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Laser Machining of Metals
Published in V. K. Jain, Advanced Machining Science, 2023
The material capable of sustaining stimulated emission and amplifying it is called gain medium. For stimulated emission to occur, the gain medium must be supplied with external energy to pump atoms from the ground state to an excited state, also called pumping. Pumping is essential in creating a population inversion, wherein the number of atoms in the excited state is more than that in the ground state. Pumping is typically done using electrical or optical energy. The most common pumping sources are a flash lamp or another laser source. Population inversion is necessary for the gain medium to amplify light produced by stimulated emission. Light amplification is achieved by providing optical feedback by placing a pair of mirrors on either side of the gain medium, as shown in Figure 7.2. The mirrors could be flat or curved. The setup is known as an optical cavity or a laser cavity. Light confined in the optical cavity bounces back and forth upon being reflected by the mirrors, producing standing waves. Every time the light passes through the gain medium, it gets amplified. One of the mirrors is fully reflective, while the other is partially transparent (output coupler), thus allowing some light to escape the optical cavity, generating a laser beam. The laser wavelength depends on the type of gain medium used, which could be a gas, liquid, or solid. Examples of gain medium include ruby crystal, CO2 gas, helium-neon gas, Nd: YAG crystal, doped-fibers, etc.
Sub-20-fs multiterawatt lasers and x-ray applications
Published in S Svanberg, C-G Wahlström, X-ray Lasers 1996, 2020
C. P. J. Barty, T. Guo, C. Blanc, F. Raksi, C. G. Rose-Petruck, J. A. Squier, C. Walker, K. R. Wilson, V. V. Yakovlev, K. Yamakawa
We have implemented the thin film polarizer etalon in a half wave regenerative amplifier. The device not only acts at a frequency dependent attenuator but also functions at the output coupler of the optical cavity. Besides allowing one to overcome gain narrowing during amplification, one may also use the etalon to tune the center frequency of the amplifier and to amplify of two colors simultaneously with the system. [11] With multiple filters inside of a regenerative amplifier we have been able to obtain amplified pulses with bandwidths of approximately 120 nm or more than 4 times the “gain narrowing limit” of the amplifier without a filter. The transform limit of these pulses as determined from the measured spectrum is approximately 12 fs. To date we have not attempted to compress the widest bandwidth pulses.
Nonionizing Radiation
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Lasers have three major components: lasing medium, energy source, and optical cavity, as shown in Figure 9.4. The lasing medium is the medium that generates the laser light and may be gas, liquid, solid, or semiconductive. The medium is contained within the optical cavity which is terminated at either end by a mirror, one highly reflective and the other partially reflective. The latter mirror is called the output coupler mirror, and forms the aperture where the laser radiation is emitted from the optical cavity. The energy source may be electrical, electromagnetic, or chemical in nature.
Investigation of a polarization-based Cr:forsterite laser resonator cavity
Published in Journal of Modern Optics, 2021
Siba Prasad Sahoo, V. S. Rawat, Jaya Mukherjee, Swarupananda Pradhan
The broadband lasing spectrum of the Cr:forsterite laser is measured using a spectrophotometer (AvaSpec-NIR256-1). The peak wavelength is found to be 1236 nm with a full width half maxima (FWHM) spectral width of around 25 nm. The various attributes associated with a laser resonator cavity can be profoundly addressed by choosing the discussed polarization-based resonator cavity. The important parameters pertaining to the laser system, such as the cavity output energy, intracavity energy, cavity buildup time, laser pulse width, and the threshold pump energy are measured as a function of the output coupler reflectivity and are analysed using the theoretical model. For measuring the intracavity energy, M2 mirror is replaced by M3 output coupler. The other parameters like the cavity output energy, cavity buildup time, laser pulse width, and the threshold pump energy are measured with the cavity mirrors M1 and M2. It is ensured that other cavity parameters are maintained to similar values during the measurement of intracavity energy. The optimum output coupler reflectivity (maximum output energy) and the threshold output coupler reflectivity (lasing threshold) for the resonator are determined. The roundtrip resonator losses and small-signal gain coefficient of the system are determined and used to calculate the cavity output energy at different input pump energy levels.
Diode-pumped passively mode-locked Nd:GYSGG laser at 1061 nm with periodically poled LiNbO3 nonlinear mirror
Published in Journal of Modern Optics, 2020
Fangxin Cai, Luyang Tong, Ye Yuan, Yangjian Cai, Lina Zhao
The schematic experimental layout of the nonlinear mirror (NLM) mode-locked laser is shown in Figure 1. The gain medium is a Nd:GYSGG crystal with the dimensions of 8 mm × 4 mm × 4 mm and it is mounted in a water-cooled copper holder. The pump source is a fiber-coupled diode-laser with a maximum output power of 30 W at 808 nm and the core diameter is 400 μm. Pump light is imaged on the laser crystal through a 1:0.5 optical coupling system. The beam diameter on laser crystal is 200 μm. The input mirror M1 is a plane mirror with high transmissivity (T>98%) at 808nm on both sides and high reflection(R>99.5%) at 1061 nm on left side. It is placed close to the laser crystal. M2 and M3 are concave mirrors with curvature radius of 500 and 200 mm respectively and have high reflection (R>99%) at 1061 nm. M4 is a dichroic output coupler with high reflection for SH and partial reflection for FW.
Entanglement analyses of a nondegenerate optical parametric oscillator with a higher-transmissivity cavity mirror
Published in Journal of Modern Optics, 2018
Dong Wang, Shuhong Hao, Lixu Xie, Xianshan Huang
However, to our knowledge, there is no theory for an above-threshold NOPO which has a higher-transmissivity output mirror to generate entangled lights. Although both the intracavity and mirror loss were considered before, the existing quantum or semiclassical theory is obtained in the approximation that the mirrors are highly reflective (9–12, 21, 28). If one misuse them in the less-high-reflection condition, it would lead to a deviation. In this paper, we present the semiclassical Langevin equations for the modes in the cavity that avoid using the high-reflection approximation. Then based on these equations, we analyse the NOPO’s classical and quantum properties. For the input–output coupler mirror, we also use the general beam splitter model instead of the previous input–output relationship under high-reflect approximation and obtain two new equations for the amplitude-difference squeezing spectrum and the phase-sum squeezing spectrum, respectively. The numerical calculations suggest that an above-threshold NOPO with a less-high-reflection mirror can really generate entangled beams, and the two kinds of squeezing can be obviously lower than the results calculated from the two equations obtained by Fabre et al. in 1989 (12).