15 December 1998 Quality modulation parameter for a quasi-static optical modulator based on frustrated total internal reflection applied to infrared spectroscopy
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Abstract
An optical modulator based on the Frustrated Total Internal Reflection represents an alternative to the optical modulation based on the classic chopping wheel. This alternative permits to eliminate the presence of moving parts within IR spectroscopy equipment. The proposed design of the modulator has two elements of dielectric material. These elements are separated by an air gap. The radiation passes through the air gap from the first element to the second one. The transmission coefficient present a non- linear dependence on the separation distance. Furthermore, the micro-movement has a non-sinusoidal waveform. Both effects result on a non-sinusoidal waveform of the intensity modulation and make the energy of the modulated radiation to be distributed among several harmonics. The quality of the modulation has been studied by means of the optical efficiency and the total harmonic distortion index. The modulator based on the Frustrated Total Internal Reflection, FTIR, and an ideal square chopper can be compared using the optical efficiency coefficient. The total harmonic distortion index shows the ratio of chopper energy that is not hold by the main harmonic does.
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Juan Antonio Ortega Redondo, Juan Antonio Ortega Redondo, Juan A. Chavez, Juan A. Chavez, Jordi Salazar, Jordi Salazar, Antoni Turo, Antoni Turo, Miguel J. Garcia, Miguel J. Garcia, } "Quality modulation parameter for a quasi-static optical modulator based on frustrated total internal reflection applied to infrared spectroscopy", Proc. SPIE 3493, Spectroscopic Atmospheric Environmental Monitoring Techniques, (15 December 1998); doi: 10.1117/12.332648; https://doi.org/10.1117/12.332648
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