WIDELY TUNABLE FOURIER-TRANSFORM-LIMITED TERAHERTZ PULSES GENERATED BY OPTICAL FREQUENCY DIFFERENCE

E. Peytavit, G. Mouret, J.F. Lampin, S. Arscott, P. Masselin, L. Desplanque, O. Vanbesien, R. Bocquet, F. Mollot and D. Lippens, IEE Proc.-Optoelectron.E. Peytavit, S. Arscott, D. Lippens, G. Mouret, S. Matton, P. Masselin, R. Bocquet, J.F. Lampin, L. Desplanque and F. Mollot, Appl. Phys. Lett.A. Schneider, M. Neis, M. Stillhart, B. Ruiz, R. U. A. Khan and P. Gunter, J. Opt. Soc. Am. BAuthor Institution: Laboratorium fur Physikalische Chemie, ETH-Zurich, 8093; Zurich, SwitzerlandFourier-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$^\prime$-N$^\prime$-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