Laser-induced plasma imaging for low-pressure detection

Abstract

A novel technique based on laser induced plasma imaging is proposed to measure residual pressure in sealed containers with transparent walls, e.g. high voltage vacuum interrupter in this paper. The images of plasma plumes induced on a copper target at pressure of ambient air between 10Pa and 10Pa were acquired at delay times of 200ns, 400ns, 600ns and 800ns. All the plasma images at specific pressures and delay times showed a good repeatability. It was found that ambient gas pressure significantly affects plasma shape, plasma integral intensities and expansion dynamics. A subsection characteristic method was proposed to extract pressure values from plasma images. The method employed three metrics for identification of high, intermediate and low pressures: the distance between the target and plume center, the integral intensity of the plume, and the lateral size of the plume, correspondingly. The accuracy of the method was estimated to be within 15% of nominal values in the entire pressure range between 10Pa and 10Pa. The pressure values can be easily extracted from plasma images in the whole pressure range, thus making laser induced plasma imaging a promising technique for gauge-free pressure detection.

On-line vacuum degree monitoring of vacuum circuit breakers based on laser-induced breakdown spectroscopy combined with random forest algorithm

“…The researchers proposed a segmented feature extraction method using three metrics (distance between the target and the plasma center of mass, integrated intensity of the plasma spectral line, and plasma plume length) to distinguish between different pressure ranges, from 10 −2 Pa to 10 5 Pa for the vacuum level. 25 In our 2022 study, we veried that laser induced plasma has good stability and repeatability, further conrming the feasibility of the vacuum level detection method for vacuum switches using the LIBS technique. 26 Despite the promising results, this method still requires further improvement in terms of efficiency, accuracy, and anti-interference capability of the feature extraction algorithm to address complex working conditions in future practical applications.…”

Optical diagnostics of laser-produced plasmas

“…Here, plume splitting and late time nanoparticle thermal emissions are observed. 2D gated images of expanding LPPs are also used for matrix correction in LIBS (Zhang et al, 2020) and measurement of residual pressure in sealed containers (Yuan et al, 2018). Monochromatic imaging is performed by positioning narrow bandpass filters corresponding to various emission lines in front of the camera, and this method is useful for recording the spatial distribution of species (atoms, ions, molecules, etc.)…”

Radial characteristics of laser-induced plasma under the influence of air pressure

“…The LIP process is very complex due to the dynamics of massive microscopic particles, in which the timescale ranges from femtoseconds to microseconds [8]. As a key factor that influences the LIP process, the air pressure can significantly affect the collision and movement between LIP initial particles and gas molecules, which have been studied by spectral and fast imaging analyses [9][10][11][12].…”

“…To clarify the influence of air pressure on LIP and its mechanism, researchers have carried out a lot of work on LIP in vacuum. Yuan et al analyzed Cu plasma at low air pressure using fast imaging and found that ambient pressure could significantly affect the plasma morphology [11]. Farid et al induced Cu plasma with a femtosecond pulsed laser at 10 −5 -760 Torr, and found that the spectra of Cu plasma were the strongest at 300 Torr, and the spectral intensity at 760 Torr was weaker than that at 300 Torr [13].…”