Tunable THz Generation by the Interaction of a Super-luminous Laser Pulse with Biased Semiconductor Plasma
- BAE Systems-ATI, University of Maryland, College Park MD 20742 (United States)
- BAE Systems-ATI, Hebrew University (Israel)
Terahertz (THz) radiation is electromagnetic radiation in the range between several hundred and a few thousand GHz. It covers the gap between fast-wave electronics (millimeter waves) and optics (infrared). This spectral region offers enormous potential for detection of explosives and chemical/biological agents, non-destructive testing of non-metallic structural materials and coatings of aircraft structures, medical imaging, bio-sensing of DNA stretching modes and high-altitude secure communications. The development of these applications has been hindered by the lack of powerful, tunable THz sources with controlled waveform. The need for such sources is accentuated by the strong, but selective absorption of THz radiation during transmission through air with high vapor content. The majority of the current experimental work relies on time-domain spectroscopy using fast electrically biased photoconductive sources in conjunction with femto-second mode-locked Ti:Sapphire lasers. These sources known as Large Aperture Photoconductive Antennas (LAPA) have very limited tunability, relatively low upper bound of power and no bandwidth control. The paper presents a novel source of THz radiation known as Miniature Photoconductive Capacitor Array (MPCA). Experiments demonstrated tunability between .1 - 2 THz, control of the relative bandwidth {delta}f/f between .5-.01, and controlled pulse length and pulse waveform (temporal shape, chirp, pulse-to-pulse modulation etc.). Direct scaling from the current device indicates efficiency in excess of 30% at 1 THz with 1/f2 scaling at higher frequencies, peak power of 100 kW and average power between .1-1 W. The physics underlying the MPCA is the interaction of a super-luminous ionization front generated by the oblique incidence of a Ti:Sapphire laser pulse on a semiconductor crystal (ZnSe) biased with an alternating electrostatic field, similar to that of a frozen wave generator. It is shown theoretically and experimentally that the interaction results in the emission of an electromagnetic wave at the plasma frequency of the ionization front. The device resembles the well-known DARC plasma device with two significant differences. First, the frozen wave is on a semiconductor crystal and not on a gas (Azulene Vapor). Second, the ionizing front is super-luminous. These differences result in a device with superior tunability, efficiency, compactness and flexibility. The paper concludes with examples of THz imaging using the MPCA.
- OSTI ID:
- 20787677
- Journal Information:
- AIP Conference Proceedings, Vol. 807, Issue 1; Conference: 7. workshop on high energy density and high power RF, Kalamata (Greece), 13-17 Jun 2005; Other Information: DOI: 10.1063/1.2158802; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Novel DARC sources
Experiments of Frequency Upshift by Use of a Laser-Produced Ionization Front
Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
ANTENNAS
AZULENE
CAPACITORS
CRYSTALS
ELECTROMAGNETIC RADIATION
GHZ RANGE
IONIZATION
LANGMUIR FREQUENCY
LASER-PRODUCED PLASMA
PULSES
SAPPHIRE
SEMICONDUCTOR MATERIALS
SOLID STATE LASERS
SPECTROSCOPY
VAPORS
WAVE FORMS
ZINC SELENIDES