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An overview of the high resolution etalon based system

In the earlier versions of the University of Wisconsin HSRL, the separation between aerosol and molecular backscatter signals was made with a high resolution etalon with 0.5 pm bandpass. The Figure 3 shows the receiver of the etalon based system [13]. The backscattered light was collected by the receiver telescope and directed through a fiber optics scrambler. The fiber optics scrambler was used to reduce the range dependence of the receiver spectrometer bandpass due to the angular sensitivity of the etalon transmission [12]. After collimation, the signal was prefiltered with an interference filter and a pair of low resolution etalons. After passing the dual aperture, the light was directed to the high resolution etalon. The high resolution etalon was slightly tilted with respect to the optical axis. This allowed the light that did not pass through the etalon to be reflected back to the dual aperture and to the molecular channel photodetector (PMT1). The light that passed through the high resolution etalon was detected with the aerosol channel photodetector (PMT2). The signal detected with the aerosol channel was a combination of aerosol backscatter spectrum and the center of molecular backscatter spectrum. The signal detected with the molecular channel was a combination of the wings of the molecular spectrum and the part of the aerosol backscatter spectrum that did not pass the high resolution etalon.

  
Figure 3: The receiver of the high resolution etalon based system. The backscatter signal is collected with a telescope. The fiber optics scrambler reduces the range dependence of the receiver spectrometer bandpass due to the angular sensitivity of the etalon transmission. The signal is background filtered with a interference filter and a pair of low resolution etalons. The separation between aerosol and molecular backscatter signals is done in the high resolution etalon. The part of the spectrum that transmits the etalon is combination of aerosol backscatter spectrum and the center of molecular backscatter spectrum (PMT2). The signal detected with PMT1 is a combination of the wings of the molecular spectrum and the part of the aerosol backscatter spectrum that did not pass the high resolution etalon.



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Next: A short introduction Up: Introduction Previous: Introduction
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Paivi Piironen
Tue Mar 26 20:49:55 CST 1996