Transient Absorption Spectroscopy
Spectral dynamics of β-carotene in solution, acquired using the HARPIA-TA transient absorption spectrometer.
Measurement conditions: 100 kHz repetition rate, 490 nm pump wavelength, < 10 nJ pump pulse energy, 13 s per spectrum (per delay point) acquisition time.
Pump-dump-probe dynamics of DCM laser dye, acquired using the HARPIA-TB third beam delivery module, with the dump pulse resonant to the emission band of DCM.
Measurement conditions: 50 kHz repetition rate, 515 nm pump wavelength, 700 nm dump wavelength, 21 ps dump delay, 90 nJ pump pulse energy, 190 nJ dump pulse energy.
The transient absorption (TA) experiment allows quantitative characterization of time-dependent absorption of an optically excited sample. It requires two light pulses: a femtosecond narrow-bandwidth pump pulse to excite the sample and a delayed broad-bandwidth probe pulse to measure changes in sample transmittance. The resulting difference absorption signal is measured as a function of probe wavelength and the temporal delay between the pump and probe pulses.
The transient absorption spectrum is much more elaborate than, e.g., a steady-state absorption or fluorescence decay spectrum. It provides information not only on the excited states of the system but also on all the intermediate evolutionary transients and non-emissive states in both the ground and excited states.
In HARPIA-TA, the transient absorption experiment can be easily customized to gain additional insight into ultrafast dynamics of photoactive systems. For example, measuring transient reflection instead of absorption provides more details on material surface photodynamics. Performing pump intensity-resolved absorption helps estimate the annihilation and saturation processes. Carrying the transient absorption experiments with different linear or circular pump pulse polarizations allows obtaining molecular aggregation properties or molecular-level chirality-dependent spectra.
When transient spectroscopy is not enough, the HARPIA-TA spectrometer can be expanded to perform time-resolved multi‑pulse and fluorescence spectroscopies using HARPIA-TB and HARPIA-TF modules, respectively.
