Instrumentation optical bench

At a high enough temperature, any element can be characterised and quantified because it will begin to emit. Elemental analysis from atomic emission spectra is thus a versatile analytical method when high temperatures can be obtained by sparks, electrical arcs or inert-gas plasmas. The optical emission obtained from samples (solute plus matrix) is very complex. It contains spectral lines often accompanied by a continuum spectrum. Optical emission spectrophotometers contain three principal components the device responsible for bringing the sample to a sufficient temperature the optics including a mono- or polychromator that constitute the heart of these instruments and a microcomputer that controls the instrument. The most striking feature of these instruments is their optical bench, which differentiates them from flame emission spectrophotometers which are more limited in performance. Because of their price, these instruments constitute a major investment for any analytical laboratory. 

Fig 3.7. Components on the optical bench of a generalized four-parameter flow cytometer. (The drop charging, the deflection plates, and the drops moving into separate test tubes apply only to sorting cytometers [see Chapter 9] and not to benchtop instruments.) Adapted from Becton Dickinson Immunocytometry Systems. 

Figure 2.3. A schematic of the Chandra Observatory showing the typical components including the solar arrays, aspect cameras, mirror assembly, instrument module, and optical bench. The Chandra Observatory weighs 4800 kg and orbits the Earth every 64 hours in a 10,000 by 140,000 km orbit that extends 1/3 of the distance the moon. Including the solar panels, the observatory s dimensions are 14m by 20m.

Although standard IR spectrometers are used for studying the amide bands, FTIR spectrometers are more accurate and reliable. FT-IR spectrophotometers are based upon the Michelson interferometer. A typical instrument (Fig. 7.1) comprises an optical bench housing the interferometer, sample, infrared source and detector, coupled to a computer, which controls the spectral scanning, analysis and data processing (for review see Griffiths, 1980). 

The basic instrument consists of an analyzer that includes an optical bench that has a low-power visible wavelength laser, a lens train, a photodetector, a receiver and an amplifier/analog-to-digital converter linked to a microprocessor and monitor (Figure 10.4). Misalignment of the photodetector and incident laser beam is found to have severe effects on results [137]. If the inclination is limited to < 2.5° and the beam eccentricity to less than 0.10 pm the resulting error is less than 0.5%. 

The instruments designed for these analyses comprise several parts the device responsible for bringing the sample in the form of excited or/and ionized atoms (based on gas plasmas, sparks or lasers), an high quality optical bench which conditions the analytical performances, a detector with a sensor (PMT or diode... 

The characteristic that most distinguishes these spectrometers from AA or FE instruments is their optical bench and sometimes their impressive size. They are reserved to analytical laboratories that have to treat a great deal of samples. 

As seen before, fiber optic sensor collects the portion of the electromagnetic radiation after interaction with the internal structure of the sample and transfers it to the spectrophotometer. The optical fiber is connected to the optical bench of the instrument. The optical bench allows to decompose the electromagnetic radiation and recording the intensity at different wavelengths. 

Optical bench of this type of instrument generally consists of five components ... 

To use atomic spectra for analytical purposes, regardless of the application, certain basic instrumentation is required. Included are a spectral isolation device—filter, prism, or grating a slit to permit the radiation to strike the monochromator as a narrow beam a device to allow observation of the spectrum and the necessary optics, lenses, mirrors, etc. to collect and focus the incident light beam. These devices, assembled into one instrument, constitute the monochromator. Some lenses and mirrors, an optical bench, and the instrumentation for observing the spectrum are or may be external to the basic monochromator. 

The Applied Photophysics ir -180 kinetic spectropolarimeter, is a fully integrated kinetic and steady state CD instrument. The Tr -180 instrument is designed in a modular format being built around a high-performance direct coupled optical bench with built in control and acquisition electronics. Alternate sample handling units, both kinetic and steady state, can be coupled to its... 

A particle size analyzer determines the particle size distribution of powders either dry or dispersed in solvent by laser light scattering based on the Fraunhofer scattering theory. This type of equipment has an optical bench whose combined dynamic range is nominally 0.7-2000 pm. The instrument calculates mean diameters and distribution data. An interfaced computer generates sample histograms. This technique has been applied to the study of particle size and particle size distributions for polymer powders and polymer suspensions in a variety of solvents. 

A noncommercial apparatus will be described in this section. The apparatus is constructed of separate instruments arranged on an optical bench. The advantages over a commercial unit are that it provides a more pedagogic approach to the subject and has a higher flexibility in configuration for unusual experiments. The disadvantages are that it occupies more floor space and is much more time consuming to operate. 

Many composites, such as PMCs reinforced with carbon and aramid fibers, and silicon carbide particle-reinforced aluminum, have low CTEs, which are advantageous in applications requiring dimensional stability. Examples include spacecraft structures, instrument structures, and optical benches. By appropriate selection of reinforcements and matrix materials, it is possible to produce composites with near-zero CTEs. 

Water vapor in the beam of FT-IR spectrometers is a major source of interference. Thus, the optical bench should ideally either be purged with dry air or evacuated completely. Some low-resolution spectrometers are hermetically sealed and desiccated, so that the only humid air is in the sample compartment. These instruments are adequate if the spectra of conventional films, KBr disks, and solutions... 

The length of the instrument from the slit to the end of the plate holder is about 1.2 metres, and it is supported on a massive base which raises the optical parts about 30 cm above bench level. An optical bar of steel is attached to the base of the instrument, from which it projects about 90 cm it is parallel with the optical axis. The bar serves to carry lenses, an arc and spark stand (Gramont stand) for holding samples, and other ancillary equipment. 

Newer techniques for measuring the refractive index allow for instantaneous, real-time measurement in process streams, or alternatively, a special continuous-flow sample well can be installed on bench top instruments. Small, pocket-sized refractometers also make held measurement very simple and reliable. Fiber optic sensors find uses in biomedical applications. 

In addition to these collision/reaction cell instruments, since 2002 Thermo Fisher Scientific has been selling the XSeries ICP-MS with a hexapole collision cell (developed from ThermoElemental PQExel ICP-MS) as a bench top instrument on the analytical market. A special ion extraction system in Thermo s XSeries", ion optics together with a hexapole collision cell to minimize the interference problem in ICP-MS, provides the lowest background signals for ICP-QMS (< 0.5 cps). 

Advances in TOF/MS technology, such as reflectron ion optics, delayed ion extraction, and orthogonal ion acceleration, have given rise to bench-top instrumentation with resolution capabilities in excess of that obtained by quadra-pole MS systems. Each of these devices limits or corrects the kinetic energy spread of ions with identical m/ ratios. 

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