METHOD FOR EVALUATING AND CONTROLLING TEMPERATURE INFLUENCE ON A HOMOGENEITY TEST FOR INFRARED OPTICAL MATERIALS

Abstract

The present application relates to the measurement technology of the homogeneity in optical materials, and more particularly to a method for evaluating and controlling temperature influence on a homogeneity test for infrared optical materials. The precision of the test results is found to be affected by local small temperature changes of the sample during the homogeneity test for the refractive indexes of infrared optical materials, the invention establishes a two-dimensional numerical table in which the test precision requirements of a refractive index homogeneity test for infrared optical materials correspond to the ambient control temperatures in the test room corresponding to the influence of temperature changes on the refractive index of different infrared optical materials. In addition, related calculation formulas are established for theory analysis, numerical calculation and form-designing. The method of the present invention accurately guides the temperature control for the precision of the homogeneity test for infrared optical materials.

Claims

1. A method for evaluating and controlling temperature influence on a homogeneity test for infrared optical materials, comprising: 1) setting test precision requirements for the homogeneity test of refractive index as P.sub.n, a thickness of a sample as t.sub.0, the number of times that an infrared radiation flux passes through the sample as N, a wavefront distortion of reference waves corresponding to P.sub.n as W.sub.P; wherein W.sub.P is calculated according to:
W.sub.P=Nt.sub.0P.sub.n(1); 2) when an ambient temperature in a test room changes, bringing a local temperature increment T of the sample and a wavefront distortion W.sub.T of the reference waves; setting a nominal refractive index of infrared optical materials of samples as n.sub.0, a thermo-optical coefficient of infrared optical materials as G, a thermal expansion coefficient of infrared optical materials of the samples as , and a temperature gradient coefficient of refractive indexes of infrared optical materials of the samples as dn/dt; wherein the wavefront distortion of the reference waves brought by the local temperature increment T of the sample is W.sub.T, and W.sub.T is calculated according to: $\begin{array}{cc}.Math.W_{.Math.T}=N.Math.t_0.Math..Math..Math.\mathrm{TG}=N.Math.t_0.Math..Math..Math.T.Math..Math.\left(n_0-1\right).Math.+\frac{\mathrm{dn}}{\mathrm{dt}}.Math.;& \left(2\right)\end{array}$ 3) enabling the test precision requirements of the homogeneity test for infrared optical materials to satisfy:
W.sub.TkW.sub.P(3); wherein k is the precision control factor of the influence of temperature; and transforming formula (3) into formula (4): $\begin{array}{cc}.Math.Tk.Math.\frac{P_{.Math.n}}{G};& \left(4\right)\end{array}$ 4) determining a range of the test precision requirements P.sub.n of the samples of the infrared optical materials; 5) determining a range of the thermo-optical coefficient G of the infrared optical materials based on the formula (2); 6) according to the formula (4) in step 3, the range of the test precision requirements P.sub.n determined in step 4, and the range of the thermo-optical coefficient G of the infrared optical materials determined in step 5, establishing a temperature influence control numerical table corresponding to the test precision requirements of the homogeneity test for the infrared optical materials; and 7) controlling the ambient temperature in the test room during test using corresponding temperature control data in the temperature influence control numerical table according to the test precision requirements and materials of the samples.

2. The method of claim 1, wherein k is , , , or ; the smaller a value of k, the smaller an influence of temperature changes on precision of the homogeneity test; and a minimum precision of the homogeneity test is obtained when k is set as .

3. The method of claim 1, wherein in step 4, the range of the test precision requirements P.sub.n of the homogeneity test for the infrared optical materials is determined to be 110.sup.5110.sup.4; the test precision requirements P.sub.n are divided into four levels by multiplying by 2 times or approximately 2 times each time from the highest to the lowest test precision requirements, and the four levels of the test precision requirements P.sub.n are: 110.sup.5, 210.sup.5, 410.sup.5, and 1010.sup.5.

4. The method of claim 3, wherein in step 5, based on the formula (2), according to the thermo-optical coefficient G of a germanium crystal material in which a refractive index is the most sensitive to temperature changes, and the thermo-optical coefficient G of a fused silica material in which a refractive index is the least sensitive to temperature changes, and a concentration relationship of the thermo-optical coefficient G of other infrared optical materials, the thermo-optical coefficient G is divided into seven levels: 110.sup.5/ C., 210.sup.5/ C., 410.sup.5/ C., 610.sup.5/ C., 1010.sup.5/ C., 1510.sup.5/ C. and 4010.sup.5/C.

5. The method of claim 4, wherein in step 6, the temperature influence control numerical table is Table 1: TABLE-US-00003 TABLE 1 Temperature influence control numerical table corresponding to test precision requirements of homogeneity test for infrared optical materials Precision requirements of homogeneity Thermo-optical coefficient Gs of the infrared optical materials test 1 10.sup.5/ C. 2 10.sup.5/ C. 4 10.sup.5/ C. 6 10.sup.5/ C. 10 10.sup.5/ C. 15 10.sup.5/ C. 40 10.sup.5/ C. 10 10.sup.5 10k 5k 2.5k 1.67k 1k 0.67k 0.25k 4 10.sup.5 4k 2k 1k 0.67k 0.4k 0.27k 0.1k 2 10.sup.5 2k 1k 0.5k 0.34k 0.2k 0.14k 0.05k 1 10.sup.5 1k 0.5k 0.25k 0.17k 0.1k 0.07k 0.03k.

6. The method of claim 5, wherein when using temperature control data in Table 1 for control, the values taken for the temperature control are equal to or less than the values in Table 1; and the precision control factor k of the influence of temperature in Table 1 is determined according to the test precision requirements of the homogeneity test.

7. The method of claim 1, wherein in step 7, before an interferometry is carried out for the homogeneity test for infrared optical materials, the sample is placed on a test bench for a certain period of heat preservation until the temperature of the sample is completely uniform, so as to avoid that uneven temperature changes affect the homogeneity test for infrared optical materials.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a diagram showing a wavefront distortion corresponding to an allowable precision of a homogeneity test for an infrared optical material.

[0024] FIG. 2 is a diagram showing the wavefront distortion caused by a local temperature change of an infrared optical material.

[0025] FIG. 3 is a comparison diagram of the wavefront distortion corresponding to the allowable precision and the wavefront distortion caused by the local temperature change in the homogeneity test for an infrared optical material.

DETAILED DESCRIPTION OF EMBODIMENTS

[0026] The present invention will be further described in detail with reference to the accompanying drawings and embodiments, from which the purpose, content and advantages of the present invention will be clearer.

[0027] The precision of a test result is seriously affected by small local temperature changes of a sample during the homogeneity test of refractive index. The present invention establishes a two-dimensional numerical table in which the test precision requirements of a refractive index test of infrared optical materials and the ambient control temperatures corresponding to the influence of temperature changes on the refractive index of different infrared optical materials, and related calculation formulas are established. In addition, related calculation formulas are established for theory analysis, numerical calculation and table-designing. Therefore, the present invention provides a method for evaluating and controlling temperature influence on a homogeneity test for infrared optical materials to accurately control the temperature, thereby ensuring the precision of the homogeneity test for the infrared optical materials.

[0028] Based on the above-mentioned ideas, the present invention provides a method for evaluating and controlling temperature influence on a homogeneity test for infrared optical materials, comprising the following steps.

[0029] 1) The high-precision homogeneity test for the refractive index of the infrared optical materials is generally carried out by interferometry, in which the reference waves (usually planar waves) pass through the sample to obtain the wavefront distortion of the inhomogeneity of the refractive index of the sample. Test precision requirements of a homogeneity test for the refractive index are set as P.sub.n; a thickness of the sample is set as to; the number of times that the infrared radiation flux passes through the sample is set as N; and a wavefront distortion of the reference waves corresponding to P.sub.n is set as W.sub.P (an allowable wavefront distortion of homogeneity of the refractive index), as shown in FIG. 1; and W.sub.P is calculated according to formula (1):

W.sub.P=Nt.sub.0P.sub.n(1).

[0030] 3) When the ambient temperature in the test room changes, the local temperature increment T of the sample is caused (because the sudden change of the ambient temperature is non-uniform), and the wavefront distortion of the reference waves is W.sub.T. A nominal refractive index of the infrared optical materials of samples is set to be n.sub.0; a thermo-optical coefficient of the infrared optical materials of the samples is set to be G; a thermal expansion coefficient of the infrared optical materials of the samples is set to be , and a temperature gradient coefficient of refractive indexes of the infrared optical materials of the samples is set to be dn/dt. The wavefront distortion of the reference waves caused by the local temperature increment T of the sample is W.sub.T, as shown in FIG. 2; and W.sub.T is calculated according to formula (2)

[00003]$\begin{array}{cc}.Math.W_{.Math.T}=N.Math.t_0.Math..Math..Math.\mathrm{TG}=N.Math.t_0.Math..Math..Math.T.Math..Math.\left(n_0-1\right).Math.+\frac{\mathrm{dn}}{\mathrm{dt}}.Math..& \left(2\right)\end{array}$

[0031] 3) In order to guarantee the test precision requirements P.sub.n of the homogeneity test for the infrared optical materials, the wavefront distortion W.sub.T caused by the local temperature increment T of the samples of the infrared optical materials should be less than or equal to a product of the wavefront distortion W.sub.P of the reference waves corresponding to the test precision requirements P.sub.n of the homogeneity of refractive index and the precision control factor k of the influence of temperature; where k may be , , or . The smaller a value of k, the smaller an influence of temperature changes on precision of the homogeneity test, and a minimum precision of the homogeneity test is obtained when k is set as . The test precision requirements should satisfy formula (3):

W.sub.TkW.sub.P(3); and

[0032] formula (3) is transformed into formula (4):

[00004]$\begin{array}{cc}.Math.Tk.Math.\frac{P_{.Math.n}}{G}.& \left(4\right)\end{array}$

[0033] If the magnitude of the wavefront distortion W.sub.T caused by the local temperature increment T of a certain portion of the sample of infrared optical materials is not controlled, it will be higher than or significantly higher than the wavefront distortion W.sub.P corresponding to the allowable precision P.sub.n for the homogeneity test of refractive index, so that the test precision exceeds or significantly exceeds the allowable precision. The comparison between the wavefront distortion W.sub.T and the wavefront distortion W.sub.P is shown in FIG. 3.

[0034] 4) The range of the test precision requirement P.sub.n of the samples of infrared optical materials is determined. The lowest test precision requirement of the infrared optical materials is 110.sup.4, and the highest test precision requirement thereof is 110.sup.5. Therefore, the range of the test precision requirement P.sub.n is from 110.sup.5 to 110.sup.4. The range of the test precision requirement P.sub.n is divided into four levels by multiplying by 2 times or approximately 2 times each time from the highest to the lowest test precision requirement to meet the more requirements of test precision. The four levels of the test precision requirement P.sub.n are 110.sup.5, 210.sup.5, 410.sup.5, and 1010.sup.5.

[0035] 5) The range of the thermo-optical coefficient G of infrared optical materials is determined. Since the thermo-optical coefficient G of infrared optical materials is equal to (n.sub.01)+dn/dt, the refractive index no of the infrared optical materials ranges from 1.4 to 4.0, and dn/dt of the infrared optical materials is generally an order of magnitude higher than a, so the thermo-optical coefficient G of infrared optical materials is mainly determined by dn/dt. The refractive index of the germanium crystal material is the most sensitive to temperature changes, and the germanium crystal material has a thermo-optical coefficient G of 410.sup.4/ C.; the refractive index of a fused silica material is the least sensitive to temperature changes, and the fused silica material has a thermo-optical coefficient G of 110.sup.5/ C. Most of infrared optical materials have intermediate sensitivities for temperature changes, and thermal-optical coefficient G of these infrared optical materials ranges from 210.sup.5/ C. to 1510.sup.5/ C. According to a concentration relationship of thermo-optical coefficient G of other infrared optical materials, the thermo-optical coefficient G is divided into seven levels: 110.sup.5/ C., 210.sup.5/ C., 410.sup.5/ C., 610.sup.5/ C., 1010.sup.5/ C., 1510.sup.5/ C. and 4010.sup.5/ C.

[0036] 6) According to formula (4) in step 3, the range of the test precision requirements P.sub.n determined in step 4, the range of the thermo-optical coefficient G of the infrared optical materials determined in step 5, the temperature influence control numerical table corresponding to the test precision requirements of the homogeneity test for the infrared optical materials is established (see Table 1), so as to control the temperature in the homogeneity test for various infrared optical materials according to different test precision requirements. When using the temperature control data in Table 1 for control, the values taken for the temperature control are equal to or less than the values in Table 1. The precision control factor k of the influence of the temperature in Table 1 is determined according to the precision requirement of the test:

TABLE-US-00002 TABLE 1 Temperature influence control numerical table corresponding to precision of homogeneity test for the infrared optical materials Precision requirements of homogeneity Thermo-optical coefficient Gs of infrared optical materials test 1 10.sup.5/ C. 2 10.sup.5/ C. 4 10.sup.5/ C. 6 10.sup.5/ C. 10 10.sup.5/ C. 15 10.sup.5/ C. 40 10.sup.5/ C. 10 10.sup.5 10k 5k 2.5k 1.67k 1k 0.67k 0.25k 4 10.sup.5 4k 2k 1k 0.67k 0.4k 0.27k 0.1k 2 10.sup.5 2k 1k 0.5k 0.34k 0.2k 0.14k 0.05k 1 10.sup.5 1k 0.5k 0.25k 0.17k 0.1k 0.07k 0.03k

[0037] 7) Two measures are taken to avoid that uneven temperature changes affect the homogeneity test for infrared optical materials. First, before an interferometry is carried out for the homogeneity test of infrared optical materials, the sample is placed on the test bench for a certain period of heat preservation until the temperature of the sample is completely uniform. Second, the ambient temperature in the test room is controlled using corresponding temperature control data in the temperature influence control numerical table in Table 1 according to the test precision requirements and materials of the sample.

[0038] It is found that small temperature changes during test have a serious effect on the test results. A relationship of the ambient control temperatures in the test room is established, in which the range of the test precision requirements of the homogeneity test of infrared optical materials corresponds to the range of the temperature influence coefficient to the refractive index, and related algorithm formulas for numerical calculation are established. A numerical table in which ambient control temperatures in the test room correspond to the test precision requirements of homogeneity tests for the infrared optical materials is established.

[0039] The invention provides a method for evaluating and controlling temperature influence on the homogeneity test for infrared optical materials, which can provide specific values of the ambient control temperatures in the test room corresponding to the precision of the homogeneity test for the infrared optical materials. In addition, the method of the present invention can be used not only to evaluate the temperature influence on the homogeneity test for infrared optical materials but also to evaluate that of the optical materials of visible light and ultraviolet light and so on.

[0040] The invention can provide a specific guidance for the test precision requirements of the homogeneity test for infrared optical materials and for the temperature influence control of homogeneity test of refractive index of various materials such as infrared optical crystals, infrared glass, infrared ceramics, so as to obtain actual results of the homogeneity test for infrared optical materials. The range of the test precision requirements calculated above can be expanded and subdivided as required. The method of the invention can also be used to evaluate and control the ambient temperature of the tests to obtain test result parameters by testing relevant wavefronts of the samples.

[0041] The above are only preferred embodiments of the present invention. It should be noted that improvements and modifications made by those ordinary skill in the art without departing from the principle of the present invention shall fall within the protecting scope of the present invention.