GB/T 7962.2-2010Test methods of colourless optical glass - Part 2: Optical homogeneity - Fizeau plano-interferometry (English PDF)

1 Scope

This Part of GB/T 7962 specifies the test methods, test procedures, data processing for the optical homogeneity of colorless optical glass.

This Part applies to the test of the optical homogeneity of colorless optical glass, whose diameter or side length is greater than 100 mm AND thickness is not less than 40 mm.

2 Normative references

The provisions in following documents become the provisions of this Part through reference in this Part of GB/T 7962. For the dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this Part; however, parties who reach an agreement based on this Part are encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies.

GB/T 903 Colorless optical glass

3 Terms and definitions

The following terms and definitions apply to this Part.

4 Principles

This Part uses a Fizeau plano-interferometer to measure the optical homogeneity of colorless optical glass. The sample is placed vertically, in the initial test optical path of the interferometer. When the refractive index distribution of the sample is not uniform, the wavefront of the light wave, which is reflected back through the sample twice, is no longer a strict plane, BUT becomes a curved surface. The transmitted wavefront's P value, V value and PV value is measured. Calculate the refractive index deviation delta n, delta n+, delta n- of the tested glass, by formula (1), formula (2), formula (3), respectively.

5 Instruments

5.1 The principle of optical system for measuring optical homogeneity by Fizeau plano-interferometry is as shown in Figure 1.

AND meets the requirements of 6.4, the sample can be directly placed vertically into the test optical path for testing, without the attaching plate.

8 Measurement steps

8.3 Perform sampling measurement and data processing, on the interference streaks, which are generated in the test area, to obtain the P value, V value, PV value of the transmitted wavefront.

8.4 For the glass whose aperture is larger than the aperture of the attaching plate or the instrument, use the zoning measurement method, to make measurement. Repeat steps 8.2 ~ 8.3, to measure P1, V1; P2, V2; P3, V3..., (PV)1, (PV)2, (PV)3... of each area, respectively. Select the maximum PV value from them, as the measurement result.

8.5 Use a thickness measuring instrument, to measure the clear thickness L of the sample; record the result.

9 Data processing

9.1 Substitute PV value, P value, V value, L value, lambda value into the formula (1), formula (2), formula (3), formula (4), to calculate delta n+, delta n-, delta n, respectively.

Where:

delta n - The maximum deviation of the absolute value of the refractive index, at each point of the glass under test, within the range of the test aperture;

L - The clear thickness of the sample under test, in millimeters (mm); PV - The peak-valley value of the transmitted wavefront;

lambda - The wavelength of the light wave used for the test, in nanometers (nm).

Where:

delta n+ - The maximum positive deviation of the refractive index, at each point in the glass, as relative to the average refractive index of the glass, within the test aperture range; P - The peak value of the transmitted wavefront;

L - The clear thickness of the sample under test, in millimeters (mm). […]