Laser beam, light intensity, calculation

The light-intensity (or photon flux) of the laser beam (/0) was calculated from the measured power output and from the known value of the energy of the photons at the desired wavelength 328 kJ.mol-1 for the emission line at 363.8 nm and 354 kJ.mol-1 for the emission line at 337.1 nm. The maximum value of /0 obtained at full power operation were respectively ... 

Because the incident laser light intensity was not uniform over its area, the theoretical curves in Figures 1 and 2 were calculated by first measuring the incident laser beam intensity at 900 equally spaced points over its area. 

Figure 3.83. Theoretically calculated square of the light intensity isophotes of a focused laser beam in normalized axial (u) and lateral (v) coordinates. (From Ref. [580] with permission of the American Institute of Physics.)...

The scattered light is detected by a photomultipler tube (PMT). The area that is seen by the PMT encloses the spot of the laser beam on the film. The PMT signal is fed either to a correlator or to a spectrum analyzer. The correlator consists of a fast analogue-to-digital converter and a minicomputer, programmed to calculate the time autocorrelation function of the signal. The correlation function, calculated in this way, is proportional to the time autocorrelation function of the fluctuations in the scattered intensity. 

The diffraction efficiency (DE) of diffraction grating covered by a 20 nm layer of A1 by thermal deposition in vacuum is shown on Fig. 7a. Determination of diffraction efficiency was performed at a normal incidence of a laser beam onto the surface of a hologram. The intensites of diffraction light was measured in both first maxima and diffraction efficiency was calculated with the help of the formula DE=(I+i+Li)/Io, where lo is an intensity of the incident beam, and I+i and I-i are intensities of the first diffraction maxima. 

Bartoli and Litovitz [6] found values of C of about 0.2% for some typical polarised (A) bands - by making measurements on the 459 cm" band of CCl which has a well-known [18] depolarisation ratio. Calculation of I ((1d) is then straightforward. Polarisation scrambling behind the main entrance slit ensures that the monochromator is equally sensitive to transmission of and lyy scattered light. There have been reports of local heating effects caused by a relatively high powered laser beam. However, we have never found this to be a problem although, of course, it is not possible to physically monitor the microscopic temperature. Stokes/Antistokes intensity ratios which measure the Boltzman population factors (and hence the microscopic temperature) have always corresponded well to the laboratory (bath) temperature even for input powers up to 2w. 

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