Time-resolved Raman spectroscopy with a tunable ultraviolet kilohertz nanosecond laser

Time-resolved resonance Raman (TR3) spectra are obtained with a pair of Q-s witched Nd:YLF-pumped a:sapphire lasers, generating tunable (810-920 nm) si milar to 20 ns pulses at a 1 kHz repetition rate. Frequency doubling in lit hium berate (LBO) provides blue (405-460 nm) pump and probe pulses, while U V probe pulses, tunable from 205 to 230 mm, can be generated by doubling th e second harmonic in beta-barium berate (BBO), Pump and probe pulse timing are controlled electronically. A timing sequence is implemented in which ex posure of the multichannel detector alternates between positive and negativ e time delays between pump and probe pulses, so that accumulated difference spectra are free of artifacts from spectrograph drift or gradual decomposi tion of the sample. The system was tested on the carbonmonoxy hemoglobin (H bCO) photocycle, for which UV TR3 spectra have previously been reported. Hb CO was pumped at 419 nm, at the maxima of the strong Soret absorption band, and saturation of the photoresponse (maximum deligation) was established b y measuring the intensity ratio of the HbCO and deoxyHb nu(4) porphyrin RR bands, generated with 425 nm probe pulses. UV TR3 difference spectra were o btained at time intervals from 0.06 to 20 mu s using 229 nm probe pulses. T hey are in good agreement with those recorded previously with a pair of 300 Hz excimer-dye lasers, The time required to achieve a comparable signal-to -noise ratio was eight times shorter with the 1 kHz Nd:YLF-Ti:S lasers, Cop yright (C) 1999 John Wiley & Sons, Ltd.