SU1429705A1 - Method of measuring radius of spatial coherence - Google Patents

Abstract

The invention relates to the field of measuring laser radiation parameters and can be used to remotely measure the radius of the spatial coherence of infrared sources of arbitrary power. The purpose of the invention is to provide distance and increase measurement efficiency. To measure the radius of the spatial coherence of the investigated radiation, the laser beam is focused using an optical system in a selected area of the scattering medium, the scattered radiation from the focusing area is received at least at two points simultaneously, the radiation is recorded and converted into electrical signals, their mutual correlation function is determined , the radius of spatial coherence rc is determined by distance 6, between the points of reception of scattered radiation, at which the correlation function Decreased by m times, according to the formula p p, (- ln-ni), where is 1 / e or 1/2. Receiving scattered radiation from the focusing region of the investigated radiation, where the radiation density is maximum, allows an increase in the signal-to-noise ratio and, accordingly, increases the measurement range. Measurement of the radius of spatial coherence is possible At a distance from several tens of meters to several kilometers. 1 il. i (Л С

Description

The image relates to the field of laser radiation parameters and can be used to remotely measure the radius of the spatial coherence of the sources of infrared radiation of arbitrary power.

The aim of the invention is to achieve distance and to increase the efficiency of measuring the spatial coherence radius.

The drawing shows a diagram of a device implementing a method for measuring the radius of the spatial coherence of laser radiation.

The investigated radiation from Laser 1 using the optical system 2 is focused in region 3 of the scattering medium. The radiation scattered by the medium through receiving apertures 4.5 receive photo receivers 65, where the radiation is converted into electrical signals. Using the strobe unit 8 and the commutators 9, 10 "and the correlometer 1, the electric signals are proportional to the intensity of the radiation scattered from the focusing region 3 and the distance between the receivers or by setting several receivers to separate distances another, determine the distance p between the points of reception of scattered radiation, at which the sorption function B | (p) of the intensity of the dissipation radiation 1 and 1-, received through the receiving apertures 4 and 5, is ha compared with his knowledge HAND at distance p and 0.

The correlation function E, (p) is determined by the averaging denoted by the signs:

B, (p) ° (I4,) (Is - «: T5).

Usually take m ™, where

e - the base of the natural logarith

mov p or m "1/2,

The coherence radius p is determined by the formula PI, p, (-lnm) .. The average size p of the partially coherent beam as a distance L from the source and in a turbulent atmosphere is determined by the formula

p „.: p - and (-b-

.

where a is the radius of the radiating aperture of the optical system 2; F is the radius of curvature of the wave front in the center

"I

radiating perturs; k,

L- wavelength; p (1, 45k C L) is the coherence radius of a plane wave; C - structures on the characteristic of fluctuations of the refractive index.

If the partially coherent radiation is focused (--- 1) large

aperture fZ optical system 2

ka 52, 1 at a given range

Jj

L, the first addend (geometric size) vanishes, and the second is negligible compared to the third.

In multimode laser beams excited by a spherical laser resonator,

R"

- / 2 „N,

where N, is the number of transverse modes, and the ratio of the third term to the second is N, therefore, the second term can be neglected

The last term determines the effect of turbulence on the average beam size. Let L be 10 m, a - 5. m, 10.6-10 m. Herewith

, -2 Q 6-10 and condition Q 1 is fulfilled.

Consider the most unfavorable case when Sc s, 10 m. Then, for a radius p, we obtain an estimate of ρ0.37 m, and the ratio of the third term to the fourth is found to be equal to (pk / rd), 3 N,. Therefore, the fourth term can also be neglected. As a result, we have

l, LR

Due to the random position of a large number in the scattering region, the intensity of the scattered radiation is a Gaussian random variable whose correlation function is defined as B, (p)} r, j (p) | where 1 is the mutual coherence function of the scattered radiation. As a result, in the plane of observation of the ai.

with a characteristic size of inhomogeneities n,, where p, is the correlation radius of fluctuations of interatism p, L /

).

Since RV

GTG Radius RS:

the coherence of the field of scattered radiation coincides with the radius rc of the coherence of the source, t. (. p Pk is the value of p, is related to it by the relation p.

p / l. Hence p, p. This formula corresponds to the value of m 1 / e.

At the same time, in GOST 24A53-80, the measurement of parameters and characteristics

Laser tick, terms and definitions and letter designations Spatial coherent radius of the axis is defined as the distance between points at which the degree of spatial coherence takes the value equal to 1/2. Then the formula for p takes the form p P (J 1/2) /. If the scales of p and rc are determined by the killing of the corresponding functions by m times, then

.r p, (-In t) / l1T, (or

m

e

The distance of measurements is provided by the reception of scattered radiation from the focusing area, which allows an increase in the signal / noise ratio and, accordingly, an increase in the measurement range.

Increasing the measurement efficiency is achieved by directly determining the desired parameter using the correlometer readings, which allows one to measure the desired parameter almost in real time.

An example of the ratio of parameters, Let L 10, ar I m, A 10,6

9705

, then p,

g and

4 Yu-

g / i

V4

in

m., N, 10, 2.5 cm. To eliminate the averaging effect of receivers, my fluctuations of the intensity of scattered radiation, the input apertures should have dimensions of 0.25 cm, and the distance between them should vary within 0.5 js p, 5 cm.

The invention permits measurements of the coherence radius of high power radiation, since scattered radiation is used. The resolution also increases, which, when photographed, is limited by the power of the radiation under study due to the presence of photographic materials. 20

five

five

0

Claims (1)

Formula of gain The method of measuring the radius of the spatial coherence of laser radiation, which consists in illuminating the scattering object with the laser radiation being investigated, focusing the radiation on the object and registering the scattered radiation, which is so that, in order to achieve distance and speed, it scatters This radiation is received from the focusing region of the radiation under study simultaneously at least at two points, the conversion of the intensity of the scattering of the other radiation into electrical signals is determined and mutual correlation function, and spatial coherence radius r is determined by the distance p between the dots receiving scattered radiation, wherein the correlation is reduced to funktsn m RAE formula PR p, (-In t). / Je 8