CO2 laser (Lab Report Sample)

CO2 Laser Introduction The usage of CO2 laser technology, also known as carbon dioxide laser, has significantly advanced since its introduction in the mid-1960s. The leading field in the usage of CO2 laser technology is medical; other areas such as metal industries are also using the technology in several activities. Generally, laser technology has been incorporated in many areas because of its multiple applications in many aspects of everyday life. In the medical industry, various medical activities implement CO2 laser from skin treatments to surgery. The CO2 laser technology has proven to be the safest laser technology when handled with care, making it suitable in most therapies. 1 History of CO2 laser The history of carbon dioxide laser is dated back to the introduction of the theory of laser in physics by Albert Einstein in 1917. He described molecular and atomic interaction with electromagnetic energy based on spontaneous energy emission and absorption [5]. Einstein marked his research by concluding on the possibility of stimulated energy emissions. Based on the concept explained by Einstein, Drs Schawlow and Townes developed the first microwave amplification instrument in 1959 [3]. The instrument was identified as microwave amplification through the stimulated emission of radiation (MASER). In 1960, Theodore Maimon came up with the first laser device that used ruby crystals. This was a significant achievement, and most of the clinical research based on laser technology began during this time [2]. The development of laser technology was at its peak during this period, and in 1961, the helium-neon laser was designed, followed by argon laser in 1962. In 1964, the CO2 laser was developed by Kumar Patel [1]. The laser is among the best lasers that are still in existence to date. This is because the laser makes use of powerful continuous laser waves that are available. However, the CO2 laser had limitations on the energy parameters, which resulted in frequent scarring and injuries. Anderson brought about selective photo thermolysis (SPTL), and it was successful in developing lasers that are specifically tailored for medical purposes [3]. The device was labeled pulse dye laser (PDL) and was primarily implemented to treat the port wine stains in young patients [6]. In the mid-1990s, the creation of short-term duration lasers enhanced the development and operation of the CO2 lasers [1]. During this period, the high-intensity flash lamp was introduced, which became a suitable method of treating vascular lesions. Furthermore, the modification of the CO2 laser was also enhanced by introducing intense pulsated light (IPL). To date, the transformation experienced on the CO2 laser is basically on the technical parts to enable easy usage of the instrument together with safety concerns. 2 CO2 laser physics Lasers are instruments that are dependent on the stimulated radiation emission to produce light. The device comprises three main parts: the active medium, energy source, and resonating chamber [6]. Most lasers have a population of atoms that are identified as the active medium. The active medium is a laser component with a specific size, shape, purity, and concentration [3]. This material can vary in type depending on the type of lasers, such as solid, liquid, gas, or plasma. The gas lasers are generally composed of gases such as argon, krypton, vapor, copper, CO2, and helion-neon. When an atom is resting, the electrons are usually orbited around the nucleus occupying the lowest energy levels. When an electron is powered by an energy source such as a chemical, electrical field, or light source, the electrons change positions and occupy the highest energy levels [4]. When the electrons get back to their positions, photons are generated because of the energy released from the process. C02 laser uses a mixture of carbon dioxide, nitrogen and helium gasses as its medium. The C02 laser emits infrared light with a wavelength of 10,600 nm, which is invisible to the human eye [6]. For the light to be seen, a second gas, coaxial helium-neon (He-Ne), is introduced to the laser as a pointer. He-Ne laser has a low intensity with a wavelength of 6328 nm [5]. The electromagnetic light produced by the He-Ne laser has the color red, which is visible. For efficient use, the C02 laser is used with the He-Ne laser for a coaxial arrangement. The alignment is often checked before use to avoid the beam from striking away from the axis. The beam transmission system consists of a laser power supply, laser oscillator, reflecting mirrors, cutting torch, gas cylinders, water chiller, and air pump. The air pump continuously supplies clean and dry air into the laser tubes where the laser beam is generated [5]. In the laser tube, the fusion of gasses is actuated by diodes that emit energy in the form of light. The electrons in the tube orbit around absorbing energy from an energy source; when they become excited, they orbit into higher orbitals. When they fall back into their resting orbitals, they emit energy that releases photons. The photons have the same wavelength as the excited atom; thus, all photons in the laser beam have the same wavelength. There are two reflective mirrors in which the photons and atoms are reflected back and forth. As the photons continue to collide with the electrons, more energy is built up. One of the mirrors is partially reflective and partially transparent, allowing the photons to pass through as a beam [3]. The emitted light energy can be either visible or invisible reliant on its wavelength, ranging from short rays (10 -11m) to long rays of wavelength (>10cm) [3]. The laser beam is then concentrated and focused on the cutting edge by a focusing lens into a thin concentrated beam. The beam then passes a nozzle where it is magnified and focused into a single narrow point in the worktable. The water chiller is used to cool the laser tubes since after carbon dioxide has been converted to the laser, the remaining energy is converted into heat that is cooled off. Absorption is the energy conversion from laser to heat when the photon strikes the chromosphere [2]. The process undergoes a mechanism known as selective photo thermolysis. 3 Working Principle and Mechanism When an electric current is stimulated to the gas mixture, the nitrogen molecules gain the required energy; the molecules become excited. Nitrogen is preferred in carbon dioxide because it has a long period of excitement [6]. In this state, the nitrogen molecules do not release energy either in the form of light or photons. The molecules of nitrogen release vibration of high energy, which excites the CO2 molecules [6]. During this stage, the laser leads to the attainment of the population inversion state. The stage is characterized by a high number of excited particles compared to the non-excited particles. Energy emission in photon form is enhanced by the excitement of the nitrogen atoms. The light beam is produced whenever the excited nitrogen atoms are in contact with the cold atoms of helium. [3]. The light produced is powerful than the ordinary light because of the surrounding mirrors of the gas tube. The mirrors have a crucial role during this stage as they reflect the light produced during the nitrogen excitement process. The light intensity keeps on increasing because of the reflections in the tube. Figure 2.0 below shows the working mechanism of the CO2 laser. Figure 1.0: CO2 laser working mechanism 4 Properties of the CO2 Lasers This type of laser is very powerful when compared to various types of lasers. The laser has a wavelength of 10.3 um, with different types of CO2 lasers ranging from 9 to 11 um [4]. The nitrogen molecules are charged by the exiting gas, which makes them discharge energy to the CO2 molecules, making them active [6]. The CO2 laser varies in its power which includes ten watts, kilowatts, and megawatts. The high-power laser requires fast gas flow in the tube, while the low-power laser uses laser tubes that have no laser flow in the sealed tube [4]. The CO2 laser does not easily attain diffraction even when using the powerful types of CO2 laser. Table 1.0: Properties of CO2 lasers Aspect Properties important types multi-kW TEA lasers; low-power, sealed-tube lasers pump source electrical current power efficiency order of 10% accessible wavelengths mostly around 10.6 μm with other lines at 9-11 μm wavelength tuning quite limited average output power between 1 W and 50 kW beam quality normally diffraction-limited continuous-wave operation Yes nanosecond pulse generation yes, with mode-locking or Q switching picosecond & femtosecond pulse generation No 5 Designs of CO2 Laser * Longitudinal-flow and transverse-flow lasers With this design, the laser gas is pumped into the vacuum by using the vacuum pump. The design is simple and makes use of high-energy laser output [6]. Through the discharge of current in the tube, the mixture of carbon dioxide is split into oxygen and carbon monoxide. The tube system uses the pump to continuously circulate the mixture of gases, making it efficient to remove heat loss. The transverse-flow laser is scalable to a multi-kilowatt level. The laser power can be scaled up by increasing the volumetric flow and discharge volume, which means that the discharge instability limits the maximum input power density. Depending upon the stability ensured by a particular scheme, the maximum input power density ranges from 5-50 W/cc. Figure 3.0: Longitudinal-flow and transverse-flow lasers * Sealed-off laser In this laser design, the pump is not used, and it’s replaced by oxygen, hydrogen, water vapor, and oxygen. These mixtures of gases help in enabling the reaction of the carbon monoxide through platinum electrodes leading to carbon dioxide [5]. The catalytic reaction of the mix...