FR2624623A1 - DEVICE FOR RECORDING A RADIAL DIFFRACTIVE NETWORK - Google Patents

Abstract

The invention relates to a device for recording a radial diffracting grating. According to the invention, it comprises a source of coherent radiation 7 and, one after the other on the path A of the coherent radiation, a splitting interferometer 8 and a rotating disc 3 carrying on its surface a photosensitive layer 4 for recording therein. a radial diffracting grating 5; the optical axes 14 and 15 of the arms 12 and 13 of the interferometer 8 intersect at an intersection point Q located at the surface of the layer 4, in the zone of the network to be recorded 5; the arms 12 and 13 have optical elements 22 and 23, short focus objectives, to form, in each of the arms 12 and 13, a diverging beam of coherent radiation with a spherical wave front passing through the photosensitive layer 4 of the disc 3 in the area of the network to be recorded 5, from the axis of the disk 3 towards its periphery. The invention is particularly applicable in metrology.

Description

1.

  The present invention relates to

  recording of a diffracting grating, and more particularly, the recording devices of a radial diffractive grating. The invention can be used in metrology and in systems for accurately measuring angular displacements. There is a radial diffracting grating recording device which includes a diamond cutting tool and a metallized coated glass disc to carry the radial diffracting grating thereon, rotatable about its axis with a circle splitter or plotter

  (L.P. Presnoukhin, "Information Converters

  ", 1974, Mashinostroenie, (Moscow), pages 319 to

320).

  In this device, the radial diffracting gratings are obtained by the size, using the tool of

  diamond cut, radial features on the metal coating

read from the disk.

  This device works as follows.

  The disk rotates successively at a given angle using the circle dividing machine and, after each movement, the line is cut by removing the metallized coating layer using the cutting tool.

to diamond.

  This device does not make it possible to obtain a high den-

  trait. This is due to the wear of the cutter during the recording of the grating, the tool moving a great distance to the surface of the disc, which limits the number of lines and their length. In addition to this, said wear

  also influences the variation of the form and

  position from the beginning to the end of the size, while imposing stringent requirements on the strength, vibration and thermal stability of the

device.

  The device does not make it possible to obtain a high speed of size of the lines (duration of size!

  hours) because each stroke is done separately.

  There is a recording device of a radial diffracting grating which comprises, placed one after the other, a lighting system and a disc with a photosensitive layer on its surface, to record a radial diffracting grating and able to rotate around its axis (Applied Optics, v. 20, No. 23, 1981, December 1, US, DF Horne "Optical Scales, reticles, gratings, masks and

  Standards ", pages 4000 to 4008, 4003 to 4006).

  In this device, the lighting system contains a light source in the form of a mercury lamp and, depending on the operation of the light beam, deflection mirrors, a collimator system and a mask made in the form of a lamp. flat screen non-transparent to the light beam with five transparent radial slots arranged with a determined angular pitch with respect to the axis of the disk.

  This device works as follows.

  The light beam emitted by the light source passes through the mask and creates images of the lines in the area of the photosensitive layer of the disk, which are printed there. The disc with photosensitive coating rotates about its axis at a step equal to the angular pitch between the lines of the mask, the lighting system operating continuously. The time of immobilization of the disk substantially exceeds that of passage from one position to another. During each stop of the disc, its photosensitive layer simultaneously records five lines. Such a mode of operation of the device makes it possible to reduce the influence of the errors of positioning of the disk on the accuracy of the recording of the network.

Radial diffractant on the disc.

  This device does not make it possible to record a high density radial grating because, when the density of the mask is increased to hundreds of lines per millimeter, the contrast of the images of the mask slots

  the surface of the sensitive layer of the disc begins essentially

  to depend on the value and stability of the space between the mask and the disk, which results in strong changes in diffracting efficiency by opening up

network to be registered.

  In addition to this, the mask-making technology provides for a photographic recording using a coordinatograph of an enlarged radial slot, its photographic reduction and subsequent recording using a five-slot circular plotter. radial does not allow to obtain a mask with high density of slots. The density of the network recorded by this device is equal to the

density of the mask.

  As the device operates in successive rotations mode of an angular step of the network to be recorded and

  disk stops, it takes a considerable amount of time to

  register a network proportional to the total number of its features, in other words, the device is characterized by a low speed of network registration. Thus, to record a network - at 8000 lines, it takes about

9 hours.

  So the device does not record the radial diffracting networks at a low density and

  a small recording speed.

  The object of the invention is to create a recording device

  a radial diffracting network, whose realization of the lighting system would make it possible to record a

  high density and high speed network. -

  The problem posed is solved by the fact that, in a recording device of a radial diffracting grating which comprises, one after another, a lighting system

  and a disc carrying a photosensitive layer for recording

  the diffracting grating and being able to rotate about its axis, according to the invention, the lighting system comprises a coherent radiation source and, in the direction of the coherent radiation, a splitting interferometer whose arms are arranged by relative to the surface of the disk, so that their optical axes intersect at a point of intersection on the surface of the photosensitive layer of the disk, in the area of the network

  radially diffracting to be recorded, and its symmetrical

  compared to the plane passing through the point of inter-

  section, optical axes and the axis of the disk, these arms being provided with optical elements to form, in each arm, a divergent beam of coherent radiation spherical wave front passing through the photosensitive layer of

  disc, in the region of the radial diffracting network recorded

  trer, in the direction of the axis of the disc towards its periphery, said optical elements being placed symmetrically by

to the plan indicated.

  The optical elements of the splitting interferometer can be made in the form of objectives whose main foci are arranged on the optical axes of the arms of the interferometer at the same distance from the point of intersection of these axes and between this point and

the axis of the disc.

  Such a constructive embodiment of the claimed device makes it possible to record high-density radial diffracting gratings of lines with a high speed

recording.

  The invention will emerge from the description which follows

  a concrete example of its execution, schematized in the accompanying drawings, of which: FIG. 1 represents a general diagram of the device

  recording of a radial diffracting network according to the

  vention (in perspective); FIG. 2 represents the diagram of the arrangement of the optical elements of FIG. 1 with respect to the disk (in perspective); Figure 3 shows a fixing assembly of the disc of Figure 1 (general view with partial cross-section, enlarged); FIG. 4 represents the geometrical arrangement of the centers S1 and S2 of the spherical wave fronts of the divergent beams of coherent radiation, formed by the optical elements of the interferometer of the device of FIG.

  Figure 1 according to the invention.

  The recording device of a diffracted network

  both radial according to the invention comprises a base I (Figure 1).

  The base 1 door, placed one after the other, a lighting system 2 and a disc 3 whose surface bears a

  layer 4 to record a different network.

radial fracture 5.

  The lighting system 2 comprises, on an indivudual support 6, installed in turn on the base 1, a coherent radiation source 7, in this case a laser, a dedubler interferometer 8 placed on the same support 6, on the path A of the coherent radiation, and a diaphragm in the form of a segment, placed after the interferometer 8 on the path A of the coherent radiation, on a support

  individual 9 mounted, in turn, on the base 1.

  The interferometer splitter 8 contains, after the

  source 1, on the path A of the coherent radiation, a prism

  cube It divides the coherent radiation into two beams of coherent radiation sent to arms 12 and 13

interferometer 8.

  The arms 12 and 13 of the interferometer 8 are dis-

  posed, with respect to the surface of the disc 3, so that

  their optical axes 14 and 15 intersect at a point of intersection

  section Q lying on the surface of the photosensitive layer 4 of the disk 3, in the region of the radial diffractive grating 5 to be recorded, and are arranged symmetrically with respect to the plane passing through the point of intersection of the optical axes

  14 and 15 and the axis 16 (Figure 2) of the disk 3.

  The arm 12 (FIG. 1) comprises a mirror 17 placed

6 2624623

  after the cube prism 11 on the path of one of the beams resulting from the division. coherent radiation and each arm 12 and 13 comprises, respectively, on the beam paths resulting from the division, and after the mirror 17 and the cube prism 11, mirrors 18 and 19 in the bodies and 21 optical elements 22 and 23, to form in each arm 12 and 13 a divergent beam of the coherent radiation with spherical wavefront passing through the photosensitive layer 4 of the disk 3 in the region of the grating 5 to be recorded, placed symmetrically with respect to the plane

  indicated, and pinholes 24 and 25.

  In the described variant embodiment of the device, optical lenses 22 and 23 (FIG. 2) use short-focus lenses whose main focal points 26 and 27 are located on the optical axes 14 and 15 of the arms. 12 and 13 of the interferometer 8, at the same distance from the intersection point Q of these axes 14 and 15

  and between this point Q and the axis 16 of the disk 3.

  However, the same function in the device according to

  vention, can be filled with long-focus lenses, diverging lenses and spherical mirrors used

as optical elements.

  The pinholes 24 and 25 (FIG. 1) are placed so that their orifices co-act with the main foci.

  and 27 optical elements 22 and 23.

  The diaphragm 10 is disposed above the area of the photosensitive layer 4 of the disc 3, which must be

  the radial diffractive grating 5 is recorded.

  The disk 3 (FIG. 3) is placed on a platform 28 which, in turn, is placed on the shaft 29 of a circular plotter 30. In this case, the axis 16 of the disk 3

  coincides with the axis of rotation 'of the shaft 29 of the tracer 30.

  The circular tracer 30 is rigidly fixed to the base 1.

  The recording device of the diffraction network

  radial arrangement according to the invention operates as follows.

  The beam of coherent radiation generated by the coherent radiation source 7 (FIG. 1) is divided by the cube prism 11 into two beams. Then, these beams are directed, using the mirrors 17, 18 and 19, on the optical elements 22 and 23, short-focus lenses,

  which focus them in the holes of

noped 24 and 25.

  Thus, two divergent beams of the ray-

  coherent with S1 and S2 spherical wave fronts (Figure 4) and co-interacting with the centers of the pinhole apertures 24 and 25 (Figure 1) and, respectively, with the main focal points 26 and 27 (Figure 2). short focus lenses. In the intersection zone of the two beams

  whose center coincides with the point Q of inter-

  section of the optical axes 14 and 15 of the arms 12 and 13 of

  the interferometer 8 (FIG. 1) forms an interfering field

  tiel, which, in projection on the surface of the photosensitive layer 4 of the disk 3, forms a periodic radial structure of interference fringes. In the following,

  this field will be called radial interference field.

  The radial interference field impresses the photosensitive layer 4 of the disc 3 within the limits of an area in the form of a segment of an angular dimension T,

limited by the diaphragm 10.

  The disc 3 makes, with the help of the circular plotter, rotation. successive angular steps D u = T /, where k is an integer. The interferometer 8 is adjusted so that at the rotation of such an angular step, the disk

  3 moves an integer step number of the interfering field

  that is, the ratio n = i, o is the angular pitch of the radil interference field, respectively, of the radial grating 5 to be recorded, has an integer numerical value. In this case, = 2RJ / N, where Z = 3.14 ..., and N is the

  total number of lines of the network 5 to be recorded.

  The time t1 is the time during which the disc 3 rotates an angular pitch; the time t2 is the time during which the disc 3 remains stationary. The disk 3 is always exposed to the lighting system 2 (in the light of the radial interference field) until a lap

  complete 360, after which the registration of the network differs

  radial fracture 5 ceases. This mode of operation of the

  positive embodiment of the invention ensures the recording of a

radial bucket 5 every 360.

  The coordinates of the centers S1 (a, b, h) and S2 (-a, b, h), as shown in FIG. 4, of the spherical wave fronts of the divergent beams of the coherent radiation,

  compared to the Cartesian rectangular coordinate system

  XYZ, whose XOY plane coincides with the surface of the photosensitive layer 4 of the disk 3, the axis OY passing through the point Q of intersection of the optical axes 14 and 15 (Figure 1) of the interferometer 8, while the axis OZ coincides with the axis 16 (Figure 2) of the disk 3, are determined by the following expressions: [c C2 (1 ClC a = + 1 (1)

C = (1 _?% 2 2) (2)

(4) 0

  and .302 16.r 2a 2) b = (1 -) r (4) o is the wavelength of the coherent radiation source 7; 'o r0 is the average radius of network 5, ie 4

the distance OQ (Figure 4).

  It follows from expressions (1) to (4) that the limit for the admissible values of the coordinate h is: r / 2 rh2r [1 (2 (5) h2 4 22 4.r2 4 ro Respectively, of the ratio ( 5) follows the limit for r and: 4 r2.

O \ 2 "2 1 (6)

  Expressions (1) and (4), taking into account

  expressions (5) and (6), make it possible to determine the

  data a and b to ensure the registration of the different network.

  radial fracture 5 at an angular pitch and at a radius

  the value of the coordinate h being chosen.

  The choice of h is made in view of the expression (5) so as to ensure a rather significant difference in the angle of the angle between each of the axes 14 and 15 and the surface of the photosensitive layer 4 of the disk 3, to reduce the part of

  reflected light and, consequently, to increase the effi-

  interaction efficiency of the incident radiation with the layer

photosensitive 4 of the disc 3.

  To increase the recording speed of the radial diffractive grating 5, it is necessary to use a radial interference field segment of sufficiently large angular size. The angular dimension of the segment of the interferential field created by two beams of coherent radiation with spherical wave fronts is related to the desired accuracy of the angular position of the radially interferential field lines by the following expression = 2. + 3b2.h 2] 1.73 (a + h 2s 2 (7)

  o a and b are defined by the expressions of (1) to (4).

  Such a constructive execution of the

  diqué makes it possible to record radial diffracting gratings with a high average density of features (up to 1000 lines / mm and more, respectively, with an angular pitch of the grating of 2 "and less, for a mean radius of the grating r = 100 mm ), while o

  reducing the time T of the network recording from 8 to 12 times by

  8 to 12 times the angular pitch of rotations of the disk, the speed

  V se registration of network features increases by 300

  500 times and reaches 4000 to 7000 lines / min.

  Thus, the device according to the invention ensures a significant increase in the density of the recorded radial diffracting grating and the speed of its recording, while

preserving its precision.

  The device according to the invention has made it possible

  radially diffracting the following parameters: N = 32 400, = 1.910-5 rad = 4 ", r0 = 100 mm,

0 = 516 lines / mm.

  The characteristics of the device were then as follows: h = 25 mm, a = 15.5 mm, b = 9.6 mm, λ = 0, 2 ",

  t = 20, (= 30 ', n = 450, k = 4. The function device

  the following scheme: t1 = 4 s, t2 = I s,

T = I h, V = 5400 lines / min.

l1

Claims (2)

R E V E N D I C AT IO N S   1. Device for recording a diffracted network   radial type, of the type comprising, in series, one after the other   a lighting system and a disc bearing   a photosensitive layer for recording a radial diffractive grating and rotatable about its axis, characterized in that the illumination system (2) comprises a coherent radiation source (7) and, in the path (A) of the radiation coherent, a splitting interferometer (8)   whose arms (12, 13) are arranged with respect to the   face of the disc (3), so that their optical axes (14, 15) intersect at a point of intersection (Q) on the surface of the photosensitive layer (4) of the disc (3), in the area of the radial diffractive grating (5) to be recorded, and are arranged symmetrically with respect to the plane passing through the point (Q) of intersection of the optical axes (14, 15) and the axis (16) of the disk (3), said arms having optical elements (22, 23) for forming, in each of the arms (12, 13), a beam diverging from the radiation coherent with   a spherical wavefront passing through the photosensitive layer   ble (4) of the disk (3) in the region of the radial diffractive grating (5) to be recorded from the axis (16) of the disk (3) towards its periphery, said optical elements   being installed symmetrically in relation to the indicated plan.   2. Device according to claim 1, characterized in that the optical elements (22, 23) of the arms (12, 13) of the doubling interferometer (8) have the form of objectives including main foci (26, 27). located on the optical axes (14, 15) of the ras (12, 13) of the interferometer (8),   at the same distance ({) from the point (Q) of inter-   section of. these axes (14, 15) and between this point (Q) and the axis (16) of the disc (3).