Laser Technology

Author: B. Serhat Cengiz

A laser is a device that emits light through an optical amplification process based on stimulated emission electromagnetic radiation. The term "laser" emerged as an acronym for "Light Amplification by Stimulated Emission of Radiation." The first laser was built by Theodore H. Maiman in 1960 at Hughes Research Laboratories, based on the theoretical work of Charles Hard Townes and Arthur Leonard Schawlow. A laser emits light coherently compared to other light sources. Spatial coherence allows a laser to focus tightly on a point and thus enables applications such as cutting and lithography with lasers. Spatial coherence allows a laser beam to be narrowed over long distances (collimation), making applications such as laser pointers possible. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, meaning they can emit a single light color. Temporal coherence can be used to produce pulses as short as a femtosecond. Among many applications, lasers are used in optical disk drives, laser printers and barcode scanners; DNA sequencing instruments, fiber optics and free-space optical communication; laser surgery and skin care; cutting and welding materials; military and law enforcement devices for marking targets, measuring range and speed; and entertainment laser lighting displays.

Lasers in Industry

Lasers are used in many different applications in industry. Fundamentally, a distinction can be made between material processing and all other applications. Material processing includes cutting, drilling, welding, etc., and high-power lasers are typically used for these operations. There are many important advantages to using lasers in material processing. Unlike conventional machining, which requires tool tips to be sharpened and frequently replaced, no contact tool is needed. Brittle or highly flexible materials that are very difficult or impossible to machine with tools can be processed using lasers. For example, one of the first laser applications in the 1960s was drilling holes in the rubber nipple of a baby bottle, an operation that needed to be precise and sterile. Using fiber optics also provides access to previously unreachable locations. Laser processing has been easily automated to allow computer and robot control. New types of processing have been developed and continue to be developed, including the production of new surface alloys and hardening of materials. However, in addition to their advantages, there are some problems in using lasers. Some tasks, such as drilling large-diameter holes, are difficult to perform with lasers. Lasers and optics produce the best results in clean, vibration-free environments; therefore, it may not be possible to create this environment in every industrial production facility. The initial costs of laser systems can be high, and for this reason they are often limited to large industries. Low-power material absorption and heat conduction properties cause heating. To briefly illustrate this concept, while a mirror reflects most light, a dull black surface absorbs most light. Better conduction properties mean heat will flow faster and local temperature will not remain constant. If laser power is increased sufficiently to raise the temperature, the surface melts, transforming from a solid state to a liquid. If the power is quite high, the material can vaporize directly, with surface atoms turning into gas. At even higher powers, these gas molecules become ionized to form what is known as a plasma, a cloud of charged ions. At this point, efficiency drops dramatically because the plasma blocks the laser beam. Depending on the type of material processing to be applied, since pulsed lasers are used in most applications, the laser's intensity range and pulse duration will be determined. A major low-intensity application is surfaces treated with heat. Local heating changes the crystal properties of the material and can harden it. This is known as transformation hardening and can be thought of like blacksmiths heating and hammering a horseshoe to harden it. Another example is the production of synthetic diamonds by subjecting graphite, a form of carbon used in pencil leads, to extremely high pressure. Today, carbon dioxide lasers are used in the automotive industry to harden steel for cylinders in motors and other parts.

Laser Surface Processing

It is claimed that laser surface processing has great growth potential in the field of laser material processing. Laser surface processing offers many diverse opportunities to achieve desired surface properties. Laser technology is used on machine components to reduce wear and increase fatigue resistance. It is effectively used on hard and possibly inexpensive base materials that require hard surface layers, and in applications where measurable thermal damage is not permitted. The principle of laser surface processing is the modification of a surface as a result of the interaction between a coherent light beam with high power density and a surface in a defined atmosphere (vacuum, protective or process gases). Light produced in a resonator is directed onto the surface of a sample through an optical transmission system (mirror systems or fiber optics). Starting from a certain average optical output power, the required power density, which is the ratio of power to the focused spot area, and the intensity distribution along the beam are modified by beam focusing and/or beam shaping optics such as lenses, mirrors, scanner units or beam integrators. As the laser beam is moved over the workpiece, a trace pattern can be created sequentially on the surface of a part. The interaction time is then determined by the beam's cross section and feed rate. Depending on the type of process and workpiece geometry, translation stages, portal systems or robots can be used to achieve such relative motion. The appropriate system for the beam and/or workpiece is primarily dependent on precision, processing speed and the masses to be handled. The time required for workpiece clamping and alignment and the investment costs are other important factors.

References

• Gould, R. Gordon (1959). "The LASER, Light Amplification by Stimulated Emission of Radiation". In Franken, P.A.; Sands

R.H. (Eds.). The Ann Arbor Conference on Optical Pumping, the University of Michigan, 15 June through 18 June 1959.p. 128. OCLC 02460155.

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•http://emrtk.uniiskolc.hu/projektek/adveng/home/kurzus/korsz_anyagtech/1_konzultacio_elemei/laser_surface_treat.htm

• https://minerva.union.edu/newmanj/Physics100/Applications/lasers_in_industry.htm