Transmission Subterahertz Imaging Utilizing Milliwatt-Range Nanosecond Pulses from Miniature, Collapsing-Domain-Based Avalanche Source

Abstract

Pulsed radars widely used in microwave and optical frequencies are not available in very interesting for applications millimeter-wave (3-0.3 mm/0.1-1 THz) spectral range due to lacking of a miniature, simple, high-power all -solid-state pulsed emitter. We suggest utilization of a phenomenon which we recently found in powerfully avalanching GaAs-based bipolar transistor structure and termed " collapsing fi eld domains". Here we explain the operating principle of the emitter and show an example of transmission sub-terahertz imaging. The pulsed imaging system uses a prototype of our new source operating in sub-nanosecond time domain in milliwatt range, and a commercial Schottky detector. The imaging traditionally utilizing pulse attenuation in the objects is compared with suggested here timedomain imaging that uses the propagation delay of the transmitted pulse. Advantages of each of those two operating modes are discussed. Presented here pulsed imaging radar is a prospective candidate for Detection of Explosives and CBRN in places of people crowding when utilization of x-ray is problematic. It can also be used in non-destructive tests when x-ray does not show suffi cient contrast, or a portable, not dangerous for humans and cost-effective system is required. Very interesting is a prospective of skin and breast cancer detection. Realization of the refl ection imaging regime using the same source is pending.

Effect of hot-carrier energy relaxation on main properties of collapsing field domains in avalanching GaAs

“…Unlike those devices, our simple miniature emitter, despite of its infancy, already provides ps-range pulses of huge power density (e.g., 1-10 MW/cm 2 at 130 GHz) at room temperature, which allowed to demonstrate mm-wave imaging in both amplitude and time-domain pulse modes with picosecond time-of-flight precision. 12 Good agreement between measured voltage waveforms during superfast avalanche switching and drift-diffusion (DD) modeling 13 introduced the collapsing domain concept, however, validate moderate carrier plasma densities. At higher densities, the carrier energy relaxation has to be taken into account, because the domain width W D becomes comparable to v c  s c , where v c is the carrier velocity and s c is the energy relaxation time.…”

“…Demonstrated and physically interpreted saturation of W D is of major importance for future application of the developed tool for analysis of the experimental results obtained for unique sub-THz emitters. (Those emitters have proven their high application potential, 12 but their structure and operation principles have not been published so far because of lacking appropriate modeling.) This approach is suited also for analysis of other GaAs-based avalanche switches such as PCSS.…”