White light absorption continuum excitation

The femtosecond transient absorption studies were performed with 387 nm laser pulses (1 khz, 150 fs pulse width) from an amplified Ti Sapphire laser system (Model CPA 2101, Clark-MXR Inc). A NOPA optical parametric converter was used to generate ultrashort tunable visible pulses from the pump pulses. The apparatus is referred to as a two-beam setup, where the pump pulse is used as excitation source for transient species and the delay of the probe pulse is exactly controlled by an optical delay rail. As probe (white light continuum), a small fraction of pulses stemming from the CPA laser system was focused by a 50 mm lens into a 2-mm thick sapphire disc. A schematic representation of the setup is given below in Fig. 7.2. 2.0 mm quartz cuvettes were used for all measurements. 

Differential absorption spectra (DAS) under excitation of high-energy transitions are studied. The pump is done by 15-ps pulses from passively mode-locked Nd YA103 laser (/l=1.08 pm). White-light continuum generated from D2O by a part of 15-ps laser pulse is used as a probe. Fig. 4 demonstrates DAS registered for sample p8 (see Fig. 1). The dots present values of differential absorption obtained from intensity-dependent transmission measurements for this glass at 1.08 pm and 1.54 pm. 

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