Atmospheric transmittance measurements of Nd:YAG, iodine and CO 2 laser radiation over 8.6 km, and statistical analysis of extinction coefficients

Abstract

A long-range multiwavelength laser transmissometer for measuring atmospheric extinction of iodine laser radiation (1.315 μm), simultaneously with Nd:YAG (1.06 μm) and CO 2 (10.6 μm) laser radiation was designed, built and operated under different atmospheric conditions, over a distance of 8.6 km in hilly terrain near Tübingen, Germany. Beam extinction was obtained by measuring the ratio of the total laser radiation to the total received radiation as collected by a mirror and focused onto a pyroelectrical detector array. Measured values of laser extinction were compared with model predictions (FASCODE 3P) based on simultaneously measured meteorological data as model input parameters. The agreement was found to be very good. It is shown that the atmospheric extinction coefficient of iodine laser radiation can be predicted to a good approximation by a linear equation containing the extinction coefficients of Nd:YAG and CO 2 laser radiation. Statistical analyses of atmospheric laser extinction coefficients are presented for these laser wavelengths. Scatter diagrams of extinction coefficients are presented for the summer and winter season together with an analysis of the annual variability. The iodine laser, if compared to the CO 2 laser, shows advantage in molecular extinction which is, however, overcompensated by aerosol extinction being often more than two orders of magnitude larger for iodine laser than for CO 2 laser radiation.