Terahertz range gas-discharge lasers part 2: Resonators of the lasers and applications

The terahertz (THz) frequency range now attracts much attention of researchers and consumers in connection with many possibilities of using it for solving a number of practical problems in science, technology and medicine. Therefore, the development of new sources of radiation and the improvement of the existing ones are actual. The results of experimental and theoretical studies of gas-discharge THz-lasers and numerous studies of the particularities of their operation are summarized in the paper. A number of new developments aimed at increasing the efficiency and expanding the functionality of terahertz gas-discharge lasers are presented. New types of laser resonators and new types of mirrors were created and offered in this paper. Laser resonators with mirrors that do not require accurate alignment are developed. Partially transparent mirrors, in the form of flat periodic structures combining the functions of concave mirrors and focusing lenses are suggested. The above mirrors are capable of reducing the diffraction loss of laser radiation. Resonators with new principles of fine tuning of the radiation output from them are presented. The multi-frequency lasers were developed. The systems for fine tuning of the frequency of electromagnetic laser radiation where the tuning is carried out without using the frequency measuring equipment are designed for such lasers. All these new developments provided herein make it possible to improve the parameters of terahertz lasers and to expand the scope of their application. Some spheres of the THz-laser applications, in particular, medical applications and their use in the field of measurements are provided. New ways of measuring the refractive indices of various substances and materials in the terahertz range using the developed lasers are also presented in this paper. © 2017 by Begell House, Inc.