CN115615600A - Device and method for measuring stress birefringence of glass material - Google Patents

Abstract

The invention provides a device and a method for measuring stress birefringence of a glass material. A fixed reflector of the 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 vertical to the laser axis; the force applying mechanism can adjust the internal stress of the anti-reflection window sheet; measuring the frequency difference of two orthogonal polarization modes through an avalanche photodetector and a frequency meter; the light intensity of two orthogonal polarization modes is measured by two photodetectors. When a glass sample to be measured is not placed in the resonant cavity, calculating phase delay corresponding to the stress birefringence of the anti-reflection window; after a glass sample is placed, adjusting a corner to enable the equivalent fast axis and the slow axis of the glass sample to coincide with the equivalent fast axis of the anti-reflection window twice, and calculating the frequency difference of a splitting mode; and calculating the glass stress birefringence index according to the interval of the split mode frequency difference and the phase retardation of the anti-reflection window. The invention can carry out precise measurement on the stress birefringence of the glass material, has simple structure and is easy to realize automatic measurement.

Description

Device and method for measuring stress birefringence of glass material

technical field

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

Background technique

During the processing and use of optical glass materials and glass components, various factors will cause internal stress, such as thermal stress due to temperature gradients during glass melting, and thermal stress due to cutting or grinding forces during component processing. Surface stress, compressive stress generated by heavier components due to their own weight, and stress generated by the mounting mechanism on the clamping force of components, etc. The internal stress will cause the original isotropic glass element to exhibit 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 beam will also be distorted, thereby reducing the optical system. In severe cases, it may even cause component damage, such as the neodymium glass component used in laser nuclear fusion devices. When transmitting high-energy laser beams, due to stress birefringence, the energy distribution of the focused spot will be uneven, and heat accumulation will also cause component rupture and affect the laser. The system works. Precise measurements of stress birefringence in optical glass materials and components are therefore required to assess quality or mitigate effects.

Generally, there are many methods for measuring the stress birefringence of optical components, which can be mainly divided into two categories based on the principle of polarized light and the principle of light interference: the former uses optical components such as polarizers to convert the change of the polarization state of light after passing through an optical glass sample into light intensity. The change of stress birefringence can be obtained. Since the measurement is carried out by light intensity, it is easily affected by 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 the light passes through the optical glass sample. That is, the change of the phase, the stress birefringence is obtained, and the measurement accuracy is high, but the optical path structure is complicated. At the same time, none of the above-mentioned methods can be traced to the measurement standard, and their comparability with each other is poor. It is necessary to study an optical glass stress birefringence measurement device and method with high precision, simple optical path and traceable measurement results.

Contents of the invention

The object of the present invention is to overcome the shortcomings of the optical stress measurement method in the prior art, and provide a glass material stress birefringence measurement device and method.

In order to achieve the above purpose, the technical scheme adopted is:

Device for measuring stress birefringence in glass materials, including:

Laser gain tube: the first end is provided with a fixed reflector, and the second end is provided with an anti-reflection window;

Independent reflector: set on the second end side of the gain tube, located outside the anti-reflection window, combined with the laser gain tube and fixed reflector to realize orthogonally polarized laser oscillation;

Piezoelectric actuator: connected with the independent reflector to drive the independent reflector to move along the laser axis;

Glass sample: set between the anti-reflection window and the independent mirror;

Rotary table: the glass sample is installed on the rotary table, and the rotation axis of the rotary table coincides with the laser beam, so as to drive the glass sample to adjust the rotation angle in a plane perpendicular to the laser beam;

Force application mechanism: it is arranged in the radial direction of the anti-reflection window, and can apply pressure along the radial direction of the anti-reflection window; the force application mechanism is connected with a force adjustment mechanism, which can adjust the force applied to the anti-reflection window, so that The stress birefringence causes the frequency difference between two adjacent longitudinal mode intervals in the orthogonal polarization direction of the laser to be within the threshold frequency difference f within the positive and negative threshold range, and the anti-reflection window along the direction of the applied pressure 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;

Photodetector: set on the outside of the polarizer, used to receive the beat frequency signal of two orthogonal polarization modes of the laser and the beat frequency signal of the split mode;

Frequency meter: communicate with the photodetector, 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;

Data processor: based on the frequency difference of two orthogonal polarization modes, calculate the phase delay corresponding to the stress birefringence of the glass material.

In some embodiments of the present invention, the surface of the glass sample is coated with an anti-reflection film.

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

In some embodiments of the present invention, the light transmission direction of the polarizer and the laser polarization direction form an included angle of 45°.

In some embodiments of the present invention, the range of the threshold frequency difference f is 15-20 MHz.

Some embodiments of the present invention further provide a method for measuring stress birefringence of glass materials, which is characterized in that it includes the following steps:

S1: Before the glass sample is placed in the laser resonator, gradually increase the pressure in the radial direction of the anti-reflection window, adjust the piezoelectric ceramic actuator, and judge the beginning of the phenomenon based on the light intensity recorded by the two photodetectors. When the mode jumps, reduce the pressure of the anti-reflection window until no mode jump occurs, that is, when the split-mode frequency difference Δv _w introduced by the stress birefringence of the anti-reflection window is close to the threshold frequency difference f, 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, measure the frequency difference Δ ₁₀ of the two orthogonal polarization longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, and measure the two orthogonal polarization longitudinal modes of the laser The frequency difference Δ ₂₀ ;

Calculate the split mode frequency difference Δv _w introduced by the stress birefringence of the AR window:

f≈Δv _w =|Δ ₁₀ -Δ ₂₀ |/2;

Calculate the phase delay Δφ _w corresponding to the stress birefringence of the AR window:

Δφ _w = (λ/2)|Δ ₁₀ -Δ ₂₀ |/(Δ ₁₀ +Δ ₂₀ );

Calculate the initial longitudinal mode spacing frequency difference Δ ₀₀ of the laser:

Δ ₀₀ =|Δ ₁₀ +Δ ₂₀ |/2;

S2: The calculation steps of the frequency difference Δ ₀ of the laser longitudinal mode interval caused by the stress birefringence in the orthogonal polarization direction of the laser include:

S21: Adjust the rotary table so that when the equivalent fast axis or equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the frequency difference _Δ0 of the laser longitudinal mode interval;

Measure the frequency difference Δv ₁₁ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv ₁₂ of the two orthogonally polarized longitudinal modes of the laser; Further setting the frequency difference judgment threshold, comparing the size of Δv ₁₁ and Δv ₁₂ and their sum with the size of Δ ₀₀ ;

If Δv ₁₁ and Δv ₁₂ are equal, then when the piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, and the value of Δv _1t and the longitudinal mode interval Δ ₀ are not included;

If Δv ₁₁ and Δv ₁₂ are not equal, then further judge:

If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t = min(Δv ₁₁ , Δv ₁₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₁₁ +Δv ₁₂ ;

If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t =|Δv ₁₁ -Δv ₁₂ |/2, and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ =( Δv ₁₁ +Δv ₁₂ )/2;

S22: Further adjust the rotary table to turn it through 90°, so that when the equivalent slow axis or the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the frequency difference of the laser longitudinal mode interval:

Measure the frequency difference Δv ₂₁ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv ₂₂ of the two orthogonally polarized longitudinal modes of the laser; According to whether mode hopping occurs in step S21, the size of Δv ₂₁ and Δv ₂₂ and their sum judgment:

If no mode hopping occurs in step S21, and Δv ₂₁ is equal to Δv ₂₂ , then when the current piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, which is not included in Δv _2t value;

If Δv ₂₁ and Δv ₂₂ are not equal, then further judge:

If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t = min(Δv ₂₁ , Δv ₂₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₂₁ +Δv ₂₂ ;

If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t =|Δv ₂₁ -Δv ₂₂ |/2; the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ =( Δv ₂₁ +Δv ₂₂ )/2;

If no mode hopping occurs in steps S21 and S22, the frequency difference _Δ0 of the longitudinal mode interval obtained twice is equal;

S3: In step S2, when adjusting the piezoelectric actuator, record the light intensity of the two orthogonal polarization modes at the same time, according to the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the antireflection When the axis coincides with the equivalent fast axis of the anti-reflection window, the split mode frequency difference Δv _1t and Δv _2t value caused by the total stress birefringence in the resonator cavity, and the longitudinal mode interval Δ ₀ value, judge and calculate:

区间，则计算玻璃材料的应力双折射相位延迟为：Δφ_g＝Δφ_w-(λΔv_t)/(2Δ₀)；If at the double coincidence position, the piezoelectric actuator is adjusted to change the length of the resonant cavity, the horizontally polarized light and the vertically polarized light undergo a mode hop, and the split-mode frequency differences Δv _1t and Δv _2t measured during the two coincidences The one corresponding to the time when no mode hopping occurs is set to Δv _t , and

interval, then the stress birefringence phase retardation of the glass material is calculated as: Δφ _g = Δφ _w -(λΔv _t )/(2Δ ₀ );

If there is no mode hopping in the horizontally polarized light and vertically polarized light during the process of adjusting the piezoelectric actuator to change the length of the resonant cavity at the two overlapping positions, the split-mode frequency differences Δv _1t and Δv _2t measured during the two overlapping They are in [2f, 3f] MHz and [0, f] MHz respectively, then, take the split mode frequency difference corresponding to [0, f] MHz as the Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g = Δφ _w +(λΔv _t )/(2Δ ₀ );

If at the double coincidence position, adjust the piezoelectric actuator to change the length of the resonant cavity, the horizontally polarized light and the vertically polarized light undergo a mode hop, or no mode hop occurs, and the measured If the split mode frequency difference Δv _1t and Δv _2t are both > 2fMHz, then take the larger intermediate frequency difference between Δv _1t and Δv _2t measured during two coincidences as the Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g = (λΔv _t )/(2Δ ₀ )-Δφ _w ;

In the above formulas: λ is the laser wavelength.

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

Compared with prior art, advantage and positive effect of the present invention are:

1. The present invention can measure the stress birefringence of glass materials by laser frequency or frequency difference. The measurement accuracy of the two frequencies is high, and the stress birefringence of materials can be precisely measured, and the measurement can be traced to the light wavelength (ie frequency).

2. Apply pressure to the anti-reflection window of the laser gain tube, and rotate the glass sample during the measurement to make it coincide with the fast and slow axes of the anti-reflection window twice, which can avoid the measurement failure due to the strong competition effect of the laser oscillation mode. According to the progress, the stress birefringence of any size in the glass material can be directly measured, the system structure is simple, and it is easy to realize automatic measurement.

Description of drawings

Figure 1 is a schematic diagram of the frequency distribution of the longitudinal mode of laser oscillation;

Figure 2a is a schematic diagram of the frequency difference formed by the splitting of each longitudinal mode of the laser by the glass sample;

Figure 2b is a schematic diagram of the frequency difference formed by the change of the distance between the longitudinal modes of adjacent stages of the laser caused by the glass sample;

Figure 3a is a schematic diagram of the mode hopping of two orthogonal polarization modes during the cavity length adjustment process;

Figure 3b is a schematic diagram of two orthogonal polarization modes without mode hopping during cavity length adjustment;

Figure 4 is a schematic diagram of the coincidence of the equivalent fast/slow axis of the glass sample in the resonator and the equivalent fast axis of the anti-reflection window;

Fig. 5 is a schematic diagram of measurement intervals of glass samples with different stress birefringence sizes;

Fig. 6 is a schematic diagram of a device for measuring stress birefringence of a glass material.

In each of the above figures:

1- gain tube;

2 - fixed mirror;

3- anti-reflection window;

4- independent reflector;

5 - piezoelectric actuator;

6- The glass sample to be tested;

7-Rotary table;

8-polarizer;

9 - photodetector;

10 - frequency meter;

11-polarization beam splitter;

12 - a first photodetector;

13 - second photodetector;

14 - Data processing unit.

detailed description

In the following, the present invention will be specifically described through exemplary embodiments. It should be understood, however, that elements, structures and characteristics of one embodiment may be beneficially incorporated in other embodiments without further recitation.

The device and method for measuring stress birefringence of glass materials provided by the invention are based on the principle of laser frequency splitting measurement.

Firstly, the principle of laser frequency splitting measurement is described.

For a standing wave laser, the longitudinal mode capable of forming oscillations in the resonator satisfies the resonance condition, as shown in Figure 1. Within the range of the laser gain band, there are two adjacent longitudinal modes v _q and v _q+1 that can gain gain and form laser output. Due to the competition between laser modes, the polarization directions of adjacent longitudinal modes are along the two eigendirections of the laser, that is, the polarization states are orthogonal to each other, denoted as ⊥ polarization state and ∥ polarization state. As the laser cavity length changes, other order longitudinal modes such as v _q-1 and v _q-2 will sequentially enter the gain band to form oscillations. The relational expression satisfied by the oscillation longitudinal mode is:

Among them, v _q is the frequency of the longitudinal mode of oscillation, L0 is the cavity length of the resonator, n is the equivalent refractive index in the resonator, c is the speed of light in vacuum, and q is the ordinal number of the longitudinal mode, which is a positive integer. From this, it can be obtained that the frequency difference of adjacent longitudinal modes, that is, the longitudinal mode interval satisfies:

As shown in Figure 2a, when the glass sample is placed in the laser resonator, due to the stress birefringence of the material, the refractive index along the principal stress direction and the perpendicular principal stress direction are no longer equal, making the resonance in these two directions The physical cavity length of the cavity has a fixed offset. According to the resonance conditions satisfied by the longitudinal modes, the two physical cavity lengths correspond to two different longitudinal mode sequences, that is, each longitudinal mode will split into two, and their polarization states are orthogonal to each other as a whole.

Among them, due to the stress birefringence of the glass material, its corresponding phase delay Δφ _g causes the laser to produce a splitting effect on the longitudinal mode. That is to say, each longitudinal mode will split into a new longitudinal mode, for example: the longitudinal mode v _q is split into longitudinal modes v _q and v′ _q , the new longitudinal mode v′ _q has a certain frequency difference from the original longitudinal mode, The frequency difference between the two is Δv, according to formula (1) and formula (2), it can be calculated that the two satisfy relational formula (3). The polarization states of adjacent levels of the original longitudinal mode are the same, and the polarization state of the new longitudinal mode becomes perpendicular to that of its adjacent longitudinal modes of the same level.

The length of the laser cavity can be further tuned so that the adjacent longitudinal modes enter the gain band, and the frequency difference Δv' between the modes v' _q and v _q-1 can be measured, and the frequency difference between it and the split longitudinal mode v _q Δ ₀ =Δv+Δv′ is satisfied. It can be known from formula (3) that the frequency difference between two adjacent split longitudinal modes is proportional to the stress birefringence, and the stress birefringence Δφ _g of the glass material can be accurately measured by precise measurement of Δv and Δv′, the unit of which is nm.

In fact, the stress birefringence of glass materials is usually not very large, resulting in a small amount of longitudinal mode splitting Δv in the two orthogonal polarization directions v _q and v′ _q , and the two split longitudinal modes are very close. For the He-Ne laser, when the splitting amount is less than a certain frequency difference value, there is a strong mode competition effect between the two oscillation modes, and 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 parameters such as the cavity length of the laser, and is generally about 30-40 MHz, which can be defined as a strong competitive frequency difference.

As shown in Figure 2b, the modes corresponding to the dotted lines cannot oscillate. It is adjacent longitudinal modes that can enter the laser gain band to form oscillations, and their polarization states are orthogonal to each other to reduce mode competition. Taking the implementation shown in the accompanying drawings as an example, at this time, adjacent longitudinal modes: the frequency difference between v _q-1 and v _q , and between v _q and v _q+1 , that is, the interval between adjacent longitudinal modes is no longer The initial value Δ ₀ , but a fixed deviation value Δv is generated, and the frequency difference between v _q-1 and v′ _q is obtained as Δ ₁ =Δ ₀ -Δv. Further tune the length of the laser cavity so that v′ _q and the next longitudinal mode v _q+1 move into the gain band to form an oscillation, and at the same time the longitudinal mode v _q-1 moves out of the gain band, then the oscillation between the longitudinal mode v _q+1 and v′ _q The frequency difference between them is Δ ₂ =Δ ₀ +Δv. Therefore, the frequency difference and longitudinal mode interval of the split mode can be calculated according to the two measured intervals of adjacent longitudinal modes:

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

The above formulas (3) and (5) show that the stress birefringence phase retardation of the glass material can be obtained by measuring the frequency difference of the two oscillation modes twice before and after. This situation occurs when the frequency difference between the two oscillation modes in the cavity is less than half of the frequency difference of the strong competition. However, when the frequency difference generated by intracavity stress birefringence is in the range of about half to one times the frequency difference of the strong competition, the same-level longitudinal modes with orthogonal polarization states will undergo mode hopping. As shown in Figure 3a, the frequency difference of adjacent longitudinal modes is measured for the first time to be Δ ₁ . During the process of continuing to tune the laser cavity, the ⊥-polarized mode will suddenly turn from oscillation to suppression, and the ∥-polarized mode will turn from suppression to suppression. for oscillation. In this case, the second measurement of the frequency difference of the adjacent longitudinal modes corresponds to the first measurement that the light intensity of the ∥ polarization mode decreases while the light intensity of the ⊥ polarization mode increases, and the measured value at this time is still Frequency difference Δ ₁ , frequency difference Δ ₂ cannot be measured, nor can it be calculated using formula (5) (in the actual two measurements, Δ ₁ is the one with the smaller frequency difference, and Δ ₂ is the one with the larger frequency difference). This is different from the situation that when the stress birefringence of the glass sample is small, the splitting frequency difference is smaller than the threshold frequency difference f, and the mode hopping does not occur during the cavity length tuning, as shown in Figure 3(b). Among them, the threshold frequency difference f is about half of the strong competition frequency difference. For lasers with different parameters, this value is slightly different, generally between 15 and 20 MHz. In this patent, determined by the characteristics of the laser, the threshold frequency difference can take a value of about 16MHz.

Based on the above analysis, it can be obtained that after the glass sample is placed in the laser resonator, there are three situations as the cavity length is tuned:

(a) When the frequency difference between the two split modes produced by the stress birefringence of the glass material is 0~16MHz (corresponding to 0~f), the cavity length can be changed, and the frequency difference Δ ₁ and Δ ₂ of the adjacent longitudinal modes can be measured, and substituted into Formula (5) is calculated;

(b) When the frequency difference between the two split modes produced by the stress birefringence of the glass material is 16~32MHz (corresponding to f~2f), due to the mode hopping, only the smaller frequency difference formed by the adjacent longitudinal mode can be measured. is Δ ₁ , but the frequency difference Δ ₂ cannot be measured, and the measurement cannot be performed;

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

In order to overcome the unmeasurable situation caused by mode hopping, it is necessary to make the longitudinal mode frequency difference generated by the total birefringence in the cavity be in the range of 0-16MHz (corresponding to 0-f) or ≥32MHz (corresponding to >2f). For this reason, stress birefringence is additionally introduced into the laser resonance, as shown in Fig. 4 . Both ends of the gain tube 1 of the semi-external cavity laser are formed by sealing a fixed mirror 2 and an anti-reflection window 3 . If 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 equivalent fast axis direction of the anti-reflection window. Adjust the force F 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 along the equivalent fast axis and slow axis of the AR window respectively. After putting the glass sample 6 to be tested into the resonant cavity, it can be driven by the rotating table 7 to rotate in a plane perpendicular to the laser axis. Adjust the rotation angle of the glass sample so that the equivalent fast axis of the stress birefringence coincides with the fast axis after the window is stressed, then the total stress birefringence in the resonator is the superposition of the two Δφ _t = Δφ _w - Δφ _g ; If the fast axes of the slow axis windows with equivalent stress birefringence are superimposed after being stressed, the total stress birefringence in the resonant cavity is Δφ _t =Δφ _w +Δφ _g .

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

调整旋转台使玻璃样品的快轴与激光器窗片的快轴重合(当调谐激光腔长，两偏振方向中之一出现光强为零则达到两轴重合条件)，则腔内总的应力双折射Δφ_t＝Δφ_w+Δφ_g产生的频差为

处于激光模式跳变区间，不能测量，需继续转动玻璃样品使其慢轴与窗片快轴重合，得到腔内总的应力双折射为Δφ_t＝Δφ_w-Δφ_g，产生的频差为

可以按上述第(a)情况进行测量。此时Δφ_g越大，Δv_t越小，如图5所示的A区间。When Δφ _g produces frequency difference alone

Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window (when the length of the laser cavity is tuned, and the light intensity in one of the two polarization directions is zero, the two-axis coincidence condition is reached), the total stress in the cavity doubles The frequency difference generated by refraction Δφ _t = Δφ _w + Δφ _g is

It is in the laser mode jump interval and cannot be measured. It is necessary to continue to rotate the glass sample so that the slow axis coincides with the fast axis of the window, and the total stress birefringence in the cavity is Δφ _t = Δφ _w - Δφ _g , and the resulting frequency difference is

It can be measured according to the above case (a). At this time, the larger Δφ _g is, the smaller Δv _t is, as shown in Figure 5, the A section.

调整旋转台使玻璃样品的快轴与激光器窗片的快轴重合，则腔内总的应力双折射Δφ_t＝Δφ_w+Δφ_g产生的频差为

可以按上述第(c)情况进行测量。继续旋转玻璃样品使其慢轴与激光器窗片的快轴重合，则腔内总的应力双折射Δφ_t＝Δφ_g-Δφ_w产生的频差为

可以按上述第(a)情况进行测量，如图5所示的B区间。When Δφ _g produces frequency difference alone

Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window, then the frequency difference generated by the total stress birefringence in the cavity Δφ _t = Δφ _w + Δφ _g is

It can be measured according to the above case (c). Continue to rotate the glass sample so that the slow axis coincides with the fast axis of the laser window, then the frequency difference generated by the total stress birefringence in the cavity Δφ _t = Δφ _g -Δφ _w is

The measurement can be carried out according to the above (a) situation, as shown in the B section shown in Figure 5.

调整旋转台使玻璃样品的快轴与激光器窗片的快轴重合，则腔内总的应力双折射Δφ_t＝Δφ_w+Δφ_g产生的频差为

可以按上述第(c)情况进行测量。继续旋转玻璃样品使其慢轴与激光器窗片的快轴重合，则腔内总的应力双折射Δφ_t＝Δφ_g-Δφ_w产生的频差为

要么处于激光模式跳变区间，无法测量，要么可以直接测量，

如图5所示的C区间。When Δφ _g produces frequency difference alone

Adjust the rotating stage so that the fast axis of the glass sample coincides with the fast axis of the laser window, then the frequency difference generated by the total stress birefringence in the cavity Δφ _t = Δφ _w + Δφ _g is

It can be measured according to the above case (c). Continue to rotate the glass sample so that the slow axis coincides with the fast axis of the laser window, then the frequency difference generated by the total stress birefringence in the cavity Δφ _t = Δφ _g -Δφ _w is

Either it is in the laser mode jump interval and cannot be measured, or it can be measured directly,

C interval as shown in Figure 5.

In summary, the stress birefringence of the glass sample can be judged and obtained according to the frequency difference between the two orthogonal polarization longitudinal modes of the laser measured twice after the fast axis and the slow axis of the glass sample coincide with the fast axis of the window respectively.

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

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

Laser gain tube 1: the first end is provided with a fixed reflector 2, and the second end is provided with an anti-reflection window 3,

Independent reflector 4: set on the second end side of the laser gain tube 1, located outside the anti-reflection window 3, and cooperate with the laser gain tube 1 and the fixed reflector 2 to realize orthogonally polarized laser oscillation in combination;

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

Glass sample 6: set between the anti-reflection window 3 and the independent mirror 4; the purpose of the present invention is to measure the stress birefringence phase delay of the glass sample 6, and use the phase delay to evaluate the stress birefringence index of the glass. The surface of glass sample 6 is coated with an anti-reflection coating at the laser wavelength.

Rotary table: the glass sample 6 is installed on the rotary table, the rotary table can rotate in the vertical plane, the rotation axis of the rotary table coincides with the laser beam, so as to drive the glass sample to adjust the rotation angle in the plane perpendicular to the laser beam; as shown in Figure 4 As shown, rotate around the z-axis.

Force application mechanism: it is arranged in the radial direction of the anti-reflection window 3, and can apply pressure radially along the anti-reflection window 3; the force application mechanism is connected to the force adjustment mechanism, which can adjust the pressure applied to the anti-reflection window to The stress birefringence causes the frequency difference between two adjacent longitudinal modes in the orthogonal polarization direction of the laser to be within the threshold frequency difference f within the positive and negative threshold range, and the antireflection window along the direction of the applied pressure is the equivalent fast axis direction; The threshold frequency difference f is determined according to the performance of the laser, the threshold frequency difference f ranges from 15 to 20 MHz, and 16 MHz is used in this embodiment;

The force clamping mechanism is arranged symmetrically at both ends of the anti-reflection window in the radial direction, so as to apply a clamping force symmetrically to the anti-reflection window in the radial direction. The structure of the force applying mechanism is not specifically limited, and there are various implementations in practical applications.

Polarizer 8: set outside the independent reflector 4; the light transmission direction of the polarizer 8 forms an included angle of 45° with the laser polarization direction.

Photodetector 9: arranged outside the 8 polarizers, used to receive the beat frequency signals of two orthogonal polarization modes and the split mode beat frequency signals of the laser. The two orthogonal polarization modes of the laser mentioned here may be two longitudinal modes or split modes.

Frequency meter 10: communicating with the photodetector to obtain the frequency values of the beat frequency signals of the two orthogonal polarization modes;

Data processor: Calculate the frequency difference of the split mode based on the frequency difference of two orthogonally polarized longitudinal modes, and calculate the stress birefringence phase delay of the glass material based on the frequency difference of the split mode. The specific calculation method is described in detail in the second embodiment.

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

S1: Before the glass sample is placed in the laser resonator, gradually increase the pressure in the radial direction of the anti-reflection window, adjust the piezoelectric ceramic actuator, and judge the beginning of the phenomenon based on the light intensity recorded by the two photodetectors. When the mode jumps, reduce the pressure of the anti-reflection window so that no mode jump occurs, that is, when the split-mode frequency difference Δv _w introduced by the stress birefringence of the anti-reflection window is close to the threshold frequency difference f,

Calculating the split-mode frequency difference Δv _w and the corresponding phase delay, the steps include: when the independent reflector is at the initial position, measure the frequency difference Δ ₁₀ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, and change the length of the resonant cavity, Measure the frequency difference Δ ₂₀ of the two orthogonal polarization longitudinal modes of the laser;

Calculate the split mode frequency difference Δv _w introduced by the stress birefringence of the AR window:

f≈Δv _w =|Δ ₁₀ -Δ ₂₀ |/2;

Calculate the phase delay Δφ _w corresponding to the stress birefringence of the AR window:

Δφ _w = (λ/2)·(Δ ₁₀ +Δ ₂₀ )/(Δ ₁₀ +Δ ₂₀ );

Calculate the initial longitudinal mode separation Δ ₀₀ of the laser:

Δ ₀₀ =|Δ ₁₀ +Δ ₂₀ |/2;

Specifically, the frequencies of the two orthogonal polarization longitudinal modes ⊥ polarization state and ∥ polarization state are measured by the photodetector 9, and the frequency meter 10 calculates the laser splitting modes v _q and v _q ′ based on the frequencies of the two orthogonal polarization longitudinal modes The frequency difference Δv _w between. In this step, since the glass sample 6 is not introduced, stress birefringence is introduced for the antireflection window 3 . The initial position is not limited, and the length of the resonant cavity before and after changing is not limited. During this process, the stress in the radial direction of the anti-reflection window 3 is adjusted so that Δv _w is close to the threshold frequency difference of 16 MHz. The near-threshold frequency difference mentioned here refers to allowing a certain threshold range, and the threshold can be set as required.

Before the measurement, firstly adjust the split mode frequency difference of the anti-reflection window to reach a certain value threshold frequency difference. This is a pre-finished work, once adjusted, there is basically no need to change it in the subsequent test process, as long as the glass sample is measured each time First, measure the frequency difference of the split mode caused only by the anti-reflection window 3, calculate the phase delay, and record it as the initial value for later use when measuring the glass sample.

When the glass sample 6 is not placed in the cavity, the frequency difference generated by the stress birefringence of the anti-reflection window 3 is the same as the split frequency difference generated by the stress birefringence of the anti-reflection window 3 after the sample is placed. slightly different because the equivalent cavity length has changed. Therefore, in the following processing methods, the phase delay introduced by the stress birefringence of the anti-reflection window 3 is uniformly deducted, which corresponds to the stress birefringence one-to-one, and the size remains the same, instead of deducting the phase delay caused by the anti-reflection window 3 split frequency difference.

S2: The calculation steps of the frequency difference Δ ₀ of the laser longitudinal mode interval caused by the stress birefringence in the orthogonal polarization direction of the laser include:

S21: Adjust the rotary table so that when the equivalent fast axis or equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the frequency difference _Δ0 of the laser longitudinal mode interval;

Measure the frequency difference Δv _{11 of the two orthogonally polarized longitudinal modes of the laser,} adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv1 ₂ of the two orthogonally polarized longitudinal modes of the laser; Further setting the frequency difference judgment threshold, comparing the size of Δv ₁₁ and Δv ₁₂ and their sum with the size of Δ ₀₀ ;

If Δv ₁₁ and Δv ₁₂ are equal, then when the piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, and the value of Δv _1t and the longitudinal mode interval Δ ₀ are not included;

If Δv ₁₁ and Δv ₁₂ are not equal, then further judge:

If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t = min(Δv ₁₁ , Δv ₁₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₁₁ +Δv ₁₂ ;

If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t =|Δv ₁₁ -Δv ₁₂ |/2, and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ =( Δv ₁₁ +Δv ₁₂ )/2;

S22: On the basis of step S21, further adjust the rotary table to make it turn 90°, so that when the equivalent slow axis or the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the laser The frequency difference of the longitudinal mode interval. If it is adjusted in step S21 so that the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, then in step S22, after the turntable rotates through 90°, the equivalent slow axis of the glass sample coincides with the equivalent slow axis of the anti-reflection window The equivalent fast axis coincides with . Similarly, if the adjustment in step S21 makes the equivalent slow axis of the glass sample coincide with the equivalent fast axis of the anti-reflection window, then in step S22, after the rotating table rotates 90°, the equivalent fast axis of the glass sample and the anti-reflection window The equivalent fast axis of the window is coincident.

Measure the frequency difference Δv ₂₁ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv ₂₂ of the two orthogonally polarized longitudinal modes of the laser; According to whether mode hopping occurs in step S21, the size of Δv ₂₁ and Δv ₂₂ and their sum judgment:

If no mode hopping occurs in step S21, and Δv ₂₁ is equal to Δv ₂₂ , then when the current piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, which is not included in Δv _2t value;

If Δv ₂₁ and Δv ₂₂ are not equal, then further judge:

If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t = min(Δv ₂₁ , Δv ₂₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₂₁ +Δv ₂₂ ;

If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t =|Δv ₂₁ -Δv ₂₂ |/2; the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ =( Δv ₂₁ +Δv ₂₂ )/2;

If no mode hopping occurs in steps S21 and S22, the frequency difference _Δ0 of the longitudinal mode interval 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 be calculated once. The results obtained in these two times are the same, and one or the other can be chosen or the average value can be used in the formula for calculating the phase delay in step S3.

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

S3: In step S2, when adjusting the piezoelectric actuator, record the light intensity of the two orthogonal polarization modes at the same time, according to the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the antireflection When the axis coincides with the equivalent fast axis of the anti-reflection window, the split mode frequency difference Δv _1t and Δv _2t value caused by the total stress birefringence in the resonator cavity, and the longitudinal mode interval Δ ₀ value, judge and calculate:

区间，则计算玻璃材料的应力双折射相位延迟为：Δφ_g＝Δφ_w-(λΔv_t)/(2Δ₀)；If at the double coincidence position, the piezoelectric actuator is adjusted to change the length of the resonant cavity, the horizontally polarized light and the vertically polarized light undergo a mode hop, and the split-mode frequency differences Δv _1t and Δv _2t measured during the two coincidences Corresponding to one time when no mode transition occurs, it is set to

interval, then the stress birefringence phase retardation of the glass material is calculated as: Δφ _g = Δφ _w -(λΔv _t )/(2Δ ₀ );

If there is no mode hopping in the horizontally polarized light and vertically polarized light during the process of adjusting the piezoelectric actuator to change the length of the resonant cavity at the two overlapping positions, the split-mode frequency differences Δv _1t and Δv _2t measured during the two overlapping They are in [2f, 3f] MHz and [0, f] MHz respectively, then, take the split mode frequency difference corresponding to [0, f] MHz as the Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g = Δφ _w +(λΔv _t )/(2Δ ₀ );

If at the double coincidence position, adjust the piezoelectric actuator to change the length of the resonant cavity, the horizontally polarized light and the vertically polarized light undergo a mode hop, or no mode hop occurs, and the measured If the split mode frequency difference Δv _1t and Δv _2t are both > 2fMHz, then take the larger intermediate frequency difference between Δv _1t and Δv _2t measured during two coincidences as the Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g = (λΔv _t )/(2Δ ₀ )-Δφ _w ;

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

Among them: the fast axis and the slow axis of the two components of the glass sample and the anti-reflection window are 90°, and when the fast axis coincides, the slow axis also coincides. The two situations are: 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.

In some embodiments of the present invention, the method for determining mode hopping of horizontally polarized light and vertically polarized light includes:

In the process of adjusting the length of the laser resonator cavity, record the light intensity of the vertically polarized and horizontally polarized two orthogonally polarized lights;

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

In the process of changing the cavity length by half wavelength, the light intensity of the vertically polarized light and the light intensity of the horizontally polarized light reach the position where the light intensity difference is zero twice, if the sign of the light intensity difference changes from negative to positive or both from positive If it becomes negative, it is judged that mode hopping occurs in horizontally polarized light and vertically polarized light.

Wherein, the measurement of the light intensity of the vertically polarized light and the light intensity of the horizontally polarized light is realized by a light point detector.

In practical applications, it is also possible to judge whether mode hopping occurs through light intensity. As shown in Figure 3, during the process of tuning the laser cavity length, record the light intensity of the vertically polarized light and the horizontally polarized light, and take the light intensity difference between the two as the flag. If no mode hopping occurs, two passes through the vertical When the light intensity difference between the polarized light and the horizontally polarized light is zero before and after the equal light intensity point, the sign of the flag is reversed once, that is, from positive to negative and from negative to positive, or vice versa; and if When the mode jumps, 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 the sign of the flag is always From positive to negative or both from negative to positive. Therefore, it can be judged whether the vertically polarized light and the horizontally polarized light have jumped according to the change of the sign of the light intensity difference.

The method of the invention can quickly, directly and precisely measure the stress birefringence index of the glass material, and the system has a simple structure and is easy to realize automatic measurement.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention to other forms. Any skilled person who is familiar with this profession may use the technical content disclosed above to change or modify the equivalent of equivalent changes. The embodiments are applied to other fields, but any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solutions of the present invention without departing from the content of the technical solutions of the present invention.

Claims (6)

1. The glass material stress birefringence measuring device is characterized in that, comprising: Laser gain tube: the first end is provided with a fixed reflector, and the second end is provided with an anti-reflection window; Independent reflector: set on the second end side of the gain tube, located outside the anti-reflection window, combined with the laser gain tube and fixed reflector to realize laser oscillation; Piezoelectric actuator: connected with the independent reflector to drive the independent reflector to move along the laser axis; Glass sample: set between the anti-reflection window and the independent mirror; Rotary table: the glass sample is installed on the rotary table, and the rotation axis of the rotary table coincides with the laser beam, so as to drive the glass sample to adjust the rotation angle in a plane perpendicular to the laser beam; Force application mechanism: it is arranged in the radial direction of the anti-reflection window, and can apply pressure along the radial direction of the anti-reflection window; the force application mechanism is connected with a force adjustment mechanism, which can adjust the force applied to the anti-reflection window, so that The stress birefringence causes the frequency difference between two adjacent longitudinal mode intervals in the orthogonal polarization direction of the laser to be within the threshold frequency difference f within the positive and negative threshold range, and the anti-reflection window along the direction of the applied pressure 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: set on the outside of the polarizer, used to receive the beat frequency signals of the two orthogonal polarization modes of the laser; Frequency meter: communicate with the avalanche photodetector to obtain the frequency value of the beat frequency signal of two orthogonal polarization modes; Polarization beam splitter: set on one side of the fixed reflector of the laser gain tube, used to split the light of two orthogonal polarization modes into beam 1 and beam 2; Photodetector: including a first photodetector and a second photodetector, which are respectively arranged on the propagation optical path of the first beam, and on the propagation optical path of the second beam, to detect the light intensity of the first beam and the second beam; Data processing unit: receive the light intensity signals of two photodetectors; receive the frequency difference value of two orthogonal polarization mode beat frequency signals measured by the frequency meter, and calculate the frequency difference value of the orthogonal polarization mode beat frequency signal; The strong signal and frequency difference values calculate the phase retardation corresponding to the stress birefringence of the glass material. 2. The device for measuring stress birefringence of glass materials according to claim 1, wherein the surface of the glass sample is coated with an anti-reflection film. 3. glass material stress birefringence measuring device as claimed in claim 1, is characterized in that, described force application mechanism is symmetrically arranged on the two ends of anti-reflection window radial direction, to anti-reflection window along radial direction Apply force symmetrically. 4. The device for measuring stress birefringence of glass materials according to claim 1, characterized in that the light transmission direction of the polarizer and the laser polarization direction form an angle of 45°. 5 . The device for measuring stress birefringence of glass materials according to claim 1 , wherein the range of the threshold frequency difference f is 15-20 MHz. 6. The method for measuring stress birefringence of glass materials, comprising the following steps: S1: Before the glass sample is placed in the laser resonator, gradually increase the pressure in the radial direction of the anti-reflection window, adjust the piezoelectric ceramic actuator, and judge the beginning of the phenomenon based on the light intensity recorded by the two photodetectors. When the mode jumps, reduce the pressure of the anti-reflection window until no mode jump occurs, that is, when the split-mode frequency difference Δv _w introduced by the stress birefringence of the anti-reflection window is close to the threshold frequency difference f, 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, measure the frequency difference Δ ₁₀ of the two orthogonal polarization longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, and measure the two orthogonal polarization longitudinal modes of the laser The frequency difference Δ ₂₀ ; Calculate the split mode frequency difference Δv _w introduced by the stress birefringence of the AR window: f≈Δv _w =|Δ ₁₀ -Δ ₂ x|/ ₂ ; Calculate the phase delay Δφ _w corresponding to the stress birefringence of the AR window: Δφ _w = (λ/2)|Δ ₁₀ -Δ ₂₀ |/(Δ ₁₀ +Δ ₂₀ ); Calculate the initial longitudinal mode spacing frequency difference Δ ₀₀ of the laser: Δ ₀₀ =|Δ ₁₀ +Δ ₂₀ |/2; S2: The calculation steps of the frequency difference Δ ₀ of the laser longitudinal mode interval caused by the stress birefringence in the orthogonal polarization direction of the laser include: S21: Adjust the rotary table so that when the equivalent fast axis or equivalent slow axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the frequency difference _Δ0 of the laser longitudinal mode interval; Measure the frequency difference Δv ₁₁ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv ₁₂ of the two orthogonally polarized longitudinal modes of the laser; Further setting the frequency difference judgment threshold, comparing the size of Δv ₁₁ and Δv ₁₂ and their sum with the size of Δ ₀₀ ; If Δv ₁₁ and Δv ₁₂ are equal, then when the piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, and the value of Δv _1t and the longitudinal mode interval Δ ₀ are not included; If Δv ₁₁ and Δv ₁₂ are not equal, then further judge: If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t = min(Δv ₁₁ , Δv ₁₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₁₁ +Δv ₁₂ ; If the absolute value of the difference between the sum of Δv ₁₁ and Δv ₁₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _1t =|Δv ₁₁ -Δv ₁₂ ^| /2, and the frequency difference of the laser longitudinal mode interval is calculated as Δ ₀ =( Δv ₁₁ +Δv ₁₂ )/2; S22: Further adjust the rotary table to turn it through 90°, so that when the equivalent slow axis or the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the anti-reflection window, calculate the frequency difference of the laser longitudinal mode interval: Measure the frequency difference Δv ₂₁ of the two orthogonally polarized longitudinal modes of the laser, adjust the piezoelectric actuator, change the length of the resonant cavity, make the adjacent longitudinal modes enter the gain band, and measure the frequency difference Δv ₂₂ of the two orthogonally polarized longitudinal modes of the laser; According to whether mode hopping occurs in step S21, the size of Δv ₂₁ and Δv ₂₂ and their sum judgment: If no mode hopping occurs in step S21, and Δv ₂₁ is equal to Δv ₂₂ , then when the current piezoelectric actuator changes the resonant cavity length, mode hopping occurs in horizontally polarized light and vertically polarized light, which is not included in Δv _2t value; If Δv ₂₁ and Δv ₂₂ are not equal, then further judge: If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t = min(Δv ₂₁ , Δv ₂₂ ), and the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ = Δv ₂₁ +Δv ₂₂ ; If the absolute value of the difference between the sum of Δv ₂₁ and Δv ₂₂ and 2Δ ₀₀ is less than the frequency difference judgment threshold, then Δv _2t =|Δv ₂₁ -Δv ₂₂ |/2; the frequency difference for calculating the laser longitudinal mode interval is Δ ₀ =( Δv ₂₁ +Δv ₂₂ )/2; If no mode hopping occurs in steps S21 and S22, the frequency difference _Δ0 of the longitudinal mode interval obtained twice is equal; S3: In step S2, when adjusting the piezoelectric actuator, record the light intensity of the two orthogonal polarization modes at the same time, according to the equivalent fast axis of the glass sample coincides with the equivalent fast axis of the antireflection When the axis coincides with the equivalent fast axis of the anti-reflection window, the split mode frequency difference Δv _1t and Δv _2t value caused by the total stress birefringence in the resonator cavity, and the longitudinal mode interval Δ ₀ value, judge and calculate: If at the double coincidence position, adjust the piezoelectric actuator to change the length of the resonant cavity, a mode jump occurs for the horizontally polarized light and the vertically polarized light, and the split-mode frequency differences Δv _1t and Δv _2t measured during the two coincidences The one corresponding to the time when no mode hopping occurs is set to Δv _t , and

MHz interval, the stress birefringence phase retardation of the glass material is calculated as: Δφ _g = Δφ _w -(λΔ _vt )/(2Δ ₀ ); If there is no mode hopping in the horizontally polarized light and vertically polarized light during the process of adjusting the piezoelectric actuator to change the length of the resonant cavity at the two overlapping positions, the split-mode frequency differences Δv _1t and Δv _2t measured during the two overlapping They are respectively in [2f, 3f] MHz and [0, f] MHz intervals, then, take the split mode frequency difference corresponding to [0, f] MHz interval as Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g =Δφ _w +(λΔ _vt )/(2Δ ₀ ); If at the double coincidence position, adjust the piezoelectric actuator to change the length of the resonant cavity, the horizontally polarized light and the vertically polarized light undergo a mode hop, or no mode hop occurs, and the measured If the split-mode frequency difference Δv _1t and Δv _2t are both > 2fMHz, then take the larger intermediate-frequency difference between Δv _1t and Δv _2t measured during two coincidences as the Δv _t value, and calculate the stress birefringence phase delay of the glass material as: Δφ _g = (λΔv _t )/(2Δ ₀ )-Δφ _w ; In the above formulas: λ is the laser wavelength.

Images