LALINET

The multiwavelength raman Lidar is operational in the Atmospheric Research Laboratory site since September 2016. It uses a Continumm Surelite II Nd-YAG laser at 1064 nm, 532 nm and 355 nm with total energy for all wavelength at exit port of 590 mJ and 10 Hz repetition rate. Laser beam is not expanded with a laser divergence around 0.5 mrad. The optical system uses a coaxial configuration setup pointing 5 degrees out of the zenith. The Newtonian telescope’s mirror has 203 mm diameter. Focal length is 1000 mm resulting in a f/5 system. An iris is used at the focal plane which gives a full overlap around 200 m.

No fiber optics are used and light passing through the iris goes directly in the optical detection box. Beam splitter, polarizing bandpass filters and interference filters separate the signals. Elastics back scattered signal 1064 nm are collected in a Avalanche photodiode from Licel. Elastic signals from 532 nm and 355 nm (cross and co polarized) and the inelastic signals due to the raman cross-section of N2 (387 nm and 607 nm), H2O (408 nm) are collected in different photo-multiplier-tubes. Signals from 355 and 532 nm (cross and co polarized) are recorded in analog and photon-count modes simultaneously, while 607 nm and 408 nm only in photon counting mode. A neutral density filter is used to attenuate the elastic signal avoiding saturation, and a good signal to noise ratio (S/N) is found around 15 km depending on the atmospheric conditions. The N2 channel, 1-min average signals have good S/N up to 10 km but only during night time. For the H2O channel, 1-min average signals have good S/N only up to 4 km during night time.