N.Maragos 1 , S.Maltezos 1 , V.Gika 1 , E. Fokitis 1 , T.Omatsu 2
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SLM Laser Optical Amplification Design for HSRL Atmospheric Monitoring in UHE Cosmic Ray ObservatoriesN.Maragos1, S.Maltezos1, V.Gika1, E. Fokitis1, T.Omatsu21National Technical University of Athens2Chiba University, Japan
1outline FrameworkAtmospheric monitoring in VHE Gamma Ray and UHE Cosmic Ray observatoriesLimitations of standard elastic lidar and Raman lidar.High Spectral Resolution LidarRecent progressFocus in HSRL laser transmitter. Design of an optical amplification configuration for the energy scaling of a pulsed SLM Nd:YVO4 laser. Simulations Experimental setup and preliminary results22CR observatories and atmospheric monitoring When UHECR and VHE Gamma rays strike the Earth's atmosphere, they initiate cascades of secondary particles called Air Showers.
Detailed observation of the AS can give information about the energy and the nature of the primary cosmic ray. A variety of Air Shower detection techniques have been studied and implemented in cosmic ray observatories. (fluorescence telescopes UHECR, Cherenkov telescopes for VHE-Gamma Rays)
Atmosphere can alter the received signal significantly and thus give misleading results about the energy spectrum of the Cosmic Rays.
Lidar systems (simple elastic, Raman) are installed to monitor the transparency of the atmosphere. Lidar data can be applied in the reconstruction process3
Limitations of simple elastic and raman lidar Simple elastic lidar
= mol+ aer : atmospheric backscatter coefficient = mol+ aer : atmospheric extinction coefficient The molecular parts can be accurately predicted if atmospheric density is known. Two remaining unknowns: aer , aerTheoretical models (eg Klett Applied Optics, Vol 20, pp 211) to predict aer /aer are implemented to solve the lidar equation but lead to significant systematic errors. RAMAN lidarRaman lidar technique solves this problem with the help of an extra lidar profile where aer =0. This is accomplished with the detection of the inelastic (Raman-shifted) backscattered signal from the atmospheric molecules.Limitations derives in this case because the Raman signal is almost 1000 times weaker than the elastically backscattered one.
4High spectral resolution lidar (HSRL)This method utilizes the Doppler frequency shifts produced when photons are scattered from molecules in random thermal motion.
The elastically backscatter signal consists of :
a Doppler broadened (~1 GHz FWHM) signal from the lightweight, fast moving atmospheric molecules a much less Doppler affected (~30 MHz FWHM) signal from the heavier aerosols or cloud particles.
These signals are spectrally isolated with the use of narrow iodine filters or Fabry-Perot interferometers, giving an extra lidar profile with aer =0, as in the Raman lidar method but with much stronger signal.
First demonstrated in: "High spectral resolution lidar to measure optical scattering properties of atmospheric aerosols. 1: Theory and instrumentation", S. T. Shipley, D. H. Tracy, E. W. Eloranta, J. T. Trauger, J. T. Sroga, F. L. Roesler, and J. A. Weinman, APPLIED OPTICS / Vol. 22, No. 23 / 1 December 1983,5Hsrl developmentWe are working on the development of a prototype HSRL to be used for the atmospheric monitoring in Cosmic Ray observatories.In our resent work we are focusing in designing the laser transmitter.Laser specification to be used in the HSRL transmitter:Narrow spectral output (