Broadband Two-Dimensional Far-Field Beam Profiling of Commercial CW Terahertz Photomixers from 0.2 to 1.5 THz

TL;DR

This study systematically characterizes the far-field beam profiles of commercial terahertz photomixers across 0.2-1.5 THz, revealing frequency-dependent divergence and diffraction patterns crucial for optimizing THz system design.

Contribution

It introduces a comprehensive 2D raster scanning method for detailed beam profiling of terahertz photomixers, providing quantitative metrics for device comparison.

Findings

Frequency-dependent beam divergence observed.

Emergence of Airy diffraction patterns at certain frequencies.

Quantitative metrics enable objective device comparison.

Abstract

We present a systematic far-field characterization of four commercial PIN diode terahertz photomixers over the 0.2-1.5 THz frequency range using a two-dimensional (2D) raster scanning method. The emission pattern of each transmitter, equipped with an integrated hyper-hemispherical silicon lens, was characterized using a broadband Schottky diode receiver over a 35 mm x 35 mm grid grid. The results reveal consistent frequency-dependent beam divergence and the emergence of distinct Airy diffraction patterns at intermediate frequencies, attributed to lens-induced aperture effects. In addition to qualitative mapping, we extract quantitative metrics -- including divergence slope, beam asymmetry, ellipticity, and centroid variability -- that enable objective comparison of beam profiles across devices and frequencies. This comprehensive mapping underscores the importance of full 2D beam profiling for understanding THz propagation and offers insights into lens design and photomixer packaging for optimized system performance.