CN101118199A - Method for measuring birefraction optical devices phase-delay quantity and fast axis direction and device - Google Patents
Method for measuring birefraction optical devices phase-delay quantity and fast axis direction and device Download PDFInfo
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Abstract
The present invention relates to a measurement method and a device for the phase delay quantity and the fast axle direction of a birefringent optical device, which can well solve the problem of poor measurement accuracy in a measurement process. The method is that a pair of orthogonal dual-frequency lasers emitted from an optical laser is divided into reflected light and transmitted light; in a reflected light path and a transmitted light path, through the birefringence of a measured sample measuring point after the polarizing angle of at least one path is changed, and then through the measured sample measuring point after returning, the phases of the polarized components of the two frequencies in the light beams are delayed differently, thus leading to the phase change; then after being synthesized by an analyzer, the two light paths are respectively transformed into a reference beat frequency signal and a measurement beat frequency signal with different phase differences; at least two times of phase differences are obtained, and then the phase delay quantity and the fast axle direction of the measured point can be calculated; the method and the device of the present invention make the measurement of two parameters become simple and eliminate the principle error and the system error.
Description
Technical Field
The invention belongs to the technical field of laser precision measurement, and particularly relates to a method for measuring the phase retardation and the fast axis direction of a birefringent optical device by using laser.
Background
The birefringence parameter of the birefringent optical device is an important index for measuring the performance of the birefringent optical device, and comprises the phase retardation and the fast axis direction thereof, and the birefringence parameter can be applied to many aspects such as residual stress detection of optical materials, photoelasticity measurement, phase retardation measurement of wave plates, characteristic detection of materials and liquid crystals, and the like.
The existing detection methods include a quarter wave plate method and a dual-frequency laser interference method. The colorless optical glass test method edge stress birefringence test method GB7962.6-87 is based on quarter-wave plate measurement, adopts a white light source, is manually operated, visually reads, and has lower measurement precision and speed.
The japanese unict company adopts a measurement method based on a dual-frequency laser, and the implementation device of the method is shown in fig. 1 and comprises the following steps: the laser comprises a transverse Zeeman double-frequency laser 101, a beam splitter 102, a first rotating platform 103, a half-wave plate 104, an XY two-dimensional translation platform 105, a sample 106, a second rotating platform 107, a measurement analyzer 108 and a measurement photoelectric detector 109, wherein the beam splitter 102, the first rotating platform 103, the half-wave plate 104, the XY two-dimensional translation platform 105, the sample 106, the second rotating platform 107, the measurement analyzer 108 and the measurement photoelectric detector 109 are sequentially arranged on the optical path axis of the beam splitter, a reference analyzer 111 and a reference photoelectric detector 112 are sequentially arranged on the optical path axis of the beam splitter, a measurement preamplifier 110 and a reference preamplifier 113 are connected with the measurement photoelectric detector 109, and a phase measurement unit 114, an analog-to-digital converter 115, a controller 116 and a computer 117 are connected with the rotating platform and the translation platform.
The working principle of the device is explained as follows:
1. a transverse Seeman double-frequency laser 101 is used as a light source, the laser outputs two orthogonal linearly polarized light, and the two linearly polarized light have a certain frequency difference;
2. the linearly polarized light which is orthogonal with each other is divided into two parts of reflected light and transmitted light after passing through a spectroscope 102;
3. the reflected light is synthesized by a reference analyzer 111 and received by a reference photodetector 112 to form a reference signal;
4. the transmitted light is measurement light, sequentially passes through a half wave plate 104, a measured sample 106 and a measurement analyzer 108, and is received by a measurement photoelectric detector 109 to form a measurement signal;
5. the zero point direction of the first rotating table 103, the zero point direction of the second rotating table 107, the fast axis direction of the half-wave plate 104 and the polarization direction of the measurement analyzer 108 are adjusted to all point to the horizontal direction;
6. the computer 117 operates the XY two-dimensional translation stage 105 through the controller 116 connected thereto so that the transmitted light passes through the measured position on the measured sample 106;
7. the computer 117 operates, through a controller 116 connected to it, the first rotary table 103 and the second rotary table 107, rotating the former by a certain angle α and the latter by twice the angle 2 α;
8. sending the measuring signal in the step 4 and the reference signal in the step 3 to a phase measuring unit 114 for phase comparison, sending the output result to an analog-to-digital converter 115 for conversion, sending the converted result to a computer 117, and storing the converted result together with the angle alpha mentioned in the step 7, wherein the converted result is the phase difference of a single measurement;
9. repeating the step 7 and the step 8 to obtain a series of phase differences and angles, performing Fourier transform on the phase differences and angles to obtain the amplitude and the phase angle of the 4 frequency multiplication component, and obtaining the phase delay amount and the fast axis direction of the birefringence at the measured position on the measured sample 106;
10. repeating steps 6-9 can obtain birefringence parameters at different positions on the measured sample 106.
The measurement range of the phase delay of the device is 0-150 degrees, the resolution is 0.006 degree, and the precision is +/-0.2 percent; the measuring range in the fast axis direction is +/-90 degrees, the resolution is 0.1 degree, and the precision is 0.5 degree.
In step 7, the two rotating tables are required to rotate synchronously, and the angle is strictly twice, but in practice, the deviation is inevitable, which brings errors to the measurement result. The measuring light of the device can not change the direction after passing through the measured sample, otherwise, the measuring light can not enter the measuring photoelectric detector, so that the device can only be used for measuring samples such as flat glass. In addition, the data processing of the device adopts Fourier transform, which is only approximate calculation and is only realized when the phase delay amount is small, and a large principle error exists when the phase delay amount is large.
Disclosure of Invention
The invention overcomes the defects of poor measurement precision or device errors and principle errors in the measurement in the prior art, and provides a method for measuring the birefringence phase delay and the fast axis direction by using double-frequency laser.
The invention also provides a measuring device adopting the method, compared with the existing measuring device, the invention not only can conveniently and quickly realize accurate measurement, but also has simple structure.
The method for measuring the birefringence phase retardation and the fast axis direction by using the double-frequency laser is as follows: splitting a pair of orthogonal double-frequency lasers emitted by a laser into reflected light and transmitted light; at least one of the two paths of light of the reflected light and the transmitted light passes through a birefringence measured sample measuring point after the polarization angle is changed, and then is turned back and passes through the measured sample measuring point, so that the phases of polarization components of two frequencies in the light beam are delayed differently to cause phase change; then, after being respectively synthesized by an analyzer, the two paths of light are respectively converted into a reference beat frequency signal and a measurement beat frequency signal with different phase differences; calculating the phase delay amount and the fast axis direction of the measuring point by obtaining at least two phase differences; and recording the phase difference between the reference beat frequency signal and the measurement beat frequency signal of each measurement point of the measured sample, and calculating to obtain the phase delay and the fast axis direction of the measured sample.
The measured sample measuring point can be a measuring area within an error allowable range.
The turning back of the light is realized by sequentially arranging a convergent lens and a plane mirror after passing through the sample to be measured in the light path of the sample to be measured, or by adopting a corner cube or a hollow corner cube.
The at least two phase differences are realized by arranging a half wave plate on a light path in front of a measured sample, and only transmitting part of light passes through the wave plate in the forward direction and the reverse direction, so that at least two phase changes are obtained when the main shaft of the wave plate is respectively positioned at least two angles, and thus at least two phase differences of a reference beat frequency signal and a measurement beat frequency signal are obtained.
The method for realizing the at least two phase differences comprises the following steps: a half wave plate is arranged on an optical path in front of a measured sample, the half wave plate is partially positioned in the optical path, so that part of the transmitted light passes through the wave plate, the transmitted light passing through a measuring point of the measured sample comprises two parts with changed polarization angles and two parts without changed polarization angles, then the two parts of the light are separated before the synthesis of an analyzer, and then the two measured beat frequency signals respectively pass through the analyzer, and are respectively compared with a reference beat frequency signal to form two phase differences.
The measuring device adopting the measuring method comprises a spectroscope arranged on a transmitting light path of the dual-frequency laser, a half-wave plate, a sample to be measured, a convergent lens and a plane reflector which are sequentially arranged in the transmission direction of the spectroscope, and analyzers respectively arranged in the reflected light direction and the reverse direction of the spectroscope, wherein the analyzers are respectively connected with a photoelectric conversion device and then connected with a calculating device; the plane mirror is disposed on a focal plane of the condensing lens.
The converging lens and the plane reflector in the device can be replaced by a pyramid prism or a hollow corner prism.
The half wave plate is partially positioned in the light path, part of the transmitted light passes through the wave plate, a wedge-shaped reflecting mirror is arranged in the direction opposite to the direction of the reflected light of the spectroscope, the light beam returning from the spectroscope is divided into two parts, namely the light beam with the changed polarization angle and the light beam without the changed polarization angle, and an analyzer is arranged on the light path of the divided light beams.
The technical effects are as follows:
the method changes the transmitted light in the existing double-frequency laser measuring method into the transmitted light after the transmitted light passes through the measured sample once and turns back, and then the transmitted light passes through the measured sample again, the change action of the measured sample on the light beam is opposite, the two are mutually offset, equivalently, the light beam directly passes through an equivalent device, the phase delay amount is two times of that of the measured sample, the birefringence effect of the measured sample as the equivalent device acts on two polarization components with different frequencies in the light beam to cause the phase change between the two polarization components, and the phase change of the measured beat signal is converted into the phase change of the measured beat signal after being synthesized by an analyzer. Because the data processing does not adopt the Fourier transform which is only approximately calculated, but also adopts the accurate calculation, the measuring precision is doubled, and the principle error is eliminated; and because the light rays can pass through the device for changing the polarization angle or the position of the light path after being folded back, the influence of the device on the rotation angles of the two frequencies is mutually counteracted, and the parts and related complex operation (namely at least one rotating table and synchronous rotation) of the polarization analyzer for eliminating the influence of the rotation angles are saved, so that the measurement is very simple, and the system error is eliminated. The change action of the measured sample on the light beam is mutually counteracted before and after, so that the direction of the measuring light beam is not changed due to the deflection action of the measured sample, the light receiving is very simple, and the variety of the measured sample is not limited to the plate glass any more, but also expanded to the optical wedge.
Therefore, the measuring device adopting the method not only can conveniently and quickly realize accurate measurement, but also has simple structure.
The measured sample measuring point is limited to the measuring area within the error allowable range, so that the means for realizing the method has various choices.
The converging lens and the plane mirror are implemented using a corner cube or using a hollow corner cube.
The transmission light passes through the half wave plate twice before and after, the rotation of the analyzer is not needed, compared with the prior art, a rotating device of the analyzer is omitted, the system structure is simplified, the cost is reduced, the reliability is improved, errors caused by inaccurate rotation angle are avoided, and the measurement precision is improved.
When the half-wave plate is partially positioned in the light path, and part of the transmitted light passes through the half-wave plate, although any part of the path of light only passes through the half-wave plate once, because the two parts are separated before the analyzer is combined (the two parts can be separated by using the wedge-shaped reflecting mirror), measurement beat frequency signals with different phase changes are obtained after respectively passing through the analyzer, and two phase differences compared with a reference beat frequency signal can also be obtained by corresponding to two phase changes obtained by the half-wave plate positioned at different angles. Compared with the specific measurement method of passing through the half wave plate twice, although one analyzer and the wedge-shaped reflector are added, the half wave plate is not required to be rotated, another rotating device is omitted, meanwhile, due to the fact that the half wave plate is not rotated, the measurement time is saved, system errors caused by rotation are eliminated, self-correction can be achieved, and the measurement precision is further improved.
Description of the drawings:
the invention is further described with reference to the accompanying drawings:
fig. 1 is a schematic structural diagram of a conventional dual-frequency laser birefringence phase retardation and fast axis direction measuring device.
FIG. 2 is a schematic diagram illustrating the principle of an embodiment of the method for measuring birefringence phase retardation and fast axis direction of a dual-frequency laser according to the present invention.
Fig. 3 is a schematic structural diagram of a measuring device for implementing the embodiment of the method shown in fig. 2.
Fig. 4 is a schematic diagram of another embodiment of the measuring method of the present invention.
The specific implementation mode is as follows:
example 1:
the principle of the measurement method of the present invention is shown in fig. 2, 203 is a spectroscope, 201 and 202 are analyzers,204 is a half wave plate, 205 is the sample to be measured, 206 is a converging lens, and 207 is a plane mirror. The beam splitter 203 is a neutral non-polarizing beam splitter. The measured sample 205 has certain birefringence characteristics and is characterized by a phase retardation and a fast axis direction, wherein the magnitude of the phase retardation is recorded as delta, and an included angle between the fast axis direction and the X axis is recorded as theta. The included angle between the fast axis direction of the half-wave plate 204 and the X axis is . Incident light having a frequency f 1 And f 2 With directions parallel to the X-axis and the Y-axis, respectively.
The orthogonal dual-frequency laser light emitted from the laser is split into two parts of reflected light and transmitted light by the beam splitter 203 as incident light. The reflected light is combined by an analyzer 202, f 1 And f 2 Interference occurs to form a frequency of | f 1 -f 2 And the reference beat frequency signal is a reference signal, and the phase of the reference beat frequency signal is not changed in the measurement process. This part of the optical path is called the reference optical path.
The transmitted light passes through the half-wave plate 204, the sample 205 to be measured and the converging lens 206 in turn, is reflected by the plane mirror 207, returns along the original path, passes through the converging lens 206, the sample 205 to be measured and the half-wave plate 204 in turn, and then passes through the converging lens 206, the sample 205 to be measured and the half-wave plate 204And then back to the beam splitter 203 where reflection and transmission again occur, the transmitted part of which is omitted and the reflected part is combined by the analyzer 202, as above, f 1 And f 2 Interference occurs to form a frequency of | f 1 -f 2 The measured beat signal is a measurement signal whose phase includes information of the birefringence parameter of the measured sample 205. This part of the light path is called the measurement light path.
After the light beam in the measuring light path passes through the half-wave plate 204 for the first time, when the fast axis rotates by a certain angle, f 1 And f 2 Then the polarization direction of the sample is rotated, the polarization angle is twice the fast axis angle, the propagation direction is the same, and the sample passes through the measured sample 205. And the light beam passes through the half-wave plate for the second time from the opposite direction after returning 1 And f 2 The size of the rotation angle of (2) is the same as that of the first time, and the direction is opposite. It can be seen that the half-wave plate has opposite actions, and the actions cancel each other out, and the action is equivalent to rotating the sample 205 around the light beam. And because the light beam passes through the measured sample 205 twice, the measuring optical path is equivalent to letting the light beam pass through an equivalent device directly, the phase delay amount of the measuring optical path is twice of that of the measured sample 205, the half wave plate rotates for one circle, and the fast axis rotates for two circles. The birefringence of the equivalent device acts on two polarization components with different frequencies in the light beam to cause phase change between the two polarization components, and the two polarization components are converted into phase change of a measurement beat frequency signal after being synthesized by the analyzer. Since the phase of the reference beat signal is constant, the phase difference between the measurement beat signal and the reference beat signal is compared, and the phase change of the measurement signal at the measurement point can be obtained. The analytical expression is as follows:
from the above analysis, the phase retardation of the equivalent device is 2 Δ, and the fast axis direction is θ -2 . Without loss of generality, without f 1 ＞f 2 When theta-2 =0, its fast axis is parallel to the X axis, f 1 Fractional phase advance f 2 Component 2 Δ, where the phase difference between the measured beat signal and the reference beat signal has the maximum value, denoted as Ψ max Two, twoThe angle of the one-half wave plate is max (ii) a Similarly, when θ -2 = π/2, the fast axis is parallel to the Y axis, f 1 Phase lag f of the component 2 Component 2 Δ, the phase difference occurs at a minimum, denoted as Ψ min The angle of the half wave plate is min . Therefore, the phase delay amount and the fast axis direction of the device to be tested are obtained as follows:
Also, if f 1 ＜f 2 We have:
I.e. measuring Ψ max And Ψ min The corresponding is known max And min The phase delay amount and the fast axis direction of the measured point of the measured sample can be known.
Example 2
FIG. 3 shows a schematic structural diagram of a measuring apparatus according to embodiment 1 of the method of the present invention, including: the system comprises a dual-frequency laser light source 301, a beam splitter 302, a rotating platform 303, a half-wave plate 304 arranged on the rotating platform 303, a two-dimensional translation platform 305, a sample 306 to be measured, a converging lens 307 and a plane reflecting mirror 308, a reference analyzer 311 and a reference photoelectric detector 312, a measurement analyzer 310 and a measurement photoelectric detector 309 which are respectively arranged on two sides of the beam splitter 302, a phase measurer 313 connected with the two photoelectric detectors, a controller 314 connected with the rotating platform and the translation platform, and a computer 315 connected with the phase measurer and the controller.
The emergent light of the double-frequency laser light source comprises two orthogonal linear polarized light components with different frequencies, and the frequency difference between the two orthogonal linear polarized light components is dozens of kilohertz to dozens of megahertz;
the working process of the device of the invention is as follows: the orthogonal polarized light emitted by the dual-frequency laser light source 301 passes through the beam splitter 302, and the incident light is divided into reflected light and transmitted light, wherein the reflected light is used as reference light, and the transmitted light is used as measurement light. The reference light is synthesized by the reference analyzer 311, received by the reference photodetector 312, and converted into an ac electrical signal, i.e., a reference beat signal. The measurement light firstly passes through the half wave plate 304, the measured sample 306 and the converging lens 307 in sequence, then is reflected by the plane mirror 308, returns along the original path, passes through the spectroscope 302 again, the transmitted light is omitted and not used, the reflected light is synthesized by the measurement analyzer 310, is received by the measurement photoelectric detector 309 and is converted into an alternating current signal-measurement beat frequency signal. The two-dimensional translation platform drives the measured sample to translate, so that the measuring light passes through the measuring point. The rotation stage drives the half-wave plate 304 to rotate, so that the included angle between the polarization direction of the two frequency components in the measurement light and the fast axis direction of the measured sample 306 is changed, the phase relationship between the two frequency components is changed, and the phase of the measurement beat signal relative to the reference beat signal is changed. And comparing the phases of the reference beat frequency signal and the measurement beat frequency signal by using a phase measurer, recording the rotation angle of the half wave plate 304, and sending the result to a computer for data processing to obtain the phase delay amount and the fast axis direction of the measured sample 306.
The detailed data of the device of the invention are described below: wherein, the dual-frequency laser light source 301 adopts PT-1105C type dual-frequency laser head, frequency stabilization precisionDegree 10 -8 Frequency difference is 3.006MHz; the light transmission aperture of the half wave plate 304 is 10mm; the rotating angle range of the rotating platform is 360 degrees, and the resolution is 0.1 degree; the movement range of the two-dimensional translation stage 305 is 100mm × 100mm, and the resolution is 0.1mm; the two photoelectric receivers 310 and 312 adopt PT-1303CThe frequency response range of the high-speed receiver is 100 kHz-10 MHz; the phase measurer 313 adopts a PT-1313B type multifunctional digital phase card, the phase resolution is 0.01 degrees, the output end of the phase measurer is connected with the computer 315, and the input end of the phase measurer is connected with the output ends of the two photoelectric receivers. The rotating table, the half-wave plate, the two-dimensional translation table, the controller and the computer adopted in the embodiment are all universal devices
The measurement process is as follows:
1. the dual-frequency laser light source 301 outputs two orthogonal linearly polarized light with the frequency difference of 3.006MHz;
2. the mutually orthogonal linearly polarized light is divided into two parts of reflected light and transmitted light after passing through a spectroscope 302;
3. the reflected light is synthesized by the reference analyzer 311 and received by the reference photodetector 312 to form a reference beat signal;
4. the transmitted light is measurement light, sequentially passes through a half-wave plate 304, a measured sample 306 and a converging lens 307, is reflected by a plane mirror 308, sequentially passes through the converging lens 307, the measured sample 306 and the half-wave plate 304, and then passes through a spectroscope 302 again, the reflected light is synthesized by a measurement analyzer 310, and is received by a measurement photoelectric detector 309 to form a measurement beat frequency signal;
5. adjusting the direction of the rotating platform 303 to make the fast axis direction of the half-wave plate 304 parallel to the horizontal direction, and setting the current angle of the rotating platform 303 as a zero point;
6. the computer 315 operates the two-dimensional translation stage 305 through the controller 314 connected thereto so that the measuring light passes through the measured point on the measured sample 306;
7. sending said reference signal of step 3 and said measured beat signal of step 4 to a phase measurer 313 for phase comparison, and reading the result by a computer 315;
8. the computer 315 operates the rotary table 303 via the controller 314 connected thereto to rotate from the zero point, and the value of the rotation angle is read by the computer 315 via the controller 314;
9. repeating the step 7 and the step 8, recording the corresponding phase difference and angle, finding out the maximum value and the minimum value of the phase difference and the corresponding rotation angle thereof, and calculating the phase delay amount of the measured sample 306 at the measured point and the included angle between the fast axis direction and the horizontal direction according to the formula;
10. repeating steps 6-9 can obtain birefringence parameters at different positions on the sample 306 to be measured.
In the embodiment of the present device, a pyramid prism or a hollow cube corner prism may be used to implement the converging lens 307 and the plane mirror 308 to achieve the returning function of the light path, which is a cat eye device with the same efficacy.
Example 3:
referring to fig. 4, there is another embodiment of the method of the present invention, which is different from embodiment 1 in that a second-half wave plate 404 is partially located in the optical path, and this embodiment is partially disposed after the beam splitter 403 and before the sample 405 to be measured, and functions to change the polarization angle of half of the light, while the other half remains unchanged; a wedge-shaped reflector is added to divide the light beam returned from the beam splitter 403 into two halves, the polarization angles of which are changed and unchanged respectively; two analyzers 401, 409 are respectively arranged after being separated by a wedge-shaped reflecting mirror 408In the beam of light of (a). The two half beams of light are received by analyzers 401 and 409 to form two measurement beat frequency signals, and the two measurement beat frequency signals are compared with the reference beat frequency signal synthesized by the analyzer 402 to obtain two phase differences, so that the phase delay amount and the fast axis direction of the measured sample 405 are calculated. For example, half-wave plate 404 has 22.5 degrees included angle between the fast axis and the X-axis, the analyzing directions of analyzers 401 and 409 are parallel to the Y-axis, and the phase difference obtained from the beams 401 and 409 is denoted as Ψ 1 And Ψ 2 When the sample 405 is testedWhen the included angle between the fast axis and the X axis is a small angle, we have the following simplified formula:
amount of phase delay:
the fast axis direction: θ = arctan (Ψ) 1 ，Ψ 2 )
Compared with the method shown in the embodiment 1, the method does not need to rotate the half wave plate, saves a rotating device and time consumed by rotation, and can quickly obtain the measurement result.
In order to eliminate the phase change caused by other devices and circuits in the optical path, the device of the embodiment can be used for self-correction, and the process is as follows: the measured sample 405 is moved out of the optical path, and the two phase differences are recorded as psi 1o And Ψ 2o (ii) a Then, the measured sample 405 is inserted into the optical path to obtain two phase differences psi 1 ' and Ψ 2 '; therefore, the phase difference due to the birefringence of the sample 405 to be measured, excluding other influences, is:
Ψ 1 ＝Ψ 1 ′-Ψ 1o
Ψ 2 ＝Ψ 2 ′-Ψ 2o
by substituting them into the foregoing formula calculations, more accurate results can be obtained.
Similarly, the difference of the measurement apparatus using the method of this embodiment compared with embodiment 2 is that the half-wave plate 404 is arranged in a different manner, and a rotation apparatus for fixing the half-wave plate 404 is omitted, and meanwhile, a wedge-shaped mirror 408 and an analyzer are added in the direction opposite to the incident and reflected light direction of the spectroscope 403, and the measurement apparatus can also use a pyramid prism or a hollow cube prism to implement the return function of the light path by the converging lens 406 and the plane mirror 407, and is a cat eye apparatus with the same efficacy.
In the method and apparatus of this embodiment, the half-wave plate 404 may also be partially disposed in the optical path before the beam splitter 403.
Claims (8)
1. A method for measuring phase delay and fast axis direction of a birefringent optical device is to divide a pair of orthogonal dual-frequency lasers emitted by a laser into reflected light and transmitted light; at least one path of light in the two paths of reflected light and transmitted light passes through a birefringence measured sample measuring point after the polarization angle is changed, and the method is characterized in that the path of light is turned back and passes through the measured sample measuring point, so that the phases of polarization components of two frequencies in the light beam are delayed differently, and phase change is caused; then, after being respectively synthesized by the analyzer, the two paths of light are respectively converted into a reference beat frequency signal and a measurement beat frequency signal with different phase differences; obtaining the phase difference at least twice, and calculating the phase delay amount and the fast axis direction of the measuring point; and recording the phase difference between the reference beat frequency signal and the measurement beat frequency signal of each measurement point of the measured sample, and calculating to obtain the phase delay amount and the fast axis direction of the measured sample.
2. A method for measuring retardation and fast axis direction of a birefringent optical device according to claim 1, wherein the measured sample measurement point is a measurement area within an error tolerance range.
3. A method for measuring retardation and fast axis direction of a birefringent optical device according to claim 1 or 2, wherein the light is turned back by arranging a converging lens and a plane mirror in sequence after passing through the sample to be measured in the light path of the sample to be measured, or by using a corner cube or by using a hollow corner cube.
4. A method for measuring retardation and fast axis direction of a birefringent optical device according to claim 1 or 2, wherein the at least two phase differences are achieved by disposing a quarter-wave plate on the light path before the sample to be measured, and the transmitted light passes through the wave plate in forward and reverse directions, so that the main axis of the wave plate is at least two angles respectively, and at least two phase changes are obtained to obtain at least two phase differences of the reference beat signal and the measurement beat signal.
5. A method for measuring retardation and fast axis direction of a birefringent optical device according to claim 1 or 2, wherein said at least two phase differences are achieved by: a half wave plate is arranged on an optical path in front of a measured sample, and the half wave plate is partially positioned in the optical path, so that part of the transmitted light passes through the wave plate, the transmitted light passing through a measuring point of the measured sample comprises two parts with changed polarization angles and two parts without changed polarization angles, then the two parts of the light are separated before the synthesis of an analyzer, and then the two parts of the light respectively pass through the analyzer, and two obtained measured beat frequency signals are respectively compared with a reference beat frequency signal to form two phase differences.
6. The measuring apparatus using the measuring method according to any one of claims 1 to 5, comprising a spectroscope disposed on the emission light path of the dual-frequency laser, a half-wave plate, a sample to be measured, a condensing lens and a plane mirror disposed in this order in the transmission direction of the spectroscope, and analyzers disposed in the reflected light direction of the spectroscope and the opposite direction thereof, the analyzers being connected to the calculating apparatus after being connected to the photoelectric conversion apparatus, respectively; the plane mirror is disposed on a focal plane of the condensing lens.
7. A measuring device according to claim 6, characterized in that the converging lens and the plane mirror in the device can be replaced by a corner cube or a hollow corner cube.
8. A measuring apparatus according to claim 6 or 7, wherein the half-wave plate is located partially in the path of the light, a portion of the transmitted light is passed through the wave plate, and a wedge-shaped mirror is provided opposite the direction of the reflected light from the beam splitter to split the beam returning from the beam splitter into two halves, a beam with a changed and an unchanged angle of polarization, and a polarization detector is provided in the path of the split beam.
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