Transient absorption spectroscopy is an effective method for characterizing excited states of molecules. Also called laser flash photolysis or pump-probe experiments, transient absorption relies on quickly populating the excited state followed by probing the excited state. In order to obtain an “instantaneous” population of excited states within a sample, a laser source is generally used. Detection of the excited state is commonly performed by a xenon lamp. Measurements are recorded by a PMT or CCD camera detector connected to a personal computer. Additionally, time-resolved measurements are possible, allowing for kinetic data of the excited states to be resolved.
Shematic of a transient absorption apparatus in our lab. Excitation is provided by a laser and optional OPO shown by the blue path. Probing is achieved with a xenon lamp shown by the red path. The probe path is split using beam splitters to provide simultaneous collection of a reference (black path). A spectrograph and intensified CCD camera connected to a personal computer collect and record the data.
Schematic of a nonlinear absorption apparatus. The output of an OPO pumped by a Nd:YAG laser is focused through the sample, and then collected by a detector. Neutral density filters help attenuate the intensity of the incident light. A beam splitter is used to direct light to a reference detector. The output of the detectors is collected and displayed by a personal computer for instant analysis.