SU769356A1 - Pulsed pyroelectric radiation receiver - Google Patents

Description

one

The invention relates to the field of apparatus for measuring the characteristics of radio fluxes, namely to thermal radiation detectors, and can be used in devices for measuring the energy and power of pulsed laser radiation.

Pyroelectric radiation receivers are known that have sufficient speed (up to c) and a high degree of non-selectivity: from vacuum ultraviolet to submillimeter spectral range.

However, measurements of the energy parameters of high-power pulsed lasers are associated with great difficulties, since the generation of radiation, as a rule, is accompanied by significant acoustic effects. The impact of a sound wave on a sensitive element of the receiver leads to the appearance of a parasitic signal in it, masking the useful signal and, consequently, to a decrease in the measurement accuracy of the laser pulse parameters.

A pyroelectric radiation detector is also known, in which the sensitive element is made of a material with large acoustic losses 2. This leads to attenuation of the sound wave propagating in the sensitive element and to a decrease in the amplitude of the parasitic signal. The specified receiver has the following disadvantage: the introduction into the material of the sensitive element of the impurities,

5 increases the acoustic loss, leads to the deterioration of the pyroelectric characteristics of the material and to reduce the sensitivity of the receiver. Closest to the invention is a pyroelectric detector comprising two sensitive elements mounted so that they are subjected to the same acoustic transients. One of the elements in a known device is shielded from the detected radiation. Means are provided for subtracting signals taken from sensing elements in order to suppress spurious, piezoelectric signals arising under

20 vibrations.

A disadvantage of the known pyroelectric detector is that, due to the non-identity of sensitive elements, there is always a difference in the amplitudes n

25 phases of harmonic components of the piezoelectric signals, and these differences will be especially strong in the frequency ranges close to the frequencies of mechanical resonances of sensitive elements, where

The effect of vibrations is most significant.

The purpose of the invention is to improve the accuracy of the measurement of the energy characteristics of the power of the pulsed radiation by separating in time the parasitic signal caused by the acoustic effect and the useful signal caused by the radiation effect.

The goal is achieved by the fact that a separating layer is placed between the absorbing coating and one of the electrodes of a material whose thermal diffusion time is longer than the decay time of the sound wave, and the heat capacity is less than the heat capacity of the sensitive element, and the thickness of the layer is determined by the condition

6 "

, C, p,

-Temperature diffusivity of the thermal layer;

C is the specific heat capacity of the separation layer;

-the density of the separation layer;

PI speed of sound in separator

V layer;

WITH,

specific heat of the pyroactive layer;

- density of the pyroactive layer;

P2 d - thickness of the pyroactive layer.

. FIG. 1 is a diagram of a pulsed pyroelectric radiation detector; in fig. 2 - temporal dependence of thermal (Wi) and acoustic (Wan) pulses; and - on the irradiated electrode; b - on the pyroactive layer after passing through the separation layer.

The pulsed pyroelectric radiation detector consists of an absorbing coating 1, electrodes 2, 3, pyroactive layer 4, separation layer 5.

The principle of operation of the radiation receiver is as follows. A radiation impulse with a power and an acoustic impulse with a power of WaK (FIG.

2, a). The radiation pulse acting on the absorbing coating causes a change in the temperature of the latter. The further propagation of acoustic and heat waves in the radiation receiver is subject to various laws. Acoustic wave reaches sensing element through

the time interval Ti -, where / is the thickness of the separation layer; v - the speed of sound in it.

The heat wave is delayed by the separation layer for a time proportional to its diffusion time constant

/ 2

where n is the thermal diffusivity. In particular, from the solution of the heat conduction equation, it follows that the pyroelectric current and the receiver under consideration reach their maximum value after a time interval, Tzad, after the onset of the pulse. Thus, if the condition

(one)

,, ead j 6

the electrical signal due to the radiation pulse and the signal due to the acoustic pulse will be separated in time (Fig. 2.6), which makes it possible to carry out accurate measurements of the energy characteristics of the radiation pulse. From (1) follows the first requirement imposed on the thickness of the separating layer.

/.-. (1, a)

V

In order for the separation layer not to significantly degrade the sensitivity of the receiver, it is necessary that its heat capacity not exceed the heat capacity of the pyroactive layer. From here we get the second requirement for the thickness of the separating layer:

,

(2) Cipi

Cbpi

specific heat capacity and density of the separation layer; , Q-P2 is the thickness, specific heat and density of the pyroactin layer.

The use of a radiation detector will make it possible to improve the accuracy of measuring the energy characteristics of high-power pulsed radiation by temporarily Cfitting the components of the signal, due to the measured radiation and acoustic noise.

The annual economic effect of using a pulsed pyroelectric radiation detector can be obtained by virtue of the fact that this receiver improves the accuracy of measurements of the energy characteristics of high-power lasers. In order to obtain the average value of the output power of such a laser, the number of radiation pulses can be reduced by a factor of two. This constitutes an economic effect: on the order of 10 to 15 thousand rubles. per year on one laser machine.

Claims (3)

1. USSR Author's Certificate No. 346597, MKI G 01J 5/50, 1970. 2. US patent number 3571592, NCI 250-83, published. 1977. 3. The patent of Great Britain No. 1464555, NKI G 1A, 1977 (prototype). W fut.t 2 tt I v h  -Tu r "