Stimulated Raman Scatterings

If the incident laser intensity II becomes very large, an appreciable fraction of the molecules in the initial state Ej is excited into the final state E and the intensity of the Raman-scattered light is correspondingly large. Under these conditions we have to consider the simultaneous interaction of the molecules with two EM waves the laser wave at the frequency Wl and the Stokes wave at the frequency Wg = or the anti-Stokes wave at = 

The Raman medium is taken as consisting of N harmonic oscillators per unit volume, which are independent of each other. Due to the combined action of the incident laser wave and the Stokes wave the oscillators experience a driving force F which depends on the total field amplitude E 

The equation of motion for a driven oscillator with mass m and vibrational eigenfrequency Wy is then 

Comparison of the time-dependent terms on both sides of (8.20) shows that w = WL-Wg. The molecular vibrations are therefore driven at the difference frequency WL-Wg. Solving (8.20) for qy yields 

Inserting q from (8.19,21) and E from (8.15) yields the nonlinear polarization 

The force F = - grad Wpot acting on the molecule gives 

The equation of motion for the molecular oscillator with oscillation amplitude q, mass m, and vibrational eigenfrequency wv is then 

If the incident laser intensity becomes very large, an appreciable fraction of the molecules in the initial state E. is excited into the final state 

The force acting on the molecule is F = which gives, according to 

Comparison of the time-dependent terms on both sides of (9.17) shows that dec 

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Pausch R, Held M, Chen T, Schwoerer H and Kiefer W 2000 Quantum control by stimulated Raman scattering J. Raman Spectrosc. 31 7... 

Unlike the typical laser source, the zero-point blackbody field is spectrally white , providing all colours, CO2, that seek out all co - CO2 = coj resonances available in a given sample. Thus all possible Raman lines can be seen with a single incident source at tOp Such multiplex capability is now found in the Class II spectroscopies where broadband excitation is obtained either by using modeless lasers, or a femtosecond pulse, which on first principles must be spectrally broad [32]. Another distinction between a coherent laser source and the blackbody radiation is that the zero-point field is spatially isotropic. By perfonuing the simple wavevector algebra for SR, we find that the scattered radiation is isotropic as well. This concept of spatial incoherence will be used to explain a certain stimulated Raman scattering event in a subsequent section. 

Laubereau A 1982 Stimulated Raman scattering Non-Linear Raman Spectroscopy and its Chemical Applications ed W Kiefer and D A Long (Dordrecht Reidel)... 

Wang 0-S 1969 Theory of stimulated Raman scattering Phys. Rev. 182 482-94... 

Yan Y X, Gamble E B and Nelson K A 1985 Impulsive stimulated Raman scattering general importance in femtosecond laser pulse interactions with matter, and spectroscopic applications J. Chem. Phys. 83 5391-9... 

Walsh A M and Loring R F 1989 Theory of resonant and nonresonant impulsive stimulated Raman scattering Chem. Phys. Lett. 160 299-304... 

Figure 9.20 (a) Stimulated Raman scattering experiment, (b) Concentric rings observed, in the... 

A light pulse of a center frequency Q impinges on an interface. Raman-active modes of nuclear motion are coherently excited via impulsive stimulated Raman scattering, when the time width of the pulse is shorter than the period of the vibration. The ultrashort light pulse has a finite frequency width related to the Fourier transformation of the time width, according to the energy-time uncertainty relation. 

Figure 4. The sample cell arrangement in the DCSHG experiment, where the sample solution was inserted between two glass slips (lop), and the optical design for the DCSHG dispersion experiment, where the compressed H gas medium was pumped by a tunable pulsed dye laser source for Stokes generation by stimulated Raman scattering (bottom). (E° is the static electric field.) Key beam guiding prisms P, Stokes...

Fig. 2.2. Two generation models of coherent optical phonons, (a), (c), (e) impulsive stimulated Raman scattering (ISRS). (b), (d), (f) displacive excitation of coherent phonons (DECP). Graphs (e) and (f) display the time evolution of the driving force (grey areas) and that of the displacement (solid, curves) for ISRS and DECP, respectively...

Savchenkov, A. A. Matsko, A. B. Mohageg, M. Maleki, L., Ringdown spectroscopy of stimulated Raman scattering in a whispering gallery mode resonator, Opt. Lett. 2007, 32,... 

The technique of stimulated Raman scattering (SRS) has been demonstrated as a practical method for the simultaneous measurement of diameter, number density and constituent material of micrometer-sized droplets. 709 The SRS method is applicable to all Raman active materials and to droplets larger than 8 pm in diameter. Experimental studies were conducted for water and ethanol mono-disperse droplets in the diameter range of 40-90 pm. Results with a single laser pulse and multiple pulses showed that the SRS method can be used to diagnose droplets of mixed liquids and ensembles of polydisperse droplets. 

Raman scattering Infrared absorption Inelastic harmonic light scattering (Hyper-Raman) Neutron inelastic scattering Stimulated Raman scattering... 

J. B. Snow, S.-X. Qian, and R. K. Chang, Stimulated Raman scattering from individual water and ethanol droplets at morphology-dependent resonances, Opt Lett 10, 37-39 (1985). 

J.-Z. Zhang, D. H. Leach, and R. K. Chang, Photon lifetime within a droplet Temporal determination of elastic and stimulated Raman scattering, Opt. Lett. 13, 270-272 (1988). 

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