Illumination uniform beam

Uniform preillumination is discussed in the literature in two different time regimes. Fast diffraction response is obtained from materials which are illuminated uniformly and intensely for a few seconds before a second writing beam is used to pattern the intensity in the material and begin hologram formation. This maximizes the mobile hole density in the material at the time of hologram formation and helps to reach the charge generation limit of Eq. (1). 

As an example, Fig. 4.5 shows the calculated normalised beam profile (right) for a given wavenumber and for a telescope diameter Dja = 3 m illuminated uniformly (left). 

Figure 10 illustrates schematic drawing of objective-type TIRFM. A high numerical aperture objective lens is mounted on an inverted microscope. A laser beam is passed through a neutral density filter (ND) and a beam expander (BE) to adjust its power and diameter. When the laser polarized linearly is used, the polarization of the laser beam is converted from linear to circular by a quarter-wave plate (A/4). The laser beam is focused by a lens (L) on the back focal plane of the objective, so that specimens are illuminated uniformly with Koehler illumination. By shifting the position of the mirror (M) located between the lens (L) and dichroic mirror (DM), the path of the incident laser light is shifted from the center to the edge of the objective. At the center position, the microscope can be used as a standard epi-fluorescence microscope (Fig. 10b). 

Fields at the endface 20-3 Fields of the illuminating beam 20-4 Gaussian and uniform beams 20-5 Modal amplitudes and power... 

Later in the chapter we shall consider illumination by Gaussian and uniform beams. The Gaussian beam has an infinite width, and the radial distribution and... 

Illumination by an infinite plane wave corresponds to the uniform beam in the limit Pj- 00. We can then repeat the calculation of Section 20-7 for oblique incidence at angle... 

To complement our examples of beam illumination of the infinite parabolic-profile fiber, we now derive expressions for the efficiency of a uniform beam in exciting the modes of a weakly guiding, step-profile fiber. 

Fig. 20-4 (a) The fraction of total power in a uniform beam that excites modes of a step-profile fiber as a function of the tilt angle 0j, where P includes all modes with the same values of U in Fig. 14-4, and bm is the total excited power [2]. (b) Variation of the excitation efficiency with the fiber parameter for on-axis illumination, where solid curves denote the exact solution of Eq. (20-27c) and the dashed curve is the Gaussian approximation of Eq. (20-28a). (d) The corresponding curves for the fundamental mode for various ratios of beam to core radii calculated from Eqs. (20-27c) and (20-28b). (c) Plots of Pq/Pi for the fundamental mode and different ratios of beam to core radii. 

A critical difference between the transient and CW measurements is that while the CW probe source uniformly illuminates the sample, both the transient pump and probe beams have Gaussian distributions. Equation (7.7) can be rewritten for the transient case as ... 

Figure 9.6. The point spread function of a circular aperture for 4 different values of the edge taper with Gaussian illumination. The four curves are for uniform illumination or 0 db taper, 9, 18 and 27 db taper. The sidelobe level decreases with increasing taper, while the width of the main beam increases slightly.

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