Femtosecond white-light continuum for characterization of organic molecules

Summary form only given. Measurements of the nonlinear absorption spectra and the dispersion of the nonlinear refraction are of interest in modeling nonlinear optical materials and determination of structure/properties relations. In the past, most of these experiments were performed at a single wavelength. Tuning over a broad spectral region can provide with a comprehensive information but, often times, one has to perform calibration of the experiment at each wavelength. An alternative is to use a white-light continuum produced by focusing short pulsed lasers into suitable media (e.g. sapphire) and using a pump-probe geometry where the probe is the continuum and the pump is an intense pulse that induces the nonlinearity. We have developed a femtosecond continuum spectrometer to measure nondegenerate spectra from 300 nm in the UV to 1.7 /spl mu/m in the IR. The pump beam is the output of a regeneratively amplified fiber ring oscillator at 775 nm or the output of a subsequent optical parametric generator/amplifier producing wavelengths from 500 nm to 1650 nm. The continuum is produced by focusing /spl sim/2 /spl mu/J of different frequencies from these two sources. Dual diode arrays for the IR and visible are used to measure the spectral changes in the transmittance against a reference beam. The spectra can be obtained as a function of time delay between pump and probe pulses. This method is applied for measuring nonlinear absorption spectra of organic materials.