scholarly journals A Short Review of Cavity-Enhanced Raman Spectroscopy for Gas Analysis

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1698
Author(s):  
Christian Niklas ◽  
Hainer Wackerbarth ◽  
Georgios Ctistis
Keyword(s):  
Raman Spectroscopy ◽  
Laser Beam ◽  
Gas Sensors ◽  
Optical Sensors ◽  
Lower Cost ◽  
Short Review ◽  
Gas Analysis ◽  
Beam Power ◽  
Laser Beam Power ◽  
Wide Range

The market of gas sensors is mainly governed by electrochemical, semiconductor, and non-dispersive infrared absorption (NDIR)-based optical sensors. Despite offering a wide range of detectable gases, unknown gas mixtures can be challenging to these sensor types, as appropriate combinations of sensors need to be chosen beforehand, also reducing cross-talk between them. As an optical alternative, Raman spectroscopy can be used, as, in principle, no prior knowledge is needed, covering nearly all gas compounds. Yet, it has the disadvantage of a low quantum yield through a low scattering cross section for gases. There have been various efforts to circumvent this issue by enhancing the Raman yield through different methods. For gases, in particular, cavity-enhanced Raman spectroscopy shows promising results. Here, cavities can be used to enhance the laser beam power, allowing higher laser beam-analyte interaction lengths, while also providing the opportunity to utilize lower cost equipment. In this work, we review cavity-enhanced Raman spectroscopy, particularly the general research interest into this topic, common setups, and already achieved resolutions.

scholarly journals The influence of laser re-melting on microstructure and hardness of gas-nitrided steel

2016 ◽  
Vol 36 (1) ◽  
pp. 18-22 ◽  
Author(s):  
Dominika Panfil ◽  
Piotr Wach ◽  
Michał Kulka ◽  
Jerzy Michalski
Keyword(s):  
Laser Beam ◽  
Laser Treatment ◽  
Diffusion Zone ◽  
Nitrided Layer ◽  
Nitriding Process ◽  
Beam Power ◽  
Gas Nitriding ◽  
Nitrided Steel ◽  
Laser Beam Power ◽  
And Diffusion

Abstract In this paper, modification of nitrided layer by laser re-melting was presented. The nitriding process has many advantageous properties. Controlled gas nitriding was carried out on 42CrMo4 steel. As a consequence of this process, ε+γ’ compound zone and diffusion zone were produced at the surface. Next, the nitrided layer was laser remelted using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as single tracks with the use of various laser beam powers (P), ranging from 0.39 to 1.04 kW. The effects of laser beam power on the microstructure, dimensions of laser tracks and hardness profiles were analyzed. Laser treatment caused the decomposition of continuous compound zone at the surface and an increase in hardness of previously nitrided layer because of the appearance of martensite in re-melted and heat-affected zones

Laser beam power fade induced by system and atmospheric effects

1982 ◽  
Vol 21 (13) ◽  
pp. 2432 ◽  
Author(s):  
U. Halavee ◽  
M. Tamir ◽  
E. Azoulay
Keyword(s):  
Laser Beam ◽  
Beam Power ◽  
Atmospheric Effects ◽  
Laser Beam Power ◽  
Power Fade

scholarly journals Manufacturing Technology and Properties of Fe/TaC Metal Matrix Composite Coatings Produced on Medium Carbon Steel Using Laser Processing—Preliminary Study on the Single Laser Tracks

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5367
Author(s):  
Dariusz Bartkowski
Keyword(s):  
Laser Beam ◽  
Metal Matrix Composite ◽  
Matrix Composite ◽  
Laser Processing ◽  
Metal Matrix ◽  
Steel Substrate ◽  
Composite Coatings ◽  
Tantalum Carbide ◽  
Beam Power ◽  
Laser Beam Power

The paper presents study results of Fe/TaC metal matrix composite coatings produced on tool steel using laser processing of TaC pre-coat. The Fe/TaC coatings were produced in two steps. First, a pre-coat in the form of a paste based on tantalum carbide and water glass was made and then applied to the steel substrate. In the second step, the TaC pre-coat was remelted with steel substrate using a diode laser beam with a rated power of 3 kW. A constant scanning speed of the laser beam of 3 m/min and three types of laser beam power: 500 W, 800 W and 1100 W were applied. Tests were carried out on three different thicknesses of the TaC pre-coat: 30 µm, 60 µm and 90 µm. The influence of pre-coat thickness and laser beam power on the microstructure, chemical composition and microhardness were analyzed. A possibility of producing coatings with a characteristic composite structure was found, where the iron from the substrate became the matrix, and the introduced tantalum carbides—the reinforcing phase. It was found that too high power of the laser beam leads to complete melting of the introduced primary TaC particles. It was also found that the use of a thicker TaC pre-coat contributes to microhardness increase.

scholarly journals Retrieval of the photochemical reflectance index for assessing xanthophyll cycle activity: a comparison of near-surface optical sensors

2014 ◽  
Vol 11 (22) ◽  
pp. 6277-6292 ◽  
Author(s):  
A. Harris ◽  
J. A. Gamon ◽  
G. Z. Pastorello ◽  
C. Y. S. Wong
Keyword(s):  
Optical Sensors ◽  
Xanthophyll Cycle ◽  
Lower Cost ◽  
Photosynthetic Activity ◽  
Spectral Response ◽  
Systematic Bias ◽  
Diurnal Changes ◽  
Near Surface ◽  
Photochemical Reflectance Index ◽  
Wide Range

Abstract. Unattended optical sensors are increasingly being deployed on eddy covariance flux towers and are often used to complement existing vegetation and micrometeorological measurements to enable assessment of biophysical states and biogeochemical processes over a range of spatial scales. Of particular interest are sensors that can measure the photochemical reflectance index (PRI), which can provide information pertaining to leaf pigments and photosynthetic activity. This interest has facilitated the production of a new range of lower-cost multispectral sensors specifically designed to measure temporal changes in the PRI signal. However, little is known about the characteristics (spectral, radiometric and temporal) of many of these PRI sensors, making it difficult to compare data obtained from these sensors across time, geographical locations and instruments. Furthermore, direct testing of the capability of these sensors to actually detect the conversion of the xanthophyll cycle, which is the original biological basis of the PRI diurnal signal, is largely absent, often resulting in an unclear interpretation of the signal, particularly given the wide range of factors now known to influence PRI. Through a series of experiments, we assess the sensitivity of one of the leading brands of PRI sensor (Skye SKR 1800) to changes in vegetation photosynthetic activity in response to changing irradiance. We compare the results with those obtained using a more expensive industry-standard visible to near-infrared hyperspectral spectrometer (PP Systems UniSpec) and determine the radiometric compatibility of measurements made by the different instruments. Results suggest that the SKR 1800 instrument is able to track rapid (seconds to minutes) and more gradual diurnal changes in photosynthetic activity associated with xanthophyll cycle pigment conversion. Measurements obtained from both the high and lower cost instrument were significantly linearly correlated but were subject to a large systematic bias, illustrating that differences in instrument configuration (e.g. spectral response functions and band positions) can have a large impact on the PRI measurement values obtained. Despite differences in absolute PRI values, significant correlations were observed between the canopy PRI derived from both the SKR 1800 and the UniSpec instruments, and the epoxidation state of the xanthophyll cycle (r2 = 0.46 p < 0.05 and r2 = 0.76 p < 0.01, respectively). However, the dynamic range of the SKR 1800 PRI signal was often lower than more expensive instruments and thus the lower cost multispectral instrument may be less sensitive to pigment dynamics related to photosynthetic activity. Based on our findings, we make a series of recommendations for the effective use of such sensors under field conditions and advocate that sensors should be fully characterized prior to their field deployment.

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