Optical Instruments

The design of an optical instrument begins with a consideration of the structural and dynamic information that is desired from a sample, and their relationship to its optical properties. This information must be combined with the particular flow or sample geometry that will be probed and the timescales of the dynamics to be monitored. 

Description of a typical element in the schematic of an optical train. 

Spectrometers can be arranged either as single-beam or as double-beam instruments (Fig. 2.67). hi both cases, the optical properties of the sample are compared to those of a reference. In double-beam spectrometers, the light beam is divided so that one partial beam interacts with the sample, the second one with the reference. The light detector accepts both beams in parallel, and their intensity is compared. In single-beam spectrometers, the comparison of sample and reference effects is done consecutively, i.e. two consecu- 

Gas lasers became available to date thanks to reasonable prices. Their restrictions are the same as those of gas discharge lamps. Generally, with lasers the emission lines are more narrow-band. Tunable dye lasers would be the ideal light source. However, they are too sophisticated and too expensive. Furthermore, the dyes used are not sufficiently stable due to their light sensitivity. 

Among discontinuously emitting sources, LEDs are particularly attractive for sensor applications. The reasons are their small dimensions, their low energy demand and their manufacturing technology, which is compatible with 

Laser diodes (Fig. 2.69, bottom) are made from the same materials as LEDs, but their structure is somewhat more complex, and they are processed differently. Low current density at the pn-junction results in non-coherent emission. 

Wavelength Selection and Light Detectors. There are two ways to separate a certain range of wavelengths, either by means of optical Zfers or by monochromators. Optical filters absorb parts of a wavelength mixture in such a way that only 

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Proceedings of the S odety ofPhoto-Optical Instrumentation Engineers, Journal of Vacuum S dence and Technology, Journal of Electrochemical S odety. 

Chopra, Proceedings of the S ociety of Photo-Optical Instrumentation Engineers (Smart Structures and Materials 1996—Smart Structures and Integrated Systems) Proceedings of the Conference, San Diego, Calif., Feb. 26—29, 1996) 2717, 20—26, (1996). 

R. O. Claus and K. A. Murphy, Proceedings of the Society of Photo-Optical Instrumentation Engineers 2nd International Conference on Optoelectronic Science and Engineering 94, Beijing, Chiaa, Aug. 15—18,1994, 2321, 404—407 (1994). 

M. S. Khan, Proceedings of the Society of Photo-Optical Instrumentation Engineers (Metalj Nonmetal Microsystems Physics, Technology, and Applications Proceedings of the Workshop, Polanica Zdroj, Poland, Sept. 11—14, 1995, 2780, 56—59 (1996). 

In electron-optical instruments, e.g. the scanning electron microscope (SEM), the electron-probe microanalyzer (EPMA), and the transmission electron microscope there is always a wealth of signals, caused by the interaction between the primary electrons and the target, which can be used for materials characterization via imaging, diffraction, and chemical analysis. The different interaction processes for an electron-transparent crystalline specimen inside a TEM are sketched in Eig. 2.31. 

The impact of electron-optical instruments in materials science has been so extreme in recent years that optical microscopy is seen by many young research workers as faintly fuddy-duddy and is used less and less in advanced research this has the unfortunate consequence, adumbrated above, that the beneficial habit of using a wide range of magnifications in examining a material is less and less followed. 

Leonelli, J., and Althouse, M.L. (eds) (1999) Air Monitoring and Detection of Chemical and Biological Agents, SPIE Society of Photo-optical Instrumentation Engineers. 

The Munsell book standards corresponding to the limiting colors may even serve as material standards for industrial color control. In a material standard system the sample is compared with a standard by eye without the use of any meter or optical instrument. The success and popularity of these systems are largely due to their simplicity of application. The ability of the human eye to compensate for various illuminants and surroundings makes it possible for this system to give results even under mediocre conditions. The most critical work with material standards requires carefully controlled observing conditions. 

Hiraoka, H., Sendova, M., Lee, C.H., Latsch, S., Wang, T.M., Sung, J., Hung, C.T., and Smith, T., Proceedings of the SPIE—The International Society for Optical Engineering, Society of photo-optical instrumentation engineering, Bellingham, WA, 1995, 260. 

Figure 7.8 Optical properties of solid gold spheres of indicated diameters, (a) absorption, (b) scattering. Redrawn from Cortie et a. [118], Copyright (2005) Society of Photo-Optical Instrumentation Engineers.

Advanced computerisation and sensorisation and developments in the field of multielement optical detectors (CCD and PDA) and fibre optic remote spectroscopy have added modularity and flexibility. Silica-silica fibres used for spectroscopy applications are multimode with core diameters from 50 to 1000 p,m. The application of new technologies to optical instrumentation (e.g. improved gratings in spectrographs, the use of... 

Diaz-Garcia J., Costa-Femandez J.M., Bordel-Garcia N., Sanz-Medel A., Room-Temperature Phosphorescence Fiber-Optic Instrumentation for Simultaneous Multiposition Analysis of Dissolved Oxygen, Anal. Chim. Acta 2001 429 55-64. 

Different approaches based on NIR spectroscopy have led to the development of different optical instrumentation which are almost all at a research level58. 

Wolfbeis O.S., Fluorescence-based optical sensors for biomedical applications, In Scheggi A.M.V., Martelluci, S., Chester, A.N., Pratesi, R. (Eds.), Biomedical Optical Instrumentation and laser-Assisted Biotechnology, Kluwer Academic Publishers, 1996, p.327-337. 

Proceedings Biomedical Optical Instrumentation and Laser-Assisted Biotechnology Editors A.M. Verga Scheggi, S. Martellucci, A.N. Chester and R. Pratesi. Publisher Kluwer Academic (1996)... 

B Medical, precision and optical instruments, watches and clocks... 

In all walks of life and on all levels of society, one has so many opportunities to admire the marvellous play of light, the importance and the effectiveness of the help provided by optical instruments to extend our sight, and to compensate for its defects,... ]... 

J. R. Lakowicz, ed., Time-Resolved Laser Spectroscopy in Biochemistry III, SPIE (The Society of Photo-Optical Instrumentation Engineers) 1640, Billingham, Washington (1992). 

T. Hirschfeld, M. J. Block, and W. Mueller, Virometer An optical instrument for visual observation, measurement and classification of free viruses, J. Histochem. Cytochem. 25, 719-723 (1977). 

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