Different lasers use different materials as the active medium. The medium can be either solid, liquid, or gas, and there are advantages for each in the amount of energy that can be stored, ease of handling and storage, secondary safety hazards, cooling properties, and physical characteristics of the laser output.
Another group of applications is collectively known as materials processing. This includes the processes used in manufacturing. Production facilities use lasers to cut, weld, drill, mark, and heat-treat numerous materials such as metals, plastics, wood, ceramics, and even diamonds. Lasers are much more precise than other mechanical means used to process materials, and lasers make it possible to build devices with tiny, even microscopic, dimensions. A subgroup of this category, medical device manufacturing, relies on lasers to machine stents and other devices for implantation into the human body.
Military uses for lasers are abundant, from range finding to guided munitions to laser aiming devices on firearms. Warfare has been revolutionized by the laser. Law enforcement uses lasers to lift hard-to recover fingerprints and in laser radar speed guns.
Laser printers, bar code readers, unmanned freeway tollbooths, laser pointers—none of these very common devices would be possible without laser technology. This is just a minor sampling; the list of laser applications goes on and on.
Solid-State Lasers
The term “solid-state laser” refers to lasers that use solids as their active medium. However, two kinds of materials are required: a “host” crystal and an impurity “dopant.” The dopant is selected for its ability to form a laser population inversion. The Nd:YAG laser, for example, uses a small number of neodymium ions as a dopant in the solid YAG (yttrium-aluminum-garnet) crystal. Solid-state lasers are pumped with an outside source such as a flash lamp, arc lamp, or another laser. This energy is then absorbed by the dopant, raising the atoms to an excited state. Solid-state lasers are sought after because the active medium is relatively easy to handle and store. Also, because the wavelength they produce is within the transmission range of glass, they can be used with fiber optics.
Diode (Semiconductor) Lasers
Also using solids but considered separately because of their unique characteristics, diode lasers are the most common lasers in use. Compact size and reliability are the chief benefits of this kind of laser. The two common families of diode lasers contain active mediums composed of GaAlAs (gallium-aluminum arsenite) or InGaAsP (indium/phosphorus). These media emit radiation in the infrared range. Much like those working with radar in the 1940s and ‘50s, researchers in the 1980s and ‘90s found ways to shorten wavelengths of lasers produced by diode-pumped to reach into the range of blue visible light.
The idea of using an absorption fluid as a refrigerant carrier derived from the drawback of VCR (vapor–compression refrigeration) systems that the gas compression requires a high work input. A pump that requires practically no work to increase the pressure in the refrigeration system replaces the complicated and work-consuming compressor. There are two major advantages of absorption refrigeration systems (ARSs) compared with VCRs (vapor–compression refrigeration): No CFCs or HCFCs are used as refrigerants, and they use heat from different sources, such as combustion, industrial processes, waste heat (an economical solution for recovery), or solar heat. (more…)
Microtechnology-Based Energy and Chemical Systems will most likely employ combustion for driving processes such as vapor generation and vapor barrier, endothermic chemical reactions, and (most notably) fuel reforming. Both fuel reformers and combustors will be of a miniature design relying on embedded catalysts for promoting chemical reactions at moderate temperatures (350–7501C). Many potential configurations exist depending on the application and constraints on the design. Microchannel arrays are a potential configuration; mesh and post architecture is another to achieve the desired surface area and small diffusional lengths necessary. (more…)
At present, in the United States and worldwide, motor vehicles are fueled almost exclusively by petroleum based gasoline (or reformulated gasoline) and diesel fuels. Since the first oil price shock in 1973, efforts have been made to seek alternative fuels to displace gasoline and diesel fuels and achieve energy and environmental benefits. Some of the alternative fuels that have been researched and used are liquefied petroleum gas (LPG), compressed natural gas (CNG), liquefied natural gas (LNG), methanol (MeOH), dimethyl ether (DME), Fischer– Tropsch diesel (FTD), hydrogen (H 2 ), ethanol (EtOH), biodiesel, and electricity. Production processes associated with gasoline, diesel, and each of these alternative fuels differ. (more…)
Thermo chemical processing of biomass yields gaseous, liquid, and solid products and offers a means of producing useful gaseous and/or liquid fuels. Biomass gasification is a total degradation process consisting of a sequence of thermal and thermo chemical processes that converts practically all the carbon in the biomass to gaseous form, leaving an inert residue. The gas produced consists of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), methane (CH4), and nitrogen (N2) (if air is used as the oxidizing agent) and contains impurities, such as small char particles, ash, tars, and oils. The solid residue will consist of ash (composed principally of the oxides of Ca, K, Na, Mg, and Si) and possibly carbon or char. (more…)
Estimation of the future technical potential of biomass as an energy source is dependent on assumptions with respect to land availability and productivity as well as conversion technologies. With the emergence of energy crops as the major source of biomass fuel, land use conflicts, especially in relation to food production, may arise. However, with efficient agricultural practices, plantations and crops could supply a large proportion of energy needs, with residues playing a smaller role without compromising food production or further intensifying agricultural practices. (more…)
In recent years, there has been a greater understanding of the role of automotive emissions as environmental pollutants. Sulfur dioxide, nitrogen oxides, and carbon monoxide degrade the earth’s atmosphere and are health hazards. Carbon dioxide adds to the atmospheric buildup of greenhouse gases and in turn accelerates the process of global warming. (more…)
The gradual change in the energy consumption pattern of the United States from 1860 to 1990. In the mid-1800s, biomass, principally woody biomass, supplied over 90% of U.S. energy and fuel needs, after which energy biomass consumption began to decrease as fossil fuels became the preferred energy resources. For many years, a safe illuminant had been sought as a less expensive substitute for whale oils. (more…)
The increased use of fossil energy since the industrial revolution, and especially since 1950, has been the major cause of increased emissions of air pollutants and, correspondingly, many environmental problems. Emissions due to the use of energy are major sources of sulfur dioxide, nitrogen oxides, carbon dioxide, and soot and constitute a large contribution of methane, non-methane volatile organic compounds, and heavy metals. (more…)
Separation is a unit operation used in absorption heat pumps and chemical processing applications such as solvent extraction and product separations. A typical separation process in a heat pump application involves the desorption of ammonia from a water–ammonia solution. Although a number of configurations have been studied for this process at the macroscale, most are based on gravity and have relatively low rates of desorption. (more…)
