Development of a broadband picosecond infrared spectrometer and its incorporation into an existing ultrafast time-resolved resonance Raman, UV/visible, and fluorescence spectroscopic apparatus

We have constructed a broadband ultrafast time-resolved infrared (TRIR) spectrometer and incorporated it into our existing time-resolved spectroscopy apparatus, thus creating a single instrument capable of performing the complementary techniques of femto-/picosecond time-resolved resonance Raman (TR³), fluorescence, and UV/visible/infrared transient absorption spectroscopy. The TRIR spectrometer employs broadband (150 fs, ∼150 cm^-1 FWHM) mid-infrared probe and reference pulses (generated by difference frequency mixing of near-infrared pulses in type I AgGaS₂), which are dispersed over two 64-element linear infrared array detectors (HgCdTe). These are coupled via custom-built data acquisition electronics to a personal computer for data processing. This data acquisition system performs signal handling on a shot-by-shot basis at the 1 kHz repetition rate of the pulsed laser system. The combination of real-time signal processing and the ability to normalize each probe and reference pulse has enabled us to achieve a high sensitivity on the order of ΔOD ∼ 10^-4-10^-5 with 1 min of acquisition time. We present preliminary picosecond TRIR studies using this spectrometer and also demonstrate how a combination of TRIR and TR³ spectroscopy can provide key information for the full elucidation of a photochemical process.