B. Time-resolved Raman Spectroscopy and Fourier Transform Raman Spectroscopy
- Although transient optical absorption is a powerful technique to study
the molecular dynamic processes, it does not provide information regarding
the structure of the intermediates. Vibration spectroscopy is a very
powerful tool to achieve this goal. This can be studied by either time
resolved Raman techniques (TRR) or time-resolved infrared spectroscopy.
Even for molecules with very broad electronic transitions, the Raman
spectrum, which gives the vibrational frequencies of short-lived
transients, can be relatively sharp.
- Our ps OPO's pumped by the CPA-1000 regenerative amplifier are versatile, tunable Raman excitation sources. The Raman signal is detected by a liquid nitrogen cooled CCD detector which is mounted on a spectrograph. This system provides stray light rejection and thus enables us to detect Raman signals of less than 200 cm-1 from the excitation wavelength. The pump and probe wavelengths can be tuned independently from 240 nm to 1000 nm with energies between a few microJ to 100 microJ. Time delays may be varied from 1 ps to tens of nanoseconds. This picosecond OPA system provides a spectral resolution of ~30 - 40 cm-1. When the nanosecond MOPO 730 and the PDL-1/DCR-1 lasers are used, the time resolution of the time-resolved Raman can be extended to a range of 10 ns to tens of milliseconds.
- The advantage of resonance Raman spectroscopy is that it enables us to study the changes in the vibration spectra of the chromophores in biological systems without the interference of the more dense vibrations of the surrounding protein residues. This is done by using Raman excitation wavelengths in the absorption region of the chromophore and away from that of the protein residues.
For Fourier Transform Raman spectroscopy, there is a Nicolet 860 FT Raman Module which allows us to acquire Stokes and anti-Stokes steady-state Raman spectra with the high sensitivity that is characteristic of interferrometric detection methods. The excitation source is 1064 nm light from a Nd:YAG laser incorporated in the commercial unit. One application of this technique is the measurement of surface enhanced Raman spectra (SERS) of molecules adsorbed on gold nanoparticle aggregates
- Our ps OPO's pumped by the CPA-1000 regenerative amplifier are versatile, tunable Raman excitation sources. The Raman signal is detected by a liquid nitrogen cooled CCD detector which is mounted on a spectrograph. This system provides stray light rejection and thus enables us to detect Raman signals of less than 200 cm-1 from the excitation wavelength. The pump and probe wavelengths can be tuned independently from 240 nm to 1000 nm with energies between a few microJ to 100 microJ. Time delays may be varied from 1 ps to tens of nanoseconds. This picosecond OPA system provides a spectral resolution of ~30 - 40 cm-1. When the nanosecond MOPO 730 and the PDL-1/DCR-1 lasers are used, the time resolution of the time-resolved Raman can be extended to a range of 10 ns to tens of milliseconds.
Other
Facilities