Circular polarization states

A single image recorded for a fixed enantiomer and fixed circular polarization state in principle carries the full information sought consisting, after inversion, of the parameters and the radial distribution function n r). After... 

As described above, there are two forms of vibrational optical activity, one derived from infrared absorption and the other from Raman scattering. Both forms involve the differential response of a molecule to the modulation of polarization of the interacting radiation between right and left circularly polarized states. In the case of infrared absorption, VCD is defined as die differential absorbance for left minus that for right circularly polarized infrared radiation. This is expressed by the relation ... 

For the measurement of differential absorption spectra in the visible and ultraviolet spectral region, a light modulation technique was introduced over two decades ago [7]. The principle of this measurement also governs the measurement of infrared VCD. This technique involves the high frequency modulation of the exciting beam between left and right circular polarization states via a photoelastic modulator, and measuring the differential absorption with a lock-in amplifier tuned to the modulation frequency. 

Circular dichroism employs standard dispersive or interferometric instrumentation, but uses a thermal source that is rapidly modulated between circular polarization states using a photoelastic or electro-optic modulator. Using phase-sensitive detection, a difference signal proportional to the absorption difference between left- and right-polarized light, AA = — Aj, is recorded as a function of wavenumber. Relative differential absorptions... 

S in Figure 3.8(a), can be converted into a circular polarization state by using two quarter-wave plates [4]. This can be done in two steps ... 

FIGURE 13.4 Various wave polarization states (a) vertical polarization, (b) right-hand circular polarization, (c) representing linear polarization as the superposition of two circular polarized states, (d) right-handed elliptical polarization. 

A right circularly polarized light, which is obtained by equal amplitudes of vibration in the p and s directions and the phase of / -vibration lagging behind that of 5-vibration by 90° (A= —90°) is represented by the point r. The opposite point / is for the left circularly polarized state in which A is +90°. 

Angular momentum The intrinsic spin of each photon is associated with an angular momentum, a feature that plays an important role in the selection rules for many spectroscopic processes. Circularly polarized photons have the special property of quantum angular momentum the two circular polarization states, left- and right-handed, respectively carry -i-l or -1 unit of angular momentum, fi. 

Zeeman poiarimetry Photoelectric method for measuring the displacement in the hydrogen Balmer lines by measuring modulation in the line wing between two opposite circularly polarized states. 

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