Optical elements for focusing of terahertz laser radiation in a given two-dimensional domain

Binary silicon-based diffractive optical element (DOE)—Gaussian-to-Square focuser (diameter of aperture is 30 mm) for the terahertz spectral range has been designed and characterized using terahertz radiation of the Novosibirsk Free Electron Laser (NovoFEL) at the wavelength of 141 μm. The preliminary experiments have demonstrated feasibility of application of binary silicon DOE for focusing of terahertz radiation into pre-given focal domain.     

A terahertz scanning near-field optical microscope with an attenuated total internal reflection module

The first terahertz scanning near-field optical microscope with an attenuated total internal reflection module and a free-electron laser (FEL) as the radiation source was developed. A scanning system with positioning using a confocal sensor with chromatic coding and a surface-subwavelength probe touch sensor were developed and tested. A new technique for sensing the distance between the probe and a conducting surface via corona-discharge current measurement was developed. A specific lock-in system for detection of probe-scattered pulse-periodic radiation, which includes a hot-electron superconducting bolometer and an electronic signal-storage circuit, was developed to operate with the Novosibirsk terahertz FEL. All elements of the microscope were tested, and their working capacity was demonstrated. Experiments on the detection of microscope-probe-scattered terahertz radiation have been initiated.     

Relaxation of the Excited States of Arsenic in Strained Germanium

Semiconductors - The relaxation times of the lower p states of the arsenic donor in a germanium crystal strained along the [111] crystallographic direction are studied. Measurements are performed...     

Real-Time Imaging Using a High-Power Monochromatic Terahertz Source: Comparative Description of Imaging Techniques with Examples of Application

Gradually appearing high-power terahertz sources require the development of adequate imaging techniques. This paper describes four imaging techniques (with a thermal recorder, temperature-sensitive phosphor plates, a visible-light thermal sensitive Fizeau interferometer, and an uncooled microbolometer array) applied with the Novosibirsk terahertz free electron laser as a radiation source. The space and time resolutions of the devices were examined thoroughly. Examples of the application of these techniques, including in-line holography and real-time moving-objects detection, are given.     

Silicon diffractive optical elements for high-power monochromatic terahertz radiation

This paper presents a fabrication technique and results of studies of silicon binary diffractive optical elements (DOEs): a diffractive lens and a 1 : 2 diffractive beam splitter with an aperture diameter of 30 mm for the terahertz spectral range. The elements were fabricated in two versions: with and without an antireflection coating of parylene C. The DOE characteristics were investigated in the beam of the Novosibirsk free electron laser at a wavelength of 141 μm. The results are given of a study of the radiation resistance of the coating, which remained intact upon exposure to an average radiation power density of 4 kW/cm²; the peak power in a 100 ps pulse was almost 8 MW/cm². Experimental estimates of the diffraction efficiency of the elements coated with the antireflection coating are in good agreement with theoretical estimates.