This paper describes the design and performance of a ruggedized passive Terahertz imager, the frequency
of operation is a 40GHz band centred around 250GHz. This system has been specifically targeted at
vehicle mounted operation, outdoors in extreme environments. The unit incorporates temperature
stabilization along with an anti-vibration chassis and is sealed to allow it to be used in a dusty
Within the system, a 250GHz heterodyne detector array is mated with optics and scanner to allow real
time imaging out to 100 meters. First applications are envisaged to be stand-off, person borne IED
detection to 30 meters but the unique properties in this frequency band present other potential uses such
as seeing through smoke and fog. The possibility for use as a landing aid is discussed.
A detailed description of the system design and video examples of typical imaging output will be
Passive millimetre wave imaging is now an established and accepted technology that is finding viable commercial
applications in many areas, particularly security and border control. The upper frequency of operation has largely been
governed by the availability of solid state uncooled detectors to around 100GHz. Passive operation at higher
frequencies potentially offers some unique features such as higher optical resolution for a given system size, increased
depth of focus and improved scene contrast. However, the technological challenges involved in realising arrays of
terahertz detectors with the required sensitivity, packing density, repeatability and reliability are considerable.
Nevertheless we have developed such detector arrays and these now provide the core technology base upon which to
explore many new commercial applications that require such benefits.
The first commercial application for this technology has been in the realisation of a compact passive real time imaging
system primarily aimed at the detection of concealed contraband and firearms at a remote distance. This paper describes
such an imager.
Some of the practical advantages of imagery at these wavelengths, such as the ability to operate un-illuminated either
outdoors or indoors, will be described as well as some of the practical system aspects such as bandwidth, scanning
methodology and optical design.
Examples of typical real time imagery is provided.
From a commercial point of view the terahertz region from 100GHz to 10THz remains largely unexplored. The main reason for this has been the lack of readily available, rugged solid state detection technology that has sufficient sensitivity for applications such as passive imaging. This is particularly true when arrays of such detectors are considered.
Until recently the main technology driver has been ground based Radio Astronomy. Here the drive for absolute noise performance has focused effort towards the development of cryogenically cooled detection techniques, primarily utilising liquid Helium cooled superconducting devices. Commercially, the use of such cryogens will usually rule out most potential high volume applications largely for practical reasons such as running cost, convenience and health and safety issues. In order to kick-start the commercial exploitation of the terahertz region an alternative detection technology is required.
The detector technology reported here has its origins in remote sensing applications where the low noise performance requirements are not quite so stringent. Here, reliability, low power operation, low mass and volume are combined with rugged design. These so happen to be the main prerequisites for any commercial solution. For space borne technology, however, cost is not usually an issue and correspondingly until the application of manufacturing methodology the technology has been prohibitively expensive to adopt.
This paper reports on the current state of the art in solid state detector array technology aimed at exploiting commercial applications in the terahertz region. An overview of the technology background is provided combined with a forward look outlining the areas where rapid technology advancement can be expected. The utilisation of this detector technology in the application of real time passive terahertz imaging will be shown.
We describe a unique and powerful global time-domain simulation technique for terahertz diodes such as GaAs Schottky diode mixers, GaAs Schottky diode frequency multipliers, and InP Transferred Electron Oscillators (TEOs). 1D, finite difference, drift-diffusion nonlinear device simulation codes have been linked with a convolution- based circuit analysis. These simulators allow designers to observe both the transient and steady state time domain behavior of the nonlinear circuits. Since physical device simulators have been used, the spatial and temporal behavior of the electrons and electric field within the device under large signal drive can be observed. This gives great insight into the internal device physics at high frequencies. The mixer code allows for the direct and fully self-consistent calculation of the conversion loss and noise temperature; the TEO code allows for fully autonomous calculation of oscillator start-up and frequency selection. Simulation results for 2.5 THz GaAs Schottky mixers and 140 GHz InP TEOs are given.
A picosecond excimer laser-plasma source has been constructed which generates an x-ray average power of 2.2 Watt and 1.4 Watt at the wavelengths required for proximity x-ray lithography: 1.4 nm (steel target) and 1 nm (copper target), respectively. The plasma source could be scaled to the 50 - 75 W x-ray average power required for industrial lithographic production by scaling the total average power of the commercial excimer laser system up to 1 kW. The 1 nm x-ray source is used to micromachine a 2.5 THz microwave waveguide-cavity package with a 48 micrometers deep, 3D structure, using the LIGA technique.
Fabrication of 3D terahertz waveguide components is demonstrated using a novel x-ray micromachining process with integral and embedded x-ray masks. 1 nm x-rays generated by a laser-plasma source are used to expose chemically amplified resist. A repeated exposure and development technique shortens the total x-ray exposure time to 10 min to obtain the required 48 micrometers high structures. A 2.5 THz waveguide cavity is fabricated in gold by electroplating the above resist microstructure.