Near-infrared imaging of water vapour in air

Abstract

This study proposes a near-infrared (NIR) imaging method for two-dimensional distributions of water vapour (WV) in the open air. A wavelength of 1872 nm, at which the dependence of the absorption coefficient on the WV concentration is the largest in the ν 2 + ν 3 band of water molecules, was employed for imaging. The measurement system was a star imaging system, comprising a laser light source and an NIR camera. A measurement space with 0.08-m diameter and 0.30-m length was ensured to obtain the 2D absorbance images of moist air emitted from a gas nozzle and the breath air exhaled from a human subject with and without a mask. The images clearly showed the distributions of WV that flowed around a pipe and impinged on a plate. The exhaled air was clearly visualised, and the difference in air permeability between the masks was demonstrated. These results indicate the potential of the NIR imaging method for various applications that require WV flow visualisation, WV source identification, and evaporation process observation.

Chip-scale, CMOS-compatible, high energy passively Q-switched laser

“…Ever since its invention, Q-switching has remained the common technique for generating pulses of very high energy which found applications in range nding and sensing, micromachining, and medicine among others [2][3][4][5][6][7][8][9][10][11]. In the eye safe spectral window of the extendedshort-wave infrared >1.7 µm, which is important for biological imaging, environmental monitoring, spectroscopy, free space communications and even recently envisaged local area networks (where ber loss is acceptable) [12][13][14][15], a high energy pulsed laser can play a key role. For example, Q-switched lasers are used in laser surgery for precise cutting of biological tissue, such as in ophthalmic and spinal surgery [5][6][7][8].…”