Indium-tin-oxide nanowhiskers were employed as transparent electrodes in a liquid-crystal terahertz phase shifter. Transmittance of the device was as high as ∼75%. Phase shift exceeding π/2 at 1.0 THz is achieved in a ∼500  μm-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work.

We have used terahertz time-domain spectroscopy to investigate the complex optical constants and birefringence of a widely used liquid crystal mixture E7 in both nematic and isotropic phases ͑26°C-70°C͒. The extinction coefficient of E7 at room temperature is less than 0.035 and without sharp absorption features in the frequency range of 0.2-2.0 THz. The extraordinary ͑n e ͒ and ordinary ͑n o ͒ indices of refraction at 26°C are 1.690-1.704 and 1.557-1.581, respectively, giving rise to a birefringence of 0.130-0.148 in this frequency range. The temperature-dependent ͑26°C-70°C͒ order parameter extracted from the birefringence data agrees with that in the visible region quite well. Further, the temperature gradients of the terahertz optical constants of E7 are also determined. The optical constants of E7 in the terahertz or sub-millimeter wave range are found to deviate significantly from values predicated by the usual extended Cauchy equations used in the visible and near-infrared.

We report the generation of tunable femtosecond pulses from 380nm to 465nm near the degenerate point of a 405-nm pumped type-I BBO noncollinearly phase-matched optical parametric amplifier (NOPA). The tunable UV/blue radiation is obtained from sum frequency generation (SFG) between the OPA output and the residual fundamental beam at 810-nm and cascaded second harmonic generation (SHG) of OPA. With a fixed seeding angle, the generated SFG and SHG covers from 385 nm to 465-nm. With a pumping energy of 75 J at 405 nm, the optical conversion efficiency from the pump to the tunable SFG is more than 5% and the efficiency of SHG of the OPA is about 2%.

Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancingangle deposition can serve simultaneously as transparent electrodes and alignment layer for liquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding p/2 at 1.0 THz was achieved in a $517 lmthick cell. The phase shifter exhibits high transmittance ($78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxidesemiconductor (CMOS) and thin-film transistor (TFT) technologies. V

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