Light incoherent

Schaertel S A, Albrecht A C, Lau A and Kummrow A 1994 Interferometric coherent Raman spectroscopy with incoherent light some applications Appi. Rhys. B 59 377-87... 

Morita N and Yajima T 1984 Ultrafast-time-resolved coherent transient spectroscopy with incoherent light Rhys. Rev. A 30 2525-36... 

Asaka S, Nakatsuka H, Fujiwara M and Matsuoka M 1984 Accumulated photon echoes with incoherent light in Nd -doped silicate glass Rhys. Rev. A 29 2286-9... 

Kummrow A and Lau A 1996 Dynamics in condensed molecular systems studied by incoherent light Appi. Rhys. B 63 209-23... 

Dugan M A, Melinger J S and Albrecht A C 1988 Terahertz oscillations from molecular liquids in CSRS/CARS spectroscopy with incoherent light Chem. Rhys. Lett. 147 411-19... 

Conventional, incoherent light sources suitable for industrial-scale photochemistry and the reactors exploiting them have been reviewed in depth (2). Subsequent improvements in traditional light sources have been incremental. 

Due to diffraction effects of micron-sized mirrors in a regular array, commonly used techniques for surface characterization based on interferometry are inefficient. To overcome the diffraction effects we have developed a novel surface characterization method with an incoherent light source, based on the Foucault s knife-edge test (Zamkotsian and Dohlen, 1999). Since Leon Foucault introduced the knife-edge test in the last century (Foucault, 1859), it has been widely used for testing optical surfaces (see Ch. 3). The test offers a simple way of obtaining easily understandable, qualitative information of the surface shape. 

Figure 9.20 Light emission (a) normal spontaneous emission produces incoherent light, and (h) stimulated emission produces coherent fight.

Light is emitted from the bulk material at random times and in all directions, such that the photons emitted are out of phase with each other in both time and space. Light produced by spontaneous emission is therefore called incoherent light. 

It is already a fact that lasers are replacing conventional lamps in a great variety of spectroscopic applications. The origin of this substitution lies in their superior performance over incoherent light in many experimental situations. Many spectroscopic experiments have been improved, and moreover new techniques have been developed due to the particular advantages provided by lasers. The characteristics of laser radiation on their own constitute real advantages and justify their widespread use in many applications. 

Figure 20. Diffraction of coherent and incoherent light from a grating pattern with a spatial frequency, p = (26 ) ...

In linear superposition, the method is literally that of adding components. When treating the optics of coherent light, for example, the instantaneous values of the field vectors are superimposed. Incoherent light, on the other hand, requires us to deal with the time-averaged square of the field. In nonlinear optics, superposition breaks down as it does in other nonlinear systems. Even when it does not hold exactly, however, superposition is often useful as a first-order approximation. 

A critical point, in our view, is that performing experiments with short pulses allows one to observe the behavior of individual molecules by forcing the whole ensemble to travel together (this is literally what coherence means) until dissipation sets in. But when the process is initiated with incoherent light, individual molecules behave in the same way as they did in the short-pulse experiment, except that now there is a stochastic distribution of... 

Replacement of the conventional incoherent light source with a laser has allowed CD measurements to be made on extremely small samples, such as those encountered in capillary electrophoresis. In addition, the unique spatial properties of the laser are utilized to advantage in thermal lens spectroscopy. TL detection of CD, either via a single beam, or a differentially configured arrangement, has demonstrated significant improvements in the measurement SNR. Application to HPLC detection, or time-resolved studies, are currently under investigation. 

The method for obtaining particle size distributions using optical incoherent space frequency analysis is detailed in [209,210] and resulted in the development of a low price, robust, on-line dry powder measuring system, the Jenoptik PSl-Z, (Particle Sizing using Incoherent light) which covered 32 size intervals in the range 1.5 pm to 2 mm. This was later expanded to 0.7 to 2500 pm [211]. For particles smaller than 50 pm a dispersion nozzle had to be fitted. 

The Crystalsizer is based on the principle of incoherent light diffraction thus turning the traditional optical structure back to front. Thus the same physical effect is measured as with traditional devices, but without using coherent laser light. The size distribution is determined using Fraunhofer diffraction theory. The robust construction of the instrument makes it suitable for use on-site . Typically, samples are removed from the process and fed to the Crystallizer sequentially. 

The theory of sum-frequency conversion of incoherent light can be found in the literature [133-134]. The intensity of the sum-frequency light at a given delay time is proportional to the correlation function of the fluorescence intensity with the intensity of the oj beam. A time profile of the fluorescence intensity is obtained by change of the arrival time of one of the pulses with the aid of an optical delay line. 

This article reviews direct and indirect (e.g., afterimage, flash blindness) light hazards from common incoherent light sources. For direct hazards specific to lasers and other specialized coherent sources, the reader is referred to organizations such as the Laser Institute of America and the International Electrotechnical Commission. 

Ordinary incoherent) light is seldom fully polarized, and a beam of depolarized (or natural) light can be considered a mixture, in equal amounts, of two (incoherent) beams polarized in arbitrary but orthogonal directions. 

Puech. K.. Henari, 1. . Blau, W., Ditff, D., Schmid. G. Investigation of the ultrafast dephasing time of gold nanopaiticles using incoherent light. Chem. Phys. Lett. 247, 13—17 (1995)... 

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