Development of a NIR-VIS-UV lidar echo emulator

Abstract

Near-infrared, visible and ultraviolet (NIR-VIS-UV) lidar echo emulator (LEE) was developed to emulate the returns of a spatial lidar at three wavelengths (355 nm, 532 nm and 1064 nm) within the framework of the HOLDON project. It is used to characterize the detection chain formed by a HgCdTe avalanche photodiode (MCT APD), read-out integrated circuit (ROIC), and surrounding electronics, which will be used in a lidar remote sensing of earth s atmosphere. It emulates two echoes in the three wavelengths. A short echo (pulse width <10 ns) with optical power dynamic range between 0.2 nW and 200 nW and a long echo (pulse width of about 270 μs) in range from 0.1 pW to 25 pW. The long echo has two adjustable parameters which allow changing the shape of the pulse (from a ramp to a rectangular pulse). The combination of both echoes allows characterizing the detector over the full 60 dB dynamic range, the target for the detection chain. The system consists of only one laser diode at 1064 nm, a driver, and an arbitrary wave generator (AWG) as seed to create the three waveleghts. The second harmonic generation (SHG) technique was used to generate the beam at 532 nm from the 1064nm laser diode. In this case, a non-linear KTP crystal was used. The sum frequency generation (SFG) technique was used to generate the beam at 355 nm from both previous beams. For the SFG, two Periodic Poled Lithium Niobate (PPLN) crystals were used. To optimize the output at 355 nm the temperature of the PPLN crystals was controlled by means of Peltier elements. A LabView program was designed to control all the configuration parameters of both echoes (long and short) and the laser. The software controls also the optimal temperatures where the highest power is reached at 355 nm. The overall system was assembled as an elegant breadboard for easy transportation. The NIR-VIS-UV LEE offers all the necessary requirements for exhaustive characterization of the lidar detection chains at three wavelengths and high dynamic range.