Light collection

The ( harge from the diode will be collected with a charge sensitive preamplifier, mounted in close proximity to the diode. Both the diode and the preamplifier wall be shielded to eliminate electronic noise pickup. The required noise characteristics of the preamplifier 

With these parameters, the mis electronic nois/ for tin PIN diode can be as low /is 500 - 600 e , j)roviding an excellent signabto-nois/ ratio even at low photon energi/is see Section 5.3.3. 

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Even while Raman spectrometers today incorporate modem teclmology, the fiindamental components remain unchanged. Connnercially, one still has an excitation source, sample illuminating optics, a scattered light collection system, a dispersive element and a detechon system. Each is now briefly discussed. 

A point light source is imaged onto the specimen by the objective and the transmitted light collected by the collector lens and detected by a broad-area detector in the case of reflection microscopy, the objective lens also serves simultaneously as a collector (see figure Bl.18.10. The resolution is solely detennined by the objective lens, because the collector has no imaging fimction and only collects the transmitted light. The... 

A sample holder, including optics for focusing the incident light and collecting the luminescence. Efficient light collection is important, and the sample holder may need to allow for a cryostat, pressure cell, magnet, or electrical contacts. 

Fluorescence was collected perpendicular to the laser beam propagation direction (i.e. 90 degree light collection) using... 

Figure 2. The spectral analysis of light collected by the fiber placed in a pH=7 phosphate-buffered distilled water sample. The spectriun shows the important interferences which must be eliminated to relate the fluorescence intensity to concentration.

The maximum light collection efficiency (r = 0.5) is achieved when the emitting sample is in close contact with the detector. When the detector is coupled with a lens, the light collection efficiency may be much lower. 

The entrance pupil is nothing more than the area of a lens that accepts radiation and defines the relative useful portion of the lens. Since a coherent source is a point source (zero diameter), the image in the entrance pupil will also have zero diameter and thus incoherent source is rigorously a source of infinite extent (a = >) and is only of academic interest since all light collected from any real source is always imaged within the entrance pupil, so that c is always <1. In practice, partially coherent sources are used. 

Fig. 32 Dependence of cosine of A and tangent of where A and are ellipsometric angles related to the change of amplitude and phase shift of the incident polarized light, on the wavelength of the incident polarized light collected from PDMAEMA- -PAA brushes immersed in solutions of a constant ionic strength 0.001 M) and pH ranging from 3.52 to 9.50. The data in figures a and b (c and d) have been collected at the position 1 (4). For clarity the data for cos(A) and tan(V ) collected at pH > 3.53 were shifted vertically by - 0.2 relative to each previous set...

Light collection from the plasma (in the transversal or longitudinal direction) is carried out as a function of the element depending on whether an ionic or atomic line is used for measurement. The temperature varies from 9 000 to 2 000 K between the bottom and the top of the torch. It is colder in the axis and at the solution nebulisation site. 

It is essential to correctly evaluate the absorption cross-section a relative to the laser line profile, the spectral resolution of the light collection optics, and the natural HO line width as influenced by Doppler, Voigt, or collisional broadening. The principles governing absorption measurements of HO over a distance through the atmosphere are discussed by Hiibler et al. (38). 

Through the use of freeze-fracture and freezeetching techniques of electron microscopy, it is possible to see, embeddded in the thylakoid membranes, particles which may represent individual photosyn-thetic units (also called quantosomes).227 256-258 They are about 20 nm in diameter, and at least many of them presumably contain a reaction center surrounded by light-collecting chlorophyll-protein complexes. Others may represent the cytochrome b6f complex and... 

Laser light scattered by the particles is collected by the tip of a glass rod, ensuring an efficient light collection, in a rather wide spatial angle. The direct laser light is absorbed in a... 

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