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Optical Cavities: Free-Space Laser Resonators
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
The spectral properties of laser resonators are determined by the laser gain medium and the temporal character of the laser as well as by the resonator. The gain bandwidth of the active laser medium can be many times wider than the free spectral range of the resonator and support many longitudinal modes. As the laser oscillations build up, there is a frequency narrowing or frequency selection similar to transverse mode selection. High-gain pulsed lasers, however, typically have insufficient time to resolve single-mode operation. Effects such as spectral and spatial ‘hole burning’ can also limit frequency selection.
Nature of Light
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
A traditional laser (Figure 3.3) is a system that consists of an energized active medium for optical amplification, pump to energize the lasing medium, and a resonator to produce optical feedback of the amplified beam back into the gain medium (Vandergriff 2008). The active laser medium may be comprised of atoms, molecules, or ions in either a gaseous, liquid, or solid form. To be effective, the electron energy level of the laser medium must have an upper excited level with a long spontaneous lifetime and a lower excited level that can decay rapidly back to the ground state. In addition, a pumping source is required to provide energy to the atoms and molecules in the lasing medium in order to produce the excited states at the upper level for prolonged periods of time. The energy can be fed by the pump to the lasing medium by means of highly energetic electrons, energetic heavy particles such as protons and neutrons, or in the form of optical radiation. Optical methods (e.g., flash lamps) are used to pump crystalline and liquid dye lasing media while electrical voltage pumping methods are used to activate semiconductor and gas-based lasers (Nikumb and Sekhar 2012).
Laser processing of glass fiber reinforced composite material: a review
Published in Australian Journal of Mechanical Engineering, 2019
Vineeta Bhaskar, Dhiraj Kumar, K. K. Singh
CO2 lasers are continuous wave lasers of 100 kW peak power and known for the efficiency lies in the range of 10–15%. The active laser medium is a gas discharge which can be air-cooled (water-cooled in high power applications). The filling gas in discharge tube comprises of CO2 gas, N2 gas and He in the ratio of 3:8:4. The laser yield wavelength of 10.6 μm utilised as a part of the handling of materials and medicinal applications. They have relatively high efficiency and features very good beam quality. Figure 4 shown below the CO2 laser machining unit.