CN1752730A - Aperture aspherical optical elements medium-high frequency difference detection method - Google Patents

Abstract

A kind of aperture aspherical optical elements medium-high frequency difference detection method, relate to a kind of to the optical component surface shape error, the improvement of the detection method of especially surperficial face shape medium-high frequency difference.Utilize the information processing technology that the data that the laser digital interferometer obtains are handled, take to utilize two-dimensional power spectrum density to find the solution encircled power and estimate element quality, to realize testing goal.The method that the present invention proposes has been considered tested optical component surface shape information comprehensively, thus the face shape quality of objective appraisal optical element more.The present invention adopts two-dimensional power spectrum density that the optical component surface shape quality is estimated, and the new way of a detection faces shape quality is provided, and the quality assessment of high quality optical element is had important use be worth.

Description

Aperture aspherical optical elements medium-high frequency difference detection method

Technical field

The present invention relates to a kind ofly, especially, belong to the optic test field for the improvement of the medium-high frequency error detection method of optical element surface to the optical component surface shape error.

Background technology

The large scale non-spherical reflector has the characteristics of himself: bore is big, and auxilliary retouching technology in the processing must be brought the medium-high frequency error of suitable proportion to the mirror-quality that machines, and this minute surface high frequency error plays conclusive effect to the beam system quality.The evaluation index of traditional optical element machined surface shape quality mainly is peak-to-valley value, the root-mean-square value of reflection (or transmission) wavefront, zernike polynomial etc., and the element surface information that these indexs comprised is quite limited to the optical element quality.Modern precision optical system and large laser beam emissions system have proposed new requirement to the quality assessment of optical element, promptly require the spectrum distribution of wavefront error is estimated and controlled, and traditional face shape index has only covered the low frequency frequency range of surperficial face shape, in view of the situation, caused the concern of people to wavefront power spectrum density (PSD) measurement and assessment technique.

The U.S. has carried out systematic research to optical assessment standard, theory and method under light laser, high cumulative or the high resolving power condition in " national portfire (National IgnitionFacility-NIF) " process of development laser ICF engineering.U.S. Lao Lunsilifu mole National Laboratory is in the development process of NIF, according to the principle of design of bore, adaptive optics alignment technique and the spatial filter of optical element, the foozle of optical element specifically is divided into high, medium and low three sections according to the difference of spatial frequency.They have proposed to estimate the new method of optical element surface quality and foozle, promptly determine the content of different frequency range error with wavefront PSD.

In existing primary mirror mirror-quality evaluation method, wavefront PSD also only is used for the middle frequency difference analysis of ICF system optics at present, measures at the middle frequency difference of aperture aspherical and does not then appear in the newspapers; Existing wavefront PSD detection method is and adopts one dimension mean P SD to come the face shape quality of optical element is made evaluation, estimates element quality with the average quality of optical component surface shape, may cause the disappearance of local message, thereby can't reflect the quality of element comprehensively.

Content of the present invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of aperture aspherical optical elements medium-high frequency difference detection method is provided, this method is by the Two-dimensional PSD of calculating optical element, ask for encircled power, to determine the method for corresponding frequencies scope energy loss, consider tested optical element information comprehensively, thus the face shape quality of objective appraisal optical element more.

Technical solution of the present invention: aperture aspherical optical elements medium-high frequency difference detection method is characterized in that: can finish by following steps:

1. adopt the wavefront of optical components pick-up unit to obtain the Wave-front phase data of tested optical element;

Adopt interferometer or Hartmann that aspheric surface is implemented check.During as detecting instrument, light source needs the spherical reflector autocollimatic outward on the right with interferometer; During as detecting instrument, need provide LASER Light Source with the Hartmann;

2. the Wave-front phase data are carried out the pre-service of data;

Utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to Design of Filter principle designing filter;

3. pretreated data are made the wavefront power spectrum density and calculate, obtain the two-dimensional power spectrum density function of tested element;

(x y) calculates the wavefront power spectrum density, and the computing formula of obtaining the two-dimensional power spectrum density function of tested element is: PSD (f to utilize pretreated data φ _x, f _y)=Φ ^*(f _x, f _y) Φ (f _x, f _y) l _xL _y, Φ (f wherein _x, f _y)= _-∞∫ ∫ ^∞φ (x, y) exp (j2 π (f _xX+f _yY)) dxdy, Φ ^*(f _x, f _y) be Φ (f _x, f _y) conjugation, l _x, l _yBe the sampling length of corresponding horizontal direction and vertical direction, f _x, f _yBe spatial frequency;

4. further calculate the some diffraction function of the element of surveying by the two-dimensional power spectrum density function;

Computing formula is: $\mathrm{PSF}(\mathrm{\α},\mathrm{\β})=[1-{\left(\frac{4\mathrm{\π\σ}}{\mathrm{\λ}}\right)}^2]\mathrm{\δ}(\mathrm{\α},\mathrm{\β})+{\left(4\mathrm{\π}\right)}^2\·\mathrm{PSD}(\mathrm{\α},\mathrm{\β}),$ (α β) is impulse response function to δ, and σ is the root-mean-square value on surface, α=f _xλ d, β=f _yλ d, λ are optical wavelength, and value is 632.8nm, f _x, f _yBe spatial frequency;

5. calculate the encircled power of tested element by a diffraction function, thereby determine whether encircled power meets the demands in certain spectral range, to determine whether tested element meets the requirements;

Computing formula is: $E\left(r_0\right)={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051008665700093.png"\; state="\{\{state\}\}">r</figure-callout>}}_0}\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})\mathrm{\&rho;d\&rho;d\&phi;},$ α=f _xλ d, β=f _yλ f, f _x, f _yBe spatial frequency, λ is an optical wavelength, and it is qualified that the encircled power value is considered as greater than 83.3%.

The present invention's advantage compared with prior art is: the present invention compares with existing optical component surface shape quality determining method has full frequency band evaluation optical component surface shape quality, considers the advantage of the whole face shape of element comprehensively.Be applicable to the detection of the medium-high frequency difference that solves numerical control high precision aspheric optical element surface shape.

Description of drawings

Fig. 1 is a wavefront of optical components pick-up unit synoptic diagram of the present invention, and 1 is tested optical element, and 2 is standard flat, 3 is light source, 4 is detecting instrument (interferometer or Hartmann), and when using interferometer as detecting instrument, light source needs the spherical reflector autocollimatic outward on the right; During as detecting instrument, need provide LASER Light Source with the Hartmann;

Fig. 2 is that the embodiment of the invention 1 detects gained sample interferogram at detecting bore φ=110mm aspheric mirror, and testing tool is the laser digital interferometer, and interferometer resolution is 640 * 480;

Fig. 3 is the embodiment of the invention 1 process pre-service, calculates the two-dimensional power spectrum density map of gained after the filtering.

Embodiment

Embodiment 1, detects the process of bore φ=110mm aspheric mirror by method of the present invention:

1. adopt wavefront of optical components pick-up unit as shown in Figure 1, promptly digital wavefront interferometer obtains the Wave-front phase data of tested optical element, obtains interferogram shown in Figure 2; It is 446 * 446 that efficiently sampling is counted;

2. the Wave-front phase data are carried out the pre-service of data, filtering noise and garbage;

Utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to Design of Filter principle designing filter, promptly utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to infinite impulse response (IIR) Design of Digital Filter principle design Butterworth bandpass filter;

3. pretreated data are made the wavefront power spectrum density and calculate, obtain the two-dimensional power spectrum density function of tested element, as shown in Figure 3;

(x y) calculates the wavefront power spectrum density, obtains the two-dimensional power spectrum density function of tested element to utilize pretreated data φ; Computing formula is: PSD (f _x, f _y)=Φ ^*(f _x, f _y) Φ (f _x, f _y) l _xL _y, Φ (f wherein _x, f _y)= _-∞∫ ∫ ^∞φ (x, y) exp (j2 π (f _xX+f _yY)) dxdy, Φ ^*(f _x, f _y) be Φ (f _x, f _y) conjugation, l _x, l _ySampling length for corresponding horizontal direction and vertical direction; f _x, f _yBe spatial frequency, the effective frequency span is: 3/L＜f _x, f _y＜N/ (4L), L=l at this moment _x=l _y=110mm, so N=446 is 0.027mm ^-1≤ f _x≤ 1.014mm ^-1, 0.027mm ^-1≤ f _y≤ 1.014mm ^-1, the result as shown in Figure 3;

4. further calculate the some diffraction function of the element of surveying by the two-dimensional power spectrum density function;

Computing formula is: $\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})=[1-{\left(\frac{4\mathrm{\&pi;\&sigma;}}{\mathrm{\&lambda;}}\right)}^2]\mathrm{\&delta;}(\mathrm{\&alpha;},\mathrm{\&beta;})+{\left(4\mathrm{\&pi;}\right)}^2\&CenterDot;\mathrm{PSD}(\mathrm{\&alpha;},\mathrm{\&beta;}),$ (α β) is impulse response function to δ, and σ is the root-mean-square value on surface, α=f _xλ d, β=f _xλ d, λ are optical wavelength, and value is 632.8nm;

5. calculate the encircled power of tested element by a diffraction function, thereby determine whether encircled power meets the demands in certain spectral range, to determine whether tested element meets the requirements;

Know that by known parameters the effective range of its frequency is: 0.027mm ^-1≤ f _x≤ 1.014mm ^-1, 0.027mm ^-1≤ f _X≤ 1.014mm ^-1, by an encircled power of the diffraction function calculating element of surveying, computing formula is: $E\left(r_0\right)={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051008665700093.png"\; state="\{\{state\}\}">r</figure-callout>}}_0}\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})\mathrm{\&rho;d\&rho;d\&phi;},$ Result of calculation is 0.841, greater than 0.833, so this sample is at the measured frequency scope f of institute _x, f _yIn meet the requirements;

Embodiment 2, detect the process of bore φ=400mm aspheric mirror by method of the present invention:

1. adopt wavefront of optical components pick-up unit as shown in Figure 1, promptly digital wavefront interferometer obtains the Wave-front phase data of tested optical element, obtains the interferogram of the element of surveying; It is 452 * 452 that efficiently sampling is counted;

2. utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to Design of Filter principle designing filter;

Utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to infinite impulse response (IIR) Design of Digital Filter principle design Butterworth bandpass filter;

3. (x y) calculates the wavefront power spectrum density, obtains the two-dimensional power spectrum density function of tested element to utilize pretreated data φ; Computing formula is: PSD (f _x, f _y)=Φ ^*(f _x, f _y) Φ (f _x, f _y) l _xL _y, f Φ (f wherein _x, f _y)= _-∞∫ ∫ ^∞φ (x, y) exp (j2 π (f _xX+f _yY)) dxdy, Φ ^*(f _x, f _y) be Φ (f _x, f _y) conjugation, l _x, l _ySampling length for corresponding horizontal direction and vertical direction; f _x, f _yBe spatial frequency, the effective frequency span is: 3/L＜f _x, f _y＜N/ (4L), L=l at this moment _x=l _y=400mm, N=452,0.008mm ^-1≤ f _x≤ 0.283mm ^-1, 0.008mm ^-1≤ f _y≤ 0.283mm ^-1

4. further calculate the some diffraction function of the element of surveying by the two-dimensional power spectrum density function; Computing formula is: $\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})=[1-{\left(\frac{4\mathrm{\&pi;\&sigma;}}{\mathrm{\&lambda;}}\right)}^2]\mathrm{\&delta;}(\mathrm{\&alpha;},\mathrm{\&beta;})+{\left(4\mathrm{\&pi;}\right)}^2\&CenterDot;\mathrm{PSD}(\mathrm{\&alpha;},\mathrm{\&beta;}),$ (α β) is impulse response function to δ, and σ is the root-mean-square value on surface, α=f _xλ d, β=f _yλ d, λ are optical wavelength.

5. know by known parameters that the effective range of its frequency is: 0.008mm ^-1≤ f _x≤ 0.283mm ^-1, 0.008mm ^-1≤ f _x≤ 0.283mm ^-1, by an encircled power of the diffraction function calculating element of surveying, computing formula is: $E\left(r_0\right)={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="A20051008665700093.png"\; state="\{\{state\}\}">r</figure-callout>}}_0}\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})\mathrm{\&rho;d\&rho;d\&phi;}.$ Result of calculation is 0.817, less than 0.833, so this sample is at the measured frequency scope f of institute _x, f _yInterior undesirable, need further processing.

Claims (5)

1, a kind of aperture aspherical optical elements medium-high frequency difference detection method is characterized in that: mainly finish by following steps:

1. adopt the wavefront of optical components pick-up unit to obtain the Wave-front phase data of tested optical element;

2. the Wave-front phase data are carried out the pre-service of data;

3. pretreated data are made the wavefront power spectrum density and calculate, obtain the two-dimensional power spectrum density function of tested element;

4. further calculate the some diffraction function of the element of surveying by the two-dimensional power spectrum density function;

5. calculate the encircled power of tested element by a diffraction function, thereby determine whether encircled power meets the demands in certain spectral range, to determine whether tested element meets the requirements.

2, a kind of aperture aspherical optical elements medium-high frequency difference detection method according to claim 1, it is characterized in that: the described pre-service that the Wave-front phase data are carried out data is to utilize least square method that the Wave-front phase data are eliminated trend term, aforementioned data is done data pre-service work such as cancelling noise, filtering according to Design of Filter principle designing filter.

3, a kind of aperture aspherical optical elements medium-high frequency difference detection method according to claim 1, it is characterized in that: describedly utilize pretreated data φ (x, y) calculate the wavefront power spectrum density, the computing formula of obtaining the two-dimensional power spectrum density function of tested element is:

PSD (f _x, f _y)=Φ ^*(f _x, f _y) Φ (f _x, f _y) l _xL _y, wherein:

Φ (f _x, f _y)= _-∞∫ ∫ ^∞φ (x, y) exp (j2 π (f _x+ f _yY)) d _xd _y, Φ ^*(f _x, f _y) be Φ (f _x, f _y) conjugation, l _x, l _yBe the sampling length of corresponding horizontal direction and vertical direction, f _x, f _yBe spatial frequency.

4, a kind of aperture aspherical optical elements medium-high frequency difference detection method according to claim 1 is characterized in that: the described computing formula of further calculating the some diffraction function of the element of surveying by the two-dimensional power spectrum density function is: $\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})=[1-{\left(\frac{4\mathrm{\&pi;\&sigma;}}{\mathrm{\&lambda;}}\right)}^2]\mathrm{\&delta;}(\mathrm{\&alpha;},\mathrm{\&beta;})+{\left(4\mathrm{\&pi;}\right)}^2\&CenterDot;\mathrm{PSD}(\mathrm{\&alpha;},\mathrm{\&beta;}),$ (α β) is impulse response function to δ, and σ is the root-mean-square value on surface, α=f _xλ d, β=f _yλ d, λ are optical wavelength.

5, a kind of aperture aspherical optical elements medium-high frequency difference detection method according to claim 1, it is characterized in that: the described computing formula of being calculated the encircled power of tested element by a diffraction function is: $E\left(r_0\right)={\&Integral;}_0^{2\mathrm{\&pi;}}{\&Integral;}_0^{T_0}\mathrm{PSF}(\mathrm{\&alpha;},\mathrm{\&beta;})\mathrm{\&rho;d\&rho;d\&phi;}.$

Images