Light intensity fluctuations

These circumstances may explain why it took ten years for the phenomenon to be experimentally observed after the prediction. In 1973, prior to this finding, Lon Hocker, George Benedek, and Tanaka realized that a gel scattered light, and the light intensity fluctuated with time [5]. They established that the scattering is due to the thermal density fluctuations of the polymer network and derived a theory that explained the fluctuation. These fluctuations are similar to... 

The detection of photoelectrons is a doubly-stochastic Poisson process wherein the light intensity fluctuates and causes a random modulation in discrete number of measured photoelectrons, which are themselves subject to intrinsic fluctuations in the shot-noise limit. Suppose there are n photoelectrons counted in an integration time G, the mean photo-count is... 

Property measured Angular light scattering Light intensity fluctuations Settling speed Electrical pulse Image size Mass... 

Micheau, J. C., Horsthemke, W. Lefever, R. (1984). Sensitivity of biphotonic systems to light intensity fluctuations experimental evidence in the thermoluminescence of fluoresceine in boric acid glasses. J. Chem. Phys., 81, 2450-7. 

The spectral distribution of the light intensity fluctuation can be obtained by an autoconvolution of the optical spectrum [25] ... 

D. C. van Eck, R. J. J. Zijlstra, Spectral analysis of light intensity fluctuations caused by orientational fluctuations in nematics, J. Physique 1980,47, 351. 

The scattering techniques, dynamic light scattering or photon correlation spectroscopy involve measurement of the fluctuations in light intensity due to density fluctuations in the sample, in this case from the capillary wave motion. The light scattered from thermal capillary waves contains two observables. The Doppler-shifted peak propagates at a rate such that its frequency follows Eq. IV-28 and... 

The phase Doppler method utilizes the wavelength of light as the basis of measurement. Hence, performance is not vulnerable to fluctuations in light intensity. The technique has been successfully appHed to dense sprays, highly turbulent flows, and combustion systems. It is capable of making simultaneous measurements of droplet size, velocity, number density, and volume flux. 

Time traces OH light intensity I, flame surface area A, pressure fluctuahons p, and computed pressure fluctuations kdA/dt. Circles indicate extracted flame surface areas A in cm (S and A are used indifferently to designate the flame surface). Black circles marked a, b, c, d correspond to flame patterns presented in images from Figure 5.2.3. 

The temporal evolution of P(r,t 0,0) is determined by the diffusion coefficient D. Owing to the movement of the particles the phase of the scattered light shifts and this leads to intensity fluctuations by interference of the scattered light on the detector, as illustrated in Figure 9. Depending on the size of the polymers and the viscosity of the solvent the polymer molecules diffuse more or less rapidly. From the intensity fluctuations the intensity autocorrelation function... 

The reference beam in the atomic absorption instrument does not pass through the blank, but merely bypasses the flame. Thus the fluctuations in light intensity are accounted for, but the blank adjustment must be made at a separate time. 

This effective Q,t-range overlaps with that of DLS. DLS measures the dynamics of density or concentration fluctuations by autocorrelation of the scattered laser light intensity in time. The intensity fluctuations result from a change of the random interference pattern (speckle) from a small observation volume. The size of the observation volume and the width of the detector opening determine the contrast factor C of the fluctuations (coherence factor). The normalized intensity autocorrelation function g Q,t) relates to the field amplitude correlation function g (Q,t) in a simple way g t)=l+C g t) if Gaussian statistics holds [30]. g Q,t) represents the correlation function of the fluctuat-... 

The variation of scattered light intensity with 0 as typified by Fig. 9.19 clearly becomes more complex as the particle size increases, with sharp oscillations seen at a 10. However, recall that this is for a spherical homogeneous particle of a fixed size and for monochromatic light (e.g., a laser) when the particle is irregular in shape, these oscillations are far less prominent. This is also true for a group of particles of various sizes, that is, a polydisperse aerosol, where the overall scattering observed is the sum of many different contributions from particles of various sizes. Finally, nonmonochro-matic light and fluctuations in polarization also help to smooth out the oscillations. 

The scattered light intensity from a polymer solution arises from the fluctuations in both the solvent density and the polymer concentration. These fluctuations are considered as stable during the timescale of the measurement in the static mode of light scattering (for more details, see Evans (1972)). The light scattered from just the polymer (in excess of the light scattered from the pure solvent) is given by (Burchard, 1994)... 

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