Broadband Terahertz Source Based on Photomixing in Laser-Assisted Field Emission with Clusters of Carbon Nanotubes

Abstract

Terahertz (THz) radiation, which is electromagnetic energy at frequencies in the nominal range of 1011 to 1013 Hz (0.1-10 THz), is being studied for at least 18 different applications (Davies et al., 2002) including urgent needs for medical diagnosis and security applications for the detection of non-metallic concealed weapons, biological and chemical agents, and explosives. However, the present sources of THz radiation present “hurdles” because of their limited tunable bandwidth and output power, and some require fragile, large, and expensive femtosecond lasers or even particle accelerators (Zhang, 2002). Some of the methods that have been used to generate THz radiation are backward wave oscillators with chains of frequency multipliers (Maiwald et al., 2000), the Smith-Purcell Effect (Mross et al., 2003), quantum cascade lasers (Davies et al., 2002), synchrotron radiation from high-energy accelerators (Carr et al., 2002), bulk electro-optic rectification and ultrafast charge transport in semiconductors (Davies et al., 2002), and photomixing in semiconductors (Verghese et al., 1997). For example, photomixing (optical heterodyning) of two lasers at different wavelengths in low-temperature-grown (LTG) GaAs at the feed point of an antenna can generate an output power of only 1 μW at 1 THz, which falls off by 12 dB per octave or 1/F4 at higher frequencies (F), so the power is reduced to 100 pW at 10 THz.