Miniature field deployable Terahertz source

Mark G. Mayes*

Applied Physical Electronics L.C.

P.O. Box 341149 Austin TX 78734

ABSTRACT

Recent developments in terahertz sources include compacted electron beam systems, optical mixing techniques,

and multiplication of microwave frequencies. Despite significant advances in THz science, however, few source

technologies are mobile or suited for field deployment. Strategies in source development have approached generation

from either end of the THz spectrum, from up-conversion of high-frequency microwave to down-conversion of optical

frequencies. In this paper, we present the design of a THz source which employs an up-conversion method in an

assembly that integrates power supply, electronics, and radiative component into a man-portable unit for situations in

which a lab system is not feasible. This unit will ultimately evolve into a ruggedized package suitable for use in extreme

conditions, e.g. temporary security check points or emergency response teams, in conditions where THz diagnostics are

needed with minimal planning or logistical support. In order to meet design goals of reduced size and complexity, the

inner workings of the unit ideally would be condensed into a monolithic active element, with ancillary systems, e.g. user

interface and power, coupled to the element. Therefore, to attain these goals, the fundamental component of our design

is a THz source and lens array that may be fabricated on either a printed circuit board or wafer substrate. To reduce the

volume occupied by the source array, the design employs a metamaterial composed of a periodic lattice of resonant

elements. Each resonant element is an LC oscillator, or tank circuit, with inductance, capacitance, and center frequency

determined by dimensioning and material parameters. The source array and supporting electronics are designed so that

the radiative elements are driven in-phase to yield THz radiation with a high degree of partial coherence. Simulation

indicates that the spectral width of operation may be controlled by detuning of critical dimensions. We discuss

simulation results and frequency response for a single element and the source array, and the component density

necessary to achieve target output intensities. After securing the primary objective of a designing a compact fieldable

THz source, the secondary goal is developing a fabrication recipe which draws upon existing methods in PCB/integrated

circuit manufacturing to obtain a device that may be produced at volume with high yield.

Keywords: Terahertz, metamaterial, split ring resonator, helical antenna, photolithography, sol-gel

1. INTRODUCTION

A. Background

Radiation in the THz regime, 0.3 to 30 THz, presents a bit of an anomaly to workers in the field; because the

band is positioned between microwave and optical frequencies, it does not easily give way to approaches that are all-

electronic or all-optical. Legacy THz sources, e.g. synchrotrons and free electron lasers, are massive systems that require

extensive laboratory facilities and large operating budgets, hence are typically within reach of only national labs and

research institutions. Although technology limitations slowed the exploration of THz, a sizable body of literature and

data has accumulated detailing the interaction of these frequencies with various media.

Applications include THz radiography for high-contrast images similar to x-ray, but without harmful charging

effects. THz imaging has thus been heralded as a replacement for x-ray in soft tissue imaging and security screening.

Spectroscopy is another valuable application due to the strong interaction of THz with organic compounds which create

chemical signatures for detection and identification. THz spectroscopy is widely documented as a countermeasure

against concealed explosives and contraband, and for detection and neutralization of biohazards such as anthrax [1, 2].

Because this frequency range offers significant benefits for numerous applications, much effort has been spent on

development of smaller cheaper THz technologies. Early technologies were based primarily on electron beam machines.

The cyclotron for example, generated radiative by-products through acceleration and deceleration of electrons. The free

electron laser employs a similar mechanism to generate radiation hence relies upon e-beam technologies. Due to the size

*

Send correspondence to mgmayes@apelc.com