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Short Pulses
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Gain switching can be regarded as the most direct method to generate pulsed laser radiation. During gain switching, the pumping process is modulated which results in switching the amplification in the laser medium. In general, after the pumping process has been switched on, the population inversion starts to build up. When the critical inversion is reached, i.e. the gain becomes larger than losses or the loop gain reaches 1.0, the laser starts to oscillate. The oscillation continues until the pumping process is switched off, or until the losses become higher than the amplification. In contrast to the Q-switch mode, which is described in the following section, gain switching is primarily controlled by the pumping process [1]. Gain switching can make use of the transient spiking phenomena in the laser oscillator in order to achieve a high-peak-power pulse. If a laser medium is pumped at a very fast rate and the population inversion exceeds the threshold significantly before the oscillation starts, the laser reacts by relaxation oscillations, i.e. spiking occurs. If the pump pulse is not only fast but also stops directly after the first peak, a laser pulse is generated which consists of only one spike. The inversion after the first peak is below the threshold, and due to the absence of further pump power, there is no possibility for further emission.
Lasers
Published in Robert G. Hunsperger, Photonic Devices and Systems, 2017
Gain switching is not the preferred way of operating most pulsed lasers because Q switching (described below) can greatly reduce the initial delay, give better pulse-to-pulse reproducibility, and provide higher-energy pulses. However, pulsed semiconductor diode lasers normally operate very well using gain switching due to their very high gain and very short relaxation times.
Photon bursts at lasing onset and modelling issues in micro-VCSELs
Published in Journal of Modern Optics, 2020
T. Wang, G. P. Puccioni, G. L. Lippi
A more suitable analogy to describe this regime is laser gain-switching (or, more properly, pump-switching). However, at this stage this remains a simple pictorial analogy since the observation of photon bursts cannot be due to changes in the pump, since the short-term pump stability is in our experiment ((21) and in its accompanying Supplementary Information section). Nonetheless, a simplified analysis based on REs can show that if the carrier number is temporarily driven above the threshold value then a pulse will ensue, and that it is possible to predict both the typical duration of a pulse and a maximum repetition rate (devoid of regularity, in agreement with the experiment) with quantitative values in good agreement with the observations (65). The analysis of Section 4 gives a sounder foundation to these considerations and supports the more detailed stochastic predictions.
All-fibre Q-switching YDFL operation with bismuth-doped fibre as saturable absorber
Published in Journal of Modern Optics, 2018
A. R. Muhammad, H. Haris, H. Arof, S. J. Tan, M. T. Ahmad, S. W. Harun
Figure 2(a) shows the output spectra of the YDFL at the input pump power of 215.6 mW for cases of with and without BDF SA. It should be noted that without the BDF SA inside the cavity, the output laser is continuous wave. The Q-switched laser self-started as the operating pump power is raised to 215.6 mW and operates at wavelength of 1046.14 nm with a peak power of −17 dBm when the BDF SA is present in the cavity. The pulse operation is made possible by the gain switching action that occurs when the Bismuth ions interact with the oscillating Ytterbium laser. The Bismuth ions induced a high absorption loss that allows a large amount of energy to be stored in the gain medium.