When standard spectroscopy tools are not enough to unravel the intricate ultrafast dynamics of photoactive systems, multi-pulse time-resolved spectroscopic techniques can be utilized to yield additional insight. Light Conversion's HARPIA‑TB is a third beam delivery module for the HARPIA‑TA mainframe system that adds an additional dimension to typical time resolved absorption measurements. A temporally delayed auxiliary (third) laser pulse, (up to 4 ns), can be introduced before or during the pump-probe interaction to perturb the on-going pump-induced photodynamics.
An auxiliary pulse resonant to a stimulated emission transition band can deliberately depopulate the excited state species and thereby revert the excited system back to the ground state potential energy surface. This type of experiment is usually referred ad pump-dump-probe (PDP).
When the wavelength of the third pulse corresponds to an induced absorption resonance, the pulse is thus able to elevate the system to a higher excited state (that may or may not be detectable in the standard photoevolution) or return it to an earlier evolutionary transient. This type of measurement is typically referred as pump-repump-probe (PrPP).
When the auxiliary pulse is resonant to an electronic ground-to-excited state transition, it makes it possible to either “replenish” the excited state population or to prepare a small portion of excited state population before the “main” pump pulse. This type of measurement is typically referred as prepump-pump-probe (pPPP).
Since both probe and the auxiliary pulse can be delayed in time in respect to one another, both kinetic trace and action trace experiments can be performed with a HARPIA‑TB setup. In other words, we can obtain either the information on how a perturbation disturbs the standard photodynamic behavior of the investigated system (when the probe pulse is propagated in time), or we can monitor how the exact timing of perturbation influences the transient absorption spectrum at a fixed evolutionary phase system (when the auxiliary pulse is propagated in time).
Moreover, HARPIA‑TB can be utilized to deliver frequency-narrowed (i.e., picosecond) pulses, thus providing the capability to perform time-resolved femtosecond stimulated Raman scattering (FSRS) spectroscopic measurements.
MODES
- FEMTOSECOND STIMULATED RAMAN SCATTERING (FSRS)
Delivering frequency-narrowed ps pulses allows to perform FSRS measurements. It is a relatively recent yet moderately widespread time-resolved spectroscopy technique for observing changes in the vibrational structure of optically excited molecular systems. - MULTI-PULSE TIME-RESOLVED TRANSIENT ABSORPTION
Multi-pulse time-resolved spectroscopic techniques are a way to manipulate the reactions and access new regions of the higher excited states. It allows to time a series of pulses to trigger a photoreaction and to perturb it at a certain point of its ongoing evolution. In some cases, it is desirable to use a additional “pump” pulse to re-excite some of the molecules and depending on the delay between several pump pulses, the excitation might change the outcome of the reaction. - NIR PROBE
An additional narrow-bandwidth or broadband NIR probe option with a 4 ns delay is available, while retaining an 8 ns delay for UV-VIS experiments.
Download the HARPIA datasheet here.
