The lidar system has three main subsystems. The laser system and launch facility produces the laser pulses, collimates them, and projects them vertically up through the atmosphere. The receiving telescope collects the returned light and focuses it onto the detector. The detector converts incoming photons to electrical pulses and measures and records their time of arrival. It typically takes 300 millionths of a second for light to travel from the sodium atom  to the telescope.


The LZT lidar system

Pic 2The lidar system employs a frquency-doubled 13 watt Nd:YAG laser (white box) to produce 10 ns pulses at a wavelength of 532 nm. These pulses are used to pump a dye laser (blue box) that is tuned to the sodium D2-line resonanace wavelength of 589 nm. The pulses from the dye laser pass through a diverging lens and 45-degree mirror and then enter the 15 cm launch telescope (white cylinder). The telescope collimates the light, producing a parallel that passes horizontally through a hole in the wall, into the main observatory room.

Pic 2After passing over the 6-metre liquid primary mirror of the Large Zenith Telescope, the beam strikes a flat mirror that reflects it vertically upward.telescope.

Light emitted by sodium atoms excited by the laser is collected by the LZT primary mirror and focussed on the detector, located nine meters above, at the telescope's prime focus.

Pic 2The detector employs four sensitive photomultiplier tubes that produce an electrical pulse for each detected photon.

Pic 2

These pulses are recorded by an electronic system that can count up to a billion pulses per second and record their arrival times to an accuracy of a few billionths of a second.