A tunable femtosecond stimulated Raman scattering system based on spectrally narrowed second harmonic generation

Anotacija

In this work we present a femtosecond stimulated Raman scattering system. The setup is based on a commercial femtosecond laser system supplemented by a pair of travelling-wave optical parametric amplifiers. One of the parametric amplifiers is used to generate the femtosecond actinic pump pulses, whereas the output of the other (high-power) parametric amplifier undergoes a combination of spectrally narrowed second harmonic generation in a long non-linear crystal and subsequent spectral filtering for the generation of narrowband Raman pump pulses. Chirped white light supercontinuum is used as the Raman probe. The setup offers tunability of the Raman pump pulses in the 400–800 nm range, and spectral and temporal resolutions of ca. 6 cm^–1 and ca. 70 fs, respectively. We present the basic technical and optical aspects of the system along with data acquisition and signal retrieval techniques. We characterize the system by exploring the time-resolved vibrational dynamics of the S₂(1¹B_u⁺) and S₁(2¹A_g^–) excited states of β-carotene.