SU978047A1 - Method of measuring speed of moving reflective surface - Google Patents

Description

t54) METHOD OF MEASURING THE RATE OF MOVING REFLECTIVE

t

The invention relates to a measurement technique and can be used to change the speeds of movement of the surfaces of solids when exposed to shock waves.

An intermetric method for measuring the speed of movement of a surface is known based on the use of Doppler pattern. The method consists in directing the moving object light from the source of luminochromatic coherent oscillations 1 of the laser, combining this probe with a reference beam containing, in addition to the fundamental frequency, an additional constant frequency, and then registering the result of interference of these two rays C13.

The main disadvantage of this method is the limitation of the upper limit of the measured speed associated with the limited frequency capabilities of the recording equipment.

The closest to the present invention is a method for measuring the speed of movement of a reflecting surface by irradiating the surface under study with a probe laser beam, combining the probe beam with

SURFACE

reference and recording the result of their interference 12.

The disadvantage of this method is that it is impossible to measure a speed exceeding a certain limit value, since in this case the frequency will reach the limit for the equipment registered by the equipment. Increasing the speed above Vf p gains

10 to a complete loss of information about it, since the signal with a frequency higher is no longer perceived by the recording equipment, which completely excludes the possibility of its use.

15

The purpose of the present invention is to increase the upper limit of measurement of the speed of movement of the reflective surface.

20

This goal is achieved in that according to the method of measuring the speed of movement of a reflective surface by irradiating the surface under study with a probe laser beam, matching the probe beam with a reference one and recording the result of their interference, laser beams with progressive 30 ° oscillation modes are used as the probe and reference beams In this case, the frequency difference between adjacent modes is selected from the ratio f - 2fnp where ffip is the most often upper limit. ., registered by the instrument; uf is the frequency difference between adjacent modes of oscillations. The drawing shows the spectra of a strong signal, the projective intensity of light, according to the proposed method for measuring the speed of movement of the free surface (only low-frequency and high-frequency components with constant frequencies are shown). Selecting the reference and probe beams, containing their longitudinal oscillation modes with frequencies where fg is the fundamental frequency of the laser radiation; I is the speed of light in the optical resonator; laser cavity length | 1, o,.,., Leads to the following. All longitudinal frequencies with fa o-Tf-,. In addition to the main frequency, Doppler shifts in frequency are experienced when reflected from a moving surface. These shifts are almost equal to each other due to the speed, a small amount compared to the speed of light and the slightly different frequencies of the longitudinal modes of oscillation. After the probe and the downward rays are reduced, the addition of not two, but many electromagnetic oscillations with the thicknesses 11 2 And the close frequencies fo-fo A 1 occurs. And a registrar receives a signal proportional to the total light intensity. The spectrum of this signal is generally quite complex. In the drawing, it is shown for three modes with amplitudes equal to one (in relative units) with frequencies fn D g I From this spectrum, only those frequencies are recorded by the equipment that lie to the left of ff, p (indicated by a dotted line in the drawing), i.e. in the registration area. But now, besides the constant component and the low-frequency variable component q f (t), low-frequency components with constant frequencies f, af, ..., where .f, appear in the spectrum of the total signal. (fo-fj: f2 / fo-fa / -f and low-frequency components with variable frequencies,,,. All the variable components in the drawing are shown in bright lines, and the constant are darkened. In the upper part of the drawing is the case when. For this recording equipment with the upper frequency limit g - 1 l - -1- i pr-2 2 V2.U /; 1 separates from the whole spectrum only the constant component and the signal with frequency. Further, with f d. (lower part of the drawing ) the signal with frequency ceases to be perceived by the recording equipment, but at the same time the signal from the hour falls into the registration area Toto / l --a d /. And the latter decreases with increasing frequency (indicated by arrows), reaches zero as it starts to increase again, until uf reaches ff, p + 3. With increasing frequency / 4th {d / ceases to be perceived by the equipment, but at the same time a component of the frequency / df - f, /, etc. gets into the registration area. By sequentially registering these frequencies with the equipment tuned by Haff, you can increase the limit for measuring the speed of surface movement by 3, 5, .. . 2f, + times. If the longitudinal modes are arranged symmetrically with respect to the main mode, the magnification is 5, 9, ..., 4 "times, i.e. theoretically there is no limit. Using the proposed method of measuring. The speed of movement of the reflecting surface provides, in comparison with existing methods, the following advantages: a practical increase in the upper limit of measuring the speed of movement of the reflecting surface by at least an order of magnitude; The possibility of using when measuring as a recording apparatus commercially available, relatively inexpensive instruments with a frequency range bounded above, but having. as a rule, high sensitivity and reliability; the ability to use the manufactured industrial; small gas lasers (not more than

50 mW) of power, since there is no need to tune the laser to single-frequency mode by drastically reducing} at this radiation power.

Claims (1)

Invention Formula A method of measuring the speed of movement of a reflecting surface by irradiating a surface with a sponsoring laser beam, combining the probe beam with a support and recording the result of their interference, so that, in order to determine the upper limit of measurement aJx speeds, laser beams with longitudinal modes of oscillation are used as probe and reference beams; the frequency difference between adjacent modes is selected from the ratio -if where d is the frequency difference between adjacent modes fnp is the limiting upper frequency recorded by the hardware. Sources of information taken into account in the examination 1. Zastrogin yu.F. Measurement of mechanical vibration parameters using optical interferometry. Measuring equipment, 1972, O 9 C 65 15 1965, 36, I 11, p. 1617 (prototype). 20 ff ufA hfrAf4l lAffAfAl luft Afjil fnP & fl Q ufi-Affl Af4 ufi afrtfAHAfi Afjiltfi g /. r:, I I I I / Afi fjtlIf.