One method reported for the generation and detection of broadband THz radiation utilizes nonlinear optical effects, such as second order nonlinearity, optical rectification (K. H. Yang, P. L. Richards, and Y. R. Shen, Appl. Phys. Lett. 19, 320 (1971)), and electro-optical sampling (Q. Wu and X.-C. Zhang, Appl. Phys. Lett. 67, 3523 (1995), A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996), and P. U. Jepsen, C. Winnewisser, M. Schall, V. Schyia, S. R. Keiding, H. Helm, Phys. Rev. E, 53, 3052 (1996)).
Multiple broadband coherent generation and detection techniques have been demonstrated which use inorganic crystals, such as GaP (Q. Wu and X.-C. Zhang, Appl. Phys. Lett. 70, 1784 (1997)) and ZnTe crystals (Q. Wu and X.-C. Zhang, Appl. Phys. Lett. 71, 1285 (1997) and P. Y. Han, and X.-C. Zhang, Appl. Phys. Lett. 73, 3049 (1998)), the organic material DAST (P. Y. Han, M. Tani, F. Pan, and X.-C. Zhang, Opt. Lett. 25, 675 (2000)), or electro-optic polymers (A. Nahata, D. H. Auston, T. F. Heinz, and C. Wu, Appl. Phys. Lett. 68, 150 (1995) and A. M. Sinyukov, and L. M. Hayden, Opt. Lett. 27, 55 (2002)).
One alternative method uses a photoconductive antenna. The detection of broadband THz waves up to 60 THz was reported using a low-temperature-grown GaSa photoconductive antenna (S. Kono, M. Tani, and K. Sakai, IEEE Proc-Optele. 149, 105 (2002)).
The Handbook of Nonlinear Optical Crystals, (V. G. Dmitriev, G. G. Gurzadyhan, and D. N. Nikogosyan, Springer, 166-169 (1999)) describes GaSe as a nonlinear optical (NLO) crystal with layered hexagonal structure in a 62m point group. This crystal has a large electro-optic coefficient, high damage threshold, suitable transparent range, and a low absorption coefficient. GaSe is also a negative uniaxial crystal, with type-I phase matching in electro-optical sampling. Due to the large nonlinear optical coefficient (d22=54 pm/V) and birefringence properties, GaSe is used in the generation of broadband mid-infrared electromagnetic waves. Recently, collinear difference-frequency generation with a nanosecond pulse laser (W. Shi, Y. J. Ding, N. Fernelius, and K. Vodopyanov, Opt. Lett. 27, 1454 (2002)), phase-matched optical rectification with a Ti:Sapphire laser (R. Huber, A. Brodschelm, F. Tauser, and A. Leitenstorfer, Appl. Phys. Lett. 76, 3191 (2000)), and field amplitudes greater than MV/cm in GaSe were reported (K. Reimann, R. P. Smith, A. M. Weiner, T. Elsaesser, and M. Woerner, Opt. Lett. 28, 471 (2003)). However, this crystal has not been explored in the context of broadband detection.