Spectrometer optical mounting

Fig. 19. Important optical mountings for optical spectrometers with a plane (A Ebert, B Czerny-Turner) and a concave (C Seya-Namioka, D Paschen-Runge) grating, m Mirror, se entrance slit, sa exit slit, gp plane grating, gc concave grating.

A diagram of an experimental set-up used for PM IRRAS experiments is shown in Fig. 9.26 and a photograph of the spectroelectrochemical cell in Fig. 9.27. The set-up is built from components purchased from Newport and custom-machined parts in an external tabletop optical mount (TOM) box. A convergent infrared beam from the spectrometer enters a port of the TOM box where it is deflected by a flat mirror and focused onto the working electrode by a parabolic mirror (f=6 in, Nicolet). Before entering the cell, the beam passes through a static polarizer (diameter 1 in, with an anti-reflective coating -... 

Figure 9. Optical mountings for optical spectrometers with a plane grating...

Simultaneous Spectrometers. Modem simultaneous spectrometers use photoelectric radiation detection rather than the photographic plates formerly used for qualitative and semi-quantitative analyses. Simultaneous photoelectric spectrometers mostly have a Paschen -Runge optical mounting. They have many exit slits and are especially suitable for rapid determinations of many elements in a constant, well-characterized matrix the achievable precision is high. However, the... 

Ocean Optics, Inc. 380 Main Street Dunedin, FL 34698 TEL (727) 733-2447 FAX (727) 733-3962 Email info OceanOptics.com Compact spectrometer -PC mounted Wavelength cahbration source Calibrated light source A/D converters / software... 

The main features of f.a.b.-m.s. are shown schematically in Fig. 1. The hardware consists of (i) an atom gun (or ion gun, see later) which is either mounted on the source housing of the mass spectrometer or, if small enough, inside the housing on the source itself, (it) a sample probe to the end of which is attached a small metal target onto which the sample is loaded, and (Hi) suitable source-optics for the efficient extraction of ions into the analyzer of the mass spectrometer. 

Fig. 1 Schematic diagram of the integrating sphere portion of a diffuse reflectance spectrometer, illustrating the key elements of the optical train. Although the detecto has been placed in the plane of the sample and reference materials, in common practice it would be mounted orthogonal to the plane created by the intersection of the optica beams.

Optics Issues relative to hygroscopic optics and the need to pay attention to mirror mounts relative to vibration and/or thermal effects have already been addressed. Zinc selenide is an important alternative material, especially when antireflection (AR) coated. If potassium bromide absolutely has to be used for its lower transmission range (down to 400 cm ) then a protective coating such as Parylene must be used. Most process analyzers use protective windows between the spectrometer and the sample interface. If used, back reflections from the window surfaces into the interferometer must be avoided because these will cause photometric errors. Such reflection can be eliminated by wedging or tilting the optical windows, relative to the beam path. 

Because the cast films are relatively thin, the optical density of the light absorbing species can he low and can vary with time of exposure. Additionally, the depth penetration of the absorbed light can be inhomogeneous in some systems. However, thin films can be mounted directly in UV/visible or infrared spectrometers, and so the course of the photopolymerization (and the rate) can be monitored directly in some systems. The most common observation made is the disappearance of monomer (e.g., loss of double bond absorption in the IR) as a function of irradiation time. It must be emphasized that in most thin film compositions important industrially, the monomers used are multifunctional. The polymer which results is then highly cross-linked and simple kinetic arguments are usually not valid. 

Fiber-optic probes are now commercially available for transmission UV spectroscopy and, since recently, also for IR spectroscopy. In both cases a bifurcated cable carries the light from the source to the tip of a probe. The tip is constructed so the solution under study can freely flow through entry holes into the light path. The light is reflected at a mounted mirror and passes through the solution once more before it enters another cable that carries the attenuated light to the spectrometer. 

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