Photon-counting distributed free-space spectroscopy

Abstract

Spectroscopy is a well-established nonintrusive tool that has played an important role in identifying and quantifying substances, from quantum descriptions to chemical and biomedical diagnostics. Challenges exist in accurate spectrum analysis in free space, which hinders us from understanding the composition of multiple gases and the chemical processes in the atmosphere. A photon-counting distributed free-space spectroscopy is proposed and demonstrated using lidar technique, incorporating a comb-referenced frequency-scanning laser and a superconducting nanowire single-photon detector. It is suitable for remote spectrum analysis with a range resolution over a wide band. As an example, a continuous field experiment is carried out over 72 h to obtain the spectra of carbon dioxide (CO2) and semi-heavy water (HDO, isotopic water vapor) in 6 km, with a range resolution of 60 m and a time resolution of 10 min. Compared to the methods that obtain only column-integrated spectra over kilometer-scale, the range resolution is improved by 2–3 orders of magnitude in this work. The CO2 and HDO concentrations are retrieved from the spectra acquired with uncertainties as low as ±1.2% and ±14.3%, respectively. This method holds much promise for increasing knowledge of atmospheric environment and chemistry researches, especially in terms of the evolution of complex molecular spectra in open areas.

Theoretical and experimental investigation of chalcogenide suspended waveguide gas sensor

“…Different spectroscopy techniques play an important role in the field of sensing. [1][2][3][4][5][6][7][8][9][10][11] Laser absorption spectroscopy, based on Lambert-Beer law, provides information about the type and concentration of gases by measuring the wavelength and intensity of absorption lines. 12 This detection method is less affected by cross-sensitivity among gas components compared to nonoptical methods.…”

Noise-tolerant LiDAR approaching quantum-limited precision

“…In a typical LiDAR, the information of targets is encoded into some degrees of freedom of the light eld, such as amplitude, frequency 11 , phase 12,13 and polarization 14,15 . This information helps to extract signal photons and reconstruct targets.…”

Research on a capacitive MEMS pressure sensor based on through glass via

“…Various sensors are widely used in different fields. [1][2][3][4][5][6][7][8][9][10][11][12] Capacitive Microelectro Mechanical Systems (MEMS) pressure sensor has become good substitute for piezoresistive pressure sensor due to its advantages of high sensitivity, low-temperature drift, low power consumption, and low fabricated cost. 13,14 Particularly, the capacitance MEMS pressure sensor operating in touch mode can offer large dynamic range, improved linearity, and high overvoltage protection.…”