Mirror optics

Rotating anode, conventional optics Rotating anode, Gobel mirror optics Synchrotron, bending magnet (DORIS, A2) Synchrotron, insertion device (ESRF, ID2)... 

Consequently, mirror optics are more common, in particular in the mid-IR. The mirrors used are usually aluminium- or gold-coated flat or curved substrates. While near-IR mirrors are usually protected by thin SiO-layers, in the mid-IR unprotected mirrors have to be used. Disadvantages of mirror optics are the elevated space consumption and the higher prices in comparison to refractive optics, especially comparing non-standard mirrors against non-standard lens. In total, mirror optics are so preferable to fibres and refractive optics, at least in the mid-IR, that in some technical applications they are used to replace waveguides to transport IR radiation between source, sensor head and spectrometer. 

Office automation equipment such as photocopiers, prisms, mirrors, polygon mirrors, optical films... 

An important consequence of the presence of the metal surface is the so-called infrared selection rule. If the metal is a good conductor the electric field parallel to the surface is screened out and hence it is only the p-component (normal to the surface) of the external field that is able to excite vibrational modes. In other words, it is only possible to excite a vibrational mode that has a nonvanishing component of its dynamical dipole moment normal to the surface. This has the important implication that one can obtain information by infrared spectroscopy about the orientation of a molecule and definitely decide if a mode has its dynamical dipole moment parallel with the surface (and hence is undetectable in the infrared spectra) or not. This strong polarization dependence must also be considered if one wishes to use Eq. (1) as an independent way of determining ft. It is necessary to put a polarizer in the incident beam and use optically passive components (which means polycrystalline windows and mirror optics) to avoid serious errors. With these precautions we have obtained pretty good agreement for the value of n determined from Eq. (1) and by independent means as will be discussed in section 3.2. 

Diffuse Reflectance Spectroscopy with Mirror Optics Attachments... 

The designs of various commercially available mirror optics for diffuse reflectance in IR or UV-vis spectroscopy are, in principle, similar to each other. Each of these accessories is characterized by six mirrors, four flat and... 

These problems can be remedied by use of an integrating sphere behind the mirror optics accessory the light yield, however, is then very small. The advantages of mirror optics are (1) a good throughput over the entire UV-vis-NIR range, and (2) facile integration of a heatable reaction chamber. 

Reaction chambers fitting the Harrick Praying Mantis mirror optics are available commercially, and sketches or images are presented in the product description (Harrick, 2006), in the work of Weckhuysen and coworkers (Weckhuysen and Schoonheydt, 1999 Weckhuysen et al., 2000 Weckhuysen, 2002 Weckhuysen, 2003 Weckhuysen, 2004) and in a handbook article by Sojka et al. (2008). A low-pressure and a high-pressure version, suitable at pressures up to 202-303 kPa or 3.4 MPa (500 psi), are available they are characterized by a dome with either three flat, circular windows or a dome with a single quartz half-sphere shaped quartz block with a small (also half-sphere shaped) volume above the catalyst. Evacuation to pressures less than 1.33 x 10-6 hPa and a maximum temperature of 873 K (under vacuum) are specified. A low-temperature version is specified for 123-873 K and up to 202-303 kPa. In the low-pressure versions, there are several centimeters of beam path through the gas phase, so that gas phase contributions are more likely to be observed than in experiments with cells holding the sample directly at the window (this depends on the gas phase concentrations and molar absorption coefficients). 

Many cells are made of quartz hence, the pressure is limited. For use with an integrating sphere, a thick-walled cell for hydrothermal synthesis has been presented (Weckhuysen et al., 2000), and for mirror optics, a cell is available for pressures up to 3.4 MPa. Some reflectance fibers are specified for pressures up to 3.4 MPa (Stellarnet, 2006). 

The reported transmission cells exhibit severe problems in the measurement of catalytic activity because of the limited amount of catalyst in the cell, large dead volumes, and mass transfer limitations in wafers (Melsheimer and Schlogl, 1997). Cells used with mirror optics permit flow through a catalyst bed and feature small dead volumes, but allow little variation of the catalyst mass. Fiber optics requires almost no adaptation of a normal reactor for spectroscopic needs and offers the best solution from a catalytic viewpoint. 

Figure 5.3 shows a schematic illustration of our HRS measurement system [26-28]. A mode-locked Ti sapphire laser (Spectra-Physics, Tsunami) was used to induce HRS. Pulses of 70 fs at 790 nm with a repetition rate of 82 MHz were spectrally narrowed by a custom-made laser line filter (Optical Coatings Japan). The obtained pulse width was 14 cm FWHM with a pulse duration of 1 ps (measured by autocorrelation). These pulses were introduced into an inverted microscope system (Nikon, TE-2000) with a 36x, 0.52 N.A. reflective microscope objective or a 100 X, 1.49 N.A. oil-immersion microscope objective. Backscattered photons were collected by the same objective and filtered by dichroic mirrors (Optical Coatings Japan). Finally, HRS signals were detected by a charge-coupled camera (Princeton Instruments, PIXIS 400B) with a polychromator (ACTON, SP2500i). 

The microscope (SpectraTech model IR-Plan) is a research-grade optical microscope modified for application in the IR spectral range. Focusing is accomplished by Cassegrainian-type mirrors. Optical and IR beam paths are collinear and switched by tilting mirrors. Thus, samples may be characterized and selected visually before recording IR spectra. 

It should be pointed out that, in good part because of the use of large off-axis mirrors, optical aberrations can lead to significant curvature of the images under certain instrumental configurations. This has a detrimental impact on spectral resolution when multiple rows are birmed. Pelletier et al. have reported a data processing procedure to minimize this effect for situations where experimental limitations prevent improving the optical set-up [9]. In future commercial... 

Figure 6,5 Schematic diagram of the ellipsoidal mirror optical counter (Hu-sar. 1974),...

Figure 6.6 The relative response curves of the ellipsoidal mirror optical counter. The lines wen calculated from Mie theory, and the points were measured experimentally. (Courtesy S. L. HeisEe and R. B. Husar.)...

The installation of Harrick s Scientific SplitPea-ATR unit [28] in a common FT-IR spectrometer enables the recording of ATR spectra. This unit contains a microscope for fixing and adjusting the sample on the ATR crystal.The IR beam is reflected via a mirror optic into the germanium crystal (Fig. 16.4). 

The same type of problems occur when making i.r. measurements with DACs. It is now preferable to use Fourier-transform (FT) interferometers, which are commercially available. In this case, the incident i.r. beam, which is a few millimetres in diameter, must be focused to less than 100 (jim by suitable mirror optics (see Fig. 3.32). This procedure can be avoided for studies of homogeneous samples, filling the DAC experimental volume, especially when the intense beam from synchrotron radiation is used, although the useful throughput is a very small fraction (10 - 10 ) of the available light. However, it cannot be avoided when solid samples embedded in a transparent pressure medium are studied. 

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