Applications

FSRS dynamics of neoxanthin using Harpia-TA with Harpia-TB module. Measurement conditions: 25 kHz repetition rate, 440 nm actinic pump wavelength, 200 nJ pulse energy, 530 nm Raman pump wavelength, 300 nJ pulse energy.

Femtosecond stimulated Raman spectroscopy (FSRS) is a relatively recent yet moderately widespread time-resolved spectroscopy technique for observing changes in the vibrational structure of optically excited molecular systems.

At its core, FSRS is a multi-pulse technique that can be summarized as follows. First, an ultrashort actinic pump pulse acts on a molecular system in its ground state and initiates the photoreaction. Then, a pair of temporally delayed pulses probes the successive photoevolution. Here, a picosecond Raman pump and broadband femtosecond Raman probe pulse are used. The temporal overlap of these two pulses brings coherence in the excited state, resulting in the amplification of the Stokes and anti-Stokes frequencies within the probe field, i.e., stimulated Raman emission. Since a high degree of coherence is achieved only during the short temporal overlap of the Raman pump and probe pulses, FSRS spectroscopy offers a high resolution in both spectral and temporal domains.

FSRS is readily available in the HARPIA spectroscopy system, providing vibrational structural information with < 200 fs temporal and < 10 cm^-1 spectral resolution. Raman pump can be generated using SHBC, if a fixed-wavelength output at 515 nm is sufficient, or SHBC together with ORPHEUS-PS, if a wide tuning range is desired. The system is pumped by a PHAROS femtosecond laser.