Spectral transmittance measurement nonlinearity of a (280-540) nm spectrophotometer based on a tunable femtosecond pulse laser

Femtosecond pulses tunable in (280-540) nm were generated via second and third harmonic generation processes from a Ti:Sapphire femtosecond laser with a 80 MHz pulse repetition rate. The temporal widths of the pulses are ~200 fs and the spectral bandwidths are <10 nm. These pulses can be used for spectral transmittance measurement using an integrating sphere photodetector with less than 0.1% fluorescence effect. The spectral transmittance measurement nonlinearity of the femtosecond pulse laser spectrophotometer was characterized using a double-path scheme for the incident power level from 1 mW to 10 μW. The nonlinearity results were compared with those obtained using a 532 nm continuous wave laser at similar power levels. The spectrophotometer can be well applied for the spectral transmittance measurement of a wide variety of neutral optical materials after nonlinearity corrections.