Depolarization ratio measurement using single photomultiplier tube in micropulse lidar

Abstract

The conventional dual polarization micropulse lidar uses two separate photomultiplier tubes ͑PMT͒ to detect both the copolarized and cross-polarized beam. The prominent sources of error in the depolarization ratio measurement are mismatch in PMT, improper selection of discriminator threshold and unequal PMT high voltage. In the present work a technique for the measurement of lidar depolarization ratio using only one PMT sensor has been developed. The same PMT detects both copolarized and cross-polarized lidar backscatter. A stepper motor is used along with the mirrors to bring both the received polarization signals over the PMT window. Application of the same PMT minimizes the error caused in the depolarization ratio measurement due to error in photon counting of an individual channel. The design description of this technique along with the preliminary results depicting its functionality has been mentioned in this article.

Discriminator threshold selection logic to improve signal to noise ratio in photon counting

“…If P 0 is sufficiently large an analog data capture mode [19] can be used for the faithful reproduction of the detected PMT signal. The measured signal P(r) corresponds to the signal counts P s (r) due to atmospheric back-scatter and counts P N due to noise [4]. It is represented as:…”

“…Out of these sensors the PMT is most widely used in UV, visible and near infrared region. PMTs are highly sensitive optical sensor and works at even single photon detection level [2][3][4].…”

Micro-pulse polarization lidar at 15 μm using a single superconducting nanowire single-photon detector

“…The backscatter signals from the white smoke and the road dust are successfully distinguished via different LDR values. In order to eliminate the mismatch of the two detectors which are used to detect signals at two orthogonal polarization states in traditional lidars, optical receivers using a single detector are demonstrated in 2009, either by modulating the polarization state of the outgoing laser [19] or by inserting an optical switch (OS) into the receiver [20]. In such modifications, one can realize detection of the backscatter signals at two polarization states alternately.…”