Layout of the femtosecond-millisecond spectrometer (see text for description): FR is Faraday rotator, PC is Pockels cell, PCF is photonic crystal fiber, and SC is supercontinuum. Pump-probe delays up to 8 ns are generated with a translation stage. For longer delays, ancillary pulses are selected from the oscillator pulse train.
(a) The PCF SC bandwidth increases as seed pulse energy is increased (right to left) and the pulse is compressed from positive chirped (dashed) to transform limit (bold). The coupling efficiency was 0.4 for each spectrum. (b) Comparison of detected spectral amplitude from single pulse SC (dashed) and PCF SC integrated over four pulses (solid). Lower coupling efficiency resulted in sharp spectral features. (c) Comparison of base line noise in difference spectrum for PCF SC averaged for 1 s (green dashed), 10 s (red solid), and 60 s (black bold). The level of SC noise for 1 s dwell is shown with an offset (red dashed).
TA at 470 nm in aqueous PLP (circles) and PLP:KI (triangles) following photoexcitation with 400 nm, 70 fs pulses. The kinetics from 70 fs to 8 ns was probed with a SC generated in by amplified pulses. Kinetics from 10 ns to was probed with SC generated in a PCF by unamplified pulses. A multiexponential fit with time constants 1.3, 5.2, and is shown in green. Inset: comparison of transient spectra in PLP at 7 ns (bold) and 150 ns (circles).
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