No 6 (2024)

It is shown that it is necessary to create a domestic optical radiation receiver capable of measuring constant optical radiation fluxes in the illumination range from 1 to 2000 W/m², in the spectral range from 0.5 to 20 microns with a measurement time of no more than 2 seconds. The characteristics of the best domestic thermoelectric radiation receivers operating in the same ranges, but, according to the set of characteristics, do not meet the set requirements, are given.

The receiver design has been developed: the sensing unit is mounted on a standard leg, the receiver body has a diameter of 15 mm, height – 9 mm. The entrance window is zinc selenide, if necessary, windows made of other materials can be used.

A stand has been developed to measure the conversion coefficient and to study its dependence on the level of illumination. A thermoelectric receiver of the POI-1 type was used as an exemplary receiver, having a receiving element in the form of a cone on which an electric substitution winding is located. The developed receiver had the following main characteristics: ${\mathrm{{\rm K}}}_{\mathrm{P}}=\left(0,5\pm 0,2\right)$ V/W, time constant $\tau \text{=0,4}$ s, time of one measurement  $T\le 2$s, resistance $R=\left(0.5\pm 0.2\right)$ ohms, size of the receiving area ${\mathrm{A}}_{\mathrm{P}}=\left(4\times 1\right)$ mm², spectral range from 0.5 to 20 microns, detection capacity $D^{*}=8·{10}^8$см$·$ Hz^0.5 W^-1, which corresponds to the best uncooled thermal radiation receivers. The blackening coating provides a high absorption coefficient of ${\epsilon }_{\lambda }\approx 0,93-0,98$ in the range from 0.4 to 25 microns. The limit of the basic error $∆=3,5\%$.

An electrodynamic dipole model of radiation of molecules placed in various metal shells is studied. The model qualitatively describes secondary radiation from spherical dielectric microparticles coated with silver nanolayers — “caps” of various shapes. Silver nanocaps operate as plasmonic nanoantennas and provide surface-enhanced Raman scattering (SERS) signal. The change in the energy flux density emitted by the dipole is calculated depending on the thickness of the silver nanolayer on top of the polystyrene microparticles. It is shown that the thickness and shape of the silver nanocaps significantly affect the resonance characteristics of the microparticles.

It is shown that stimulated emission is essentially the same spontaneous emission, but the emission of a photon occurs not in an empty mode, but in a mode containing photons. According to the number of photons in this mode, the phenomenon has a threshold character.