Optical bench

A modern spectrophotometer (UV/VIS, NIR, mid-IR) consists of a number of essential components source optical bench (mirror, filter, grating, Fourier transform, diode array, IRED, AOTF) sample holder detector (PDA, CCD) amplifier computer control. Important experimental parameters are the optical resolution (the minimum difference in wavelength that can be separated by the spectrometer) and the width of the light beam entering the spectrometer (the fixed entrance slit or fibre core). Modern echelle spectral analysers record simultaneously from UV to NIR. 

There are two general types of experimental setup commonly used for the determination of photochemical quantum yields. The more elaborate of the two is the optical bench. A diagram of an optical bench with a good geometry is shown in Figure 2.21. 

Older beamline constructions are based on an optical bench with one or two bars (cf. Fig. 4.10). This construction principle has some disadvantages... 

The construction of sample chambers is constrained by the height and the width of the bars from the optical bench... 

In the mid-IR, routine infrared spectroscopy nowadays almost exclusively uses Fourier-transform (FT) spectrometers. This principle is a standard method in modem analytical chemistry45. Although some efforts have been made to design ultra-compact FT-IR spectrometers for use under real-world conditions, standard systems are still too bulky for many applications. A new approach is the use of micro-fabrication techniques. As an example for this technology, a miniature single-pass Fourier transform spectrometer integrated on a 10 x 5 cm optical bench has been demonstrated to be feasible. Based upon a classical Michelson interferometer design, all... 

The experimental rig is mounted on an optical bench, along which it can be moved. This ensures that the diffracted intensity is maximised by locating the ideal alignment of the diffraction lozenge and the sample (Fig. 4). The position of the solid-state detector is controlled by a series of motors which drive it remotely to the required angle. 

The drop formed is photographed by a suitable camera (Linhof, W.Germany) with a magnification of about 20 times. This magnification is sufficient for the range of Yij measured, since the diameters were measured by using a suitable microscope (with an accuracy of 0.01 mm). The whole setup was mounted on a vibration-free optical bench. 

Sealed free space setup on a transportable optical bench -(box opened for illustration)... 

Numerous pneumatic vibration isolation systems are commercially available. The prime market of these systems are for optical benches. The typical natural frequency is 1-2 Hz. For vibrations with frequencies larger than 10 Hz, a transfer function of 0.1 can be achieved. Some systems provide effective vibration isolation only in the vertical direction, whereas others are effective for horizontal directions as well. All those systems are fairly bulky. If the STM cannot be isolated from the chamber in which it resides, the entire chamber has to be vibration isolated. In this case, the commercial pneumatic system is the choice. 

The beat signal is first nulled with a glass slide in the sample position by moving the prism along the optical bench. The slide is then replaced by the fluorescent sample and the prism is again moved to a null. If X is the distance the prism must move, the lifetime T may be expressed as... 

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. 

We have now described a system in which one or more narrow beams of laser light of well-defined wavelength are used to illuminate a cell, and the light scattered by the cell and emitted by various fluorochromes in or on that cell provide signals that are registered on a group of photodetectors. From our description of the optical bench in Chapter 3 (refer back to Fig. 3.7), we should recall that there are... 

Optical bench An optical bench is the stable table ) that keeps the light beam, fluid streams, lenses, and photodetectors of a flow cytometer all precisely aligned with each other. Lack of stability in these components leads to artifactual results. 

A miniaturized Fourier transform spectrometer for near-infrared measurements (FTIR, 2500-8330 nm) was developed at the Forschungszentrum Karlsruhe [120], Near-infrared measurements give information, for example, about the oil, water and protein content of liquids or solids. The dimensions of the detector chip are 11.5 x 9.4 mm, the device is essentially a miniaturized Michelson interferometer and it consists of a micro optical bench with beamsplitter, ball lenses, mirrors and the detector chip. The light beam is coupled in via a glass-fiber and an electromagnetic actuator. The signal is derived from the signal response of the detector by Fourier transformation. 

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.

The polishing, construction and alignment of the Chandra mirrors and optical bench were critical for achieving high angular resolution. First, because of the need for grazing incidence reflection, the effective telescope area is small... 

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