Joseph D. Rowley

Broadband terahertz pulse emission from ZnGeP 2

Optical rectification is demonstrated in (110)-cut ZnGeP(2) (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak-intensity range of 0.5 GW/cm(2) to 40 GW/cm(2). ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second-order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths.

Terahertz generation by optical rectification in uniaxial birefringent crystals

The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in (110)-cut ZnGeP2 and compared to (zincblende) GaP. Although the crystals share the same nonzero second-order tensor elements, the birefringence in chalcopyrite crystals cause the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to {012}- and {114}-cut chalcopyrite crystals and predicts more efficient conversion for the {114} crystal cut over the {012}- and {110}-cuts.

Efficient picosecond optical parametric oscillator based on periodically poled lithium tantalate

Generation of transform limited picosecond pulses continuously tunable across wavelengths in the near-infrared (995–1340 nm) and midinfrared (2.1–3.6 μm) range is demonstrated in an optical parametric oscillator (OPO) based on a periodically poled stoichiometric lithium tantalate crystal. The OPO, which is synchronously pumped by a mode-locked Ti:sapphire laser, delivers about 1 W in combined average power at a repetition rate of 74 MHz, which represents close to 45% extraction efficiency in output power. With wavelength and bandwidth controlled via an intracavity diffraction grating, about 2.7 ps pulses with 3.8–10.9 cm−1 bandwidth (full width at half maximum) were generated across the tuning range in the near-infrared thus making the OPO an optimal source for use in various nonlinear spectroscopy and microscopy applications that require high spectral resolution.

Properties of broadband terahertz generation in birefringent ZnGeP 2

Generation of terahertz pulses by optical rectification is demonstrated in chalcopyrite ZnGeP2 (ZGP) as a function of pump intensity, wavelength and crystal orientation. For infrared excitation, ZGP emission exceeds that of GaAs and GaP.