Michael J. Stimson

Frequency and time resolved coherent Stokes Raman scattering in CS2 using incoherent light

Abstract A frequency and time resolved coherent Stokes Raman scattering signal from CS2( l ) using noisy light (I(2) CSRS) is presented. A broad range of frequencies are simultaneously sampled at each interferometric delay, allowing acquisition times that are at least two orders of magnitude shorter than previous single frequency detected interferometry experiments. Sub-picosecond time resolution of radiation/matter beats called Rabi detuning oscillations is achieved by controlling the relative delay between twin nanosecond broadband pulses.

Theory of coherent Raman scattering with quasi-cw noisy light for a general line shape function

The theory of electronically nonresonant coherent Raman scattering (CRS) with quasi-cw noisy light (I(2) CRS) is developed for a general material response. The (Raman) resonant–resonant and resonant–nonresonant hyperpolarizability contributions to the I(2) CRS signal are interferometrically separable. It is found that, in general, the interferometric decay of each of these terms exposes the Raman line shape function in a different manner. Only for a Lorentzian line is their decay identical. Thus, in principle, I(2) CRS provides a new way to explore the line shape function that is analytically distinct from frequency domain and time domain methods. By way of illustration, the general theory is applied to three common line shapes: Lorentzian (as in the original I(2) CRS theory), Gaussian, and Voigt. The results are shown to be consistent with the principles of factorized time correlation diagram analysis.

Frequency resolved interferometric coherent Raman spectroscopy with incoherent light: Raman frequency shifts, dephasing rate constants, and nonresonant hyperpolarizabilities of mixtures of benzene in hexane

Abstract A newly developed frequency and time resolved coherent anti-Stokes Raman scattering (CARS) technique is used to study properties of the A1g ring breathing mode of benzene in a dilution series of liquid mixtures with n-hexane. Recent advances in the interferometric use of incoherent light in CARS measurements (I(2)CARS) provide excellent precision in the recovered dephasing rate constants, vibrational frequencies, and the ratios of the resonant to non-resonant contributions to the signal. Using this technique we observe a more than two-fold decrease in the dephasing rate constant of the vibration, accompanied by a 0.54 cm−1 increase in the vibrational frequency in the limit of infinite dilution of benzene in n-hexane. These changes in the vibrational spectrum are discussed in terms of the condensed phase dynamics that are responsible. It is also seen how the non-resonant contributions to the signal manifest themselves quantitatively in these frequency and time resolved I(2)CARS measurements.

Time-Frequency ResolvedCoherent Raman ScatteringFrom Molecular Liquidsand Their Mixtures With Quasi-CwNoisy Light: I(2) CRS Spectrograms

It is demonstrated how time-frequency resolved coherent Raman scattering (CRS) signals generated by broadband, non-transform limited, quasi-cw (noisy) light can be sensitive probes of molecular vibrational dynamics. The coherent Raman scattering signals from molecular liquids and their mixtures with noisy light are dispersed onto a CCD array and probed interferometrically to produce time-frequency domain spectrograms. These spectrograms offer an extensive oversampling of the data resulting in improved precision of measured parameters over previous noisy light methods. This technique has been very useful in measuring small changes in material parameters, such as Raman frequency shifts and linewidth changes, in dilution series with Raman inactive diluents. Very recently theory and experiment have extended to include mixtures with multiple Raman resonances. Several examples of experiments are presented and discussed.

High-contrast interferometry based on anti-Stokes stimulated Raman scattering with broadband and narrow-band quasi-continuous-wave laser light.

Two versions of an anti-Stokes stimulated Raman scattering (SRS) experiment are presented, one with narrow-band light, the other with broadband light. The interferograms exhibit, at optical periods, alternation between complete signal extinction and high signal intensity with much higher contrast than seen in ordinary linear interferometry. Furthermore, for broadband excitation, the envelope of the high-contrast SRS interferogram is limited to an ultrashort time period. Possible applications of such signals for use as switches or logic gates are discussed.