Wide dynamic range laser remote sensing detection chain

Nowadays, lidar is widely used in many atmospheric applications by taking advantage of the properties of laser sources and the progress made, both in the development of new photodetectors and in the sophistication of signal conditioning and processing. Wide dynamic range is an essential feature for atmospheric lidar when the backscattered laser signal varies over many orders of magnitude. Therefore, the lidar detection chain must incorporate a device that ensures this important feature. This can be performed using a variable amplification stage in the electronic detection chain. The amplification circuit developed consists of a low noise preamplifier LNP) cascaded with a variable gain amplifier (VGA). The amplification circuit can be then operated in several gain modes, which enables a wide range of input signals to be processed over several orders of magnitude (10⁵). Low noise, high speed, linear response and stability are the main specifications pursued during the design. The amplification circuit is a main part of the optoelectronic detection chain that consists mainly of a receiving optics, a photodetector (Si APD), a low noise preamplifier (LNP: 20 dB / 300 MHz / 0.7 nV/Hz^1/2), a variable gain amplifier (VGA: 0 – 60 dB / 375 MHz / 1 nV/Hz^1/2) and a fast analog-to-digital converter (ADC: 20 MHz / 12 bit). Noise, which can significantly affect the performance of the detection chain, is discussed along with the techniques used to reduce it. In addition, noise equivalent power (NEP), signal-to-noise ratio (SNR) and detection limit achieved are presented.