Gaussian intensity distribution wavelengths

The interpretation of PDA principles based on geometrical optics is valid only for particles considerably larger than the wavelength and also when only one scattering mode is present on the detector aperture. Extensions can be introduced to account for the Gaussian beam intensity distribution (Sankar and Bachalo 1991). 

The basic principle of TLM is illustrated in Fig. 1 [1]. In a TLM, two laser beams are utilized an excitation laser beam and a probe laser beam. The wavelength of the former is tuned to the light absorption band of the sample and that of the latter is adjusted to avoid the absorption band. The excitation laser is tightly focused into the sample. The diameter of the beam waist is usually around 1 xm. The sample absorbs the excitation beam, and heat is released to the solvent around the molecule, increasing temperature of the solution. The light absorption is linearly dependent on the light intensity distribution which is a Gaussian distribution, and the resultant temperature distribution is sim-... 

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