SU794399A1 - Pyroelectric radiation receiver sensitive element - Google Patents

Description

one

The invention relates to the design of sensitive elements of pyrometers and can be used to measure the intensity of an electromagnetic, for example laser, radiation in a wide range of wavelengths from the extreme ultraviolet to the far infrared region of the spectrum.

Sensitive elements of pyro-receivers are known, which contain a pyroelectric (ferroelectric) crystal on which electrodes are applied, which are associated with the recording unit of the receiver 1.

In order to increase the absorption coefficient of the radiation, a layer of an absorbing coating, such as a layer of golden black, is applied to the sensitive element.

The closest in technical essence is a sensitive element of a pyroelectric radiation detector containing a pyrocrystal with superimposed electrodes and an absorbing coating. Absorbing coating is made of metallic black. A receiver with a sensing element is pre-assigned to measure laser radiation in a wide spectral range 2.

However, when measuring intense radiation fluxes, the thermal destruction of the absorbing coating and the polarization of the pyroactive crystal result from its overheating beyond the Curie point.

The purpose of the invention is to expand the range of measurements of the radiation energy density.

The goal is achieved by the fact that an absorbing coating of a dielectric with characteristics is applied to a sensitive element of a pyroelectric radiation detector containing a pyrocrystal with superimposed electrodes on it.

GR-GO

./

T t - 0

where y, is the radiation absorption coefficient of the material of the absorbing coating;

/ is the thickness of the absorbing coating;

Gr is the destruction temperature of the absorbing coating; Tm is the upper limit of the operating temperature range of the pyroelectric receiver;

b - temperature of the sensitive element before irradiation.

FIG. 1 - sensitive element

a pyroelectric radiation receiver;

in fig. 2 - distribution curves for themes 9-5, UrY o

Measuring the thickness of the sensing element under the action of a radiation pulse: a) without an absorbing coating; about; with absorbing coating.

The sensing element of the mono-electric radiation detector contains a pyroelectric crystal 1, on which metal electrode 2 is superimposed on one side, and the same electrode 3 on the opposite side. Electrodes have taps to the receiver's recording unit (not shown). On top of electrode 2, an absorbing dielectric coating 4 is applied, which has thermophysical, geometrical and optical characteristics in the working area of the spectrum that satisfy the condition

t. - 0

where 1 is the radiation absorption coefficient of the material of the absorbing coating;

/ is the thickness of the absorbing coating;

Gr is the destruction temperature of the absorbing coating; Tm is the upper limit of the operating temperature range of the pyroelectric receiver;

TQ is the temperature of the sensing element before irradiation.

The fulfillment of the left side of the inequality ensures that the radiation in the interlayer is almost completely absorbed. The fulfillment of the right-hand side of the inequality is necessary so that the absorbing interlayer does not collapse under the action of radiation in the entire range of measured energies, i.e., that the limiting values of the radiation pulse are determined by the properties of the pyrocrystal, and not the interlayer.

The dielectric layer transforms the radiation energy density on the surface with a decrease to the surface of the pyrocrystal. As a consequence, the pyroelectric crystal is affected by heat flux, the energy density of which is significantly less than the energy density of the measured flux, which allows to measure high-intensity radiation without destroying the sensitive element.

The described sensitive element of the pyroelectric radiation detector works as follows. A falling radiation pulse of radiation W causes a change in the temperature of the irradiated surface of the dielectric layer 4, which leads to the heating of the sensitive element and the appearance of electric charges on its surfaces. The amplitude of the signals remains proportional to the energy of the radiation pulse until the temperature of the sensitive element exceeds a certain maximum value Tm. Overheating above the temperature Tt leads to a change in the basic characteristics of the sensitive element - the pyroelectric coefficient and dielectric constant and, consequently, to a violation of its linearity. Typical TT values for such widely used materials as triglycine sulfate, barium titanium based ceramics and others are 25-55 ° C. Unlike the sensing element, the absorbing coating allows heating to the temperature of destruction Gr (1000 ° C and higher). Applying a pyroelectric layer to the dielectric layer prevents it from overheating. FIG. 2 shows the temperature distribution under the action of a powerful radiation pulse in a receiver without

protective absorption of the coating (a) and in the receiver with the absorbing coating (b). In the presence of an interlayer, the temperature to which the pyroelectric crystal 7 is heated does not exceed the maximum

T-T values. For example, a sensitive element based on barium titanate makes it possible to measure the energy density per pulse up to OD J / cm. The same element, covered with a layer of quartz with a thickness of 0.1–1 mm in the wavelength range from 5–15 µm, allows measuring the energy density in a pulse up to 20 J / cm.

In addition, the sensing element may have other options specific

fulfillment. For example, electrodes can be superimposed on the ends of a single crystal, and a dielectric absorbing coating directly on its irradiated surface.

The simplicity of the design of such a sensitive element and its speed provide a positive effect when using these sensitive elements when registering pulses of technological lasers.

The estimated economic effect obtained on one technological installation (welding of microcircuits), when applying the proposed sensitive elements, will be 10-15 thousand rubles. per year, due to the decrease in the marriage of manufactured products.

Claims (2)

1. USSR author's certificate No. 441458, cl. G 01J 5/44, 1969. 2. USSR author's certificate number 107446, cl. G 01 J 5/00, 1958 (prototype).