Instrumentation for beam profiling in the terahertz regime

Abstract

The standalone, portable Terahertz (THz) Imaging Profiler Array (TIPA) based on an Offner Relay design has been constructed as a THz beam profiler and multispectral imager. It integrates a solid-state detector technology (Schottky Diodes) that can be configured in an array to cover the frequency range from 0.60 to 0.90 THz. The reconfigurable 16 element Schottky diode detector array is utilized along with imaging and scanning mirror modules and system control hardware and software to produce high spatial or temporal beam profiles of THz beams. Images of THz source profiles are presented along with THz images of relevant targets. Potential applications are discussed. INTRODUCTIONTHz radiation is recognized as an increasingly important region for non-destructive testing and evaluation, imaging through obscurants, covert wide bandwidth communication, standoff agent detection and direct energy (DE) applications [1][2][3][4][5]. THz wavelengths are shorter than microwaves; therefore, they do not diffract as much as energy generated by high power microwave (HPM) systems. When compared to visible and near infrared (NIR) lasers, THz energy can couple better with electronics systems (much like HPM systems) [5]. The interaction between various materials and terahertz energy is also unique. Since THz frequencies exist between radio frequency (RF) and IR regions, they can penetrate certain materials (paint, clothing, paper, wood, etc.). Applications include non-destructive evaluation of components for fatigue or tampering, as well as imaging for security purposes. In free space communication applications, where atmospheric attenuation is not an issue, THz offers significant improvement in bandwidth over RF without the requirement for extreme pointing accuracy required by laser communication systems. We are currently witnessing the development of THz technologies in applications that combines the best attributes of microwave and IR spectral regions. The wealth of new science and technology opportunities found in applications of THz has fostered rapid advancement in sources with higher power levels being demonstrated in the laboratory. Most THz sources currently in use are semiconductor-based sources: photoconductive switches pumped by a Ti:Sapphire laser, quantum cascade lasers, and multiplier chains driven by microwave oscillators. The latter sources typically generate up to a few milliwatts of power. The DARPA Terahertz Imaging Focal Plane Array Technology (TIFT) program is currently investing improved designs for THz sources operating at 650 GHz that offer higher efficiencies and power levels that could reach 50 mW [6].Scientists have demonstrated 10s of W of broadband THz radiation produced by electrons in an accelerator [7]. There are three types of vacuum-based sources under development (backward wave oscillator, desktop free electron laser, optically pumped far infrared laser) that may offer THz power from 1 to 100 W. These power levels are of interest to prospective THz users for their potential to enhance operational...