Glass material stress birefringence measurement device and method

Abstract

The present invention proposes a device and method for measuring stress birefringence of glass materials. A fixed reflector of a laser gain tube and an independent reflector driven by a piezoelectric actuator form a resonant cavity with adjustable cavity length; the glass sample can adjust the rotation angle in a plane perpendicular to the laser axis; a force application mechanism can adjust the internal stress of the anti-reflection window; the frequency difference of two orthogonal polarization modes is measured by an avalanche photodetector and a frequency meter; and the light intensity of the two orthogonal polarization modes is measured by two photodetectors. When the glass sample to be measured is not placed in the resonant cavity, the phase delay corresponding to the stress birefringence of the anti-reflection window is calculated; after the glass sample is placed, the rotation angle is adjusted so that its equivalent fast axis and slow axis coincide with the equivalent fast axis of the anti-reflection window twice, and the frequency difference of the split mode is calculated; according to the interval where the split mode frequency difference is located and the phase delay of the anti-reflection window, the glass stress birefringence index is calculated. The present invention can accurately measure the stress birefringence of glass materials, has a simple structure, and is easy to realize automatic measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and in particular to a device and method for measuring stress birefringence of glass materials. Background Art

[0002] During the processing and use of optical glass materials and glass components, various factors will cause internal stress inside them, such as thermal stress caused by temperature gradient during glass melting, surface stress caused by cutting or grinding force during component processing, compressive stress caused by the deadweight of heavier components, and stress caused by the clamping force of the installation mechanism on the components. Internal stress will cause the originally isotropic glass components to show a certain stress birefringence due to the photoelastic effect. The polarization state of the light passing through it will change accordingly, and the wavefront of the light beam will also be distorted, thereby reducing the performance of the optical system. In severe cases, it may even cause damage to the components. For example, the neodymium glass components used in laser nuclear fusion devices will cause uneven energy distribution of the focused spot due to stress birefringence when transmitting high-energy laser beams. Heat accumulation will also cause component rupture and affect the operation of the laser system. Therefore, it is necessary to precisely measure the stress birefringence of optical glass materials and components to evaluate the quality or reduce the impact.

[0003] There are many methods for measuring stress birefringence of optical components, which can be mainly divided into two categories based on the principle of polarized light and the principle of optical interference: the former uses optical components such as polarizers to convert the change in polarization state of light after passing through an optical glass sample into a change in light intensity, and then obtains its stress birefringence. Since the measurement is performed through light intensity, it is susceptible to laser fluctuations and environmental disturbances, and the measurement accuracy is usually low; the latter uses an interference optical path to measure the interference fringes caused by birefringence after light passes through an optical glass sample, that is, the change in phase, to obtain its stress birefringence. The measurement accuracy is high, but the optical path structure is complex. At the same time, the above methods cannot be traced back to the metrological standard, and the comparability between each other is poor. It is necessary to study optical glass stress birefringence measurement devices and methods with high accuracy, simple optical paths, and traceable measurement results. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the optical stress measurement method in the prior art and to provide a device and method for measuring stress birefringence of glass materials.

[0005] In order to achieve the above purpose, the technical solution adopted is:

[0006] Glass material stress birefringence measuring device, comprising:

[0007] Laser gain tube: a fixed reflector is provided at the first end and an anti-reflection window is provided at the second end;

[0008] Independent reflector: arranged at the second end side of the gain tube, located outside the anti-reflection window, and combined with the laser gain tube and the fixed reflector to realize orthogonal polarization laser oscillation;

[0009] Piezoelectric actuator: connected to the independent reflector to drive the independent reflector to move along the laser axis;

[0010] Glass sample: set between the anti-reflection window and the independent reflector;

[0011] Rotating table: the glass sample is mounted on the rotating table, the rotating axis of which coincides with the laser beam, so as to drive the glass sample to adjust the angle in a plane perpendicular to the laser beam;

[0012] A force applying mechanism: arranged in the radial direction of the anti-reflection window, capable of applying pressure in the radial direction of the anti-reflection window; the force applying mechanism is connected to the force adjusting mechanism, and can adjust the magnitude of the force applied to the anti-reflection window, so that the frequency difference between the intervals of two adjacent levels of longitudinal modes in the orthogonal polarization direction of the laser caused by its stress birefringence is within the positive and negative threshold range of the threshold frequency difference f, and the direction of the anti-reflection window along which the pressure is applied is the equivalent fast axis direction; the threshold frequency difference f is determined according to the performance of the laser;

[0013] Polarizer: set on the outside of the independent reflector;

[0014] Avalanche photodetector: It is arranged outside the polarizer and is used to receive the beat frequency signal of the two orthogonal polarization modes of the laser and the beat frequency signal of the split mode;

[0015] Frequency meter: communicates with the avalanche photodetector to obtain the frequency value of the beat frequency signal of the two orthogonal polarization modes and calculate the frequency difference of the two orthogonal polarization modes;

[0016] Data processor: Calculates the phase delay corresponding to the stress birefringence of the glass material based on the frequency difference of two orthogonal polarization modes.

[0017] In some embodiments of the present invention, an anti-reflection film is coated on the surface of the glass sample.

[0018] In some embodiments of the present invention, the force applying mechanism is symmetrically arranged at two ends of the anti-reflection window in the radial direction, so as to symmetrically apply force to the anti-reflection window in the radial direction.

[0019] In some embodiments of the present invention, the light transmission direction of the polarizer forms an angle of 45° with the polarization direction of the laser.

[0020] In some embodiments of the present invention, the threshold frequency difference f ranges from 15 to 20 MHz.

[0021] Some embodiments of the present invention further provide a method for measuring stress birefringence of a glass material, characterized in that it comprises the following steps:

[0022] S1: Before placing the glass sample in the laser resonant cavity, gradually increase the radial pressure of the anti-reflection window from small to large, adjust the piezoelectric ceramic actuator and judge the beginning of mode jump according to the light intensity recorded by the two photodetectors, then reduce the pressure of the anti-reflection window until no mode jump occurs, that is, the split mode frequency difference Δv introduced by the stress birefringence of the anti-reflection window w When the frequency difference is close to the threshold value f, the split mode frequency difference Δv is calculated w and the corresponding phase delay, the steps include: when the independent reflector is in the initial position, measuring the frequency difference Δ of the two orthogonal polarization longitudinal modes of the laser q0 , adjust the piezoelectric actuator, change the resonant cavity length, and measure the frequency difference Δ between the two orthogonal polarization longitudinal modes of the laser 20 ;

[0023] Calculation of split mode frequency difference Δv introduced by stress birefringence of antireflection window w :

[0024] f≈Δv w =|Δ 10 -Δ 20 | / 2;

[0025] Calculate the phase delay Δφ corresponding to the stress birefringence of the antireflection window w :

[0026] Δφ w =(λ / 2)·|Δ 10 -Δ 20 | / (Δ 10 +Δ 20 );

[0027] Calculate the initial longitudinal mode frequency difference Δ of the laser 00 :

[0028] Δ 00 =|Δ 10 +Δ 20 | / 2;

[0029] S2: The calculation steps of the frequency difference Δ0 of the laser longitudinal mode spacing in the orthogonal polarization direction caused by stress birefringence include:

[0030] S21: Adjust the rotating stage so that the equivalent fast axis or the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference Δ0 of the laser longitudinal mode interval;

[0031] Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 11 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 12 ; Further set the frequency difference judgment threshold and compare Δv 11 With Δv 12The size and sum of 00 size;

[0032] If Δv 11 With Δv 12 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode hopping during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 1t The value of and the longitudinal mode spacing Δ0;

[0033] If Δv 11 With Δv 12 If they are not equal, further judgment:

[0034] If Δv 11 With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =min(Δv 11 ,Δv 12 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 11 +Δv 12 ;

[0035] If Δv 11 With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =|Δv 11 -Δv 12 | / 2, the frequency difference of the laser longitudinal mode spacing is calculated as Δ0=(Δv q1 +Δv q2 ) / 2;

[0036] S22: Further adjust the rotating stage to rotate it by 90°, so that the equivalent slow axis or the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference of the laser longitudinal mode interval:

[0037] Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 21 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 22 ; Depending on whether a mode jump occurs in step S21, Δv 21 With Δv 22 The size and judgment of:

[0038] If no mode jump occurs in step S21, and Δv 21 With Δv 22 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode jumps during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 2t The value of

[0039] If Δv 21 With Δv 22 If they are not equal, further judgment:

[0040] If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =min(Δv 21 ,Δv 22 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 21 +Δv 22 ;

[0041] If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =|Δv 21 -Δv 22 | / 2; the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = (Δv 21 +Δv 22 ) / 2;

[0042] If no mode hopping occurs in steps S21 and S22, the frequency difference Δ0 of the longitudinal mode intervals obtained twice is equal;

[0043] S3: In step S2, when the piezoelectric actuator is adjusted, the light intensity of the two orthogonal polarization modes is recorded at the same time, and the split mode frequency difference Δv caused by the total stress birefringence in the resonant cavity is respectively calculated when the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window and the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window. 1t Value and Δv 2t Value, and longitudinal mode interval Δ0 value, judge and calculate:

[0044] If the piezoelectric actuator is adjusted to change the length of the resonant cavity at the position of the two overlaps, the horizontally polarized light and the vertically polarized light will undergo a mode jump, and the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2t The one corresponding to the time when no mode jump occurs is set to Δv t ,and interval, the stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w -(λΔν t ) / (2Δ0);

[0045] If the horizontal polarized light and the vertical polarized light do not undergo mode hopping when the piezoelectric actuator is adjusted to change the resonant cavity length at the position of the two overlaps, the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2t If they are in the intervals [2f,3f]MHz and [0,f]MHz respectively, then the split mode frequency difference corresponding to the interval [0,f]MHz is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w +(λΔν t ) / (2Δ0);

[0046] If at the position of the two overlaps, the piezoelectric actuator is adjusted to change the resonant cavity length, the horizontal polarized light and the vertical polarized light undergo a mode jump, or no mode jump occurs, and the split mode frequency difference Δv measured at the two overlaps 1t and Δv 2t If both are >2fMHz, then take the Δv measured during the two coincidences 1t and Δv 2t The larger intermediate frequency difference is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =(λΔν t ) / (2Δ0)-Δφ w ;

[0047] In the above formulas: λ is the laser wavelength.

[0048] In some embodiments of the present invention, the threshold frequency difference f is 16 MHz.

[0049] Compared with the prior art, the advantages and positive effects of the present invention are:

[0050] 1. The present invention can measure the stress birefringence of glass materials by laser frequency or frequency difference. The dual frequency measurement has high accuracy and can accurately measure the stress birefringence of materials. The measurement can be traced back to the wavelength of light (ie, frequency).

[0051] 2. The method of applying pressure to the anti-reflection window of the laser gain tube and rotating the glass sample during measurement to make it coincide with the fast and slow axes of the anti-reflection window twice can avoid the situation where the measurement cannot be carried out due to the strong competition effect of the laser oscillation mode, so that any size of stress birefringence in the glass material can be directly measured. The system structure is simple and automatic measurement is easy to achieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the frequency distribution of the laser oscillation longitudinal mode;

[0053] Figure 2aSchematic diagram of the frequency difference formed by the splitting of each longitudinal mode of the laser by a glass sample;

[0054] Figure 2b Schematic diagram of the frequency difference formed by the change of interval between adjacent longitudinal modes of laser for glass sample;

[0055] Figure 3a Schematic diagram of mode hopping of two orthogonal polarization modes during cavity length adjustment;

[0056] Figure 3b Schematic diagram of no mode hopping in two orthogonal polarization modes during cavity length adjustment;

[0057] Figure 4 Schematic diagram of the overlap between the equivalent fast / slow axis of the glass sample in the resonant cavity and the equivalent fast axis of the antireflection window;

[0058] Figure 5 Schematic diagram of the measurement range of glass samples with different stress birefringence sizes;

[0059] Figure 6 Schematic diagram of the stress birefringence measurement device for glass materials.

[0060] In the above figures:

[0061] 1-Gain tube;

[0062] 2-Fixed reflector;

[0063] 3-antireflection window;

[0064] 4-Independent reflector;

[0065] 5- Piezoelectric actuator;

[0066] 6- Glass sample to be tested;

[0067] 7- Rotating table;

[0068] 8- Polarizer;

[0069] 9- Avalanche photodetector;

[0070] 10-Frequency meter;

[0071] 11-Polarization beam splitter;

[0072] 12- a first photodetector;

[0073] 13- a second photodetector;

[0074] 14-Data processing unit. DETAILED DESCRIPTION

[0075] The present invention is described in detail below by way of exemplary embodiments. However, it should be understood that elements, structures, and features in one embodiment may also be beneficially combined in other embodiments without further description.

[0076] The glass material stress birefringence measuring device and method provided by the present invention are based on the laser frequency splitting measurement principle.

[0077] Firstly, the principle of laser frequency splitting measurement is explained.

[0078] For a standing wave laser, the longitudinal mode that can form an oscillation in the resonant cavity satisfies the resonance condition, such as Figure 1 As shown. Within the laser gain band, there are two adjacent longitudinal modes v q and v q+1 Gain can be obtained to form laser output. Due to the competition between laser modes, the polarization directions of adjacent longitudinal modes are along the two intrinsic directions of the laser, that is, the polarization states are orthogonal to each other, expressed as ⊥ polarization state and ∥ polarization state. As the laser cavity length changes, other longitudinal modes such as v q-1 、v q-2 etc. will successively enter the gain band to form oscillation. The relationship satisfied by the oscillation longitudinal mode is:

[0079]

[0080] Among them, v q is the oscillation longitudinal mode frequency, L0 is the cavity length of the resonant cavity, b is the equivalent refractive index in the resonant cavity, c is the speed of light in a vacuum, and q is the longitudinal mode number, which is a positive integer. From this, we can get that the frequency difference of adjacent longitudinal modes, that is, the longitudinal mode interval, satisfies:

[0081]

[0082] As attached Figure 2a As shown in the figure, when the glass sample is placed in the laser resonant cavity, due to the stress birefringence of the material, the refractive index along the principal stress direction and the direction perpendicular to the principal stress are no longer equal, resulting in a fixed deviation in the physical cavity length of the resonant cavity in these two directions. According to the resonance conditions satisfied by the longitudinal mode, the two physical cavity lengths correspond to two different longitudinal mode sequences, that is, each level of the longitudinal mode will be split into two, and their polarization states are orthogonal to each other as a whole.

[0083] Among them, due to the stress birefringence of glass materials, the corresponding phase delay Δφ g The laser produces a splitting effect on the longitudinal mode. That is, each original longitudinal mode will split into a new longitudinal mode, for example: longitudinal mode v q Split into longitudinal mode v q and v q ′, the new longitudinal mode v q' has a certain frequency difference with the original longitudinal mode, and the frequency difference between the two is Δv. According to equations (1) and (2), it can be calculated that the two satisfy equation (3). The polarization states of the original adjacent levels of longitudinal modes are the same, and the polarization state of the new longitudinal mode becomes perpendicular to the polarization state of the adjacent longitudinal mode of the same level.

[0084] The laser cavity length can be further tuned to allow the adjacent longitudinal mode to enter the gain band, and the mode v can be measured. q ′ and v q-1 The frequency difference Δv′ between them is related to the split longitudinal mode v q The frequency difference between them satisfies Δ0=Δv+Δv′. From formula (3), it can be seen that the frequency difference between two adjacent split longitudinal modes is proportional to the stress birefringence. By precisely measuring Δv and Δv′, the stress birefringence Δφ of the glass material can be accurately measured. g , its unit is nm.

[0085]

[0086] In fact, the stress birefringence of glass materials is usually not very large, resulting in the two orthogonal polarization directions v q and v q The longitudinal mode splitting amount Δv of ' is very small, and the two split longitudinal modes are very close. For He-Ne lasers, when the splitting amount is less than a certain frequency difference value, there is a strong mode competition effect between the two oscillation modes. The two modes cannot oscillate at the same time, and only one mode can oscillate. The above-mentioned specific frequency difference value is related to the parameters such as the cavity length of the laser, which is generally about 30 to 40MHz, and can be defined as a strong competitive frequency difference.

[0087] As attached Figure 2b As shown, the mode corresponding to the dotted line cannot oscillate. The adjacent longitudinal modes that can enter the laser gain band and form oscillations are adjacent longitudinal modes, and their polarization states are orthogonal to each other to reduce mode competition. Taking the embodiment shown in the figure as an example, at this time, the adjacent longitudinal modes: v q-1 and v q between, and v q and v q+1 The frequency difference between the adjacent longitudinal modes is no longer the initial value Δ0, but a fixed deviation value Δv is generated, and v is obtained. q-1 and v q The frequency difference between ' is Δ1 = Δ0 - Δv. Further tuning the laser cavity length makes v q ′ and the next level longitudinal mode v q+1 Move into the gain band to form oscillation, and the longitudinal mode v q-1 Move out of the gain band, then the oscillation longitudinal mode v q+1 and v q The frequency difference between ' is Δ2 = Δ0 + Δv. Therefore, the frequency difference and longitudinal mode spacing of the split mode can be calculated based on the mode spacing of the adjacent longitudinal modes measured twice:

[0088]

[0089] Substituting the above equation into equation (3), the phase delay corresponding to the stress birefringence of the glass material can be obtained as:

[0090]

[0091] The above formulas (3) and (5) show that the stress birefringence phase delay of the glass material can be obtained by measuring the frequency difference between the two oscillation modes obtained twice before and after. This situation occurs when the frequency difference between the two oscillation modes in the cavity is approximately less than half of the strong competition frequency difference. However, when the frequency difference generated by the stress birefringence in the cavity is in the range of about half to one times the strong competition frequency difference, the same-order longitudinal modes with orthogonal polarization states will undergo mode hopping. As shown in the attached figure Figure 3a As shown in the figure, the frequency difference of the adjacent longitudinal modes measured in the first measurement is Δ1. During the process of continuing to tune the laser cavity length, the ⊥ polarization mode will suddenly change from oscillation to suppression, while the ∥ polarization mode will change from suppression to oscillation. In this case, the second measurement of the adjacent longitudinal mode frequency difference corresponds to the same thing as the first measurement, that is, the light intensity of the ∥ polarization mode decreases while the light intensity of the ⊥ polarization mode increases. At this time, the frequency difference Δ1 is still measured, and the frequency difference Δ2 cannot be measured, nor can it be calculated using formula (5) (in the actual two measurements, Δ1 is the smaller frequency difference, and Δ2 is the larger frequency difference). This is different from the situation when the stress birefringence of the glass sample is small, the splitting frequency difference is less than the threshold frequency difference f, and mode hopping does not occur during cavity length tuning, as shown in the figure. Figure 3b As shown. The threshold frequency difference f is about half of the strong competition frequency difference. For lasers with different parameters, the value is slightly different, generally between 15 and 20 MHz. In this patent, the threshold frequency difference can be about 16 MHz, determined by the characteristics of the laser.

[0092] Based on the above analysis, it can be concluded that after the glass sample is placed in the laser resonant cavity, as the cavity length is tuned, there are three situations:

[0093] (a) When the frequency difference between the two split modes caused by stress birefringence of the glass material is 0 to 16 MHz (corresponding to 0 to f), the cavity length can be changed to measure the frequency differences Δ1 and Δ2 of the adjacent longitudinal modes and substitute them into formula (5) for calculation;

[0094] (b) When the frequency difference between the two split modes caused by stress birefringence of glass materials is 16 to 32 MHz (corresponding to f to 2f), due to the existence of mode hopping, only the smaller frequency difference formed by the adjacent longitudinal modes can be measured, which is set to Δ1, but the frequency difference Δ2 cannot be measured, and measurement cannot be performed;

[0095] (c) When the frequency difference of the split modes caused by stress birefringence of the glass material is greater than 32 MHz (corresponding to >2f), the mode competition effect is very weak and the frequency difference Δv of the split modes can be directly measured and substituted into formula (3) for calculation.

[0096] In order to overcome the unmeasured situation caused by mode hopping, it is necessary to make the longitudinal mode frequency difference generated by the total birefringence in the cavity within the range of 0-16MHz (corresponding to 0-f) or ≥32MHz (corresponding to >2f). To this end, stress birefringence is introduced into the laser resonance, as shown in the attached figure. Figure 4 The two ends of the gain tube 1 of the semi-external cavity laser are sealed by a fixed reflector 2 and an anti-reflection window 3. When a symmetrical pressure F is applied radially on the anti-reflection window, the stress birefringence introduced on the anti-reflection window corresponds to a phase delay of Δφ w , and the direction along the pressure is the direction of the equivalent fast axis of the anti-reflection window. The magnitude of the applied force F is adjusted so that the frequency difference between the two split modes generated in the cavity is about 16MHz (f), and the polarization directions of the split modes are respectively along the equivalent fast axis and slow axis of the anti-reflection window. After the glass sample 6 to be tested is placed in the resonant cavity, it can be rotated in a plane perpendicular to the laser axis by the rotating table 7. Adjust the rotation angle of the glass sample so that the fast axis equivalent to its stress birefringence coincides with the fast axis of the window after the force is applied. Then the total stress birefringence in the resonant cavity is the superposition of the two Δφ t =Δφ w -Δφ g If the fast axis of the slow axis window with equivalent stress birefringence is made to coincide with the fast axis after stress is applied, the total stress birefringence in the resonant cavity is Δφ t =Δφ w +Δφ g .

[0097] Taking f as 16MHz as an example, the specific test process is as follows:

[0098] When Δφ g Separate frequency difference Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window (when the laser cavity length is tuned and the light intensity in one of the two polarization directions is zero, the two axes coincide with each other). Then the total stress birefringence Δφ in the cavity is t =Δφ w +Δφ g The resulting frequency difference is In the laser mode jump range, the measurement cannot be performed. The glass sample needs to be rotated to make its slow axis coincide with the fast axis of the window. The total stress birefringence in the cavity is Δφ. t =Δφ w -Δφ g , the resulting frequency difference is The measurement can be performed according to the above case (a). g The larger the Δv t The smaller, such as Figure 5 The A interval is shown.

[0099] When Δφ g Separate frequency difference Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window. Then the total stress birefringence Δφ in the cavity is t =Δφ w +Δφ g The resulting frequency difference is The measurement can be performed according to the above case (c). Continue to rotate the glass sample so that its slow axis coincides with the fast axis of the laser window, then the total stress birefringence Δφ in the cavity t =Δφ g -Δφ w The resulting frequency difference is The measurement can be carried out according to the above case (a), such as Figure 5 The B interval is shown.

[0100] When Δφ g Separate frequency difference Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window. Then the total stress birefringence Δφ in the cavity is t =Δφ w +Δφ g The resulting frequency difference is The measurement can be performed according to the above case (c). Continue to rotate the glass sample so that its slow axis coincides with the fast axis of the laser window, then the total stress birefringence Δφ in the cavity t =Δφ g -Δφ w The resulting frequency difference is Either it is in the laser mode jump range and cannot be measured, or it can be measured directly. like Figure 5 The C interval is shown.

[0101] In summary, the stress birefringence of the glass sample can be determined and obtained based on the frequency difference between the two orthogonal polarization longitudinal modes of the laser measured twice after the fast axis and slow axis of the glass sample coincide with the fast axis of the window respectively.

[0102] Based on the above principles, the present invention provides the following glass material stress birefringence measurement device and measurement method.

[0103] The first embodiment of the present invention first provides a glass material stress birefringence measurement device, which includes the following structural components.

[0104] Laser gain tube 1: a fixed reflector 2 is provided at the first end, and an anti-reflection window 3 is provided at the second end.

[0105] Independent reflector 4: arranged at the second end side of the laser gain tube 1, located outside the anti-reflection window 3, cooperates with the laser gain tube 1 and the fixed reflector 2, and realizes orthogonal polarization laser oscillation in combination;

[0106] Piezoelectric actuator 5: connected to the independent reflector 4 to drive the independent reflector 4 to move along the laser axis direction; in this embodiment, the piezoelectric actuator 5 is made of piezoelectric ceramics, and the vibration of the piezoelectric ceramics is adjusted by changing the voltage of the piezoelectric ceramics, thereby driving the independent reflector 4 to move, adjusting the distance between the independent reflector 4 and the fixed reflector 2, and changing the length of the resonant cavity.

[0107] Glass sample 6: arranged between anti-reflection window 3 and independent reflector 4; the purpose of the present invention is to measure the stress birefringence phase delay of glass sample 6, and use the phase delay to evaluate the stress birefringence index of glass. The surface of glass sample 6 is coated with an anti-reflection film under the laser wavelength.

[0108] Rotating table: The glass sample 6 is mounted on the rotating table, which can rotate in a vertical plane. The rotating axis of the rotating table coincides with the laser beam, so that the glass sample can be driven to adjust the angle in a plane perpendicular to the laser beam; Figure 4 As shown, it rotates around the z-axis.

[0109] A force applying mechanism: arranged in the radial direction of the anti-reflection window 3, capable of applying pressure in the radial direction of the anti-reflection window 3; the force applying mechanism is connected to the force adjusting mechanism, and can adjust the magnitude of the pressure applied to the anti-reflection window, so that the frequency difference between the intervals of two adjacent levels of longitudinal modes in the orthogonal polarization direction of the laser caused by stress birefringence is within the positive and negative threshold range of the threshold frequency difference f, and the direction of the anti-reflection window along which the pressure is applied is the equivalent fast axis direction; the threshold frequency difference f is determined according to the performance of the laser, and the range of the threshold frequency difference f is 15 to 20 MHz, and 16 MHz is used in this embodiment;

[0110] The force applying mechanism is symmetrically arranged at both ends of the anti-reflection window in the radial direction to symmetrically apply a clamping force to the anti-reflection window in the radial direction. The structure of the force applying mechanism is not specifically limited, and there are many implementation methods in practical applications.

[0111] Polarizer 8: arranged outside the independent reflector 4; the light transmission direction of the polarizer 8 forms an angle of 45° with the polarization direction of the laser.

[0112] Avalanche photodetector 9: arranged outside polarizer 8, used to receive the beat signal of two orthogonal polarization modes of laser and the beat signal of split mode. The two orthogonal polarization modes of laser mentioned here may be two longitudinal modes or split modes.

[0113] Frequency meter 10: communicates with the avalanche photodetector to obtain the frequency value of the beat frequency signal of two orthogonal polarization modes;

[0114] Data processor: Based on the frequency difference of two orthogonal polarization longitudinal modes, calculate the frequency difference of the split mode, and based on the frequency difference of the split mode, calculate the stress birefringence phase delay of the glass material. The specific calculation method is described in detail in the second embodiment.

[0115] The second embodiment of the present invention further provides a method for measuring stress birefringence of a glass material, comprising the following steps.

[0116] S1: Before placing the glass sample in the laser resonant cavity, gradually increase the radial pressure of the anti-reflection window from small to large, adjust the piezoelectric ceramic actuator and judge the beginning of mode jump according to the light intensity recorded by the two photodetectors, then reduce the pressure of the anti-reflection window to prevent mode jump, that is, the split mode frequency difference Δv introduced by the stress birefringence of the anti-reflection window w When the frequency difference f is close to the threshold,

[0117] Calculate the split mode frequency difference Δv w and the corresponding phase delay, the steps include: when the independent reflector is in the initial position, measuring the frequency difference Δ of the two orthogonal polarization longitudinal modes of the laser 10 , adjust the piezoelectric actuator, change the resonant cavity length, and measure the frequency difference Δ between the two orthogonal polarization longitudinal modes of the laser 20 ;

[0118] Calculation of split mode frequency difference Δv introduced by stress birefringence of antireflection window w :

[0119] f≈Δv w =|Δ 10 -Δ 20 | / 2;

[0120] Calculate the phase delay Δφ corresponding to the stress birefringence of the antireflection window w :

[0121] Δφ w =(λ / 2)·(Δ 10 +Δ 20 ) / (Δ 10 +Δ 20 );

[0122] Calculate the initial longitudinal mode spacing Δ of the laser 00 :

[0123] Δ 00 =|Δ 10 +Δ 20 | / 2;

[0124] Specifically, the photodetector 9 measures the frequencies of the two orthogonal polarization longitudinal modes of the polarization state ⊥ and the polarization state ∥, and the frequency meter 10 calculates the laser splitting mode v based on the frequencies of the two orthogonal polarization longitudinal modes. q and v′ q The frequency difference Δv wIn this step, since the glass sample 6 is not introduced, the stress birefringence is introduced by the anti-reflection window 3. The initial position is not limited, and the length of the front and rear resonant cavities is not limited. In this process, the stress in the radial direction of the anti-reflection window 3 is adjusted so that Δv w The frequency difference close to the threshold is 16 MHz. The frequency difference close to the threshold mentioned here refers to allowing a certain threshold range, and the threshold can be set as needed.

[0125] Before measuring, first adjust the split mode frequency difference of the anti-reflection window to reach the determined value threshold frequency difference. This is a pre-completion work. Once adjusted, it basically does not need to be changed during the subsequent tests. Just measure the split mode frequency difference caused by the anti-reflection window 3 before measuring the glass sample each time, calculate the phase delay, and record it as the initial value for use in the subsequent measurement of the glass sample.

[0126] Before the glass sample 6 is placed in the cavity, the frequency difference generated by the stress birefringence of the anti-reflection window 3 is slightly different from the split frequency difference generated by the stress birefringence of the unchanged anti-reflection window 3 after the sample is placed, because the equivalent cavity length has changed. Therefore, the following processing methods uniformly deduct the phase delay introduced by the stress birefringence of the anti-reflection window 3, which corresponds to the stress birefringence one by one and remains unchanged in size, instead of deducting the split frequency difference generated by the anti-reflection window 3.

[0127] S2: The calculation steps of the frequency difference Δ0 of the laser longitudinal mode spacing in the orthogonal polarization direction caused by stress birefringence include:

[0128] S21: Adjust the rotating stage so that the equivalent fast axis or the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference Δ0 of the laser longitudinal mode interval;

[0129] Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 11 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 12 ; Further set the frequency difference judgment threshold and compare Δv 11 With Δv 12 The size and sum of 00 size;

[0130] If Δv 11 With Δv 12 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode hopping during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 1t The value of and the longitudinal mode spacing Δ0;

[0131] If Δv 11 With Δv 12 If they are not equal, further judgment:

[0132] If Δv 11 With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =min(Δv 11 ,Δv 12 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 11 +Δv 12 ;

[0133] If Δv 11 With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =|Δv 11 -Δv 12 | / 2, the frequency difference of the laser longitudinal mode spacing is calculated as Δ0=(Δv 11 +Δv 12 ) / 2;

[0134] S22: On the basis of step S21, further adjust the rotating stage to rotate 90°, so that the equivalent slow axis or the other equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference of the laser longitudinal mode interval. If the equivalent fast axis of the glass sample is adjusted to coincide with the equivalent fast axis of the anti-reflection window in step S21, then in step S22, after the rotating stage rotates 90°, the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window. Similarly, if the equivalent slow axis of the glass sample is adjusted to coincide with the equivalent fast axis of the anti-reflection window in step S21, then in step S22, after the rotating stage rotates 90°, the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window.

[0135] Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 21 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 22 ; Depending on whether a mode jump occurs in step S21, Δv 21 With Δv 22 The size and judgment of:

[0136] If no mode jump occurs in step S21, and Δv 21 With Δv 22 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode jumps during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 2t The value of

[0137] If Δv 21 With Δv 22 If they are not equal, further judgment:

[0138] If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =min(Δv 21 ,Δv 22 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 21 +Δv 22 ;

[0139] If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =|Δv 21 -Δv 22 | / 2; the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = (Δv 21 +Δv 22 ) / 2;

[0140] If no mode hopping occurs in steps S21 and S22, the frequency difference Δ0 of the longitudinal mode intervals obtained twice is equal. That is, in step S21, if no mode hopping occurs, the longitudinal mode interval can be calculated once; in step S22, if no mode hopping occurs, the longitudinal mode interval can also be calculated once. The results obtained twice are the same, and either one or the average value can be used in the formula for calculating the phase delay in step S3.

[0141] In this step, the equivalent fast axis or the equivalent slow axis of the glass sample is selected to coincide with the fast axis of the anti-reflection window, and the frequency difference of the two orthogonal polarization longitudinal modes is measured in one case. The initial position is not limited, and the length of the resonant cavity before and after the change is not limited. After the glass sample 6 is placed in the resonant cavity, the stress birefringence effect is jointly generated by the glass sample 6 and the anti-reflection window.

[0142] S3: In step S2, when the piezoelectric actuator is adjusted, the light intensity of the two orthogonal polarization modes is recorded at the same time, and the split mode frequency difference Δv caused by the total stress birefringence in the resonant cavity is respectively calculated when the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window and the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window. 1t Value and Δv 2t Value, and longitudinal mode interval Δ0 value, judge and calculate:

[0143] If the piezoelectric actuator is adjusted to change the length of the resonant cavity at the position of the two overlaps, the horizontally polarized light and the vertically polarized light will undergo a mode jump, and the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2tThe one corresponding to the time when no mode jump occurs is set to Δv t and interval, the stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w -(λΔν t ) / (2Δ0);

[0144] If the horizontal polarized light and the vertical polarized light do not undergo mode hopping when the piezoelectric actuator is adjusted to change the resonant cavity length at the position of the two overlaps, the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2t If they are in the intervals [2f,3f]MHz and [0,f]MHz respectively, then the split mode frequency difference corresponding to the interval [0,f]MHz is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w +(λΔν t ) / (2Δ0);

[0145] If at the position of the two overlaps, the piezoelectric actuator is adjusted to change the resonant cavity length, the horizontal polarized light and the vertical polarized light undergo a mode jump, or no mode jump occurs, and the split mode frequency difference Δv measured at the two overlaps 1t and Δv 2t If both are >2fMHz, then take the Δv measured during the two coincidences 1t and Δv 2t The larger intermediate frequency difference is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =(λΔν t ) / (2Δ0)-Δφ w ;

[0146] In the above formulas: λ is the laser wavelength, and f corresponds to 16 MHz in this embodiment.

[0147] Among them: the fast axis and slow axis of the glass sample and the anti-reflection window are 90°, when the fast axis coincides, the slow axis also coincides. There are two situations: the fast axis of the glass coincides with the fast axis of the anti-reflection window, and the fast axis of the glass coincides with the slow axis of the anti-reflection window.

[0148] In some embodiments of the present invention, a method for determining that a mode jump occurs between horizontally polarized light and vertically polarized light includes:

[0149] In the process of adjusting the length of the laser resonant cavity, the light intensity of the two orthogonal polarized lights, vertical polarization and horizontal polarization, is recorded;

[0150] Calculate the difference between the intensity of vertically polarized light and the intensity of horizontally polarized light;

[0151] In the process of changing the cavity length by half a wavelength, before and after the vertical polarized light intensity and the horizontal polarized light intensity reach the position where the intensity difference is zero twice, if the sign of the intensity difference changes from negative to positive or from positive to negative, it is determined that the horizontal polarized light and the vertical polarized light have mode hopping.

[0152] Among them, the measurement of the intensity of vertically polarized light and horizontally polarized light is achieved through a light spot detector.

[0153] In practical applications, the light intensity can also be used to determine whether a mode jump has occurred. As shown in Figure 3(a) and Figure 3(b), during the process of tuning the laser cavity length, the light intensity of the vertically polarized light and the horizontally polarized light is recorded, and the light intensity difference between the two is taken as the mark flag. If no mode jump occurs, the sign of the flag is reversed once before and after the two equal light intensity points where the light intensity difference between the vertically polarized light and the horizontally polarized light is zero, that is, from positive to negative and from negative to positive, or vice versa; and if a mode jump occurs, the sign of the flag is reversed once when the mode jump occurs before reaching the equal light intensity point for the second time, and when passing the equal light intensity point twice, the sign of the flag always changes from positive to negative or from negative to positive. Therefore, it is possible to determine whether the vertically polarized light and the horizontally polarized light have undergone a jump based on the change in the sign of the light intensity difference.

[0154] The method of the present invention can quickly, directly and accurately measure the stress birefringence index of glass materials, and the system structure is simple and automatic measurement can be easily realized.

[0155] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. Glass material stress birefringence measuring device, characterized in that: include: Laser gain tube: a fixed reflector is provided at the first end and an anti-reflection window is provided at the second end; Independent reflector: arranged at the second end side of the gain tube, located outside the anti-reflection window, and combined with the laser gain tube and the fixed reflector to realize laser oscillation; Piezoelectric actuator: connected to the independent reflector to drive the independent reflector to move along the laser axis direction; Glass sample: set between the anti-reflection window and the independent reflector; Rotating table: the glass sample is mounted on the rotating table, the rotating axis of which coincides with the laser beam, so as to drive the glass sample to adjust the angle in a plane perpendicular to the laser beam; A force applying mechanism: arranged in the radial direction of the anti-reflection window, capable of applying pressure in the radial direction of the anti-reflection window; the force applying mechanism is connected to the force adjusting mechanism, and can adjust the magnitude of the force applied to the anti-reflection window, so that the frequency difference between the intervals of two adjacent levels of longitudinal modes in the orthogonal polarization direction of the laser caused by its stress birefringence is within the positive and negative threshold range of the threshold frequency difference f, and the direction of the anti-reflection window along which the pressure is applied is the equivalent fast axis direction; the threshold frequency difference f is determined according to the performance of the laser; Polarizer: set on the outside of the independent reflector; Avalanche photodetector: It is set outside the polarizer and is used to receive the beat frequency signal of the two orthogonal polarization modes of the laser. Frequency meter: communicates with the avalanche photodetector to obtain the frequency value of the beat frequency signal of two orthogonal polarization modes; Polarization beam splitter: It is set on one side of the fixed reflector of the laser gain tube and is used to split the light of two orthogonal polarization modes into beam one and beam two; Photoelectric detector: including a first photoelectric detector and a second photoelectric detector, which are respectively arranged on the propagation optical path of the light beam 1 and the propagation optical path of the light beam 2 to detect the light intensity of the light beam 1 and the light beam 2; Data processing unit: receiving light intensity signals from two photodetectors; receiving the frequency values ​​of the beat frequency signals of two orthogonal polarization modes measured by a frequency meter, and calculating the frequency difference value of the beat frequency signals of the two orthogonal polarization modes; and calculating the phase delay corresponding to the stress birefringence of the glass material based on the light intensity signal and the frequency difference value.

2. The glass material stress birefringence measuring device according to claim 1, characterized in that: The surface of the glass sample is coated with an anti-reflection film.

3. The glass material stress birefringence measuring device according to claim 1, characterized in that: The force applying mechanism is symmetrically arranged at two ends of the anti-reflection window in the radial direction, so as to symmetrically apply an action force to the anti-reflection window in the radial direction.

4. The glass material stress birefringence measuring device according to claim 1, characterized in that: The light transmission direction of the polarizer forms an angle of 45° with the polarization direction of the laser.

5. The glass material stress birefringence measuring device according to claim 1, characterized in that: The threshold frequency difference f ranges from 15 to 20 MHz.

6. A method for measuring stress birefringence of glass material, characterized in that: The following steps are involved: S1: Before placing the glass sample in the laser resonant cavity, gradually increase the radial pressure of the anti-reflection window from small to large, adjust the piezoelectric ceramic actuator and judge the beginning of mode jump according to the light intensity recorded by the two photodetectors, then reduce the pressure of the anti-reflection window until no mode jump occurs, that is, the split mode frequency difference Δv introduced by the stress birefringence of the anti-reflection window w When the frequency difference is close to the threshold value f, the split mode frequency difference Δv is calculated w and the corresponding phase delay, the steps include: when the independent reflector is in the initial position, measuring the frequency difference Δ of the two orthogonal polarization longitudinal modes of the laser 10 , adjust the piezoelectric actuator, change the resonant cavity length, and measure the frequency difference Δ between the two orthogonal polarization longitudinal modes of the laser 20 ; Calculation of split mode frequency difference Δv introduced by stress birefringence of antireflection window w : f≈Δv w =|D 10 -D 20 | / 2; Calculate the phase delay Δφ corresponding to the stress birefringence of the antireflection window w : Df w =(λ / 2)·|D 10 -D 20 | / (D 10 +D 20 ); Calculate the initial longitudinal mode frequency difference Δ of the laser 00 : D 00 =|D 10 +D 20 | / 2; S2: The calculation steps of the frequency difference Δ0 of the laser longitudinal mode spacing in the orthogonal polarization direction caused by stress birefringence include: S21: Adjust the rotating stage so that the equivalent fast axis or the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference Δ0 of the laser longitudinal mode interval; Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 11 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 12 ; Further set the frequency difference judgment threshold and compare Δv 11 With Δv 12 The size and sum of 00 size; If Δv 11 With Δv 12 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode hopping during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 1t The value of and the longitudinal mode spacing Δ0; If Δv 11 With Δv 12 If they are not equal, further judgment: If Δv 11 With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =min(Δv 11 ,Δv 12 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 11 +Δv 12 ; If Δv qq With Δv 12 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 1t =|Δv 11 -Δv 12 | / 2, the frequency difference of the laser longitudinal mode spacing is calculated as Δ0=(Δv 11 +Δv 12 ) / 2; S22: Further adjust the rotating stage to rotate it by 90°, so that the equivalent slow axis or the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, and calculate the frequency difference of the laser longitudinal mode interval: Measuring the frequency difference Δv between two orthogonal polarization longitudinal modes of laser 21 , adjust the piezoelectric actuator, change the resonant cavity length, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv between the two orthogonal polarization longitudinal modes of the laser 22 ; Depending on whether a mode jump occurs in step S21, Δv 21 With Δv 22 The size and judgment of: If no mode jump occurs in step S21, and Δv 21 With Δv 22 If Δv is equal, the horizontal polarized light and the vertical polarized light will undergo mode jumps during the process of the piezoelectric actuator changing the resonant cavity length, which is not included in Δv. 2t The value of If Δv 21 With Δv 22 If they are not equal, further judgment: If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =min(Δv 21 ,Δv 22 ), the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = Δv 21 +Δv 22 ; If Δv 21 With Δv 22 The sum of 00 The absolute value of the difference is less than the frequency difference judgment threshold, then Δv 2t =|Δv 21 -Δv 22 | / 2; the frequency difference of the laser longitudinal mode spacing is calculated as Δ0 = (Δv 21 +Δv 22 ) / 2; If no mode hopping occurs in steps S21 and S22, the frequency difference Δ0 of the longitudinal mode intervals obtained twice is equal; S3: In step S2, when the piezoelectric actuator is adjusted, the light intensity of the two orthogonal polarization modes is recorded at the same time, and the split mode frequency difference Δv caused by the total stress birefringence in the resonant cavity is respectively calculated when the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window and the equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window. 1t Value and Δv 2t Value, and longitudinal mode interval Δ0 value, judge and calculate: If the piezoelectric actuator is adjusted to change the length of the resonant cavity at the position of the two overlaps, the horizontally polarized light and the vertically polarized light will undergo a mode jump, and the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2t The one corresponding to the time when no mode jump occurs is set to Δv t ,and MHz range, the stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w -(λΔν t ) / (2Δ0); If the horizontal polarized light and the vertical polarized light do not undergo mode hopping when the piezoelectric actuator is adjusted to change the resonant cavity length at the position of the two overlaps, the split mode frequency difference Δv measured at the two overlaps is 1t and Δv 2t If they are in the intervals [2f,3f]MHz and [0,f]MHz respectively, then the split mode frequency difference corresponding to the interval [0,f]MHz is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =Δφ w +(λΔν t ) / (2Δ0); If at the position of the two overlaps, the piezoelectric actuator is adjusted to change the resonant cavity length, the horizontal polarized light and the vertical polarized light undergo a mode jump, or no mode jump occurs, and the split mode frequency difference Δv measured at the two overlaps qt and Δv 2t If both are >2fMHz, then take the Δv measured during the two coincidences 1t and Δv 2t The larger intermediate frequency difference is taken as Δv t The stress birefringence phase delay of the glass material is calculated as: Δφ g =(λΔν t ) / (2Δ0)-Δφ w ; In the above formulas: λ is the laser wavelength.

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