Stimulated Raman loss

This is not the case for stimulated anti-Stokes radiation. There are two sources of polarization for anti-Stokes radiation [17]. The first is analogous to that in figure B1.3.3(b) where the action of the blackbody (- 2) is replaced by the action of a previously produced anti-Stokes wave, with frequency 03. This radiation actually experiences an attenuation since the value of Im x o3 ) is positive (leading to a negative gam coefficient). This is known as the stimulated Raman loss (SRL) spectroscopy [76]. Flowever the second source of anti-Stokes polarization relies on the presence of Stokes radiation [F7]. This anti-Stokes radiation will emerge from the sample in a direction given by the wavevector algebra = 2k - kg. Since the Stokes radiation is... 

Fig. 6.13. A Stimulated Raman loss (SRL) imaging of self-assembled 2.4-pm polystyrene beads in water recorded at a Raman shift of 2904 cm-1. B Measured SRL spectrum (filled circles) when focused on a single bead. Both the aliphatic symmetric vs (CH2) and antisymmetric /y1K (CH2) Raman modes of polystyrene at 2853cm-1 and 2912 cm-1, respectively, are resolved, directly reproducing the spontaneous Raman spectrum (solid line) of bulk polystyrene (Adapted from Nandaku-mar et al. [13].)...

Fig. 6.15. Multiplex stimulated Raman loss microspectroscopy of 20-pm polystyrene beads dispersed in water. A Raman spectra retrieved from SRL spectra of an individual bead and of bulk water at locations indicated by circles and squares, respectively, in the images. B Reconstructed Raman images of the beads representing the density maps of three characteristic Raman resonances at 1003 cm-1, 2904 cm-1, and 3066 cm-1 of polystyrene (Courtesy of Evelyn Ploetz et al., after [21])...

Pulsed laser-Raman spectroscopy is an attractive candidate for chemical diagnostics of reactions of explosives which take place on a sub-microsecond time scale. Inverse Raman (IRS) or stimulated Raman loss (.1, ) and Raman Induced Kerr Effect (2) Spectroscopies (RIKES) are particularly attractive for singlepulse work on such reactions in condensed phases for the following reasons (1) simplicity of operation, only beam overlap is required (2) no non-resonant interference with the spontaneous spectrum (3) for IRS and some variations of RIKES, the intensity is linear in concentration, pump power, and cross-secti on. 

Figure 3.6-4 Schematic diagram for a few techniques in nonlinear (coherent) Raman spectroscopy (CSRS Coherent Stokes Raman Spectroscopy SRGS Stimulated Raman Gain Spectroscopy IRS Inverse Raman Spectroscopy (= SRLS Stimulated Raman Loss Spectroscopy) CARS Coherent anti-Stokes Raman Spectroscopy PARS Photoacoustic Raman Spectroscopy).

Michele Marrocco, PhD, is a researcher in laser spectroscopy at ENEA (Rome, Italy) (1999 to present). He received his degree in physics from the University of Rome in 1994. He was employed as a postdoctorate at the Max-Planck Institute for Quantum Optics (Munich, Germany), as a researcher at the Quantum Optics Labs at the University of Rome (Rome, Italy), and as an optics researcher by the army. His research activities include traditional and innovative spectroscopic techniques for diagnosis of combustion and nanoscopic systems studied by means of optical microscopy. The techniques used include adsorption, laser induced fluorescence, spontaneous Raman, stimulated Raman gain, stimulated Raman loss, coherent anti-Stokes Raman, degenerate four wave mixing, polarization spectroscopy, laser induced breakdown, laser induced incandescence, laser induced thermal gratings. He has over 30 technical publications. 

Fig. 7 Raman gain = stimulated Raman gain spectroscopy (SRGS), inverse Raman = inverse Raman spectroscopy (IRS) or stimulated Raman loss spectroscopy (SRLS), coherent anti-Stokes Raman spectroscopy (CARS), photoacoustic Raman spectroscopy (PARS), or ionization-detected stimulated Raman spectroscopy (IDSRS). In the following sections, the various methods are briefly described. More detailed information can be found in books [59-61], reviews [45,46,57,58,62,63] and conference reports [64-73].

Other Raman-based forms of nonlinear spectroscopy include stimulated Raman gain (SRG) or stimulated Raman scattering, stimulated Raman loss (SRL) or inverse Raman spectroscopy, and Raman induced Kerr effect spectroscopy (RIKES). Some information on these techniques are provided in Table 1. Many of these other forms do not produce light at wavelengths that are different from the input lasers, do not involve phase matching, and may be susceptible to multiple effects that may interfere with the measurement. Consequently, these techniques have not been as widely used as CARS. 

Stimulated Raman loss or inverse Raman spectroscopy Intensity decrease at (Op... 

Figure 2.5 Schematics of the concepts for (a) ionization-loss stimulated Raman spectroscopy (ILSRS), where resonant two photon ionization of the molecular parent, follows the depletion of ground state reactant species as a result of SRS and (b) VMP, where preexcited molecules are dissociated and the ensuing H photofragments are probed by (2 -I-1) resonantly enhanced multiphoton ionization. Reproduced with permission from Ref. [86]. Copyright (2009) AIP Publishing LLC.

Inverse Raman scattering Inverse Raman scattering (IRS) is a coherent process involving stimulated loss at an anti-Stokes-shifted frequency. The term inverse Raman refers to the fact that, at resonance, the probe radiation is attenuated. In spontaneous Raman spectroscopy, on the other hand radiation at Raman-active frequencies would he generated in the course of the experiment. Inverse Raman scattering (IRS) and stimulated Raman gain (SRG) are closely related. While one involves stimulated gain at an anti-Stokes-shifted frequency, the other involves stimulated loss at a Stokes-shifted frequency. 

The Stokes wave is amplified if the gain g exceeds the losses /. The amplification factor g depends on the square of the laser amplitude Ei and on the term (da/dq). Stimulated Raman scattering is therefore observed only if the incident laser intensity exceeds a threshold value that is determined by the nonlinear term (daij/dq)o in the polarization tensor of the Raman-active normal vibration and by the loss factor / =... 

With a coherent stimulated Raman process (STIRAP) (see Sect. 7.3), nearly the whole initial population Ni may be transferred into the final level If) [1048]. Here no exact resonance with the intermediate excited level ) is wanted in order to avoid transfer losses by spontaneous emission from level ). The population transfer can be explained by an adiabatic passage between dressed states (that is, states of the molecule plus the radiation field) [1049, 1050]. 

Mayorkas N, Malka I, Bar I (2011) Ionization-loss stimulated Raman spectroscopy for conformational probing of flexible molecules. PCCP 13 6808-6815... 

The mechanical or electro-optical modulation of CW lasers applied in these initial experiments was soon superceded by the use of injection-locked pulse-amplified pump lasers in combination with quasi-CW probe lasers [45,80]. When the probe laser has a higher frequency than the pump laser, one obtains a Raman loss or inverse Raman spectrum when the probe laser has the lower frequency, a stimulated Raman gain spectrum is observed by tuning one of the two lasers. Through the pulse amplification of the pump laser, its linewidth is increased over that of a CW laser to between 60 and 100 MHz (0.002 and 0.003 cm ). However, this was at first fully satisfactory, because the resolution in these experiments is largely determined by Doppler and residual pressure broadening. Moreover, the development of injection seeded Nd YAG lasers with smooth pulses has lowered the pump laser linewidth [81] to about 30 MHz. The construction of a seeded Nd YAG laser with longer pulses (35-45 ns) further reduced the linewidth to 10 MHz [82]. 

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