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J. LIU, H. SCHMUTZ AND F. MERKT, Laboratorium für Physikalische Chemie, ETH-Zürich, 8093 Zürich, Switzerland.
Fourier-transform-limited pulses of terahertz (THz) radiation (
10 MHz, peak power up to
50 µW) have been generated using (i) low-temperature-grown gallium arsenide (LTG-GaAs) photomixers with THz spiral antennas,\footnoteE. Peytavit, G. Mouret, J.F. Lampin, S. Arscott, P. Masselin, L. Desplanque, O. Vanbésien, R. Bocquet, F. Mollot and D. Lippens, IEE Proc.-Optoelectron. , \underline\textbf149, 82 (2002),\footnoteE. Peytavit, S. Arscott, D. Lippens, G. Mouret, S. Matton, P. Masselin, R. Bocquet, J.F. Lampin, L. Desplanque and F. Mollot, Appl. Phys. Lett. , \underline\textbf81, 1174 (2002) (ii) crystals of the highly nonlinear organic salt 4-N,N-dimethylamino-4'-N'-methyl stilbazolium tosylate (DAST).\footnoteA. Schneider, M. Neis, M. Stillhart, B. Ruiz, R. U. A. Khan and P. Günter, J. Opt. Soc. Am. B , \underline\textbf23, 1822 (2006) Outputs from two narrowband (
<1 MHz,
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
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.