Optical anisotropy, oscillating

In light of these wavelength dependent effects described above, Richmond and coworkers have recently completed a more extensive wavelength dependent study of the rotational anisotropy on Ag(l 11) [136, 137], One set of experiments has involved the use of photons of lower energy in the infrared in an attempt to see if the rotational anisotropy would change as the incident and SH photons are more energetically removed from surface or bulk resonances [136]. They used the 1.53 pm output from an optical parametric oscillator which was pumped by the 1064nm output of... 

The polarizability tensor, a, introduced in section 4.1.2, is a measure of the facility of the electron distribution to distortion by an imposed electric field. The structure of the electron distribution will generally be anisotropic, giving rise to intrinsic birefringence. This optical anisotropy reflects the average electron distribution whereas vibrational and rotational modes of the molecules making up a sample will cause the polarizability to fluctuate in time. These modes are discrete, and considering a particular vibrational frequency, vk, the oscillating polarizability can be modeled as... 

The application of an external field onto many materials will induce optical anisotropy. If the applied field oscillates, a time-dependent modulation of the polarization of the light transmitted by the device will result. Modulators of this sort include photoelastic modulators (PEM) [30,31], Faraday cells [32], Kerr cells [32], and Pockel cells. 

Formula (4.371) proves explicitly that the suspension birefringence is an even function of the applied field amplitude. For this reason, in response to the excitation of the frequency go the optical anisotropy Av oscillates with the basic frequency 2co. The higher-rank harmonics induced by the saturation behavior of Av((0) are the multiples of the basic one. It is also clear that besides the oscillatory contribution, the frequency spectrum of Av contains a constant component. 

Moreover, the mean polarizability approximation can yield highly accurate results for dispersion and optical anisotropy of crystalline solutions outside the absorption band. This is due to the fact that the concentration broadening in crystals of this type (with only van der Waals interactions between the molecules) does not affect the integral oscillator strength of a transition. The mean polarizability approximation served as the basis for the procedure developed by Obreimov for the analysis of the composition of multicomponent systems as applied to a wide variety of isotopic mixtures, both liquid and crystalline (for the details, see (20)). 

The method takes advantage of an excite and probe technique with polarization selective detection. A circularly polarized pxnnp pulse of ps duration generates a coherent superposition of atomic substates. The coherence induces an optical anisotropy in the atomic sample, which oscillates exactly with the splitting frequency of the respective substates. 

The applied method is an extension of a previously described technique [I] of time-resolved polarization spectroscopy into the femtosecond range. It relies on the creation of a coherent superposition of adjacent states or substates by an optical pulse, which is short compared to the reciprocal of the frequency splitting of the respective states. Such an atomic coherence causes an optical anisotropy in the sample, oscillating exactly with the splitting frequency of the coherently excited states. 

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