Femtosecond-stimulated Raman

Fig. 2 Illustration of broadband vibrational probing employed in femtosecond stimulated Raman spectroscopy [8]...

Kukura P, McCamant DW, Mathies RA (2007) Femtosecond stimulated Raman spectroscopy. Annu Rev Phys Chem 58 461 88... 

Dasgupta J, Frontiera RR, Taylor KC, Lagarias JC, Mathies RA (2009) Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy. Proc Nad Acad Sci USA 106 1784-1789... 

Kukura, R, Yoon, S., Mathies, R. A., Femtosecond Stimulated Raman Spectroscopy, Anal. Chem. 2006, 78, 5952 5959. 

Fig. 2 Experimental arrangement for time-resolved FSRS (femtosecond stimulated raman spectroscopy). The femtosecond actinic pump pulse excites the sample electronically. After a delay the femtosecond probe pulse and picosecond Raman pump pulse arrive together to interrogate the instantaneous molecular structure. The self-heterodyned signal is emitted in the probe direction, dispersed, and detected by a kHz readout CCD. Data collection is best performed by division of subsequent Raman pump-on by Raman pump-off laser shots (lower trace), however this has been performed by other groups as a subtraction of subsequent pulses (upper trace). Reproduced from ref 2 with permission from the PCCP Owner Societies (2012).

To summarize, the EOM-PMA considerably facilitates the computation of various optical signals and 2D spectra. With shght alterations, the EOM-PMA can also be applied to compute nonlinear responses in the infrared (IR). The three-pulse EOM-PMA can be extended to calculate the A-pulse-induced nonhnear polarization [51], which opens the way for the interpretation of fifth-order spectroscopies, such as heterodyned 3D IR [52], transient 2D IR [53, 54], polarizability response spectroscopy [55], resonant-pump third-order Raman-probe spectroscopy [56], femtosecond stimulated Raman scattering [57], four-six-wave-mixing interference spectroscopy [58], or (higher than fifth order) multiple quantum coherence spectroscopy [59]. 

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. 

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... 

When a femtosecond laser pulse passes through nearly any medium, coherent vibrational excitation (in general, initiation of coherent wavepacket propagation) is likely [33, 34]. One- or two-photon absorption of a visible or ultraviolet pulse into an electronic excited state can result in phase-coherent motion in the excited-state potential [35]. Impulsive stimulated Raman scattering can initiate phase-coherent vibrational motion in the electronic... 

The high costs associated with specialist ultrafast laser techniques can make their purchase prohibitive to many university research laboratories. However, centralised national and international research infrastructures hosting a variety of large scale sophisticated laser facilities are available to researchers. In Europe access to these facilities is currently obtained either via successful application to Laser Lab Europe (a European Union Research Initiative) [35] or directly to the research facility. Calls for proposals are launched at least annually and instrument time is allocated to the research on the basis of peer-reviewed evaluation of the proposal. Each facility hosts a variety of exotic techniques, enabling photoactive systems to be probed across a variety of timescales in different dimensions. For example, the STFC Central Laser Facility at the Rutherford Appleton Laboratory (UK) is home to optical tweezers, femtosecond pump-probe spectroscopy, time-resolved stimulated and resonance Raman spectroscopy, time-resolved linear and non-linear infrared transient spectroscopy, to name just a few techniques [36]. 

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