RU133283U1 - ADAPTIVE SMALL MOVEMENT RECORDER - Google Patents

Abstract

1. A small displacement recorder, consisting of a coherent light wave radiation source, a mirror installed after the radiation source and directing the radiation at right angles to a beam splitter that divides the radiation into the reference and object waves, the transmission arms of the reference and object waves, a photorefractive crystal and a photodetector, this supporting arm includes a quarter-wave plate phase sequentially installed after the beam splitter, a system of mirrors directing the reference wave at right angles to the object wave the second focusing lens, the object branch — the focusing element mounted in front of the object under study, a beam splitter, the first focusing lens, while the reference and object waves are directed into the photorefractive crystal at right angles to each other along the axes of the photorefractive crystal [010] and [100] .2. The device according to claim 1, characterized in that a cadmium telluride crystal is used as a photorefractive crystal. The device according to claim 1, characterized in that a continuous solid-state infrared laser is used as a source of light coherent wave. The device according to claim 1, characterized in that a beam splitter plate is used as a beam splitter, dividing the radiation into two beams in equal proportions. The device according to claim 1, characterized in that a lens is used as the focusing element.

Description

The utility model relates to optoelectronics and can be used in the manufacture of electronics and in metrology for non-contact measurement of small linear displacements.

A device for measuring small displacements is known, which is based on a Michelson interferometer (Harry A. Deferrariand Frank A. Andrews. Laser Interferometric Technique for Measuring Small-Order Vibration Displacements // The journal of the Acoustical Society of America. - 1966. - Vol. 39 (5) .- P.979-980). The radiation from a cw laser using a beam splitter is divided into two light waves: object and reference. The reference light wave is directed by a beam splitter to the mirror. The object beam is directed onto the reflective surface of the object under study, the movements of which are to be measured. Reflecting from the surface of the object under study, the object beam is directed to the beam splitter, where it combines with the reference beam. Then the beams fall on the scattering lens and are sent through the attenuator and diaphragm to the photodetector. From the photodetector, the signal passes through a narrow-band filter and is then processed on an oscilloscope.

The disadvantages of the analogue include:

- the device cannot register the movement of objects with dimensions less than 0.5 mm;

- the recorded amplitude of the displacement of the reflecting plate is limited to the used narrow-band filter.

A device is also known for measuring small linear displacements based on the Twyman-Green interferometer (F. Garol, PC Logofatu, D. Apostol, C. Udreaand P. Schiopu, Interferometric vibration displacement measurement, Romanian Reports in Physics, Vol. 62, No. 3 , P. 671-677, 2010). The device contains a source of coherent light radiation, a radiation expander, a collimator lens, a beam splitter separating the radiation into a reference wave and an object wave, a mirror is installed in the path of the reference wave, and an object under study is equipped with a photodetector. The reference wave after the beam splitter hits the mirror, is reflected from it and through the beam splitter enters the photodetector. After the beam splitter, the object wave hits the object under study, is reflected from it and falls back into the beam splitter. The interference signal obtained by the interaction of the reference and object waves in the beam splitter enters the photodetector.

This technical solution for its functional purpose and for its technical nature is the closest to the claimed and taken as a prototype.

The disadvantages of the prototype include:

- low stability of the interferometer;

- increased noise;

- vibration measurements required

The objective of this utility model is to create a small displacement recorder that is resistant to external noise and allows you to measure small displacements (from tenths of a nanometer to a micron) of objects, including characteristic dimensions that are less than the size of the object laser beam of the interferometer at the maximum focus or less than the radiation wavelength (nanoscale objects).

The problem is solved in that the recorder contains a coherent light wave radiation source, a beam splitter separating the radiation into the reference and object waves, the transmission arms of the object and reference waves, a mirror installed after the radiation source and directing the radiation at right angles to the beam splitter, a photorefractive crystal and a photodetector wherein the shoulder of the passage of the reference wave includes sequentially installed after the beam splitter phase quarter-wave plate, a system of mirrors guiding the a wave at a right angle to the object wave, the first focusing lens and a photorefractive crystal, the shoulder of the passage of an object wave is a focusing element mounted in front of the object under study, a beam splitter, a second focusing lens and a photorefractive crystal, while the reference and object waves are directed into the photorefractive crystal under a direct angle to each other along the axes of the photorefractive crystal [010] and [100].

The object wave reflected from the object under study passes through a focusing element, a beam splitter, and a focusing lens into a photorefractive crystal, which is used to demodulate the phase of the wave reflected from the object. The transformed wave emerging from the photorefractive crystal enters the photodetector.

As a radiation source of a coherent light wave, for example, a cw solid state laser is used.

As a photorefractive crystal, for example, a cadmium telluride crystal can be used.

As a beam splitter, it is possible to use, for example, a beam splitter plate dividing the radiation into two beams in equal proportions.

As the focusing element, you can use, for example, any lens system.

In the claimed registrar of small movements, the common features with the prototype are:

- radiation source of a coherent light wave;

- a beam splitter separating the coherent light wave into a reference and an object wave;

- the object wave from the beam splitter is directed to the object under study;

- the reference wave is directed at right angles to the object light wave.

A comparative analysis of the proposed technical solution and prototype shows that the first has, in contrast to the prototype, the following essential features:

- a mirror installed after the radiation source of the coherent light wave and directing the wave at right angles to the beam splitter,

- a system of mirrors directing the reference wave at right angles to the object light wave;

- phase quarter-wave plate;

- photorefractive crystal;

- the reference wave after the beam splitter passes through the phase quarter-wave plate and is directed through a system of mirrors focusing the lens on the photorefractive crystal;

- the object wave reflected from the object through the focusing element, the beam splitter, the photorefractive crystal is sent to the photodetector;

- a photorefractive crystal is installed at the intersection of the reference and object waves;

- the reference and object waves are directed into the photorefractive crystal at right angles to each other along the axes of the photorefractive crystal [010] and [100].

The essence of the technical solution is illustrated by the drawing (Fig.), Which shows a diagram of a device for measuring small movements of objects, where are indicated: 1 - object; 2 - focusing element; 3 - cw laser; 4 - a mirror; 5 - beam splitter; 6 - object wave; 7 - reference wave; 8 - the first focusing lens; 9 - a quarter-wave plate; 10 - a mirror; 11 - a mirror; 12 - the second focusing lens; 13 - photorefractive crystal; 14 - photodetector.

The device includes; a radiation source 3, a mirror 4, directing the radiation to the beam splitter 5. The beam splitter 5 divides the radiation into two waves: object 6 and reference 7, which then move along the corresponding optical shoulders. The object wave 6 through the focusing element 2 hits the object 1, is reflected from it and through the focusing element 2, the beam splitter 5, the first focusing lens 8 enters the photorefractive crystal (PRK) 13. At the exit from the crystal, the object wave 6 enters the photodetector 14. Reference the wave passes through the quarter-wave plate 9, is reflected from the system of mirrors 10 and 11, passes through the second focusing lens 12, and enters the photorefractive crystal 13. Elements 3-13 collectively represent an adaptive holographic interferometer.

A device for measuring small displacements of objects works as follows. Objects 1, the movements of which are subject to registration, are placed in the focal plane of the focusing element 2. Object wave 6 reflected from object 1, due to small movements of the object, is modulated in phase. The change in the phase of the object wave to the change in intensity occurs due to the interaction of the reference and object waves in the photorefractive crystal (PRF) 13. The change in the intensity of the object wave 6 at the output of the photorefractive crystal 13 is detected by the photodetector 14. The magnitude and speed are determined from the signal recorded by the photodetector.

The holographic principle of combining waves in the PRK allows exact matching of arbitrary fronts of the reference and object light waves, and the adaptive properties of the dynamic hologram stabilize the operating point of the interferometer in the region of its maximum sensitivity (quadrature conditions) under the influence of uncontrolled changes in environmental parameters. This increases the stability of the recorder, reduces noise, increases sensitivity, there is no need for accurate alignment of optical elements, and it becomes possible to study the movement of objects whose characteristic sizes are smaller than the size of the object wave at the maximum focus.

Claims (5)

1. A small displacement recorder, consisting of a coherent light wave radiation source, a mirror installed after the radiation source and directing the radiation at right angles to a beam splitter that divides the radiation into the reference and object waves, the transmission arms of the reference and object waves, a photorefractive crystal and a photodetector, this supporting arm includes a quarter-wave plate phase sequentially installed after the beam splitter, a system of mirrors directing the reference wave at right angles to the object wave the second focusing lens, the object branch — the focusing element mounted in front of the object under study, the beam splitter, the first focusing lens, while the reference and object waves are directed into the photorefractive crystal at right angles to each other along the axes of the photorefractive crystal [010] and [100] . 2. The device according to claim 1, characterized in that a cadmium telluride crystal is used as a photorefractive crystal. 3. The device according to claim 1, characterized in that a continuous solid-state infrared laser is used as a source of light coherent wave. 4. The device according to claim 1, characterized in that a beam splitter plate is used as a beam splitter, dividing the radiation into two beams in equal proportions. 5. The device according to claim 1, characterized in that a lens is used as the focusing element.

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