CN103335982B - Utilize wavelength tuning phase-shifting interferometer to measure the method for parallel flat optical homogeneity - Google Patents

Abstract

Utilize wavelength tuning phase-shifting interferometer to measure a method for parallel flat optical homogeneity, the method is utilized interferometric principle, and sample is tiltedly positioned in light path, by four step wavefront measurements, calculates the optical homogeneity of sample. Be particularly suitable for the heavy caliber parallel flat element measurement that element under test exceedes interferometer test bore. In test result, having removed two standard mirror wave surface errors of sample front and rear surfaces corrugated error and interferometer, is absolute measurement result.

Description

Utilize wavelength tuning phase-shifting interferometer to measure the method for parallel flat optical homogeneity

Technical field

The present invention relates to optical material uniformity, particularly one utilizes wavelength tuning phase-shifting interferometer to measure parallel flatThe method of optical homogeneity, the method can measurement size exceedes the element under test of interferometer test bore.

Background technology

The definition of optical homogeneity is the inconsistency of each point refractive index in same optical material, non-all also referred to as refractive indexEven property, represents with the difference of material largest refractive index and minimum refractive index conventionally.

In many field of optical applications, adopt the large-sized optical elements of hundreds of millimeter magnitude, to having relatively high expectations of material,Need measuring optical uniformity. Formerly technology comprises observational measurement and quantitative measurment, and quantitative measurment is divided into again general measure and exhaustedTo measuring, general measure refers to that test result comprises sample polishing corrugated error or posts Lamb wave surface error and tester standardMirror wave surface error etc. Absolute measurement refers to that test result does not comprise sample polishing corrugated error or posts Lamb wave surface error and testStandard of instruments mirror wave surface error. In absolute measurement, can be divided into and be less than instrument bore and be greater than instrument according to the ability of measuring sample sizeDevice bore. While being wherein greater than instrument bore, require the front and rear surfaces of sample to process certain angle, cannot survey for parallel flatAmount.

Formerly technology [1] is (referring to GBT7962.2-1987 colouless optical glass method of testing optical homogeneity parallel light tubeMethod of testing) described in method of testing adopt pair of parallel light pipe device, one is as collimator, it is two as looking in the distanceMirror, determines the uniformity of glass by resolution ratio method and asterism method, be a kind of observational measurement method, can not quantitative result.

Formerly technology [2] is (referring to the striking cable plane of GBT7962.2-2010 colouless optical glass method of testing optical homogeneityInterferometric method) described in method of testing adopt the optical homogeneity of striking cable plane interferometer measurement colouless optical glass, be onePlant method for quantitative measuring. Be placed on to samples vertical in the optical system for testing of interferometer the crest-Bo on the transmission corrugated by sampleValley, divided by thickness of sample, is optical homogeneity. In test result, comprise sample front and rear surfaces corrugated error and interferometerThe cavity corrugated error of two standard mirror compositions is general measure methods.

Formerly technology [3] is (referring to GBT7962.3-2010 colouless optical glass method of testing optical homogeneity holographic interferenceMethod) described in method of testing be to utilize holographic differential interferometry principle, by two groups of reflection interference striped and transmission interference fringesStrip record, on a hologram, from the reproduction corrugated of hologram, is tried to achieve the numerical value of variations in refractive index and varied in thickness. OnePlant the method for quantitative measuring of absolute measurement. Vertically be placed in optical system for testing the bore of element under test but require sample to placeCan not exceed interferometer bore.

Formerly technology [4] (referring to JohannesSchwider, R.Burow, K.-E.Elssner, R.Spolaczyk,andJ.Grzanna，“Homogeneitytestingbyphasesamplinginterferometry”，APPLIEDOPTICS, Vol.24, No.18, p3059,1985) described in measuring method be to utilize the optics of interferometer measurement material equalEven property, is placed on samples vertical in the optical system for testing of interferometer, measures sample front surface corrugated error, the rear table of permeable materialThe standard reflection mirror wave surface error of face wavefront error and permeable material, two standard mirror groups of then taking out sample in measurement interferometerThe cavity corrugated error becoming. The result of four measurements is calculated to optical homogeneity by formula. It is a kind of absolute measurementMethod for quantitative measuring. Vertically be placed in optical system for testing but require sample to place, the bore of element under test can not exceed interferenceInstrument bore.

Formerly technology [5] (referring to L.L.Deck, " MultipleSurfacePhaseShiftingInterferometry ", ProceedingsofSPIEVol.4451, p424,2001) described in two pacing metering methodsBe to utilize wavelength tuning phase-shifting interferometer to measure the optical homogeneity of parallel flat, samples vertical be placed on to the test of interferometerIn light path, the front surface corrugated error of sample, the rear surface wavefront error of permeable material and the standard reflection mirror wave of permeable materialSurface error affects simultaneously measures position phase, utilizes the difference that interference cavity is long, is separated at Data processing, obtains three ripples simultaneouslySurface error information. Then take out the cavity corrugated error of two standard mirror compositions of sample in measurement interferometer, utilize and comprise fourThe formula of corrugated error calculates optical homogeneity. It is a kind of method for quantitative measuring of absolute measurement. But require sample to hang downDirectly be placed in optical system for testing, the bore of element under test can not exceed interferometer bore.

Formerly technology [6] (referring to Luan Zhu etc., " method of interferometric optical material homogeneity ", Chinese Patent Application No.:201210406066.1) measuring method described in is to utilize optical element oblique incidence to place to measure heavy-calibre element opticsInhomogeneity method. First the cavity corrugated error of two of stellar interferometer standard mirror compositions, then puts sample oblique incidencePut in light path, measure about optical axis symmetry angle and place the standard reflection mirror wave surface error that sees through sample in two kinds of situations,The front surface corrugated error of sample, the rear surface wavefront error of permeable material. The formula that utilization comprises above five corrugated errorsCalculate optical homogeneity. It is a kind of method for quantitative measuring of absolute measurement. Sample can oblique incidence be placed on optical system for testingIn, but require the front and rear surfaces of sample to process certain angle, make the pip of front and rear surfaces separately, be not suitable for parallel flatMeasure.

Summary of the invention

The technical problem to be solved in the present invention is to overcome the deficiency of above-mentioned prior art, provides one to utilize wavelength tuningPhase-shifting interferometer is measured the method for parallel flat optical homogeneity, and the method is utilized interferometric principle, and sample can oblique incidenceBe positioned in light path, by four step wavefront measurements, calculate the optical homogeneity of sample. Being particularly suitable for element under test exceedesThe heavy caliber parallel flat element of interferometer test bore is measured.

Technical solution of the present invention is as follows:

Utilize wavelength tuning phase-shifting interferometer to measure a method for parallel flat optical homogeneity, feature is the methodComprise the following steps:

1. utilize wavelength tuning phase-shifting interferometer to measure standard diaphotoscope and the standard reflection of wavelength tuning phase-shifting interferometerThe corrugated error C of the interference cavity of mirror composition;

2. testing sample is tiltedly placed in described interference cavity, ensured that light beam covers described testing sample and makes interferenceThe incidence angle of instrument outgoing beam is-θ clockwise for just, to utilize wavelength to adjust when definition sample surfaces normal turns to incident beamIt is T that humorous phase-shifting interferometer is measured the corrugated error that sees through described sample and reflect through standard reflection mirror₁；

3. described sample is reapposed, the reposition of described sample and the position that 2. walks sample are about optical axis pairClaim, making the incidence angle of interferometer outgoing beam is θ, utilizes wavelength tuning phase-shifting interferometer to measure through sample with through standard reflectionThe corrugated error of mirror reflection is T₂；

4. mobile described standard reflection mirror, hangs down described standard reflection mirror and the reverberation of the front surface from sampleDirectly, measure by sample front surface reflection, the corrugated error of standard reflection mirror is A and sees through sample, through sample rear surface simultaneouslyReflection, the corrugated error of standard reflection mirror is B;

5. utilize following formula to calculate parallel flat optical homogeneity Δ n₂：

$\mathrm{\Δ}{n}_2=[2n_0\cos {\mathrm{\θ}}^{\′}\·C-(\cos \mathrm{\θ}+n_0\cos {\mathrm{\θ}}^{\′})T_1$

$+(B-A-T_2)(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})]\frac{\cos {\mathrm{\θ}}^{\′}}{2d\cos \mathrm{\θ}}$

Wherein, n₀For mean refractive index, θ is incidence angle, and θ ' is refraction angle, and d is thickness of sample, C, T₁、T₂, A, B be four stepsThe poor distribution measuring results of ripple that method is measured, T when calculating₁The corresponding boundary alignment of horizontal direction displacement and B, Δ n₂The peak of distributionValley (PV), for the refractive index of sample departs from the maximum of mean refractive index and the difference of minimum of a value, i.e. optical homogeneity.

Technique effect of the present invention is as follows:

Formerly technology [1] is measured optical material uniformity with parallel light tube, cannot obtain quantitative result. Formerly technology [2]Use general interferometric method, in acquired results, comprise sample surfaces corrugated error and interferometer standard mirror wave surface error. FormerlyTechnology [3] and [4] utilize respectively holographic differential interference method and interferometer measurement method, and formerly technology [5] is utilized wavelength tuningThe optical homogeneity of phase-shifting interference measuring parallel flat, is absolute method of measurement, but sample is placed requirement and input path is hung downDirectly, limit sample test bore and can not exceed interferometer standard aperture of mirror. It is equal that formerly technology [6] is utilized five-step approach measurement opticsEven property, the method that sample is placed in oblique incidence has increased measurement bore, but sample need to be processed into certain angle, so that front and back tableThe reflection of face separates, and is not suitable for parallel flat optical element. The present invention adopts wavelength tuning phase-shifting interference measuring parallel flatOptical homogeneity, totally four pacing amounts, sample oblique incidence is placed in light path, can measure and exceed interferometer standard aperture of mirrorSample. In test result, having removed two standard mirror wave surface errors of sample front and rear surfaces corrugated error and interferometer, is absolute measuringAmount result.

Brief description of the drawings

Fig. 1 is measuring method schematic diagram of the present invention

Fig. 2 uses coordinate system schematic diagram in the present invention

Detailed description of the invention

First refer to Fig. 1, Fig. 1 is measuring method schematic diagram of the present invention, and in figure, 1 is the mark of wavelength tuning phase-shifting interferometerAccurate diaphotoscope, face shape is Z₁, 2 is the standard reflection mirror of wavelength tuning phase-shifting interferometer, face shape is Z₂, the 3rd, testing sample. ThisThe bright wavelength tuning phase-shifting interferometer that utilizes is measured optical material uniformity employing four step rule:

The first step, as Fig. 1 (a), the transmission standard mirror 1 of stellar interferometer and the ripple of the interference cavity that standard reflection mirror 2 formsSurface error C;

Second step, then puts into sample 3, and oblique incidence is placed, to ensure that light beam covers sample. As Fig. 1 (b), sample is placedMake the incidence angle of interferometer outgoing beam be-θ, when definition sample surfaces normal turns to incident beam, clockwise for just, measureSee through the corrugated error T that sample reflects through standard reflection mirror 2₁。

The 3rd step, as Fig. 1 (c), the position in placement and the second step of sample, about optical axis symmetry, makes interferometer emergent lightThe incidence angle of bundle is θ, measures and sees through the corrugated error T that sample reflects through standard reflection mirror 2₂。

The 4th step, as Fig. 1 (d), mobile standard reflection mirror 2 is vertical with the reverberation of sample front surface (now through sampleThe reverberation of rear surface overlap with it).

The 5th step, utilizes the multi-surface analytic function of wavelength tuning phase-shifting interferometer, in the time solving according to two interference cavity(one is standard diaphotoscope 1, and sample front surface and standard reflection mirror 2 form, and another is standard diaphotoscope 1, sample rear surfaceForming with standard reflection mirror 2) length is different, and will be through the light field of sample front and rear surfaces reflection separately. One-shot measurement obtain simultaneously throughThe ripple of the standard reflection mirror 2 of the corrugated error A of the standard reflection mirror 2 of the front surface reflection of sample and the reflection of process sample rear surfaceSurface error B.

General principle is:

Measure following five equations by four steps, wherein n is sample average refractive index, and θ is incidence angle, and θ ' is refractionEnter the refraction angle in sample, d is thickness of sample, and above be known quantity in the time measuring. Unknown quantity comprises the standard transmission of interferometerMirror surface-shaped Z₁, standard reflection mirror surface-shaped Z₂, front surface face shape Z_a, rear surface face shape Z_b, oblique incidence-θ direction refractive index change delta n₁，θ direction refractive index change delta n₂。

Coordinate system as shown in Figure 2, taking the standard diaphotoscope 1 of interferometer in the corresponding points at imaging CCD center as initial point, measureCollimated light exit direction is z axle, and horizontal direction is x axle, and vertical direction is y axle. Front surface face shape Z_aWith rear surface face shape Z_bBeVertical optical element surface direction, forward is that the apparent height that points to sample outside changes. Meet following equation:

C＝Z₁+Z₂(1)

$T_1=Z_1-({Z_a}^{\′}+Z_b)(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})+Z_2-\frac{\mathrm{\Δ}{n}_{1}d}{\cos {\mathrm{\θ}}^{\′}}---\left(2\right)$

$T_2=Z_1-(Z_a+Z_b)(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})+Z_2-\frac{\mathrm{\Δ}{n}_{2}d}{\cos {\mathrm{\θ}}^{\′}}---\left(3\right)$

A＝Z₁+2Z_acosθ+Z_2f(4)

$B=Z_1+Z_a(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})-2Z_b{n}_0\cos {\mathrm{\θ}}^{\′}$

$-{Z_a}^{\′}(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})+Z_{2f}-\frac{(\mathrm{\Δ}{n}_1+\mathrm{\Δ}{n}_2)d}{\cos {\mathrm{\θ}}^{\′}}---\left(5\right)$

In formula, Z_a' be sample front surface face shape Two dimensional Distribution Z_aMove in the horizontal direction x₀Result, x₀Equal before sampleRear surface reverberation, due to the dislocation that thickness of sample causes, the distance moving along sample front surface horizontal direction.

x₀＝2dtanθ′cosθ(6)

Z_2fStandard mirror surface-shaped Z₂The result of flip horizontal. In above-mentioned equation solution process, unknown quantity Z₁，Z₂，Z_2f，Z_a，Z_a′，Z_bWith Δ n₁Middle removal can solved. Obtain the refractive index change delta n of oblique incidence θ direction₂Distribution as follows:

$\mathrm{\Δ}{n}_2=[2n_0\cos {\mathrm{\θ}}^{\′}\·C-(\cos \mathrm{\θ}+n_0\cos {\mathrm{\θ}}^{\′})T_1$

$+(B-A-T_2)(n_0\cos {\mathrm{\θ}}^{\′}-\cos \mathrm{\θ})]\frac{\cos {\mathrm{\θ}}^{\′}}{2d\cos \mathrm{\θ}}---\left(7\right)$

Wherein, n₀For mean refractive index, θ is incidence angle, and θ ' is refraction angle, and d is thickness of sample, C, T₁、T₂, A, B be four stepsThe poor distribution measuring results of ripple that method is measured, T when calculating₁The corresponding boundary alignment of horizontal direction displacement and B. Δ n₂The peak of distributionValley (PV), for the refractive index of sample departs from the maximum of mean refractive index and the difference of minimum of a value, i.e. optical homogeneity. MeasureIn result, having removed the impact of front and rear surfaces, is absolute measurement result.

In the time that sample bore is greater than interferometer standard aperture of mirror, the setting of sample placed angle θ, generally makes measuring beam coverLid sample is unified.

The front and rear surfaces machined surface shape of sample should meet interferometry requirement, and general corrugated error is not more than 3 microns.

The front and rear surfaces of sample is parallel, and the reverberation of front and rear surfaces is overlapped. The satisfied condition of tolerance angle [alpha] is as follows:

$\left(\frac{2\sqrt{n^2-\mathrm{si}{n}^2\mathrm{\&theta;}}}{\cos \mathrm{\&theta;}}\right)\mathrm{\&alpha;}<\mathrm{\&delta;}---\left(8\right)$

Wherein, the resolution angle that δ is interferometer, n is sample average refractive index, θ is incidence angle.

Testing procedure refers to Fig. 1, Fig. 2.

Testing sample 3 is of a size of 100mm × 80mm, and thickness d is 15mm, and wavelength X is 633nm, and mean refractive index is1.5, incidence angle 43.5 is spent, and refraction angle is 27.3 degree. The first step measures standard reflection mirror wave surface error distribution C, second stepMeasure sample and optical axis 45 degree placements, the standard reflection mirror wave surface error that sees through sample is distributed as T₁, the 3rd pacing amount sample withOptical axis-45 degree is placed, and the standard reflection mirror wave surface error that sees through sample is T₂, the 4th step is measured by sample front surface anti-simultaneouslyPenetrate, the corrugated error of standard reflection mirror is A and sees through sample, and through sample rear surface reflection, the corrugated error of standard reflection mirror isB。

45 degree oblique incidence directions, the refractive index difference that departs from mean refractive index distributes, and optical homogeneity is distribution Δ n₂Peak-to-valley value (PV) be:

$\mathrm{\&Delta;}{n}_2=[2n_0\cos {\mathrm{\&theta;}}^{\&prime;}\&CenterDot;C-(\cos \mathrm{\&theta;}+n_0\cos {\mathrm{\&theta;}}^{\&prime;})T_1$

$+(B-A-T_2)(n_0\cos {\mathrm{\&theta;}}^{\&prime;}-\cos \mathrm{\&theta;})]\frac{\cos {\mathrm{\&theta;}}^{\&prime;}}{2d\cos \mathrm{\&theta;}}$

Wherein, n₀For mean refractive index, θ is incidence angle, and θ ' is refraction angle, and d is thickness of sample.

Claims (1)

1. utilize wavelength tuning phase-shifting interferometer to measure a method for parallel flat optical homogeneity, be characterised in that the method bagDraw together the following step:

1. utilize the standard diaphotoscope (1) of wavelength tuning phase-shifting interferometer stellar interferometer and doing of standard reflection mirror (2) compositionRelate to the corrugated error C in chamber;

2. sample (3) is tiltedly placed in described interference cavity, ensured that light beam covers described sample (3) and makes interferometer outgoingThe incidence angle of light beam is-θ clockwise for just, to utilize wavelength tuning phase shift when definition sample surfaces normal turns to incident beamInterferometer measurement sees through described sample and is T through the corrugated error of standard reflection mirror (2) reflection₁；

3. described sample is reapposed, the reposition of described sample and the position that 2. walks sample be about optical axis symmetry,Making the incidence angle of interferometer outgoing beam is θ, utilizes wavelength tuning phase-shifting interferometer to measure through sample (3) with through standard reflectionThe corrugated error of mirror (2) reflection is T₂；

4. mobile described standard reflection mirror (2), makes the reflection of described standard reflection mirror (2) and the front surface from sample (3)Light is vertical, measures by sample (3) front surface reflection simultaneously, and the corrugated error of standard reflection mirror is A and sees through sample (3), warpThe reflection of sample rear surface, the corrugated error of standard reflection mirror is B, wherein,

A＝Z₁+2Z_acosθ+Z_2f(4)

In formula, Z_a' be sample front surface face shape Two dimensional Distribution Z_aMove in the horizontal direction x₀Result, Z_2fIt is standard reflection mirrorFace shape Z₂The result of flip horizontal, θ is incidence angle, and θ ' is refraction angle, and d is thickness of sample, oblique incidence-θ direction variations in refractive indexΔn₁, the refractive index change delta n of oblique incidence θ direction₂，Z₁For the face shape of the standard diaphotoscope of interferometer, Z₂For the standard of interferometerThe face shape of speculum, Z_aFor the front surface face shape Two dimensional Distribution of sample, Z_bFor the rear surface face shape Two dimensional Distribution of sample;

5. utilize following formula to calculate parallel flat light refractive index changes delta n₂：

Wherein, n₀For mean refractive index, C, T₁、T₂, A, B be four step rule measure the poor distribution measuring results of ripple, T when calculating₁LevelThe corresponding boundary alignment of direction displacement and B, refractive index change delta n₂The peak-to-valley value Δ n_ distributing_PVFor the refractive index of sample departs from flatThe all maximum of refractive index and the difference of minimum of a value, i.e. optical homogeneities.