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We demonstrate a novel use of the pump-probe thermal lens spectroscopy and Z-scan techniques for the measurement of the small absorption coefficient in a semiorganic, nonlinear optical crystal zinc (tris) thiourea sulphate. We measure the absorption spectrum and the absolute values of the absorption of the crystal in the near-infrared region (700–980 nm). A maximum absorption coefficient of ∼0.04 cm-1 is reported.

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We report on a detailed study of laser damage in a semiorganic nonlinear optical crystal, zinc (tris) thiourea sulfate using eight nanosecond laser pulses with a repetition rate of 10 Hz at wavelengths of 532 and 1064 nm. The damage morphology shows a correlation with the mechanical hardness anisotropy. The crystal shows a damage threshold measured to be 0.6±0.1 GW/cm2 for a single 532 nm laser pulse which reduces to 0.12±0.01 GW/cm2 as the number of shots is increased to 10 000. Single shot laser damage at 1064 nm wavelength shows an onset estimated to be about 3 GW/cm2. Multiple shots at 1064 nm result in laser ablation hindering the determination of a damage threshold. We suggest a possible role of negative thermal effects resulting in the high damage threshold observed in this crystal.