Intense Terahertz (THz)-wave generation and highly sensitive THz-wave detection were obtained by wavelength conversion with nonlinear optical susceptibility χ(2) of LiNbO3 crystals. Maximum peak output of about 50 kW (5 μJ/pulse) was demonstrated in an injection-seeded THz-wave parametric generator pumped by post-amplified emission from a microchip Nd:YAG laser. Using the sub-nanosecond pulse duration of the laser proposed herein provides effective mitigation of stimulated Brillouin scattering in LiNbO3, producing higher gain for wavelength conversion between near-infrared (near-IR) pump light and THz waves. Monochromatic THz radiation was obtained in the continuous tuning range of 0.7–2.9 THz. Additionally, highly sensitive THz-wave detection was demonstrated based on up-conversion from THz waves to near-IR light as well as efficient THz-wave generation. The signal generated with non-collinear phase-matching condition showed spectroscopic detection on the screen apart from the LiNbO3 crystal. Highly sensitive detection with minimum energy of about 80 aJ/pulse (0.8 μW at peak) and a large dynamic range of more than 100 dB were achieved in this experiment.

We have developed widely tunable terahertz (THz)-wave sources using nonlinear optical crystals. In the 1–3 THz region, a frequency-agile THz-wave parametric oscillator in a ring-cavity configuration has been realized using MgO-doped LiNbO3 as the nonlinear crystal. An organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal is promising for THz-wave generation in an ultra-wide range 1–40 THz. Difference-frequency generation from DAST, pumped using a dual-wavelength KTiOPO4 (KTP) optical parametric oscillator, is demonstrated. Additionally, THz-wave detection, with high sensitivity, fast response-time and room-temperature operation, is achieved by nonlinear up-conversion. Water concentration mapping of biological tissue samples and carrier density mapping of semiconductor wafers using frequency-agile THz-wave sources are demonstrated.Nous avons développé des sources de rayonnement térahertz basées sur des techniques d'optique non linéaire, qui sont réglables sur une très large bande fréquentielle. Dans la région 1–3 THz, nous avons construit un oscillateur paramétrique comprenant un cristal non linéaire de LiNbO3 dopé MgO au sein d'une cavité résonante en anneau. Pour la génération très large bande (1–40 THz), le cristal organique DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) présente des performances très prometteuses. Ainsi, nous l'avons utilisé pour de la génération THz par différence de fréquence entre les 2 faisceaux délivrés par un oscillateur optique paramétrique en KTP (KTiOPO4). De plus, la technique non linéaire de « up-conversion » permet une détection des ondes THz avec une extrême sensibilité et un temps de réponse très bref à température ambiante. En employant ces sources, nous avons enregistré des cartes de concentration aqueuse de tissus biologiques et des cartes de densité de charges libres dans des semi-conducteurs.