Spatial filtering of radiation from wire lasers

Abstract

In this letter we propose an approach to obtain directive radiation from wire lasers with subwavelength transverse dimensions and length much larger than the radiation wavelength (wire lasers) based on spatial filtering of their radiation using a combination of a spherical lens and a diaphragm. Theoretical modeling based on the antenna model for wire lasers shows that a directive beam with the uniform phase front can be formed when the diaphragm separates the maximum of the image field of the laser created by the lens. We demonstrate spatial filtering of wire laser radiation experimentally using a terahertz quantum cascade laser.

In vivoTHz sensing of the cornea of the eye

“…For experimental verification of the influence of THz radiation scattering from the cornea we measured the backscattering diagram. The corneal sample was exposed to a beam of polarized monochromatic THz radiation from a quantum-cascade laser [33] at a frequency 3.06 THz under normal incidence (figure 3). Back-scattered THz radiation was collected by a highly sensitive detector system based on a helium-cooled bolometer installed on the rotational arm.…”

3.9 THz spatial filter based on a back-to-back Si-lens system

“…Hollow waveguides or hyper-hemispherical silicon lenses mounted near the exit facet of the QCLs inside the cryostat window achieve a far field single-lobe beam pattern with low divergence, but the beam profile is not ideal and the mechanical robustness can be a concern [25][26][27][28]. A combination of a spherical lens and a diaphragm has been used to produce a directive beam with the uniform phase front, from a wire laser [29]. The latter is known to produce a divergent, undirective beam.…”