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Measuring velocity in electronic systems
Published in Kaveh Azar, in Electronic Cooling, 2020
The 10 to 50 Hz repetition rate of Nd:Yag lasers yields At values which are typically too large (with regard to the basic definition of velocity given above) for most applications. Therefore, a pair of lasers is commonly used to provide the two successive light pulses (Eggels et al., 1993; Molezzi and Dutton, 1993). The light beam from the pulsed lasers is formed into a light sheet and focused at the region of interest in the flow field. Consider a pulsed laser with a 50 Hz repetition rate: the time between successive pulses would be 20 msec. In a flow where the mean velocity is say 1 m/s, a particle would travel approximately 2 cm between light pulses. For most cases, this distance is far too large to consider the resultant velocity vector a point measurement. Alternatively, if one is using two lasers, the pulse trains from the two lasers could be offset by 0.3 msec, thereby allowing the particle to travel approximately 0.3 mm between two successive light pulses. However, for low-speed flows, such as those occurring in electronic cooling applications, a single laser with a 50 Hz repetition rate may be used. If the mean velocity is 2 cm/s, a particle would only travel approximately 0.4 mm between light pulses.
Full-Waveform Analysis for Pulsed Laser Systems
Published in Jie Shan, Charles K. Toth, Topographic Laser Ranging and Scanning, 2018
Concerning modulation techniques, laser systems can be divided into two groups: continuous wave (cw) and pulsed lasers. A cw laser continuously emits electromagnetic radiation. The temporal energy distribution of the transmitted signal is influenced by amplitude modulation and/or frequency modulation. Depending on the applied modulation technique specific measurement techniques (Section 7.2.3) are required. A pulsed laser emits electromagnetic radiation in pulses of short duration. For laser ranging, it is desirable to emit a pulse as short as possible and with a pulse energy as high as possible to obtain a precise range with a high probability of detection. However, design limitations on maximum peak power introduce a tradeoff that requires a compromise between the length and the energy of the pulse. The length of the pulse (full-width-at-half-maximum, FWHM) is typically between 2 and 10 ns. For applications in remote sensing with long ranges pulsed lasers with higher power density as compared with cw lasers are advantageous. In this contribution, we focus on pulsed laser systems (Figure 7.1).
Waveform Analysis for Small-Footprint Pulsed Laser Systems
Published in Jie Shan, Charles K. Toth, Topographic Laser Ranging and Scanning, 2017
Concerning modulation techniques, laser systems can be divided into two groups: continuous wave (CW) and pulsed lasers. A CW laser continuously emits electromagnetic radiation. The temporal energy distribution of the transmitted signal is influenced by amplitude modulation (AM) or frequency modulation (FM). Depending on the applied modulation technique, specific measurement techniques (Section 7.2.3) are required. A pulsed laser emits electromagnetic radiation in pulses of short duration. For laser ranging it is desirable to emit a pulse as short as possible and with a pulse energy as high as possible in order to obtain a precise range with a high probability of detection. However, design limitations on maximum peak power introduce a trade-off that requires a compromise between the length and the energy of the pulse. The length of the pulse (full width at half maximum, FWHM) is typically between 2 and 10 ns. For applications in remote sensing with long ranges, pulsed lasers with higher power density as compared to CW lasers are advantageous. In this contribution we focus on pulsed laser systems (Figure 7.1).
Impact of the Oil Temperature on the Frictional Behavior of Laser-Structured Surfaces
Published in Tribology Transactions, 2019
Andreas Janssen, Mohammad Dadgar, Wolfgang Wietheger
Microstructures can be manufactured on surfaces by various methods. LST or laser structuring is an accurate method for microstructuring that is based on ablation of material by means of laser radiation. Duration of the pulses is important in laser materials processing. The laser used in this work is an ultrashort pulse laser and delivers pulses with a pulse duration of only a few picoseconds. The ultrashort pulse laser process provides a high degree of structural flexibility and precision in terms of manufacturing technology because no melt and heat-affected zone is generated. Although this view is physically not correct, it practically can be assumed as shown in Weikert (15). This enables the surface structures to be produced with less construction time and cost compared to alternative manufacturing processes. Additionally, postprocessing is not necessary when using an ultrashort pulse laser. The characteristics and phenomenology of ultrashort pulse laser ablation and its separation from other forms of laser ablation have been discussed in the literature (Momma, et al. (16); Janssen (17); Nolte (18)).
MXene Ti3C2T x thin film as a saturable absorber for passively mode-locked and Q-switched fibre laser
Published in Journal of Modern Optics, 2021
A. H. A. Rosol, A. A. Aminuddin Jafry, B. Nizamani, N. F. Zulkipli, M. I. M. A. Khudus, M. Yasin, S. W. Harun
There are several reports on pulse generation by Q-switched and mode-locked lasers in recent years. These pulsed lasers have attracted researchers because of their extensive applications in material processing, remote sensing, medicine, range finding and telecommunications. They have plenty of advantages, such as high energy and the short period of optical pulses [1–3]. Both the mode-locked and Q-switched lasers can be generated by active or passive techniques. In comparison with the active techniques, the passive approaches are preferable due to their advantages in being simple, compact and cost effective. The saturable absorber (SA) is used as an essential device in the passive optical fibre laser cavity to produce mode-locked and Q-switched pulses.
Laser polishing of additively manufactured metal parts: a review
Published in Surface Engineering, 2022
Emanuele Manco, Ersilia Cozzolino, Antonello Astarita
Another interesting work on a different Ti alloy is a study by Z. Xu et al. that regards TiAl manufacts obtained with laser deposition metal technology. The influence on surface morphology, microstructure, defects, microhardness, wear resistance and corrosion resistance of CW and pulsed laser was reported. The CW laser parameters were as follows: power = 4000 W, laser wavelength λ = 1060 nm, scanning speed 100 mm s−1. For the pulsed laser, parameters utilized have been power = 100 W, λ = 1060 nm, pulse duration δ = 70 ns, repetition rate f = 20 kHz.