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Introductory Concept
Published in Partha Pratim Sahu, Fundamentals of Optical Networks and Components, 2020
where ℏ = Planck’s constant, Eq = energy level of quasi-stable state of electron and Eg = energy level of the ground state. In a gas laser, the distribution for Eq − Eg is given by an exponential probability distribution, known as the Boltzmann distribution, which changes depending on the temperature of the gas. Although many wavelength emissions are possible, only a single frequency determined by the cavity length is emitted from the laser. When the lasing medium has gases as excitation medium, it is called as gas laser. The examples are He Ne laser, Argon laser, CO2, etc. If the lasing medium is a solid material, then it is called as solid-state laser. If the lasing medium is liquid, then it is called as liquid laser (e.g., dye laser).
Laser Sources Based on Gaseous, Liquid, or Solid-State Active Media
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
As the name suggests, the laser-active media of this type of laser are either single atoms or molecules; often the gas filling comprises a mixture, with constituents other than the laser-active one present having auxiliary functions. Normally, the population inversion required for gain by stimulated emission is via an electric discharge in the gas (mixture); during operation, the gas comprises a significant concentration of electrically charged particles. The attraction of most gas lasers is that they emit their light with very high beam quality, often close to being diffraction-limited. On the downside, gas lasers usually require high voltages to maintain the discharge, and more often than not a substantial amount of electrical power is required. The latter is associated with the very low conversion efficiency from electric input power to laser light output power, which for the particular devices used in laser spectroscopy and imaging is rarely better than 10−3 and frequently less than 10−4. This means that for a target output power of 1 W, already 1 kW of electrical power is required as a minimum; this means that substantial cooling capacity is required to divert (discharge) heat away from the laser medium, often in the form of circulating water cooling. Because of this, powerful gas lasers are normally rather bulky and have often high operating costs, in particular if the discharge tube has to be replaced when the laser is operated perpetually over lengthy periods of time.
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
In general, gas lasers have better coherence characteristics and are cheaper than other types of lasers. The He–Ne laser is the most economical choice for measurement and control applications based on low-power cw laser output. It operates on a single line at 632.8 nm and the output can be strongly polarized. In addition, it does not require external cooling system; it is very simple to operate and has a long life. However, commercial He–Ne lasers oscillate in two to five longitudinal modes, depending on the power and have limited coherence length. Argon and krypton ion lasers deliver high-power output with extended coherence length. A single line can be selected from the multiline output of the Ar+ or Kr+ lasers, if the end mirror of the laser cavity is replaced by a prism, while a single longitudinal mode can be isolated by incorporating a Fabry–Perot etalon in the cavity.
Timing and style of high-temperature metamorphism across the Western Gawler Craton during the Paleo- to Mesoproterozoic
Published in Australian Journal of Earth Sciences, 2019
A. J. Reid, J. A. Halpin, R. A. Dutch
Zircon and monazite and geochronology was undertaken via Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) at the University of Adelaide and University of Tasmania, respectively. Zircons were separated using standard crushing, density and magnetic techniques, mounted in epoxy resin and imaged by cathodoluminescence (CL) to determine their internal structure. Analyses were performed using is a 193 nm Resonetics laser ablation unit coupled with an Agilent 7300 quadrupole ICPMS. Data from the ICPMS were processed using Iolite v2.5 software and the VisualAge data reduction scheme (Paton, Hellstrom, Paul, Woodhead, & Hergt, 2011; Paton et al., 2010). Monazite geochronology was undertaken in situ using polished rock blocks. Monazite grains were imaged on a field emission-SEM for high-resolution backscattered electron (BSE) images to reveal zonation. Analyses were performed using a 193 nm Coherent Ar–F gas laser coupled to an Agilent 7500cs quadrupole ICPMS. All monazite data reduction calculations and error propagations were done within Microsoft Excel® via macros designed at the University of Tasmania and summarised in Halpin et al. (2014).
Effects of process parameters on the quality aspects of weld-bead in laser welding of NiTinol sheets
Published in Materials and Manufacturing Processes, 2019
Susmita Datta, Mohammad Shahid Raza, Partha Saha, D. K Pratihar
Brittle intermetallic phases like Ti2Ni and Ni3Ti are formed during welding of NiTinol, and they reduce the quality of the weld considerably. [31–33] Segregation of titanium takes place during cooling and helps in the formation of Ti2Ni precipitates at grain boundaries. Mechanical properties of the alloy are greatly affected by the precipitations of the brittle intermetallic phase, which act as a center for crack initiation. [33] The intermetallic deposition in the weld pool can be reduced by achieving a higher solidification rate [34], which can be achieved through the laser welding process. [35] Thus, it is very useful for welding of materials that are sensitive to the formation of brittle phases during welding. CO2 gas laser [32,36], Nd:YAG solid-state laser [37–40], Yb:YAG laser [41] and fiber laser [42–44] were used by researchers for the welding of NiTinol alloy.
Effect of cleaning gas stream on products in selective laser melting
Published in Materials and Manufacturing Processes, 2019
Dinh Son Nguyen, Hong Seok Park, Chang Myung Lee
Influences of shielding gas in metal melting was analyzed in some prior studies.[15,16] Interactions between the shielding gas, laser beam, and plume on the laser manufacturing process,[17] as well as the effects of different shielding gases including argon, helium, and nitrogen on a laser processing, have been studied.[18] The effects of the shielding gas on the properties of products printed by powder bed fusion are obvious. However, the influence of the cleaning gas flow has not been sufficiently considered. Meanwhile, in practice, vertical blowing from the top of the chamber toward the substrate surface in an EOS M 400-4 printer and horizontal blowing in a series of printers from SLM Solution, Ltd.[19] are the main methods of cleaning gas flow. This study points out how product properties are affected by the cleaning gas flow rate in SLM process.