Design of a High Spectral Resolution Lidar for Atmospheric Monitoring in EAS Detection Experiments E. Fokitis a , P. Fetfatzis a , A. Georgakopoulou a , S. Maltezos a , and A. Aravantinos b a Physics Department, National Technical University of Athens, 9, Heroon Polytechniou, ZIP 15780, Athens, Greece b Physics Department, Technological Educational Institution of Athens, Agiou Spiridonos, ZIP 12210, Athens, Greece A High Spectral Resolution Lidar (HSRL) is designed in order to achieve high accuracy measuring the aerosol to molecular scattering coefficients ratio. This type of Lidar consists of a Continuous Wave Single Longitudinal Mode laser beam at 532 nm, a receiver with a parabolic mirror and analyzes spectrally the scattered light in a Fabry- Perot Cavity. The great wavelength sensitivity of this system allows the separation of the aerosol and molecular component due to their different levels of Doppler effects on the scattered laser light. We present a study of the effects of the various levels of CCD cooling on the sensitivity of this. Firstly we discuss preliminary experimental results based on a Fabry-Perot etalon with free spectral range (FSR) 0.1 cm -1 , the expected performance of a etalon with FSR of 0.05 cm -1 , under construction, and with finally an aerosol parameter analysis in Simulation Codes for EAS. 1. INTRODUCTION In this paper we present the work of our team in the atmospheric monitoring issue for EAS De- tection experiments. In the measurements of air- fluorescence yield for the detection of Ultra High Energy Cosmic Rays, there is a contribution due to the air-Cherenkov signal scattered mainly by the aerosol particles. Therefore, there is a need to monitor the degree of this type of scattering in or- der to correct the total signal and obtain the air- fluorescence signal. The most common method for measuring the aerosol induced scattering is using the Elastic or Raman Lidar Method. In this work, we present the progress in an alter- native method using the High Spectral Resolu- tion Lidar (HSRL). This is continuation of recent work [3], where now we emphasize on the study of the performance of a candidate laser source for the HSRL. This apparatus is designed in order to achieve high accuracy measuring the aerosol to molecular scattering ratio. It consists of a Con- tinuous Wave Single Longitudinal Mode (SLM) Laser beam at 532 nm, a receiver with a parabolic mirror, and analyzes spectrally the scattered light passing through Fabry-Perot cavities. We mention that [1], first reported a high spectral resolution lidar (HSRL) using a narrow- band laser and a high resolution Fabry-Perot etalon to separate the aerosol (Mie) and molecu- lar (Rayleigh) scattering. More recently, (see [2]), demonstrated aerosol and temperature measure- ments using a HSRL based on an iodine vapor fil- ter, and the temperature in the stratosphere was obtained from the Mie-filtered signal. The HSRL can give simultaneously, for each atmospheric height layer, both the aerosol and the molecular scattered intensity from a ground based laser emitter. This capability is due to the interferometric measurement method, that is, the Fabry-Perot interferometer in the LIDAR re- ceiver. Additionally, in the aerosol scattering HSRL, the narrow linewidth of the laser trans- mitter makes it possible both to separate the con- tributions from aerosol particles and atmospheric molecules, and to calculate the aerosol extinction without assuming the lidar ratio (defined as the ratio between the extinction and backscattering Nuclear Physics B (Proc. Suppl.) 190 (2009) 261–265 0920-5632/$ – see front matter © 2009 Elsevier B.V. All rights reserved. www.elsevierphysics.com doi:10.1016/j.nuclphysbps.2009.03.097