Compact laser flash photolysis techniques compatible with ultrafast pump-probe setups

Two new transient absorption measurement techniques are described which use commercially available pulsed laser diodes or high-power light-emitting diodes (LEDs) as monitoring beam. The semiconductor devices substitute the probe in a kilohertz-repetition-rate ultrafast pump-probe setup. A fully functional and highly compact laser flash photolysis system reaching the nanosecond to millisecond time scale is thereby added to a state-of-the-art femtosecond system.

The sample is excited with UV-Vis tunable femtosecond pulses, and for the electronically synchronized probing light either subnanosecond pulsed laser diodes for selected wavelengths or LEDs covering the visible to near infrared and UV regions are used. The applicability and reliability of the devices are demonstrated for various probe wavelengths in the visible by the investigation of excited-state decay or photoinduced bimolecular reactions.

The time resolution is found to be 400 ps for the pulsed laser diodes and a few nanoseconds for the LEDs. This provides overlap to the accessible time range of the ultrafast pump-probe experiment. In this way full reaction cycles of photo-physical or -chemical processes can be monitored with identical excitation conditions.