Raman-induced Kerr Effect Spectroscopy Research Articles

Femtosecond Optical Kerr Effect Studies of Liquid Methyl Iodide

The collective polarizability anisotropy dynamics of liquid methyl iodide at room temperature and ambient pressure was studied by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 45 fs laser pulses. The OHD-RIKES data are analyzed by using both the model-dependent approach, which assumes four distinct temporal responses, and the model-independent Fourier transform approach, which generates a spectral density. Near zero time, the OHD-RIKES transient is dominated by the instantaneous electronic response. The short-time nuclear response is characterized by two components. The first component is interpreted as arising from an inhomogeneously broadened (fwhm ≈ 62 cm-1) underdamped intermolecular vibrational mode with a mean frequency of ∼60 cm-1. The second component is an intermediate quasi-exponential response with a 1/e time constant of ∼200 fs. At longer times, the OHD-RIKES transient decays exponentially with a 1/e time constant of 1.76 ± 0.05 ps, which corresponds to the collective reorientation time of CH3I. The spectral density peaks at ∼24 cm-1 and has a fwhm of ∼80 cm-1. The spectral density can be well fitted by an ohmic distribution function with ωc ≈ 30 cm-1. The spectral density obtained from the OHD-RIKES data is consistent with previously measured depolarized Rayleigh scattering and low-frequency far infrared absorption spectra for liquid CH3I.

Structure and dynamics of molecular liquids investigated by optical-heterodyne detected Raman-induced Kerr effect spectroscopy (OHD-RIKES)

Experimental femtosecond OHD-RIKES results of benzene, 1,4-cyclo-hexadiene, 1,5-cyclo-octadiene, benzonitrile, and o-methylbenzonitrile are reported. The goal of these experiments is to elucidate the structure and dynamics of aromatic liquids and to understand the underlying intermolecular forces. The experimental results are discussed in light of recent advances in theory and experiment that have contributed to our current understanding of the aromatic-aromatic intermolecular forces.

Transient Grating Optical Heterodyne Detected Impulsive Stimulated Raman Scattering in Simple Liquids

The real and imaginary parts of individual tensor elements of the nonresonant third-order nonlinear optical susceptibility of simple liquids, carbon tetrachloride and benzene, have been characterized for the first time by transient grating optical heterodyne detected impulsive stimulated Raman scattering (TG-OHD-ISRS). Optical heterodyning is achieved through additional scattering induced by a thermal grating. Vibrational modes to 1000 cm-l are impulsively prepared and probed using 15 fs laser pulses. This technique allows for a precise determination of frequencies and dephasing times of intramolecular Raman-active vibrations. It is shown that the symmetry of these modes defines the measured phase of the oscillatory modulations of the various linearly detected tensor components of ~(~)(t). Advantages to conventional techniques, such as optical heterodyne detected Raman induced Kerr effect spectroscopy or homodyne detected impulsive stimulated Raman scattering, are demonstrated. Further detection of the real or imaginary part of the susceptibilities using phase locked femtosecond optical pulses is discussed.

Deuterium Isotope Effects on the Ultrafast Solvent Relaxation of Formamide and N,N-Dimethylformamide

We present the results of our study on the ultrafast solvent dynamics of the amides formamide (FA), N-dimethylformamide (DMF), and their deuterated analogs HCOND[sub 2] (d[sub 2]-FA) and DCON(CD[sub 3])[sub 2] (d[sub 7]-DMF) us femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). As nearly transform-limited 50 fs optical pulses and the Fourier-transform relationship, we have studied liquid dynamics in the frequency range from 0.6 to 400 cm[sup [minus]1]. In comparison to the depolarized Rayle spectroscopy technique. OHD-RIKES is shown to provide more accurate and detailed information about low-frequency region that includes the rotational reorientation, librational and collision-induced dynamic. The effect of deuterium isotope substitution on the inertial as well as diffusive reorientational dynamics these amide liquids is discussed. 91 refs., 9 figs., 4 tabs.

Femtosecond Fourier-transform spectroscopy of low-frequency intermolecular motions in weakly interacting liquids

We present new results on the temperature-dependent collision-induced low-frequency Raman spectrum of the spherical top molecule CCl4, obtained using optical-heterodyne-detected, femtosecond Fourier-transform Raman-induced Kerr-effect spectroscopy. A spectral shift to lower frequencies with increasing temperatures has been observed.

Fast responses from ‘‘slowly relaxing’’ liquids: A comparative study of the femtosecond dynamics of triacetin, ethylene glycol, and water

We have measured the ultrafast solvent relaxation of liquid ethylene glycol, triacetin, and water by means of femtosecond polarization spectroscopy, using optical-heterodyne-detected Raman-induced Kerr-effect spectroscopy. In the viscous liquids triacetin and ethylene glycol, femtosecond relaxation processes were resolved. Not surprisingly, the femtosecond nonlinear optical response of ethylene glycol is quite similar to that of water. Using the theory of Maroncelli, Kumar, and Papazyan, we transform the pure-nuclear solvent response into a dipolar-solvation correlation function for comparison with ultrafast electron-transfer reaction rates.

Techniques for measuring small changes in the intensity of a pulsed laser

Several techniques are described that compensate for the pulse-to-pulse laser fluctuations that occur when small absorption or gain measurements are taken with pulsed lasers. The best approach tested used two matched diodes that were mounted in a bridge circuit with their bias batteries. One diode was illuminated by a single beam, and a second was illuminated by a reference beam. The bridge circuit output forms the difference in the two laser intensities. Using pulsed lasers with 8-ns widths, we observed that the error in subtraction was 0.01% of the pulse area. This was only 1.5 times the shot noise of the pulses. The technique is examined for application to Raman-induced Kerr-effect spectroscopy, in which difficulties arise because of the use of polarization-sensitive detection.

The Design of an Effective “Fluorescence Filter” for Raman Spectroscopy

Since Raman scattering is inherently an inefficient process, a practical obstacle to Raman studies is interference from fluorescence. Troublesome can arise either from impurities or from the intrinsic relaxation process resulting from an electronic absorption of the sample in resonance Raman spectroscopy. To avoid the interference it is sometimes possible to choose different excitation wavelengths. In the case of resonance Raman spectroscopy, the sample can be excited to a highly electronically excited state (Sn, n > 2) in the condensed phase. Thus, Raman signals can be obtained on the high-frequency side with respect to the fluorescence. In some special cases addition of an external quenching agent, (e.g., iodide ion) to the sample is helpful, but this method usually cannot effectively eliminate the fluorescence. Furthermore, a high concentration of added iodide ion may result in a significant distortion of the molecular structure investigated. For molecules with relatively long-lived emission (>100 ns) a practical method to suppress is through time discrimination. Unfortunately, the processes which obscure Raman spectra frequently have lifetimes in the nanosecond range, while the electronic gating system is limited to several nanoseconds. Knowing that the ratio of to Raman signal could frequently be greater than 100:1, the application of an electronic gating system to efficiently discriminate Raman signals from interference is not possible. Several other techniques using nonlinear processes such as coherent anti-Stokes Raman spectroscopy (CARS), Raman-induced Kerr effect spectroscopy, and inverse Raman spectroscopy, as well as recently developed near-infrared-red FT Raman and CCD detection of diode-laser-excited Raman scattering, have also been applied in an attempt to overcome fluorescence. Although it seems that CARS may offer a high potential for eliminating fluorescence, the nonresonant background solvent susceptibility usually results in complications in the interpretation of CARS spectra. Thus, there is still no general and effective method to overcome interfering at the present time. In this report, an effective method using a transient absorption gating technique is demonstrated to suppress interfering with a relatively long lifetime. Consequently, a general fluorescence filter design based on a picosecond system is proposed.

Multiplexed optically heterodyned Raman-induced Kerr-effect spectroscopy in the blue

The technique of multiplexed optically heterodyned Raman-induced Kerr-effect spectroscopy is extended to the blue at 378 nm. Despite both weaker probe and pump lasers than in our previous research in the visible [Chem. Phys. Lett. 168, 579 (1990)], it is possible to obtain spectra with a good signal-to-noise ratio from simple solvents, demonstrating the feasibility of the technique in the blue and ultraviolet.

Optically heterodyned Raman-induced Kerr-effect spectroscopy using a white-light continuum

A multiplexed form of optically heterodyned Raman-induced Kerr-effect (OHRIKE) spectroscopy has been developed using a picosecond white-light continuum and multichannel detection. This development provides a dramatic reduction in the time needed to collect adequate signal; and examples of Raman spectra obtained using this technique in highly fluorescent environments are provided.

The third-order Raman spectrum of argon pairs

The third-order susceptibility of binary complexes of argon atoms, and hence the associated Raman spectra of bound pairs Ar2 (‘van der Waals molecule’), and of free pairs Ar-Ar in collisional interaction (‘collision-induced Raman spectra’), which are inseparable in an actual measurement, are computed. The computations show that optical heterodyne Raman induced Kerr effect spectroscopy OHD-RIKES) offers sufficient sensitivity to obtain well-resolved rotational dimer spectra even at temperatures as high as 300 K.

Raman induced Kerr effect spectroscopy using pulsed lasers

We examine the sensitivity of a coherent Raman spectrometer measuring optically heterodyned Raman induced Kerr effect spectra (OHD-RIKES) with pulsed lasers. Theoretically we show that an optimum OHD RIKES spectrometer is 10 3 more sensitive than quasi-cw stimulated Raman gain spectroscopy (SRGS). Experimental tests of OHD-RIKES using a pulsed probe laser confirm the estimated signal-to-noise ratios. With higher power lasers this technique will provide sufficient sensitivities to detect particle densities as low as 10 11 cm -3.

Femtosecond Raman-induced Kerr effect. Temporal evolution of the vibrational normal modes in halogenated methanes

We report a direct observation of the temporal evolution of coherently excited intramolecular normal-mode vibrations in chloroform and carbon tetrachloride using a time-resolved analog of optically heterodyned Raman-induced Kerr effect spectroscopy (OHD RIKES). The observed tetraherz oscillations are well described in terms of independently evolving harmonic oscillators driven through a stimulated Raman process involving the different Fourier components of the 75 fs laser pulse.

Raman Cross Section of the CH4 ν1 Line in the UV Region Determined with Raman-Induced Kerr Effect Spectroscopy

The absolute Raman cross section of the methane ν1 line at 266 nm has been determined to be (6.2±1.5)×10-33 m2/(mol·sr) with Raman-induced Kerr effect spectroscopy. The use of polarization detection is effective in improving the signal-to-noise ratio in a measurement using two pulsed lasers with a relatively large shot-to-shot fluctuation.

Nonlinear Raman Spectroscopy of Gases

The field of Raman spectroscopy has enjoyed two periods of rejuvenation in the last 25 years. The first came with the discovery of the laser in 1960, a source that provided a dramatic increase in photon density at a scattering site and hence greatly improved spontaneous Raman spectra of liquids, solids, and gases. It was realized early that further gains could be obtained by nonlinear sample mixing of several optical fields, and the observation of coherent anti-Stokes Raman scattering (CARS) was first reported by Maker & Terhune in 1965 (1). Application to gas phase studies followed shortly thereafter (2, 3), but the real impetus for the second rebirth came in 1973 with the pioneering experiments of Taran and co-workers on combustion systems (4) and with the subsequent commercial development of pulsed Nd: Y AG and tunable dye lasers of high power and narrow bandwidth. The last decade has seen a remarkable growth in the number of applications of such sources to the study of molecular and physical properties. More than 2000 papers related to coherent Raman techniques have been published in the last 10 years and, of necessity, this review is restricted to applications to gas phase systems. At present, coherent Raman spectra have been obtained at gas pressures less than a few microbar, at temperatures ranging from a few degrees Kelvin to 3600 K, and at a resolution better than 0.001 cm -1. In addition to CARS, a number of other forms of coherent Raman probing have evolved. These include stimulated Raman gain (SRG) and loss (SRL) spectroscopy, photoacoustic Raman spectroscopy (PARS), Raman-induced Kerr effect spectroscopy (RIKES), and polarization and other variants of these. Recently, studies have been extended from the

Diagnostics of water basins by Raman-induced Kerr effect spectroscopy

An investigation was made of the possibility of using Raman-induced Kerr effect spectroscopy for diagnostics of water basins. It is reported that temperatures can be deduced from deformation of the band of valence vibrations of water and that small amounts of water-dissolved hydrocarbons can be detected and identified using the lines of the C–H valence vibrations in the range 2800–3000 cm−1 .

Four-photon Raman spectroscopy using elastic scattering of pump waves

It is shown experimentally for the first time that the Raman-induced Kerr effect spectroscopy can be used in a remote measurement system when the probe wave is formed in the medium under study as a result of Rayleigh and Mie scattering of one of the pump waves. The panoramic spectrum of a strong Raman band of ethanol was obtained in the 3000–2800 cm−1 range.

Feasibility of remote diagnostics of the atmosphere by Raman-induced Kerr effect spectroscopy

The method of Raman-induced Kerr effect spectroscopy was used to record spectra of the band and a panoramic spectrum including O, , and S bands of atmospheric nitrogen with a resolution of 0.1 cm ?1 at 293 K under normal pressure. Ways of utilizing this method for remote diagnostics of the atmosphere are considered.

Single-Pulse Coherent Raman Spectroscopy in Shock-Compressed Benzene

ABSTRACTSingle-pulse backwards stimulated Raman and reflected broadband coherent anti-Stokes Raman spectroscopy (BSRS and RBBCARS) have been used to measure the vibrational frequency shifts of the 992 cm−1 ring-stretching mode of liquid benzene shock-compressed to pressures up to 1.2 GPa. The resulting shifts of ∼7.5 cm−1/GPa in the dynamic experiments are compared to spontaneous Raman scattering measurements of heated samples compressed in a diamond-anvil cell. RBBCARS was used to simultaneously measure the ring-stretching mode vibrational frequencies of liquid benzene / liquid perdeuterobenzene mixtures shock-compressed to pressures up to 1.53 GPa. Additional experiments that demonstrate the difficulty of using polarization sensitive coherent Raman techniques, such as Raman-induced Kerr effect spectroscopy (RIKES), in shock-compressed samples are described.

Coherent raman spectroscopy

A review of the salient features of five coherent Raman techniques is given, including typical spectra produced by each technique. The resonant and nonresonant signal contributions in the monochromatic plane wave limit are calculated for: (1) Coherent AntiStokes Raman Spectroscopy(CARS); (2) a polarization technique referred to as ASTERISK; (3) Raman-induced Kerr-effect Spectroscopy(RIKES); (4) Optically Heterodyned RIKES (OHD-RIKES); (5) Stimulated Raman Spectroscopy (SRS). The relevant noise contribution to each of these techniques is developed within the framework of a comparative signal-to-noise analysis, and realistic detection limits are discussed. The OHD-RIKES technique is selected as the most viable of the coherent Raman techniques which satisfies the following criteria: (A) suppression of nonresonant background signals and enhanced signal-to-noise ratio; (b) simplicity of operation and interpretation of results. This is the first known application of optical heterodyne detection and optimization to coherent Raman spectroscopy, and the principles developed are generally applicable to all forms of third-order nonlinear spectroscopu.