Light multiple mirrors

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

More complex multiple-reflection systems that give a much greater number of traversals have also been developed. For example, Tuazon et al. (1980) describe a system using four collecting mirrors that focus the light onto four field mirrors. The advantages and disadvantages of such multiple-mirror cells are discussed by Hanst (1971) and Hanst and Hanst (1994). 

Placing the array of telescopes on a common mounting with a means for optically combining the separate light beams. All OPDs can be equal (theoretically), thus requiring only modest error correction to obtain coherency between telescopes. This approach is known as the multiple mirror telescope (MMT). 

Gaseous samples require long path length cells to produce absorption bands of reasonable intensity up to several metres of optical path are obtainable from cells incorporating mirrors which produce multiple reflections. For GC-IR, light pipes provide the best sensitivity (p. 117). 

Fig. 9.1. A sorting flow cytometer (MoFlo by Cytomation). The outward complexity of this instrument compared with benchtop cytometers (see Fig. 1.5) reflects the electronic controls necessary for sorting as well as the adaptability of research cytometers with regard to multiple lasers and to the filters and mirrors in the optical light path for multiparameter analysis.

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