Knowledge Bank

Fourier-transform-limited pulses of terahertz (THz) radiation ($\Delta\nu\sim $10 MHz, peak power up to $\sim$50 $\mu$W) have been generated using (i) low-temperature-grown gallium arsenide (LTG-GaAs) photomixers with THz spiral antennas,}, \underline{\textbf{149}}, 82 (2002)}}$,$}, \underline{\textbf{81}}, 1174 (2002)}} (ii) crystals of the highly nonlinear organic salt 4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate (DAST).}, \underline{\textbf{23}}, 1822 (2006)}} Outputs from two narrowband ($\Delta\nu<$1 MHz, $\lambda\sim$800 nm) cw titanium-doped sapphire (Ti:Sa) ring lasers with a well-controlled frequency difference were shaped into pulses using acousto-optic modulators (AOM), coupled into an optical fiber, pulse amplified in Nd:YAG-pumped Ti:Sa crystals and used as optical sources to pump the THz emitters. The THz radiation can be scanned by scanning the frequency of one of the the Ti:Sa laser and keeping the frequency of the second locked. THz radiation up to 330 GHz was detected with a submillimeter-wave mixer and a spectrum analyzer. The bandwidth of the generated THz pulses was experimentally determined to be $\sim$ 10 MHz. The absorption spectrum of a pure rotational transition of OCS at 304.0 GHz was detected. Using a specially cut DAST crystal, Fourier-transform-limited pulsed radiation over the whole THz region has been generated by difference frequency generation and detected with a 4.2 K germanium bolometer.