JPH0524482B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus for recording diffraction gratings, and more particularly to an apparatus for recording radial diffraction gratings.

The invention can be used in systems of metrology and high precision measurement of angular displacements.

[Conventional technology]

A device for recording a radial diffraction grating, comprising a metal-coated glass disc and a diamond cutting tool for cutting the coating of the radial diffraction grating, the disc being rotatably mounted around an axis by a circle dividing device. is publicly known (LP
Presnukhin “Fotoelektricheskiye
preobrazovateli informa−tsii”, 1974,
Mashinostroyeniye/Moscow/, pp.319−
320).

In this device, a radial grating is formed by cutting radial grooves or lines into the metallization of the disk via a diamond tool.

The device operates as follows.

The disc is successively rotated through a predetermined angle by a circle dividing device, and after each rotation step grooves in the grating are carved by removing the layer of metallization with a diamond cutting tool.

However, this device is not capable of forming grids with a high density or frequency of grooves.
This is explained by the inevitable wear and tear of the cutting tools. That is, a relatively long distance must be traversed beyond the surface of the disk, limiting the number of grooves that can be cut and their length. Moreover, the same drawbacks also affect the shape of the grooves or lines and the accuracy of their position from the beginning to the final stage of the cutting operation. It goes without saying that prior art devices are subjected to thorough testing of vibrational stability and thermal stability. Additionally, this device cannot provide high rates of groove cutting since each groove must be cut separately (single disc cutting times extend to several hours).

Furthermore, a disk for recording a radial grating having a continuous arrangement of a disk mounted rotatably about an axis and having a surface coated with a light-sensitive layer for recording a radial grating and an illumination system. The device is known (Applied Optics Vol. 20, No. 23, 1981)
December 1, 2018 USA DF Horn, “Optical Scales, Reticles, Gratings,
"Masks and Standards" pages 4000-4008, 4003-4006
Page (Applied Optics, V.20, No.23, 1981,
December 1, US.DFHorne “Optical Scales,
Reticles, Gratings, Masks and Standards”,
pp.4000−4008, 4003−4006).

In this device, the illumination system includes a light source in the form of a mercury lamp, a deflection mirror mounted in the optical path of the light beam, a collimator system, and five transparent and a mask in the form of an opaque flat screen with radial slits.

This prior art device operates as follows.

A light beam from a light source passes through the mask and projects images of lines onto the photosensitive layer of the disk, thus imprinting these latent images onto this layer. The disk with the light-sensitive layer is rotated about the axis through an angular step equal to the angular spacing of the slit in the mask, and the illumination system is operated continuously. The stopping time of the disk in successive stationary positions is much longer than the rotation time from one position to the next. During each stop (positioning) period of the disk, five lines are simultaneously recorded by the photosensitive layer. This movement of the device may minimize the effect of errors in the angular positioning of the disk on the accuracy of recording the radiation grating on the disk.

However, this device is not capable of recording radial gratings with a high density of lines or grooves, and when the line density (grid frequency) is increased to several hundred lines per millimeter, the disc light The contrast of the image of the mask slits on the surface of the sensitive layer becomes highly dependent on the stability and value of the clearance between the mask and the disk, resulting in substantial variations in the diffraction efficiency along the recorded grating aperture. return.

Moreover, in mask manufacturing techniques with single line photographic recording with the aid of an enlarged scale coordinate graph, the photographic recording of five radial slits with a circular dividing device does not yield a mask with a high density of slits. Conversely, the grating power recorded in the device is formed by the density or power of the slits in the mask.

The device is operated in a mode of continuous rotation through angular steps equal to the angular spacing of the lines of the grid to be recorded, alternating with periods of rest of the disc, so that the recording of the grid is proportional to the total number of lines. This means that the recording rate of the grid in this device is relatively low. Thus as many as 9 hours are required to record a grid with 8000 lines.

In summary, the prior art devices described below can be used exclusively for recording diffraction gratings at relatively low line powers and at relatively low recording rates.

[Problem that the invention seeks to solve]

The object of the invention is to create a device for recording radial diffraction gratings, in which the illumination system is configured such that gratings with high line power can be recorded at an increased recording rate.

[Means to solve the problem]

The above problem comprises a disk mounted rotatably about an axis and having a surface coated with a light-sensitive layer for recording a radiation grating thereon, and an illumination system arranged in succession, The system includes a double beam interferometer and a laser beam source placed in the optical path of the laser beam, the optical path of the interferometer being placed with respect to the surface of the disk, so that each of their optical lines is aligned with the disk in the recording area of the radial grating. an optical element for forming a diverging laser beam with a spherical wavefront in each optical path, intersecting at the intersection belonging to the surface of the photosensitive layer of , which penetrates the photosensitive layer of the disc in the recording area of the diffraction grating in a direction from the axis of the disc towards the outer periphery, the optical elements being arranged symmetrically with respect to said plane. .

The optical elements of each optical path of the double-beam interferometer are at the same distance from the intersection of the optical lines, and at the same distance from this point to the axis of the disk, the objective lens has a principal focus belonging to the optical line of each optical path of the interferometer. The format may preferably be taken.

The disclosed structure of the device according to the invention makes it possible to record radial gratings with a high number of lines at an increased recording rate.

〔Example〕

The invention will be described below with reference to an embodiment in a device for recording radial diffraction gratings with reference to the accompanying drawings.

A device for recording radial gratings embodying the invention comprises a base plate 1 (FIG. 1) on which it is mounted and a radial grating on which it is arranged successively, one in front of the other. A disc 3 has a light-sensitive layer 4 coated on its surface for recording 5 and an illumination system 2.

The illumination system 2 includes an independent mount 6 mounted on the base plate 1 for a source 7 of a laser beam, which in the presently disclosed embodiment is a laser 7, the mount 6 following the optical path A of the laser beam.
A double beam interferometer 8 is further supported inside. An independent mount 9 attached to the base plate 1 is connected to the optical path A of the laser beam after the interferometer 8.
A segment-shaped pinhole 10 is supported therein.

2 directed to each optical path 12 and 13 of the interferometer 8
In order to divide the beam into two split laser beams, the double beam interferometer 8 has a Cubic prism 11 arranged after the source 7 in the optical path A of the laser beam.

The optical paths 12 and 13 of the interferometer 8 are arranged with respect to the surface of the disk 3 such that each optical line 14 and 15 intersects at an intersection point Q belonging to the surface of the photosensitive layer 4 of the disk 3 and is recorded in the area of the diffraction grating 5. The optical paths 12 and 13 are further connected to the intersection Q of the optical lines 14 and 15 and the axis 1 of the disk 3.
6 (FIG. 2).

The optical path 12 (FIG. 1) further includes a mirror 17 arranged after the Kuwik prism 11 in one optical path of the split laser beam. Each optical path 12 and 13 is connected to a mirror 1 arranged after mirror 17 in the optical path of each split laser beam.
8 or 19 and housing 20 or 21
has. The housings 20, 21 contain optical elements 22 or 23 for forming in each optical path 12 and 13 a diverging beam of laser radiation with a spherical wavefront that penetrates the photosensitive layer 4 of the disk 3 in the recording area of the diffraction grating 5. ing. element 2
2 and 23 are arranged symmetrically with respect to said plane and are associated with respective pinholes 24 and 25.

In the embodiment described, optical elements 22 and 23 (FIG. 2) are short-focus objectives, and the intersection Q of optical lines 14 and 15
and from the point Q to the axis 16 of the disk 3 with the principal foci 26 and 27 belonging to the respective optical lines 14 and 15 of the optical paths 12 and 13 of the interferometer 8.

Alternatively, the same function in a device embodying the invention may be accomplished by optical elements in the form of long focus lenses, diverging lenses, or spherical mirrors.

Pinholes 24 and 25 (FIG. 1) are positioned so that their apertures coincide with respective principal foci 26 and 27 of optical elements 22 and 23.

The pinhole 10 is positioned above the area of the photosensitive layer 4 of the disk 3 where the radial grating is to be recorded.

The disk 3 (FIG. 3) is supported on a bulky platform 28, which in turn is mounted on the shaft 29 of a circle dividing device 30 which is fixed on the base plate 1.

[Effect]

The working principle of the disclosed device for recording radial gratings is as follows.

A laser beam generated by a laser beam source 7 (FIG. 1) is split by a Cubic prism 11 into two split beams. These split beams are mirrored by mirrors 17, 18, 19.
Each optical element 22 and 23 is a short focus lens in this embodiment described by . Optical elements 22 and 23
focuses the beam on each aperture of pinholes 24 and 25.

In this way, each center S1 and S2 (Fig. 4)
Two divergent beams of laser radiation are generated with spherical wavefronts having . Each center S1 and S2 coincides with the center of the aperture of the pinholes 24 and 25 (FIG. 1) and thus each principal focus 26 of the short focus lens.
and 27 (Fig. 2). Projected onto the surface of the photosensitive layer 4 of the disk 3 within the intersection area of the two divergent beams whose centers coincide with the intersection Q of the optical lines 14 and 15 of the respective optical paths 12 and 13 of the interferometer 8 (FIG. 1). When combined, an interference field is generated which forms a radial fringe structure of interference bands. This field will be referred to below as the radial interference field.

The photosensitive layer 4 of the disk 3 thus becomes exposed to this radial interference field within a segment-shaped zone of angular dimension γ formed by the pinhole 10.

The disk 3 is rotated by the circle divider 30 through successive angular steps equal to α=γ/K. Here, "K" is an integer. The interferometer 8 is
When rotated through each angular step of the above magnitude, the disc 3 is adjusted to advance by the total number of pitches or steps of the interference field, ie the ratio n=.alpha./. Here, is the angular pitch of the radial interference field, a positive integer, and the angular pitch corresponding to the angular pitch of the diffraction grating 5 is recorded.

It will be understood that =2π/N. Here π is 3.14...
where N is the total number of lines of the radial grating 5 recorded. The rotation time t ₁ of the disk 3 through successive angular steps is substantially less than the rest time t ₂ of the disk 3 at each successive angular position. The disk 3 is thus continuously exposed to continuous radiation from the illumination system 2 (ie for illumination in the form of a radial interference field) over a rotation of 360°. The recording of the radial grating 5 then ends. The above operating mode of the device embodying the invention therefore provides a recording of the radial grating 5 over a rotation of the disk 3 through 360°.

As can be seen from FIG.
), and the axis OZ (Fig. 4) is on a straight line with the axis 16 of the disk 4 (Fig. 2).
Coordinates S1 (a, b, h) and S2 (-a, b, h) of the centers S1 and S2 of the spherical wavefront of the diverging beam of laser radiation in the Cartesian rectangular coordinate system XYZ
can be understood from the following equation.

a=[c ₁ /2 + (c ₁ ² /4-c ₂ ) ^1/2 ] ^1/2 (1) c ₁ = λ ² /4 ²・(1-λ ² /4 ²・r ₀ ² ) ( 2) c ₂ = λ ⁴ · h ² /16 · r ₀ ² · ⁴ (3) b = (1-4a ² · ² / λ ² ) Γr ₀ (4) where λ is the value of the source 7 of the laser radiation. wavelength, and r ₀ is the average radius of the grating 5, that is, the distance OQ (the fourth
Figure).

From (1), a limit on the permissible value of the coordinate "h" can be derived.

h ² 〓r ₀ ² /4[1-λ ² /4r ₀ ^{2 2} (
2−λ ² /4r ₀ ^{2 2} )] (5) Similarly from (5), restrictions on the values of r ₀ and can be derived.

4r ₀ ²・² /λ1 (6) Thus, based on equations (5) and (6) and from equations (1) and (4), the radial diffraction grating 5 with angular pitch and mean radius r ₀ can be obtained. The coordinates "a" and "b" to record may be determined with the selected value "h".

The value of "h" is selected based on equation (5), so that the angle formed by each optical line 14 and 15 with the surface of the photosensitive layer 4 of the disk 3 is adjusted in order to reduce the fraction of reflected light. Tsute disk 3
must be sufficiently larger than 0° in order to enhance the effect of the interaction of the projected light beam with the photosensitive layer 4.

In order to increase the rate of recording of the radial diffraction grating 5, the active segment of the radial interference field must encompass a sufficiently large angle.
This angular dimension γ of a segment of the interference field generated by two split beams of laser radiation with spherical wavefronts is related to the required accuracy Δ of the angular position of the lines of the radial interference field by .

γ=2・³ √6[1+3b ²・h ² /(a ²
+h ² ) ² ] ^-1/3 Γ ³ √(7) Here, "a" and "b" are determined from equations (1) and (4).

〔Effect of the invention〕

The disclosed structure of the device embodying the invention has a spacing or angular pitch of the lines of the grating that is relatively 2″ (50.8 mm) or smaller with an average radius of the grating r ₀ equal to 100 mm. Provides a record of radial gratings with a high average power v ₀ (equal to or greater than 1000 lines/mm).Meanwhile, at the same time, the angular steps of intermittent rotation of the disc are varied from 8 to 12 By increasing the time “T” for recording the grid by a factor of 8
Reduced by 12 times from The rate "V" of recording the lines of the grid is increased by a factor of 300 to 500 to 4000 to 7000 lines/min.

Thus, the disclosed apparatus advantageously increases the recording rate and the power of recorded radial grating lines while providing adequate radial recording accuracy.

A prototype model of the disclosed device was operated to record a radial grating with the following properties:

N=324.000, = 1.9×10 ^-5 rad=4, r ₀ = 100
mm, v ₀ =516 lines/mm The parameters of the apparatus are as follows.

h=25mm, a=15.5mm, b=9.6mm, Δ=0.2″,
γ=2°, α=30', n=450, k=4 The operating modes are as follows.

t ₁ = 4 seconds, t ₂ = 1 second, T = 1 hour, V = 5400 lines/min

[Brief explanation of drawings]

1 is a schematic perspective view of a device for recording a radial grating embodying the invention; FIG. 2 is an enlarged perspective view showing the arrangement of the optical elements of FIG. 1 with respect to a disk; and FIG. 1 is a partially enlarged cross-sectional view of an assembly for mounting a disk in the apparatus shown in FIG. 1, and FIG. FIG. 3 is a diagram showing the geometrical arrangement of centers S1 and S2 of a spherical wavefront. 1...Base plate, 2...Lighting system,
3... disk, 4... photosensitive layer, 5... radial diffraction grating to be recorded, 6... mount, 7... laser beam source, 8... double beam interferometer,
9...Mount, 10...Pinhole, 11...
Kubitsch prism, 12... Optical path of interferometer 8, 13... Optical path of interferometer 8, 14... Optical line, 15... Optical line, 16...
Axis of disk 3, 17...Mirror, 18...Mirror, 19...Mirror, 20...Housing, 2
1... Housing, 22... Optical element, 23... Optical element, 24... Pinhole, 25... Pinhole, 26... Principal focus, 27... Principal focus, 28... Platform,
29...shaft, 30...circle dividing device.

Claims (1)

[Claims] 1. A photosensitive layer 4 mounted rotatably around an axis 16 and for recording a radiation diffraction grating 5 thereon;
A radial grating recording device with a disk 3 having a surface coated with a radial grating and an illumination system 2 arranged in succession, the illumination system 2 comprising a double beam interferometer 8 placed in the optical path A of the laser beam and a laser beam source. 7 and interferometer 8
The optical paths 12, 13 of are arranged with respect to the surface of the disk 3, so that their respective optical lines 1
4 and 15 intersect at an intersection point Q belonging to the surface of the photosensitive layer 4 of the disk 3 in the recording area of the radial diffraction grating 5 and are symmetrical with respect to a plane that includes the axis 16 of the disk 3 and the intersection point Q of each optical line 14 and 15. , and the optical paths 12 and 13 are each optical path 1
Optical element 2 for forming a diverging laser beam with a spherical wavefront at 2, 13
2 and 23, and penetrates the photosensitive layer 4 of the disk 3 in the recording area of the diffraction grating 5 in a direction from the axis 16 of the disk 3 toward the outer periphery, and the optical elements 22 and 23 are arranged symmetrically with respect to the plane. A radial diffraction grating recording device characterized by: 2 Each optical path 12, 1 of the double beam interferometer 8
The optical elements 22 and 23 of No. 3 are at the same distance l from the intersection Q of the optical lines 14 and 15, and at the same distance l from this point Q to the axis 16 of the disk 3, each optical path 1 of the interferometer 8 is
2. A radial grating recording device according to claim 1, characterized in that it takes the form of an objective lens having principal foci 26, 27 belonging to 2, 13 optical lines 14, 15.