Velocity-matched THz generation by optical rectification in the organic nonlinear optical crystal COANP using a Ti:sapphire laser

Optical rectification of sub-picosecond laser pulses in a nonlinear optical crystal is a widely used method to generate broadband THz pulses. The standard crystal used with Ti:sapphire lasers is the inorganic semiconductor ZnTe. This paper demonstrates that the organic hydrogen-bonded crystal 2-cyclooctylamino-5-nitropyridine (COANP) is a more efficient source of THz radiation than ZnTe at the Ti:sapphire laser wavelength of 776 nm. COANP has an element of the nonlinear optical susceptibility tensor for optical rectification chi₃₃₃ which can be used for velocity-matched THz generation using a pump laser wavelength near 800 nm. Refractive index n₃ and absorption coefficient alpha₃ of COANP single crystals are measured using THz time-domain spectroscopy. The peak THz amplitude from COANP exceeds that of ZnTe in both time- and frequency-domain by a factor of 2.5 and 2.1, respectively.