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Laser Radar (LIDAR) for Atmospheric Monitoring

Transient recording and detection modules for Differential Absorption Laser Radar (DIAL)

We are partners with Licel GmbH. Licel makes high performance modular laser radar (Lidar) electronics, specifically transient recorders – a powerful data acquisition system, especially designed for remote sensing applications. To meet the demanding requirements of optical signal detection, a new concept was developed to achieve the best dynamic range together with high temporal resolution at fast signal repetition rates. Licel achieves 10^5 dynamic range by combining analog and digital (photon count data) to provide unique system capabilities. NASA uses this equipment extensively for atmospheric research.

Analog and photon counting detection techniques require different signal conditioning. High speed and high gain amplification is needed for photon counting, whereas a strictly linear amplification below the Nyquist frequency of the A/D converter is necessary for analog measurement. Only the integration of two complete acquisition chains from the preamplifier to the summation memory will therefore enable one to combine both techniques for increased linear dynamic range. This has been done in the Licel transient recorder.

In remote sensing applications like LIDAR (Laser Radar) a photomultiplier looking at a laser pulse sent out into the atmosphere is driven close to saturation by the backscattered light from the near field, but a few hundred microseconds later it is required to detect single photons returning from a distance of 40 to 80 km. This high dynamic range of up to five orders of magnitude is one of the challenges in the detection of LIDAR signals as well as in other techniques like LIF (Laser Induced Fluorescence) or CARS (Coherent Anti Raman Scattering).

 

Photo courtesy of Gerd Baumgarten

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