if the change amount of the sound frequency isThe corresponding beam deflection variation is:
in the middle ofLambda is the laser wavelength, n is the refractive index of the quartz crystal, v s Is the speed of sound. The angle of view of the positive first order Bragg diffraction output light into the electro-optic crystal 6 is (5-delta theta) B ) This will cause the phase difference of the o-light 9 and the e-light 10 to change, resulting in a decrease of the intensity of the output spot. To be used forIn order to continuously change the audio frequency in step length, when the change amount of the audio frequency is accumulated to delta omega, the intensity of the output light spot becomes 0, in the process, the light spots with different intensities are detected at different positions on the photoelectric detector 8, and the scanning precision of the acousto-optic deflector 4 is +.>The results of the implementation are shown in FIG. 6.
When the acousto-optic deflector 4 does not work, the relative intensity received by the photoelectric detector 8 is 1, namely the light intensity is maximum; when in useWhen the audio frequency is changed for step length, the corresponding change of the deflection of the light beam is delta theta B At this time, the angle of view of the positive first-order bragg diffraction output light entering the electro-optical crystal 6 will also be changed, which will lead to the weakening of the intensity of the output light spot, and as the number of step sizes increases, the intensity of the output light spot will weaken in turn, so that light spots with different intensities will be received at different positions of the photodetector 8, and the number of received light spots with different intensities is counted, so that the scanning accuracy of the acousto-optic deflector 4 can be calculated.
Further, if the measurement accuracy of the system is further improved under the condition that the laser light source 1 and the electro-optical crystal 6 are to be kept unchanged, as shown in fig. 5, the angle of view of the positive first-order bragg diffraction output light entering the electro-optical crystal 6 can be increased, and the theoretical measurement accuracy can reach nrad.
As shown in fig. 7, an apparatus for implementing measurement of scanning accuracy of an electro-optical deflector includes: the laser light source 1 with the wavelength of 355nm, the collimating lens 2, the electro-optic deflector (EOD) 4, the polarizer 5 and the electro-optic crystal 6 are uniaxial crystals, the light-transmitting aperture of the electro-optic crystal 6 is 3mm, the crystal length of the electro-optic crystal 6 is 20mm, the polarization analyzer 7 and the photoelectric detector 8. The optical axis of the laser light source 1 coincides with the collimator lens optical axis 2 and coincides with the optical axis direction of the electro-optical deflector 4. The crystal main axis directions of the electro-optic crystal 6 are x and y directions, the crystal main axis directions x and y of the electro-optic crystal 6 are taken as a reference coordinate system, the light transmission directions of the polarizer 5 and the analyzer 7 are defined as P1, P2, P1 and P2 which are mutually orthogonal, and the included angle between the light transmission directions and the crystal main axis directions x and y of the electro-optic crystal 6 is 45 degrees. Based on the above parameters, it can be calculated from the above equation that the measurement range achievable by the present measurement device is 1.7952urad when the output light after passing through the electro-optical deflector 4 enters the electro-optical crystal 6 at an angle of view of 5 °.
As shown in fig. 7, when the electro-optical deflector 4 adds an electric field, the angle of the electro-optical crystal 6 is adjusted so that the angle of view of the output light passing through the electro-optical deflector 4 and entering the electro-optical crystal 6 is 5 °, and further, considering that there may be errors in the processing and assembly of the electro-optical crystal, the angle of the electro-optical crystal 6 needs to be finely adjusted until the light intensity of the light spot detected by the photodetector 8 reaches the maximum. When the electric field strength is changed, if the change amount of the electric field is delta E The corresponding beam deflection variation is:
where L is the length of the electro-optic deflector 4, d is the thickness of the electro-optic deflector 4, n o For the principal refractive index, gamma, of the phototransistor used in the electro-optic deflector 4 63 The electro-optic coefficient of the electro-optic crystal used for the electro-optic deflector 4. Similar to the acousto-optic deflector principle described in example 1, the angle of view of the output light passing through the electro-optic deflector 4 into the electro-optic crystal 6 is (5-. DELTA.θ) E ) This will cause the phase difference of the o-light 9 and the e-light 10 to change, resulting in a decrease of the intensity of the output spot. In delta E To continuously change the magnitude of the electric field intensity in step length, when the change amount of the electric field intensity is added up to Deltav, the intensity of the output light spot becomes 0, and the photodetector 8 does not go on in the processThe light spots with different intensities are detected at the same position, and if the number of the light spots is N, the scanning precision of the electro-optical deflector 4 isThe results of the implementation are shown in FIG. 8.
Further, if the measurement accuracy of the system is further improved under the condition that the laser light source 1 and the electro-optical crystal 6 are to be kept unchanged, as shown in fig. 5, the idea of increasing the angle of view of the output light into the electro-optical crystal 6 can be adopted, and the theoretical measurement accuracy can reach nrad.
Example two
As shown in fig. 3, an apparatus for measuring small angle deflection accuracy based on cone light interference, for performing the method according to any one of the embodiments, comprises: a laser light source 1, a collimating lens 2, a deflector to be measured 3, a polarizer 5, an electro-optic crystal 6, an analyzer 7 and a photoelectric 87 which are sequentially arranged along the light path;
the collimating lens 2 is used for collimating the laser emitted by the laser source 1 to obtain a reference beam;
the deflector to be measured 3 is used for deflecting the reference beam by a small angle;
the polarizer 5 is used for converting an incident light beam into linearly polarized light;
the electro-optical crystal 6 is used for decomposing incident linearly polarized light to obtain o light and e light and generating phase delay;
the analyzer 7 is used for transmitting o light and e light in a preset direction and generating interference light;
the photodetector 8 is configured to receive a light spot generated by the interference light.
The device for measuring the small-angle deflection precision based on the cone light interference provided by the embodiment of the invention is used for executing the method for measuring the small-angle deflection precision based on the cone light interference provided by any embodiment of the invention, and the device has the corresponding functional modules and beneficial effects of the executing method.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (8)
1. The method for measuring the small-angle deflection precision based on cone light interference is characterized by comprising the following steps of:
laser emitted by a laser light source sequentially passes through a deflector to be detected and a polarizer to obtain linearly polarized light;
the linearly polarized light is injected into the electro-optical crystal at a preset angle, o light and e light are obtained through decomposition, and phase delay is generated;
the o light and the e light obtained by decomposition interfere after passing through the analyzer, and the generated interference light is received by the photoelectric detector;
rotating the electro-optic crystal until the light spot intensity received by the photoelectric detector is maximum, and recording a first incident view field angle;
the deflector to be detected scans with a scanning step length until the light spot intensity received by the photoelectric detector is 0, and a second incident view field angle is recorded;
and counting the number of resolvable light spots received by the photoelectric detector in the process of changing the light spot intensity from the maximum to 0, and calculating to obtain the scanning precision of the deflection device to be detected according to the difference between the first incident view field angle and the second incident view field angle divided by the number of light spots.
2. The method of claim 1, further comprising, before the laser light from the laser light source passes through the deflector to be measured and the polarizer in sequence:
and the laser emitted by the laser light source is collimated by the collimating lens to obtain a reference beam.
3. The method of claim 1, wherein the predetermined angle is an angle between the incident linearly polarized light and an optical axis of the electro-optic crystal, and the predetermined angle is 5 °.
4. A method according to claim 3, wherein the phase delay is:
wherein L is the thickness of the electro-optic crystal,n o 、n e the main refractive index of o light and the main refractive index of e light are respectively, and omega is a preset angle.
5. The method of claim 4, wherein the interference light has a light intensity of:
wherein A1 is the amplitude of incident linearly polarized light, θ is the angle between the projection direction De of the e-light in the xy plane and the polarizing direction P1 of the polarizer, A o2 And A e2 The amplitudes of the o light and the e light after passing through the analyzer, respectively.
6. The method of claim 5, wherein when δ = 2kβ, the interference fringes are bright fringes and the received light spot intensity on the photodetector is maximized;
when delta= (2k+1) pi, the interference fringes are dark fringes, and the intensity of a light spot received by the photoelectric detector is 0; where k represents the interference order, k=0, 1,2,3,4, … ….
7. The method of claim 1, wherein the deflector to be measured is an acousto-optic deflector or an electro-optic deflector, and if the deflector is an acousto-optic deflector, the reference beam coincides with a zero-order diffraction direction of the acousto-optic deflector.
8. Apparatus for small angle deflection accuracy measurement based on cone light interferometry, for performing the method of any of claims 1-7, comprising: the laser light source, the collimating lens, the deflector to be measured, the polarizer, the electro-optic crystal, the analyzer and the photoelectric detector are sequentially arranged along the light path;
the collimating lens is used for collimating laser emitted by the laser source to obtain a reference beam;
the deflector to be measured is used for deflecting the reference beam at a small angle;
the polarizer is used for converting an incident light beam into linearly polarized light;
the electro-optical crystal is used for decomposing incident linearly polarized light to obtain o light and e light and generating phase delay;
the analyzer is used for transmitting o light and e light in a preset direction and generating interference light;
the photodetector is used for receiving light spots generated by interference light.
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