SU1379626A1 - Method of checking aspherical surfaces - Google Patents

Abstract

This invention relates to instrumentation technology. The purpose of the invention is to improve the accuracy of control of aspherical optical surfaces due to the selection of the first harmonic of the envelope of a monochromatic light wave reflected from the surface, which is modulated sinusoidally in the focal plane of the test surface. The phase of the wave envelope is determined by the angle normal to the optical surface. In a device implementing the method, a plane wave is formed using a radiation source 1, a monochromatic radiation expander 2 and a diaphragm 3. Through a mirror 4 and a prism 5, the light beam hits the zone k, i of the surface 7. The reflected light wave is sinusoidally modulated in the focal plane with assistance of the image analyzer modulator 8, the axis of rotation of which is offset relative to the focus of the surface 7. The envelope phase of the optical signal carrying information about the angle of deviation from the normal given by surface is extracted by processing an electrical signal. 1 il. cl

Description

with

with

C5

to

O5

The invention relates to instrumentation technology and can be used in the control of aspherical optical surfaces during the manufacture of lenses and mirrors with aspheric surfaces in optical instrumentation.

The chain of the invention is an increase in the accuracy of control of aspherical optical surfaces due to the selection of the first harmonic of the monochromatic envelope of the light wave reflected by the surface, which is sinusoidal- 1.0 modulated in the focal plane surface of the controlled surface.

At the market, the flowchart VG: a trainer that implements the method.

V

device contains source 1

; lchromic radiation (laser): - C11 oritel 2 monochromatic ish / chip, forming a diaphragm 3, 1 pc, 1 A, a prism 5, mounted on the scanning unit 6 of the control 1 rueyo1 surface 7, modulator .iip. i.nH iTopa images (MAI),; ijnei-aiH :; radiation (PI) 9 of the main beam, -; l, amplifier 10, source 11 | I j riinec firo 1 3: support center beam, gri. 12 radiation reference; jH, T; ia, L-I-O B paray-hep 13, phase de i-egor 14, d, atchik 15 linear transceivers, microprocessor (MP) 16 and and: display 17.

The device works as follows.

The radiation of the laser 1, formed by the expander 2 and the diaphragm 3, is directed by means of the mirror A and -1 rm1 5 parallel to the optical axis of the optical surface 7. After the surface 7 is diverged from the controlled zone 7 in the meridional section, the radiation is placed on the MAI 8 installed in the focal the plane of the test surface 7, If there are no shape errors in the test zone, the image of the diaphragm ihi 3 coincides with the focus of the surface 7 "If there are shape errors, given by the deviation of the normal L (/

then the image of the diaphragm 3 is shifted

relative to focus on p

In this case, the center of rotation MAIi is shifted relative to the optical axis along axis Oxa, the value of b. The measurement of the value of u (f for each zone (k, i) in the device is as follows. Reflected from the surface zone

7, the optical radiation after MAI 8 falls on PI 9, the electrical signal from which is amplified and fed to the first input 4 of the Azov detector 1A. At the same time, a reference signal is formed by an optocoupler consisting of a radiation source 11 and a radiation receiver 12. Electric

the reference signal through the amplifier 10 and the phase shifter 13 is fed to the second input of the phase detector 14. The siggal from the latter and the signal from the sensor 15 linear displacements defining

controlled surface area, arrive at MP 16 at the same time. After processing the information on MP 16 according to the above algorithm, the control results are displayed on the display system 17

or on the latency (multi-command block of the machine, if the automated process control system is used in the development of the aspherical surface).

five

five

The dependence of the output signal from PI 9 of the main channel in the presence of a shape error at the monitored aspherical surface 7. To simplify the analysis, it is considered that the monitored surface 7 is a square-shaped diffraction-limited optical system with a side D, and the monochromatic radiation source 1 , dilator 2 and diaphragm 3 of square shape with side 2a. Image analysis of the diaphragm 3 is carried out in the Gauss plane (UE), where MAI 8 is located, which is rotating at a constant angular velocity. I segmented rastriz of a set of transparent and opaque sectors, the spatial period of which is 1 m, and its transmittance is described by the function Al, about „(x ,, Ur). In this case, the center of the raster is shifted in the transverse direction along the Ox axis by the magnitude b. In order to convert the energy of the optical radiation reflected from the test surface 7 into the electric one, the PI 9 is placed after the MAI 8, the center of the sensitive area of which coincides with the focus F of the test surface. The sensitivity of the square PI 9 with 2c side is described by the function

0

five

0

five

Hlc (Xp, (|), and the properties of PI 9 are determined by the sensitivity of SMOKC and characteristic 8 (/ 1), and the inertial properties of PI 9 are characterized by its frequency response And (V).

Divide the entrance pupil of the test surface by M equal to

/ - Art.

parts along the axes, and find the expression for the signal with PI 9 (Jni / (t) when examining the surface 7 with a flat coherent wave front.) A flat coherent wave with an amplitude UQ is considered to be square in area (k, i)

k,

, x-ka

, (x, y) U, rect (

Y.

where k 1, ..., N;

i 1,2, ..., N.

If we assume the linearity of the device, the signal spectrum for each zone (k, i) at the output of PI 9 is determined by the expression

HnH (fc, Vv, t) and, (Ch, Vv) hl H-0 ,, V,).

-N „au (/, -., T) ri, (V ,,),),

Gl G1 „AL 1 ,,, t) F ((t),

ten

 five

2 (

transfer function 8;

Npi (-0, v) transfer function PI 9;

O (%, vC) is the image spectrum of aperture 3;

h g is the zonal coherent transfer function of the test surface 7 in the presence of wave aberration 1 (f} due to the shape error (f is the focal distance of the test surface 7; Л is the wavelength of the probing optical radiation),

V.i

Expression for h (),, ,,) in the presence of a horizontal pattern of surface shape leading to a displacement of the image of diffraction array 3 in the Gaussian plane

along the x axis

by value

k.i

and X

AND

by the value of ii y

has the appearance

V, i

(3)

(-.f

- L f x1

1 p; AND

Oh with the rest.

(- Ii X),

;, -, +

i 1,2 ,, .., N is the number of the controlled meridian section.

The error in the shape of the aspherical surfaces is given by the angle of deviation of the normal to the real profile from

Normally to the geometrically given, At the same time, dp O, Then for aspherical surfaces, the meridian sections of which are described by the equations Z (x, y), we can obtain an expression that establishes a unique part between axV and

- 14)

  (ka-) tg 2arctR l / z (ka- |, y) +2

tg 2arctg- l / z (ka- |, y,))

Substitute in (2) the expressions for the transfer functions of the individual cascades of the conversion of the probing optical signal and the expression of the zonal coherent transfer function of the controlled surface

.N

O. l V),

if it has an error in the form specified by the angle of deviation from the normal for each zone i; , and, calculating the inverse Fourier transform of the obtained spectrum, get the expression for the signal at the output of PI 9 in the form

40

45

50

 but

and"; (t) A B + ECOS v, t + (ka-f) L TX I

tg (2arctg l / z (ka- |, y,) + 247 j tg 2arctg l / z (ka- |, y,)) i

where A 8a UoSMtfKC S (A) (, TH C;

B § SLnC4--);

- n

 T “,, ,,, / 2fia. . . E sinC4 - ;: ;-) sinC (---); z II 1 X 1 X

V. bS),

(five)

Analysis (5) shows that the information on the error shape of each is contained in the phase of the first harmonic of the signal taken from PI 9,

Thus, for each zone of the monitored surface, the phase of the first harmonic of the signal with PI 9 F. determines the amount of deviation from the normal and I /, conducted to the center of the controlled area.

Claims (1)

Invention Formula The method of controlling aspherical surfaces, which consists in forming a flat monochromatic wave of optical radiation, discretely scanning the area of the meridian sections of the aspherical surface, converting the reflected flux of optical radiation into an electrical signal, characterized in that F ,, (ka - f) Rolling, simultaneously forming the reference optical radiation flux, modulating the reflected and reference optical radiation streams sinusoidally in the focal plane of the aspherical surface, converting the modulated optical radiation fluxes into the primary and reference electrical signals, respectively, determining the phase difference between the first harmonic of the primary electrical signal and the reference electrical signal F (,, calculate for each zone (k, i) the shape error in the form of a deviation angle from the normal to the aspherical surface L. p and assist ratio I tgf 2arctp l / z (ka - |, y.) 15 tp (2arct l / z (ka - |; y.) j - one de k 1,2, ..., N i 1,2, ..., N is the number of the controlled zone in the meridional section of the surface; number of controlled meridian-anal section of the surface -one; - one five D a 0 z (x, y) aperture of the test surface; the aperture of the main plane wave optical radiation; equations of the meridian sections of the test surface.