White-light supercontinuum

S. L. Chin, S. Petit, F. Borne, K. Miyazaki, The white light supercontinuum is indeed an ultrafast white light laser, Japanese Journal of Applied Physics 38, L126 (1999)... 

Material like sapphire, which is a uniaxial crystal, does not show nonlinear fluorescence, and direct visualization of filaments is, consequently, not an option. However, the effect of rotation of plane polarization can also be probed in such materials by monitoring the spatial size of the white light disc, and of the spectrum of the super continuum that is produced. Figure 5.3 depicts some typical results obtained with 3 mm long sapphire crystals. The extent of the supercontinuum spectrum is seen to vary as a function of polarization angle. The supercontinuum spectrum has two components [39] symmetric broadening about the incident wavelength that is essentially ascribable to... 

Fig. 5.3. Top panel Polarization-dependent supercontinuum spectra obtained in sapphire. The corresponding variation in the diameter of the white light central spot as a function of incident polarization angle is shown in the lower panel...

Fig. 5.7. Supercontinuum spectra obtained in water at different energy levels using a wire mesh. Top panels show images of white light in the far field...

Using results established in previous sections., it can however be shown that this assertion represents only an approximation to the truth. Absorption from a white light or other broadband source in fact allows photon pairs of differing frequencies to be concertedly absorbed by molecules in close proximity (Andrews 1988). In this section, it is shown that this may result in a change to the appearance of absorption spectra, and yield an absorption law that departs from normal Beer-Lambert behavior. One particular case in which such effects may be expected to arise is where supercontinuum laser radiation is employed for spectroscopic purposes. 

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