RU2332638C1 - Multivalue holographic plane angle measure - Google Patents

Abstract

FIELD: metrology.

SUBSTANCE: device represents a light-sensitive material specimen with holograms written thereon and forming a system of superimposed holograms. A reference laser beam acting on the specimen makes the system of holograms induce a response forming a plane fan of several beams originating at a time or in turns, one beam being generated by one hologram. In this version of the device, the reference beam and fan of diffracted beams originating in turns are located in one plane with the angles being reproduced on turning the specimen about its axis perpendicular to the said plane. In another version, the reference beam and the plane accommodating the diffracted beams fan are mutually perpendicular. The count of angles can be effected by turning the specimen through positions whereat one of the system hologram generates a response recorded by appropriate appliance.

EFFECT: higher accuracy and resolution of a circular scale being formed.

5 cl, 6 dwg

Description

The invention relates to metrology, in particular to devices for reproducing (measures) a flat angle.

A multi-valued measure of a flat angle is known (M.G. Boguslavsky and others. The state primary standard of the angle unit is radian, Measuring equipment, 1972, No. 7, pp. 9-10), which is a multifaceted quartz prism (from fused quartz), the angles of which defined by the normals to the faces. Each normal is physically reproduced using the beam of the autocollimator when combining a crosshair in the focal plane of the autocollimator with its image resulting from the reflection of the beam from the face. The angle between the two normals is reproduced by rotating the prism around an axis perpendicular to the measuring plane of the autocollimator. Thus, in the known device, the angles are stored in the mutual arrangement of the faces of a homogeneous quartz sample, and are reproduced by reflection of a ray of light from its elements - faces and rotation of the sample.

The closest in technical essence and adopted for the prototype device is the correct multi-faceted reference prism according to GOST 2875. The prism provides reproduction of angles with real values close to (360 / n) °, where n is the number of faces, and the error due to the non-flatness and pyramidal nature of the faces and a fraction of a second of arc. The essential features of the known device are: the material from which the prism (quartz) is made; its form, including the property of correctness, i.e. equality (within normalized limits) of the angles between the normals to the faces.

The disadvantages of the known device are:

- limited overall dimensions;

- low manufacturability (manufacturing a prism is fundamentally a piece of business and requires a long time);

- the danger of spontaneous sharp changes in optical and geometric characteristics (the so-called "devitrification");

- limited discreteness of the formed circular scale of a flat angle.

Due to the shortcomings of the quartz prism, it can only be equipped with a small number of institutions that monitor carbon-fixing devices in stationary installations, the key element of which is such a prism. At the same time, there are a number of areas of use of these devices, for which operational, on-site monitoring of their stability would be extremely essential. As an example, navigation, geodetic work carried out in remote areas, the functioning of space equipment.

The problem that is solved by the invention is to improve the overall dimensions and manufacturability of the device while increasing its reliability, as well as the discreteness of the formed dial.

The problem is solved by changing the material of the sample in which the angles are stored, and, accordingly, the nature of the interaction of the sample with external optical radiation. In contrast to the known device with a fused silica sample reflecting the beam of an autocollimator, the proposed device uses a sample of a photosensitive material, upon exposure to which a reference laser beam, a response is generated in the form of several rays forming a flat fan that arise alternately or simultaneously. The angles between the response rays are analogous to the angles between the normals of a quartz prism. In the proposed device, the carrier of the angle values is a system of superimposed holograms recorded in a parallelepiped made of a photosensitive (photochromic) material, with each beam being created by one hologram, and the holograms can be arranged uniformly or unevenly in space.

The proposed device can be made in two versions. In modification (A), the reference beam and the fan of successively occurring diffracted rays are located in the same plane, and the angles are reproduced when the sample is rotated around an axis perpendicular to this plane. The reproducible angle is set by the neighboring positions of the sample, in each of which one of the holograms of the system generates a response recorded by the recording device. In modification (B), the reference beam and the plane in which the fan of diffracted rays is located are mutually perpendicular. In this case, all the holograms of the system take part in the formation of the response at the same time, and the totality of the reproduced angles is determined by the rays diffracted from the individual holograms. The angles can be counted by rotating the sample between positions, in each of which one of the holograms of the system generates a response recorded by the recording device. An alternative version of the angle reading mechanism consists in simultaneously fixing all the rays of a stationary sample on a scale, in particular circular. By analogy with a quartz prism, a sample containing a system of holograms can be called a holographic prism. The conditions for recording and using the two modifications of the holographic prism described above are discussed below.

The general requirements for a photochromic material in which a system of holograms is recorded are its high stability and resistance to external influences. For recording, it is proposed to use crystals of calcium fluoride (mineral fluorite; this term is also common with synthetic crystals) with N-centers of color obtained by calcining crystals doped with alkali metal ions (lithium, sodium) in a reducing atmosphere of metal vapor (the so-called additive dyeing crystals). These centers consist of 4 anion vacancies with electrons. When the reduced crystal is illuminated by the ultraviolet radiation of the spectrum at a temperature of (100 ÷ 200) ° C, N centers are transformed into highly aggregated color centers, including a significant number of vacancies. This process is accompanied by a change in the optical constants of the crystal, its absorption spectrum and refractive index. A photochromic medium based on fluorite crystals with color centers is protected by a patent: Korolev N.E., Mokienko I.Yu., Poletimov A.E., Shcheulin A.S. The method of registering an optical image, ed. testimonial. USSR No. 1816142, 1990.

Fluorite crystals activated by alkali metals, which are the material for recording holograms, can be prepared using known methods consisting in the cultivation of inorganic fluorides by the directed crystallization method (Bridgman-Stockbarger method) in vacuum. Additive coloring of crystals is carried out in a known device called a heat pipe, which allows heating crystals in metal vapor and provides separate control of the temperature of the painted crystal and the pressure of the reducing agent - parametal.

Due to the stability of fluorite crystals that persist in nature during geological epochs and the specific conditions under which photochromic transformations in fluorite crystals with impurities of alkali metals occur (elevated temperature, ultraviolet radiation), holograms recorded in them under normal conditions of storage and use (temperature range below 100 ° C, natural light) demonstrate high stability (retention). The characteristics of holograms recorded 15-20 years ago have not undergone any noticeable changes during this time. The achieved diffraction efficiency of holograms (about 15 percent) is sufficient for their use in the proposed metrological device. A holographic fluorite prism in the form of a cube with a rib size of 1 cm has a mass of 3.18 g.

A holographic prism, which has significantly smaller dimensions and mass and is available for mass production, is the basis for the creation of small-sized calibration and control devices that can be used directly in the field of operation of coal-setting equipment or even built into this equipment. This prism can, therefore, become the basis for the construction of a new generation of angle-locking and angle-measuring devices. The smaller size of the holographic prism makes it less sensitive to vibrations, which reduces the accuracy of measurements. An additional advantage of the holographic prism is the possibility of implementing an uneven series of angles, which allows to increase the calibration resolution, which is limited, in principle, only to the smallest module for comparing all pairs of angles of the series.

Based on the foregoing, the claimed combination of features allows to obtain a multi-valued measure of a flat angle, characterized by reduced weight and size characteristics and increased manufacturability and reliability.

The invention is illustrated by the drawings, which depict:

figure 1 is a schematic diagram of the location of the components of the installation for using the device [holographic prism], modification (A), where the following designations are introduced, uniform for all figures: 1 - source of primary radiation (reference He-Ne laser); 2 - reference beam; 3 - holographic prism (crystal with holograms); 4 - rotary device for interfacing a crystal with angle-setting equipment; 5 - diffracted beam formed by one of the holograms; 6 - receiver of radiation induced by a hologram (CCD matrix);

figure 2 is a schematic diagram of the location of the components of the installation for use of the device [holographic prism], modification (B);

figure 3 - modification (A), top view;

figure 4 - section aa for modification (A);

5 is a modification (B), a top view;

6 is a section aa for modification (B).

In modification (A), when recording holograms in a prism 3, in which the reference beam 2 and diffracted beam 5 are located in the same plane, the latter is specified by the hologram-recording beams. Moreover, the angle of information of the recording rays in the volume of the crystal 3 is selected based on the specific operating conditions of the prism (diameter of the working beams, the focal length of the lens used to register the diffracted beam, etc.). The formation of a system of holograms is carried out by sequential recording in the same volume; after recording each hologram, the crystal is rotated by a predetermined angle around an axis perpendicular to the plane of information of the recording rays. To use the holographic prism 3 recorded in this way as a measure of the angle (FIGS. 1, 3), it is also mounted on the rotary device 4, while the reference laser beam 2 is directed perpendicular to the axis of rotation of this device. As a reference laser 1, a laser with any wavelength can be used. Each hologram of the system recorded in the crystal 3 sends a diffracted beam 5 in the case when its orientation with respect to the reference beam 2 satisfies the Bragg condition. All holograms of the system give a response in the same direction, but at different positions of the crystal 3, determined by the angle of its rotation relative to the axis of rotation. Thus, the fixation of the next diffracted beam 5 at the same point of the reference (indicator) device of the receiver 6 as the previous beam indicates a rotation by one of the known constant angles due to the spatial relative position of the holograms in the system. The angles are determined when calibrating the prism 3 using a suitable standard for accuracy.

In modification (B), when recording holograms in prism 3, in which the reference beam 2 is perpendicular to the diffraction plane, the axis of rotation of the crystal 3 during recording should be located in the plane of information of the recording rays, and the angle of information of the rays should be set properly to ensure the perpendicularity of the diffracted beam 5 axis of rotation. In turn, the angle of information of the recording rays determines the necessary ratio of the wavelength of the reference laser 1 to the wavelength of the recording laser. In contrast to modification (A), reference beam 2 induces a simultaneous response from all holograms of the system. When using a prism, it is possible to fix the angles in the same way as (A) by turning the crystal 3 until the next beam 5 occupies the same position that the previous beam occupied before the rotation. An alternative option is possible when all the rays are simultaneously recorded on the scale of the reading device of the receiver 6, graduated in angular units.

An example of a specific implementation is a prototype of a holographic prism in modification (A) made of a fluorite crystal with color centers, in which seven holograms are recorded. The holograms are oriented relative to each other in such a way that the reference beam of a standard helium-neon laser (wavelength 632.8 nm, power 1 mW), directed perpendicular to the axis of rotation of the rotary device with which the sample is aligned, produces a response in a plane perpendicular to this axis. In this case, the angle between neighboring crystal positions at which the Bragg condition is satisfied (a diffracted beam occurs) is 10 °. The diffraction efficiency of each hologram equal to 0.5% was achieved in the sample, which provides a signal power at the photodetector of the order of 5 μW, sufficient for stable recording of the signal.

Claims (5)

1. A device for reproducing angles in one plane (a multi-valued measure of a flat angle) in which information on reproducible angles is stored in the form of spatial characteristics of its elements and is extracted under the influence of an external optical radiation source and a rotary mechanism, characterized in that the device’s elements holograms recorded in a photosensitive material and forming a system of superimposed holograms with a uniform or uneven arrangement in space, while the device contains a radiation receiver that provides fixation of the diffracted beam (s). 2. The device according to claim 1, characterized in that a fluorite crystal with N-color centers is used as a photosensitive material. 3. The device according to claim 1, characterized in that the source of external optical radiation provides a reference laser beam, which is converted by a system of holograms into a diffracted beam (rays). 4. The device according to claim 3, characterized in that the reference and diffracted beams are located in the same plane, and the axis of the rotary mechanism is perpendicular to this plane. 5. The device according to claim 3, characterized in that the diffracted rays that occur simultaneously form a fan of rays in a plane perpendicular to the axis of the reference beam, and the axis of the rotary mechanism coincides with the axis of the reference beam.

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