Optical Layouts

The configuration of the common components of dispersive spectroscopy systems is shown for the most used types of spectroscopy. In layouts 1 and 3, an external source of radiation is required, but for 3, the source is generally oriented at right angles to the sample. Emission, layout 2, does not require an external radiation source the excited sample is the source. For absorption, fluorescence, phosphorescence, and scattering, the source radiation 

Source — Dispersive device Sample Detector Data output 

Sample Dispersive device Detector Data output 

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Fig. 1. Schematic of the optical layout of a Fourier-transform spectrometer.

Figure 2. Simplified diagram of the optical layout of the FTIR spectrometer and A are apertures, P and P are polarizers, and the area inside the dashed box the actual interferometer assembly...

Fig. 7.3. Optical layout of the scattered circular polarization (SCP) BioToois ChiralUaman backscattering ROA instrument. Adapted from [25]...

The optical layout depends on the reflector. With diffusely reflecting reflectors, for example dense polytetrafluoroethylene (PTFE) or compacted titanium dioxide,... 

The overall combustor/optical layout is shown in Fig. 3, which illustrates temperature measurement by the Stokes/anti-Stokes method. Typical results for temperature pdf s at four radial positions (2, 7) near the centerline to near the flame boundary - and at an axial distance 50 fuel-tip diameters downstream of the fuel line tip are shown in Fig. 4. The shaded parts of the pdf contours (from 300 to 800°K), which increase in area near the flame boundary, correspond substantially to scattering from ambient temperature air, and therefore provide a measure of flow intermittency. The upper limit of these bins was chosen to be 800°K because the accuracy possible for the Stokes/anti-Stokes temperature measurement method degrades rapidly at temperatures below roughly that value (2,2) Thus, treating the fluctuation temperature data for T < 800 K in any greater detail was unwarranted. 

Also described in Ref. k is a new optical layout for LV data acquisition which permits a significant increase in the overlap between the Raman and LV probe test volumes. The worth of the various correlations of density and temperature with velocity is critically dependent upon the accuracy of this overlap at all flame measurement positions. Thus, one must either lock the Raman and LV probes together in a precise but movable fashion -a rather difficult procedure for the precision required for bench scale" laboratory flames - or else translate the flame. 

Figure 5. Current overall optical layout for laser velocimetry and Raman scattering diagnostics, shown here on new fan-induced square-cross-section movable combustion tunnel. Note the co-linear Raman and LV probe laser source axes and the colinear detection optics.

The optical layout of our FT-IR-VCD instrument is based on a Nicolet 7199 Fourier transform spectrometer. A block diagram of the optical and electronic components of the instrument is shown in Figure 4. The instrument has been described in detail in several previous publications [57,68,75], and some of the more recent changes in the instrument will be indicated below. 

Figure 3.24 illustrates a typical optical layout for a visible and near-ultraviolet doublebeam recording spectrophotometer. The arrangement is very similar to that in Figure 3.23... 

A hollow cathode lamp emits an intense line spectrum of the cathode element, of any other element present in the cathode, and of the filler gas (neon or argon). It is therefore necessary to be able to isolate the lines of the determinant element from any other emitted lines. If we do not, the difference between 7t and /0 will be greatly reduced, and the sensitivity unacceptably poor. Moreover, not all lines of the determinant element give equal sensitivity, and it is therefore also desirable to isolate the determinant line at the wavelength which gives the most useful sensitivity from all other lines. This is done with a grating monochromator. Figure 6 illustrates a typical optical layout in the monochromator of an atomic absorption spectrometer. 

The optical density (OD) of the sample was varied by repeatedly diluting the mixture with fresh gas until a value of roughly 0.8-1.2 was obtained in some cases, scans were acquired with ODs as low as 0.1. Absorbance measurements were made directly in the cell using a Mattson Research Series FT-IR spectrometer (0.25 cm1 resolution) configured for external beam operation. The optical layout makes it possible to easily switch from making ps pump-probe measurements to recording an IR spectrum. 

Optical layout for a 90"" scattering experiment. The vertical polarization direction is normal to die page. 

The Optical Layout of the CAMAG TLC Scanner Courtesy of CAMAG Inc. 

The layout for a novel scheme that overcomes the limitations of a Michelson duplexer is shown in Figure 7. The most important element of the spectrometer in Fig. 7 is the polarization-transforming reflector (PTR), which functions as a quarter-wave plate in this configuration. We will defer a detailed discussion of PTRs for the moment and focus instead on its functionality. To that end, consider Fig. 8a, where we have unfolded the optical layout between the PTR and the Fabry-Perot interferometer (FPI) in order to see the evolution of the electric field polarization more clearly. 

Figure 3.2. Optical layout of the illuminator in the Cannon PLA520FA contact proximity printer. Reproduced uMh permission from reference 17a.)...

Figure 29.3 (a) Optical layout for experiments collected by the same objective lens and was on solutions and fluorescent beads. Picosecond focused onto a photodetector, (b) Optical layout IR and visible light beams were coaxially for the cells. Both IR and visible light beams are... 

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