Terahertz-to-infrared converter based on the polyvinylchloride matrix with embedded gold nanoparticles

Abstract

Prospects for the development of devices for visualizing terahertz (THz) radiation sources can be associated with the use of the results of old studies (1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978) on the absorption of THz radiation by metal nanoparticles. This "renaissance" demonstrates that metallic nanoparticles can be used as nanotransducers of invisible THz radiation to infrared (IR) radiation detectable by a commercial IR camera. The investigated THz-to-IR converters are matrices that are transparent both in the THz radiation range to be visualized and in the operating range of the IR camera; matrices contain embedded metal nanoparticles. The latter, when irradiated with THz rays, convert the energy of THz photons into heat and become nanosources of IR radiation for the IR camera. In metal nanoparticles, the mechanisms of absorption of THz radiation and its conversion into heat are realized through dissipation of the energy of THz photons due to multiple scattering of electrons, as well as because of excitation of two types of phonons (transverse and longitudinal ones). The conversion of THz energy into the energy of transverse phonons occurs directly, while dissipation and excitation of longitudinal phonons occurs indirectly, through the excitation of Fermi electrons. Polyvinylchloride (PVC) was chosen as the matrix material, and gold nanoparticles were chosen as nanoparticles-fillers.

Terahertz-to-infrared converters for imaging the human skin cancer: challenges and feasibility

“…-The NP's size D is smaller than the penetration depth d of EM radiation with the frequency ν: D ≤ d. -The phonon wavelength λ at the frequency of the incident EM radiation ν is not larger than the NP's size D: λ ≤ D ≤ d. -The Heisenberg relation for the momenta of a phonon and an electron in an NP of size D ensures the fulfillment of the law of conservation of momentum upon excitation of a phonon. -The GNP's size D should not be smaller than the size, in which spontaneous emission of THz radiation by a (small enough) GNP begins, i.e., D > 8 nm, 58 in order to prevent the GNP's cooling via emission of THz photons. This observation was guided by our study 58 dedicated to a suggested explanation of the size effect in the heterogeneous catalysis on GNPs (see also Appendix A in this paper).…”

“…This article is based on a modified and expanded version of the SPIE Proceedings paper "Terahertz-to-infrared converter based on the polyvinylchloride matrix with embedded gold nanoparticles." 9…”

“…The GNP’s size D should not be smaller than the size, in which spontaneous emission of THz radiation by a (small enough) GNP begins, i.e., D>8 nm, 58 in order to prevent the GNP’s cooling via emission of THz photons. This observation was guided by our study 58 dedicated to a suggested explanation of the size effect in the heterogeneous catalysis on GNPs (see also Appendix A in this paper).…”

“…The GNP’s size D should not be smaller than the size, in which spontaneous emission of THz radiation by a (small enough) GNP begins, i.e., D>8 nm, 58 in order to prevent the GNP’s cooling via emission of THz photons. This observation was guided by our study 58 dedicated to a suggested explanation of the size effect in the heterogeneous catalysis on GNPs (see also Appendix A in this paper). NPs with sizes inferior to 8 nm tend to cool down due to a spontaneous emission of THz photons, hence become useless if the objective is opposite, to heat the GNPs in the THz-to-IR converter by incoming THz radiation.…”

“…For a number of years, we developed and theoretically evaluated the parameters of the so-called terahertz-to-infrared (THz-to-IR) converters 1 – 9 (see Table 1). Should the production of these devices be established, they would allow the conversion of invisible THz radiation into IR rays that could be visualized with commercial IR cameras.…”