A resonant absorption method of laser modulation

Abstract

A new method of laser modulation is discussed, which depends on certain plasma effects in semiconductors. In the presence of low-frequency background noise, an incident electromagnetic wave of frequency near the plasma frequency can be anomalously absorbed because it puts energy into damped electrostatic plasma waves. This anomalous absorption process is highly resonant and requires near-matching of the incident wave frequency and the frequency of the excited plasma waves. If the frequency of the electron plasma waves is shifted in and out of resonance by a modulating agency, the absorption coefficient can get strongly modulated, leading to amplitude modulation of the electromagnetic wave. The frequency shift can be achieved by the application of suitable electric fields to the semiconductor.