Efficient second-harmonic and terahertz generation from single BiB₃O₆crystal using nanosecond and femtosecond lasers

The paper reports the efficient UV and terahertz generation from a 1.29 mm thick and Type I, θ=28.9^∘ cut BiB₃O₆ (bismuth triborate, BIBO) crystal using femtosecond and nanoseconds laser pulses. We have employed 800 nm wavelength pulses of 50 and 140 fs obtained from a Ti:sapphire laser amplifier and oscillators at 1 kHz and 80 MHz repetition rates, respectively. The conversion efficiency of second-harmonic generation (SHG) was ∼50% while that obtained for terahertz (THz) generations was of the order of 1.85×10^-5%. In addition, LDS-698 dye laser radiation tunable between 650-700 nm was also used as a source for SHG between the 325-350 nm range. The dye laser was pumped by SHG (532 nm) radiation from an electro-optically Q-switched Nd:YAG laser having a pulse repetition rate of 10 Hz and a pulse width of 10 ns. A conversion efficiency of 4.01% was obtained for generation of UV at 343.5 nm. Finally, we have measured the transmission, refractive index, absorbance, and conductivity properties of BIBO crystal in the THz domain. We also ascertained the coherence length, relative permittivity and reflectivity of the crystal.