De La Salle University - Manila

LIDAR

LIDAR SYSTEM

The DLSU Lidar System

The DLSU Lidar system is comprised of an Nd:YAG laser, the transmitting optics, and the receiving system.

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The Laser system

The prime component of the LIDAR system is the Neodymium-doped yttrium aluminum garnet (Nd3+Y3Al5O12 or Nd:YAG) laser that serves as the source of pulsed laser radiation. It is a Q-switched, flashlamp-pumped laser with a 20-Hz pulse repetition frequency and simultaneous outputs at 1064, 532, and 355 nm with maximum output energy of 435, 175 and 125 mJ, respectively.

The Transmitting system

The transmitting system of the LIDAR (Figure 2) is comprised of mirrors and beam expanders. As the beam expanders available do not have the capability of expanding the beam for all wavelengths all at the same time in one beam expander, the beam has to be split into its different wavelength components, which is achieved by using dichroic mirrors.

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Figure 2. Schematic of the transmitting system.

The Receiving system

The receiving system's function is basically to collect the backscattered laser radiation, separate these and direct the backscattered beam for each wavelength to their corresponding detectors. A schematic of the receiving system is shown in Figure 3 below. A Newtonian telescope, with a diameter of 200 mm and a focal length of 800 mm, collects the backscattered beam and directs it to a fully optically enclosed receiver assembly containing the receiving optics. An iris is placed at the focal point of the receiving telescope, which limits the field of view of the telescope and reduces the background signal. A plano-convex lens with a focal length of 50 mm then collimates the beam.

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Figure 2. Schematic of the receiving system.