SU1327037A1 - Method of recording metrologic holographic gratings - Google Patents

Abstract

The invention relates to a precision measuring technique and makes it possible to improve the recording accuracy and increase the size of the recording grid. By illuminating the auxiliary grating 16 at the same time by two sources 1 and 6 of coherent radiation with wavelengths, respectively, h, a system of rectilinear moire bands is obtained for the photocarrier 18. By measuring with photosensors 20-24, the phase difference in the pattern of the moire bands determines the recording errors of the metrological grid. The correction of this error is accomplished by varying the delay time of the control signals of the modulating element of source 1 relative to the average period of the moire bands. The angle of inclination of the auxiliary grating 16 is changed with respect to the strokes of the grating recorded on the photocarrier 18 in order to correct the error caused by the defects of the guides, 2 Il. (CO 1HE -J about Od j

Description

The invention relates to a precision measurement technique and can be used to create large-sized high-precision metrological diffraction gratings.

The purpose of the invention is to improve the accuracy and increase the size of the recorded grid.

Fig. 1 shows an opto-electronic diagram of a device for recording metrological holographic gratings in real time; in fig. 2 - layout of photo sensors in the field of moire stripes.

The optoelectronic device for implementing the proposed method consists (Fig. 1) of coherent radiation source 1 with a wavelength; and

the modulating element associated with it, Q to produce a non-destructive reader 2, a first collimating device, a state of lenses 3 and 4, and a semi-transparent mirror 5; continuous source 6 coherent radiation

real-time systems of traveling moire strips, and carried out by measuring — the phase differences by photosensors 20–24 and the picture of these strips determine

wavelength

2

and associated with

thereto a translucent separating mirror 7, deflecting mirrors 8 and 9, a second collimating device consisting of lenses 10 and 11, a modulating element 12, a turning mirror 13 and a third collimating device consisting of lenses 14 and 15; an auxiliary grid 16 and a piezoceramic element 17 associated with it; a photo carrier 18, operating in real time and sensitive to the wavelength D, and a conventional photo carrier rigidly associated with it (length sensitive 19); photo sensors 20-24, an electronic phase metering device 25 generating control signals for the modulating elements, and an electronic phase metering device 26, expressing the recording error of the metrological grid and correcting it during recording by changing the delay time of the control signals of the modulating element 2 of the source 1 with t relative to 30 but the average period of the moire bands and the error caused by the defects of the guides, and its correction in the recording process by changing the angle of inclination of the auxiliary lattice 16 on respect to the grating strokes recorded on photocarrier 18

The essence of the method is as follows.

The auxiliary grid 1.6 is illuminated simultaneously with two beams of light blue (AO and red (A). At the same time, blue (A,) copies the grid to photo carrier 18 in real time, and red (AJ) reads the recorded on

bathe the signals controlling the pioneer 45 photocarrier grating directly

ceramic element.

The method is carried out as follows.

A prerecorded grid rigidly connected in line with the unexposed photocarrier 18 is continuously moved along guides relative to a fixed indicator grid, a system of these two grids is illuminated with a continuous coherent light source 6, and a system of traveling moire stripes transformed at the output of the grids 20-24 into a sequence of electrical signals that control the modulating element 2 of source 1, illuminating a fixed exposed grating, in series understand it on a moving photocarrier 18. At the same time, a photo material working in real time is used as a photocarrier 18, at which the second is preliminarily exposed to a limited portion of the fixed auxiliary grid 16, which combines the functions of the indicator and the exposed one, using a coherent source 1 pre-recorded and auxiliary arrays are additionally illuminated with a continuous coherent light source 6 of wavelength A, allowing real-time penetration of the system x moiré fringes, and is carried out by measuring the - phase difference film photo sensors 20-24 and these bands determined

5 division of the recording error of the metrological lattice and its correction in the recording process by changing the delay time of the control signals of the modulating element 2 of the source 1 with relative to the average period of the moire bands and the error caused by the defects of the guides, and its correction during the recording by changing the slope angle of the auxiliary the lattice 16 with respect to the strokes of the lattice recorded on the photocarrier 18,

The essence of the method is as follows.

The auxiliary grid 1.6 is illuminated simultaneously by two beams of light, blue (AO and red (A). At the same time, blue (A,) copies the grid to photo carrier 18 in real time, and red (AJ) reads the recorded on

0

five

during copying. Behind the photo carrier in red light, a system of straight line moirés is formed. If you move the photo carrier 18 exactly to the grating period 16 and again illuminate it with blue light (), the original pattern of moire fringes will be restored, and the length of the copied grating will increase by the length of the period. By moving the photo carrier 18 evenly and periodically opening the blue light source 1 (A) only with a shift by a period, a limited portion of the lattice can be consistently rewritten

16 for the entire length of the photocarrier. In case of occurrence of a copying error associated with a period change, the moire bands change their bluish shape. Using the phase metering device 25, the magnitude of these changes is determined, and G therefore the magnitude of the period change opens the blue light source 1 delay equal to the measured value. This makes it possible to correct the period errors that occur in real time. At the first stage of the method, a beam of collimated light with a wavelength, a passage through the auxiliary grid 16 at the Bragg angle, records it in real time on an incomplete photo carrier 18, which is sensitive to this wavelength. Real-time recording allows you to get an exact copy of a limited portion of the auxiliary grid 16 on the photo carrier 18 directly during the exposure process without additional

after chemical processing. Non-25 auxiliary lattice 16. At the same time

The modulated beam of light with wavelength Aj, which is collimated by a lens system 10-11, is directed at the Bragg angle through the auxiliary grating 16 to the previously recorded portion of the metrological grating. The wavelength / is chosen such that the photo carrier operating in real time is not sensitive to it. This allows non-destructive reading of previously recorded pemeTKSi. The combination of an auxiliary and prerecorded grid, illuminated by coherent light with a wavelength of D 9, forms a pattern of moire bands, in the field of which photo sensors 20–24 are placed. In the second stage, the photocarriers 18 and 19 move at a constant speed relative to the fixed auxiliary grating 16 in the direction perpendicular to its strokes. The interleaving of the photographic carrier 18 leads to the appearance of a picture of traveling moiré stripes, and the movement of the moiré: the strip for the period corresponds to the displacement for the period of the previously recorded grating. The runner the moire strips are converted by photosensors into electrical signals of a sinusoidal shape. In the case when auxiliary is 16 and prerecorded to. photocarrier 18 grids are perfectly uniform, moire stripes are bands

of the same intensity, perpendicular to the grating lines (parallel to the direction of motion). Therefore, if the photosensors 21-24 are located in a line and perpendicular to the strokes of the auxiliary grid (Fig. 2), then the phase difference between the sinusoidal signals of these photosensors is 0. Signals from photosensors 21-24 are fed to the electronic phase meter 25, which generates control signals modulating the gm element (optical shutter) 2, the shutter is opened only at the moment of passing through the photosensors of the moire strip, i.e. each time exactly at the offset for the period. Thus, the use of a stroboscopic effect makes it possible to record an extended metrological grid in real time on a moving photo carrier 18 by sequentially and repeatedly exposing a limited area.

about Q g -

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it is first read and at the same time overwrite the prerecorded part. Further reading and rewriting of previously recorded sections is carried out.

The accuracy of the recorded metrological lattice is affected by defects inherent in the mechanical part of the device and leading to a change in the distance and mutual arrangement of the auxiliary and recorded grids, and also the error of the electronic path, the appearance of local and progressive optical devices. The presence of errors in the recorded lattice leads to the curvature of the moire strips (Fig. 2), i.e. to deviate from the linear ones. However, the magnitude of the local error & (errors at this point) is determined by the deviation of the center of the curved strip from the middle linear at that point. In the case of traveling moirés, the most accurate (accurate to 21/100) determination of the local error is provided by phase measurements. In a specific example, an electronic phase meter device

25, phase differences between, the photo sensors 21-22 (LF.d) J 22-23 (/ 1F) are measured; 23-24 (LF2, 2), the average phase difference is calculated

lf

 l, d 4. lA y-2iil ii -2lL 7. hG 9 J

21st

513270

corresponding to the middle straight linear moire band, and the magnitude of the local error at the point of the photodetector is determined 23

lf d - d f 2i-2.f

The lFdoc value characterizes the time delay between the average linear strip passing through the 2T-24 photosensor line, corresponding to an ideally uniform grid, and passing time; value of the real curved band with local error 4 through the photodetector 23. The value measured in this way

lt

lok

with the opposite sign is served on

modulating element 2, changing its start time relative to the center of the middle linear band and compensating for the localized and measured write error.

The above method allows localizing, measuring, and real-time correcting errors that occur during the recording of the lattice, ensuring that the principle of stabilizing the lattice period is fully used and allowing the period to be stabilized to within the error of local error determination.

So, when using a grating with a period of d 1 μm, the distance between the photosensors is 1 1 10 mm and the root-mean-square error of phase measurements (3 2 | G / 100, the stabilization error will be d 0.01 μm at a length of 40 mm or А О505 μm at the length of 1 m, the accuracy of phase measurements is almost completely independent of the influence of amplitude factors (changes in the intensity of radiation sources, changes in diffraction efficiency, the recorded grating, scattered light, etc.), as well as the speed of movement of the moire strips, t .e. from the speed of the lattice.

In addition, the accuracy of the recorded grating is influenced by defects of the guides, leading to a change in the angles of inclination of the recorded strokes along the length, i.e. to the violation of the mutual parallelism of the strokes 5 resulting in the use of such a lattice in the linear displacement sensors, to the appearance of the Abbe solution. Defects in the guides lead to a change in the angles of inclination of the strokes of the auxiliary and recording 37 6

my lattices and, as a consequence, to the spatial period of the flat bands

d

D 2;

0

(one

0

55

. Where D is the period of moire bands; d is the period of the lattices; - the angle between the strokes of the gratings. Stabilization of the period of moire bands, and consequently of the conservation. the mutual parallelism of the lines of the recorded grating in the expected way. This is done by stabilizing the phase difference between the photosensors 20-21e located strictly along the grating lines. A change in the angle leads only to a change in the phase difference., While keeping the difference in phase 2 unchanged; ФФ22-2з П-2 The curvature of the moire strips does not

influence, if photosensors are strictly located; along the lattice line, tav; as the period of the moire stripes does not change along the direction of the grating lines. In a specific example, the phase difference dF ,,., Is measured by an electronic phase metering device 26, which produces control signals for a piezoceramic element 175, which changes the angle of inclination of the strokes of the auxiliary grid 16 relative to the one recorded by turning first. Thus, the introduction of a second stabilization loop of photosensors 20-21, a phase metering device 26 and a piezoceramic element 17 allows stabilizing the angle of inclination between the strokes of the auxiliary and recorded gratings and making it uncritical to the effect of the defect guides.

The proposed method allows one to record on a photo carrier operating in real time with an extended high-precision grating, with the contours of the Two contours of stabilization. However, photographic materials suitable for this purpose have a relatively low diffraction efficiency (-10%). In order to increase diffraction efficiency in a specific example, a rigid photo-carrier, real-time, an ordinary photo-carrier 19, is used, which allows to achieve a high diffraction efficiency () at a wavelength. When this metrologists

The grating is recorded in parallel and at the same time and onto a conventional photocarrier 19 by means of a radiation source 6 with a wavelength D of a modulating element 12 connected in parallel to the modulating element 2, a collimating system 14-15, forming a parallel beam of modulating light copying a portion of the auxiliary grating 16 onto the moving photocarrier 19.

The proposed method was implemented in a device consisting of a substrate with a real-time material, which was used as a DP-15 diazo compound rigidly attached to a substrate of the usual photocell PE-2. This diazo connection possesses spectral sensitivity to the short-wave D 0 spectrum. , 5 microns and almost completely insensitive to the long wavelength D 0.6 microns. As a source of coherent radiation, recording in real time, helium-cadmium laser LG-61 with Lina wave D, 0.44 microns, and as a source of non-destructive readout - ge- ly-neon laser LH-38 with L- wavelength 0.63 microns. A holographic grating with a period of d 1 μm and a length L AO tl was used as an auxiliary grating, with the piezoceramic TTS-23 element glued to the end face, allowing the auxiliary grating to be rotated through an angle (+1. allowing operation at frequencies up to 200 Hz.

At the first stage of recording a collimated light beam with a wavelength of D 0.44 μm, the passage through the auxiliary lattice at the Bragg angle 0 12.7 °, copied it to the diazo connection. At the same time a collimated beam of light with a wavelength D

 0.63 μm, the passage at the Bragg angle of 82 18.4 ° through the auxiliary grid and the grid recorded in real time on the diazo connection, formed a system of moire bands, in the field of which 5 PV-27k photodiodes were placed, four of which were located. they were laid in a line perpendicular to 1 grooves of the lattice, and the fifth — parallel to the strokes of the lattice. Distance between

.five

ten

20

25 DA 40 27037,

all photo diodes il 10 mm. At the second stage, the recording of the substrate with photony-- ;. The bodies were moved with a constant velocity of V 50 µm / s relative. fixed auxiliary lattice, which led to the movement of moire bands. The signals from the photodiodes entered the electronic phase-metering devices, including switching iTop, selective amplifiers U 2-6, a phase meter, a device for triggering a relay, and a high-voltage voltage amplifier controlling the piezoceramics. Simultaneously with the recording of the lattice on the BP-15 diazocompound, a parallel recording was made on the photographic plate PE-2. As a result, a metrological holographic lattice with a length of L 80mm was recorded. Total error 4 0.5 µm, diffraction efficiency t 30%.

5 o 0

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Claims (1)

Invention Formula The method of recording metrological holographic gratings, which consists in pre-recording a grating rigidly connected in line with the unexposed photocarrier, continuously moving them along guides relative to a fixed indicator grating, the system of these two gratings is illuminated with a continuous coherent light source, and the resulting at the output of the gratings, a system of running moire strips is converted by at least one photosensor into a sequence of electrical signals that control the modulating using an element of the second coherent source illuminating a fixed exposed grating, sequentially exposing it to a moving photo carrier, characterized in that, in order to improve the accuracy and increase the size of the recording grating, a real-time photo material is used as a photo carrier; using a coherent source with a modulating element and a wavelength D, by exposing a limited portion of a fixed auxiliary grating that combines the functions of the indicator and the exposed lattices prerecorded and auxiliary light grating continuous coherent light source wavelength / 1 2 9 the system of traveling moire stripes, which allows to produce a non-destructive reading, and by measuring the phase difference by photosensors in the picture of these bands, determine the recording error of the metrological grid and correct it during recording by changing the time: the delay of the control signals of the modulating element of the source c) relative to the average period of the moire bands and the error caused by the defects of the guides, and its correction in the process of recording by changing the angle of inclination of the auxiliary lattice with respect to the lines of the grating recorded on the photo carrier. FIG. 2 Editor A. Lezhnin Compiled by V. Kravchenko Tehred L. Serdyukova Proofreader V, Girn K Order 3385/42 Circulation 521 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-355, Raushsk nab., 4/5 Production and printing company, g. Uzhgorod, st. Project, 4