Folded-BOXCARS

Muller, M., Squier, J., De Lange, C. A., and Brakenhoff, G. J. 2000. CARS microscopy with folded BoxCARS phasematching. J. Microsc. 197 150-58. 

It should be pointed out that the wave vectors need not reside in the same plane. The BOXCARS phase-matching diagram could be folded along the dotted line in Fig. 3.6-12. With this folded BOXCARS arrangement (Shirley et al., 1980) a great advantage... 

The forward folded boxcar four-wave mixing technique is illustrated in Fig. la and lb. Three pulsed laser beams are directed, through variable delay lines, toward the sample. Two time-coincident short excitation pulses and a third delayed probe beam cross in the sample. Figure 1 shows the beam geometries on the surface of the sample and at the aperture plane. The three incident beams are labeled 1, 2, and 3. Beam 4 is the signal beam, generated by the input beams via The... 

Fig.8.41a-c. Basic diagram and phase matching schemes for Coherent Anti-Stokes Raman Scattering (CARS), (a) collinear, (b) BOXCARS, and (c) folded BOXCARS phase matching [8.91]... 

Figure 3 Folded BOXCARS geometry applied in several transient nonlinear optical spectroscopies. In pump-probe spectroscopy, one of the three beams is blocked and the intensity of one of the incoming beams is monitored as a function of the time delay between the remaining two beams (e.g., beam 3 is blocked and beam 2 is monitored as a function of its delay with respect to beam 1, phase-matching condition would be k2 = ki — ki -I- k2>. Beams 4 and 5 are photon echo signals generated from beams 1 and 2. Beams 6 and 7 can be stimulated photon echo or transient grating signals generated from beams 1,2, and 3. In transient grating two of the beams are time coincident. In coherent anti-Stokes Raman spectroscopy, beams 1 and 3 are time coincident and carry the same frequency the difference between this frequency and that of beam 2 (so-called Stokes beam) matches a vibrational frequency of the system and beam 6 will correspond to the anti-Stokes emission.

In the gas phase, dispersion may be negligible, making collinear phase matching possible (see Figure 2A). However, the BOXCARS approach is often preferred because it allows spatial discrimination between the input and output beams. Additional spatial discrimination may be achieved using a three-dimensional form called folded BOXCARS (see Figure 2F). 

---