Feb 28 2011
JILA scientists have created a terahertz radiation source that could prove useful to detect imaging weapons or trace gases in security screening applications. The system is resistant to damage and quite efficient when compared to similar systems.
The laser-based source of terahertz radiation, which falls between electromagnetic spectrum’s optical and radio bands, can pierce plastic and clothing. It can also be used to trace a number of substances having exceptional absorption functions at these wavelengths. A combination of optical and electronic techniques is required to build terahertz systems.
The JILA system has a semiconductor surface with metal electrodes that are activated by high-speed laser pulses. An electric current is then passed through the semiconductor while near-infrared pulses, which is generated 89 million times per second and can survive for approximately 70 fs, remove the electrons from the semiconductor. After this, the electrons gather speed in the electric field and produce terahertz radiation waves.
The technology removes two issues associated with these systems, such as generating spikes in the electric field and including a silicon oxide insulation layer between the gold electrodes and the gallium arsenide semiconductor to inhibit the electrons from getting caught in crystal defects. When a radiofrequency signal is applied, the electric field rotates quickly and assures that the electrons produced by the light do not interact to revoke the electric field. This results in an even electric field across a large region and allows the use of a laser beam and improves the efficiency of the system.
Users can increase the terahertz power by elevating the optical power without affecting the semiconductor. The innovative technique does not need high-voltage or small patterned sample electronics. The system generates a maximum terahertz field of 20 V/cm for 160 mW input power. Systems that utilize high-speed semiconductors and lasers are vital as they provide high intensity output and wide frequency range.
NIST physicist, Steven Cundiff informed that the institute has filed a patent for the technology. At present, the system utilizes a laser that is based on a sapphire crystal but can be made smaller by utilizing a compact fiber laser and semiconductor.
JILA is a joint institute of the University of Colorado and the National Institute of Standards and Technology (NIST).
Source: http://jila.colorado.edu/