Construction of picosecond time‐resolved Raman spectrometers with near‐infrared excitation

Abstract

We have constructed two types of picosecond time-resolved Raman spectrometers with near-infrared excitation. One system is based on a step-scan Fourier transform (FT) interferometer equipped with a Ge detector, and the other system is based on a dispersive spectrometer equipped with an InGaAs array detector. For the former system with pulsed Raman excitation, we have developed a new method of signal processing. This method does not require synchronization among laser pulses for Raman excitation, the stepping of the step-scan interferometer, and the sampling of the analog-to-digital converter. In spite of large fluctuation in the probe-pulse energy, the ordinary FT-Raman spectra of samples in the ground electronic state can be obtained with satisfactory signal-to-noise ratios by the former system. By the latter system, picosecond transient Raman spectra have been obtained from the first excited singlet (S 1 ) state of 9-phenylanthracene and the second excited singlet (S 2 ) state of all-trans-b-carotene by using 388-nm light for photoexcitation and 1064-nm light for Raman excitation.

Picosecond near-infrared excited transient Raman spectra of β-carotene in the excited S2 state: Solvent effects on the in-phase CC stretching band and vibronic coupling

“…[25] was used for picosecond time-resolved Raman measurements with near-infrared excitation. The 1064-nm light (repetition rate 1 kHz, pulse energy 12 lJ) from a picosecond optical parametric generator and amplifier (Quantronix TOPAS) excited by the fundamental output (wavelength 775 nm, pulse energy 800 lJ, pulse width 2.1 ps, spectral resolution 8 cm À1 , repetition rate 1 kHz) from a picosecond Ti:sapphire regenerative amplifier (Clark-MXR CPA-2000P) was used to probe the Raman scattering from the excited sample by the pump-probe technique.…”

β‐Carotene Revisited by Transient Absorption and Stimulated Raman Spectroscopy

“…[7,30,33,34] Mathies and coworkers described broad S 2 bands centered at 1100, 1300, and 1650 cm À1 that decay with the electronic lifetimeo fS 2 , [33] but we cannot reproduce their result. The difficulty lies in the populationbackground BG that rises on apst ime scale and mustbeestimated accurately,s ot hat its subtraction reveals the coherents ignal.…”

“…Corresponding results from the literature are still at variance. [7,30,33,34] In this work we re-examine bcarotene in solution with broadband transient absorption and stimulated Raman spectroscopy. The precision and accuracy of our measurements allows us to recognize and quantify hitherto unresolved aspects of the spectral evolution of b-carotene.…”

Raman spectroscopy at the beginning of the twenty‐first century

“…This approach is an extremely useful addition or alternative to the literature on time-resolved Raman methodologies. The paper by Sakamoto et al 56 describes recent developments in the field of picosecond time-resolved Raman spectroscopy. The authors focus on Raman excitation in the near-infrared spectral region and describe two methods of collecting time-resolved Raman spectra.…”