Coherent anti-Stokes-Raman scattering

The CARS process can be described as interaction of a pump beam at frequency p, a probe beam at frequency pj, and a Stokes beam at frequency with a sam- 

The signal arises from the four-wave mixing signal enhancement when the laser frequency difference matches the frequency of the probed vibrational mode. CARS is at the same time a coherent and a resonant process, meaning that it differs in nature from other nonlinear processes such as two-photon excited fluorescence (i.e., only resonant) and SHG (i.e., only coherent). Both aspects determine the peculiar features in a CARS spectroscopic image. 

As CARS is a four-wave mixing process [3], the intensity of the CARS signal is proportional to the square modulus of the induced third-order polarization 

The polarization magnitude is determined by the strength E of the electrical fields of pump and Stokes excitation beams and the nonlinear susceptibility 

In contrast to one-photon electronic resonance, the third-order susceptibility is 

Recently, degenerate four-wave mixing (Sect.8.6) has also been applied to combustion studies [10.46]. In this technique the sensitivity of LIF is combined with the advantages of a coherent signal beam characteristic to CARS. 

The techniques discussed here in connection with combustion diagnostics can clearly also be used for the monitoring of other reactive media. The techniques have been found to be valuable in the characterization of chemical vapour deposition (CVD) processes for semiconductor fabrication [10. 47]. The examples mentioned here illustrate the power of laser spectroscopic techniques in studying chemical processes. Numerous other examples of chemical applications of laser spectroscopy can be found. The field was covered in [10.48,2]. 

Still another criterion for an SHG medium is implicit in Eq. 11.18, where the presence of the nonzero second-order nonlinear susceptibility implies that the polarization P cannot simply change sign if the electric field E is reversed in direction. (The inclusion of only odd-order terms varying as E, E, . .. in P 

Coherent anti-Stokes Raman scattering (CARS) is one of several four-photon optical phenomena that can occur when a sample is exposed to two intense laser beams with frequencies coi, a 2. Some of the other phenomena, two of which are shown in Fig. 11.4, are the harmonic generation and frequency-summing 

3o)2- In CARS, two photons of frequency are absorbed, one photon of frequency 0)2 is scattered via stimulated emission, and a photon at the new frequency 0)3 = 2(o — a 2 is coherently scattered (Fig. 11.5). It is apparent in this figure that when the frequency difference cui — U2 is tuned to match a molecular vibrational/rotational energy level difference, CO3 becomes identical with an anti-Stokes frequency in the conventional Raman spectrum excited by a laser at co. In this special case (called resonant CARS), the scattered intensity at 0)3 exceeds typical intensities of Stokes bands in ordinary Raman scattering by 

As a first step in deriving expressions for CARS transition probabilities, we list in Fig. 11.6 the 12 time-ordered graphs corresponding to absorption of two photons at toj and scattering of photons at 0)3, 0 3. Using the diagrammatic techniques introduced in Section 11.1, we immediately get for the CARS contribution to the fourth-order coefficient in the time-dependent perturbation expansion (1.96) 

This coefficient is proportional to the third-order nonlinear susceptibility responsible for CARS. It may be simplified somewhat by defining 

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Depending on the relative phase difference between these temis, one may observe various experimental spectra, as illustrated in figure Bl.5.14. This type of behaviour, while potentially a source of confiision, is familiar for other types of nonlinear spectroscopy, such as CARS (coherent anti-Stokes Raman scattering) [30. 31] and can be readily incorporated mto modelling of measured spectral features. 

Coherent anti-Stokes Raman scattering spectroscopy... 

Figure 9.22 Experimental arrangement for coherent anti-Stokes Raman scattering...

Fig. 0.4. Experimental nitrogen Q-branch of coherent anti-Stokes Raman scattering spectrum (CARS) measured at 700 K and different pressures [14].

The present study demonstrates that the analytic calculation of hyperpolarizability dispersion coefficients provides an efficient alternative to the pointwise calculation of dispersion curves. The dispersion coefficients provide additional insight into non-linear optical properties and are transferable between the various optical processes, also to processes not investigated here as for example the ac-Kerr effect or coherent anti-Stokes Raman scattering (CARS), which depend on two independent laser frequencies and would be expensive to study with calculations ex-plictly frequency-dependent calculations. 

Ichimura, T, Hayazawa, N., Hashimoto, M., Inouye, Y. and Kawata, S. (2004) Tip-enhanced coherent anti-Stokes Raman scattering for vibrational nano-imaging. Phys. Rev. Lett., 92, 220801. 

Zumbusch, A., Holtom G. R. and Xie, X. S. (1999) Three-dimensional vibrational imaging by coherent anti-Stokes Raman scattering. Phys. Rev Lett., 82, 4142-4145. 

Pott, A., Dork, T., Uhlenbusch, J. et al. (1998) Polarization-sensitive coherent anti-Stokes Raman scattering applied to the detection of NO in a microwave discharge for reduction of NO, J. Phys. D Appl. Phys. 31, 2485-98. 

In order to extend the range of 2laser excitation, both CARS (Coherent Anti-Stokes Raman Scattering) and CSRS (Coherent Stokes Raman Scattering) are used. In both cases <03 = 2003 -U2 In the CARS mode 0)3 > wj > (03 in the CSRS mode <02 > (1)3. One-photon resonance effects are the same in both cases as described later. Phase matching is also the same in both cases with 3 = 2 ... 

Coherency strains, 13 501 Coherent anti-Stokes Raman scattering (CARS), 21 328 Cohesive energy, 23 90 Coho salmon, common and scientific names, 3 187t... 

S.-X. Qian, J. B. Snow, and R. K. Chang, Coherent Raman mixing and coherent anti-Stokes Raman scattering from individual micrometer-sized droplets, Opt. Lett. 10, 499-501 (1985). 

Djaker, N., Lenne, P. F., Marguefi D., Colonna, A., Hadjur, C., and Rigneault, H. 2007. Coherent anti-Stokes Raman scattering microscopy Instrumentation and applications. Nucl. Inst. Meth. Phys. Res. A 571 177-81. 

Evans, C. L., Potma, E. O., Puoris haag, M., Cote, D., Lin, C. R, andXie, X. S. 2005. Chemical imaging of tissue in vivo with video-rate coherent anti-Stokes Raman scattering microscopy. Proc. Nat. Acad Sci. 102 16807-12. 

Hashimoto, M., and Araki, T. 1999. Coherent anti-Stokes Raman scattering microscope. Proc. 5P/ 3749 496. 

Cheng, J. X., and Xie, X. S. 2004. Coherent anti-Stokes Raman scattering microscopy Instrumentation, theory, and applications. J. Phys. Chem. B 108 827 0. 

Broadband Laser Source and Sensitive Detection Solutions for Coherent Anti-Stokes Raman Scattering Microscopy... 

Hashimoto, M., Araki T., and Kawata, S. 2000. Molecular vibration imaging in the fingerprint region by use of coherent anti-Stokes Raman scattering microscopy with a collinear configuration. Opt. Lett. 25 1768-70. 

Kee, T. W., and Cicerone, M. T. 2004. Simple approach to one-laser, hroadhand coherent anti-Stokes Raman scattering microscopy. Opt. Lett. 29 2101-03. 

Paulsen, H. N., HiUigse, K. M., Thgersen, J., Keiding, S. R., and Larsen, J. J. 2003. Coherent anti-Stokes Raman scattering microscopy with a photonic crystal fiber based light source. Opt. Lett. 28 1123-25. 

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