A 1024#x00D7;8 700ps time-gated SPAD line sensor for laser raman spectroscopy and LIBS in space and rover-based planetary exploration

摘要

Raman spectroscopy is a nondestructive, label-free optical analysis technique used to obtain structural and compositional information without any advance preparation. However, the Raman signature is often overwhelmed by strong fluorescence background. Due to its generation mechanism, the fluorescence background can be filtered out in the “time domain” even though it contains exactly the same wavelength components as the Raman signature. To realize such functionality, highly sensitive, time-resolved imagers, such as an intensified charge-coupled devices (iCCDs) or streak cameras are the sensors of choice. These delicate instruments are generally costly, bulky, and unsuitable for space flight and planetary landings. Time-gated, single-photon avalanche diode (SPAD) cameras have been studied for time-resolved imaging modalities, such as fluorescence lifetime imaging microscopy [1], taking advantage of SPAD picosecond temporal resolution as well as single-photon detection capability. Recently, a 128×128, time-gated SPAD array has been proposed to tackle fluorescence background reduction from highly fluorescent minerals for laser Raman spectroscopy targeting potential future on-surface planetary instruments [2]. However, due to long gating (∼30ns), the obtained Raman signature was contaminated by background noise, which overcame minor Raman peaks. In addition, due to extensive on-pixel electronics, the fill factor was reduced, resulting in low photon detection efficiency (PDE). A larger SPAD with sub-nanosecond time-gating was proposed and implemented as a single pixel, operated with a mechanical scanning stage to obtain a Raman signature [3]. To avoid any mechanical moving parts or multiple detectors to obtain a complete Raman signature, a 2D array or line sensor format is thus required.