China
Africa
Explore chapters and articles related to this topic
Introduction to lasers and optical amplifiers
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
William S. Wong, Chien-Jen Chen, Yan Sun
An important method to generate short laser pulses is to “switch” the cavity quality factor artificially from very low to normal so that the stored energy in the gain medium can be released in a short time period, otherwise known as the Q-switching method. Lowering the cavity Q can be achieved by increasing the cavity loss or decreasing the feedback from the mirrors. The stored energy, in the form of large inversion in the gain medium, grows as pump power is applied, but the laser oscillation does not happen because of the high cavity loss or the lack of optical feedback. When the cavity Q is restored, the laser threshold is exceeded and the lightwave inside the cavity experiences a large optical gain due to the large inversion and builds up rapidly. The huge optical energy then quickly consumes the large population inversion causing the optical power starts to decrease. In addition, when the cavity Q is lowered at the same time, the optical power diminishes further as the laser is operating below its threshold. The cycle is then repeated for subsequent pulse generation. The Q switching technique is widely applied on all types of lasers, from solid-state lasers, gas lasers, to semiconductor lasers, to produce short pulses.
Generating Massive Inversions through Q-Switching
Published in Mark Steven Csele, Laser Modeling, 2017
To produce a pulsed laser output, one can switch pump power to the amplifier in a scheme known as gain switching. This will certainly produce a pulse, but there are three undesirable characteristics of the output pulse: (a) there is a significant delay between application of power and laser emission due to the required buildup of inversion up to and beyond threshold level, (b) the resulting pulse will have a relatively slow rise time while intra-cavity power builds, and (c) the maximum pulse power will never exceed CW values. In contrast to this, Q-switching produces pulses that are emitted almost immediately on command with a very fast rise time and, most importantly, with enormous peak pulse powers often exceeding hundreds of kilowatts.
Short Pulses
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Q-switching is a mode of laser operation in which energy is stored in the laser active material during pumping in the form of excited atoms and suddenly released in a single, short burst. This is accomplished by changing the optical quality of the laser cavity. The quality factor Q is defined as the ratio of the energy stored in the cavity to the energy loss per cycle. During the pumping process, the beam path in the Q-switched system is interrupted, resulting in a low Q-factor and preventing the onset of laser emission (Q ≈ 1). After a large amount of energy has been stored in the active medium, the beam path in the resonator is returned to proper alignment, and most of the stored energy emerges in a single, short pulse (Q≫1) [7–11].
Hafnium Diboride as a saturable absorber for Q-switched lasers
Published in Journal of Modern Optics, 2019
Ahasanul Haque, Monir Morshed, Haroldo T. Hattori
Q-switching can generate pulses in the range of hundreds of picoseconds to milliseconds which find applications in laser ranging, environmental sensing, material processing, telecommunications, reflectometry, medicine and nonlinear optics (1). Q-switched fibre lasers are widely used in these applications because of their high beam quality, small size, generation of extremely high peak power pulses, and wide tunable ranges (2). Several rare-earth doping materials are used as gain media for optical fibre lasers such as ytterbium, neodymium, erbium and thulium. Amongst them, ytterbium doped fibres lasers can work in the wavelength ranges between 1000 and 1200 nm (2).