Self-beat method

Equations 5.446 and 5.450 are applicable in the so-called homodyne method (or self-beating method), where only scattered light is received by the detector. In some cases, it is also desirable to capture by the detector a part of the incident beam that has not undergone the scattering process. This method is called heterodyne (or method of the local oscillator) and sometimes provides information that is not accessible by the homodyne method. It can be shown that if the intensity of the scattered beam is much lower than that of the detected nonscattered (incident) beam, the detector measures the autocorrelation function of the electrical held of the scattered light, dehned as... 

It appears noteworthy that it is in principle possible to obtain information on rotational diffusion coefficients from the self beating spectrum (the most frequently applied technique). In this case it is necessary to observe a (usually small) polarized component of the scattered light perpendicular to that of the normal scattering. Mazer, Benedek et al.143,144,145 in the US, Corti and Degiorgio29 in Italy have pioneered this method regarding its application to micellar phenomena in aqueous solutions. 

In the case of strong coupling, 72 < Wc/ i, MEG by a short light pulse is accompanied by quantum beats with the frequency Wc/ i. These oscillations are damped in the opposite case of weak coupling, 72 > Wc/ i however, the MEG process can still be very efficient. The density matrix approach is the only self-consistent method that takes into account the diverse processes responsible for MEG in NCs. 

Because the controlled reference method utilizes a constant reflected beam it has two major advantages over other methods using self beating. 

Light-scattering spectroscopy is a common method for studying the dynamics of polymers in solution.The measured self-beating photocount autocorrelation function has the form... 

On the other hand, what we can measure is the time correlation of intensity fluctuations defined by eqn [8], For the self-beating of the electric field in the optical mixing method, we have the Siegert relation for Gaussian statistics systems, providing the important relationship between andg ... 

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