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Electromagnetic Waves and Lasers
Published in Hitendra K. Malik, Laser-Matter Interaction for Radiation and Energy, 2021
The technique of producing pulses of extremely short duration typically of the order of picoseconds to femtoseconds is called mode locking. Here laser is active for a very small time interval during which the pulses of picoseconds or femtoseconds durations are emitted. Pulses so produced are separated by the time interval that a pulse takes to complete one to-and-fro movement inside the resonator cavity. As these pulses have small temporal length they spread over wide wavelength range following the principle of uncertainty due to which the output of laser has broad gain profile. In this technique, we get several longitudinal modes lasing in a coherent manner with respect to each other. These modes would form a periodic pulse train emitted from the laser. The variation of laser intensity with time in perfectly locked and random-locked situations is shown in Figure 1.4(a) and (b), respectively. Ti:Sapphire laser used for research applications is a mode-locked tunable pulsed laser.
Non/Loosely Contacting NDE Techniques
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
Picosecond ultrasonics is a particular application of laser ultrasonics at very short pulse lengths for generation of ultrasonic waves. It is a useful technique for studying the acoustic properties of thin films. The technique has already found an important application in metrology for the fabrication of ultrasonic devices such as FBAR and other applications in semiconductor fabrication.
High Frequency Optoacoustic Transducers for Ultrasonic and Photoacoustic Imaging
Published in Lihong V. Wang, Photoacoustic Imaging and Spectroscopy, 2017
Shai Ashkenazi, Yang Hou, Sheng-Wen Huang, Takashi Buma, Matt O’Donnell
Thermoelastic generation of ultrasound has been a subject of research for several decades. White [23] published the first comprehensive paper and since then, numerous studies have been performed, especially for applications in nondestructive inspection and materials characterization. A large number of these studies concentrated on noncontact generation and detection of ultrasound in solids [30,31]. Thin film measurements have also been made using subnanosecond and subpicosecond [32] laser pulses. The latter technique is often referred to as “picosecond ultrasonics”. Several authors have constructed 1D thermoelastic arrays, employing multiple laser sources and/or fibers [33–35]. Unfortunately, these systems are large and have a limited number of elements (less than 16). Many recent studies have used the thermoelastic effect for medical imaging [36,37], where image contrast is based on differential optical absorption within the sample itself. Little research has been published on the thermoelastic effect for medical transducers [37–40]. These devices rely on optical generation and detection of ultrasound from thin coatings on the tips of optical fibers.
Comprehensive Study of all-in-one Simultaneous Multiple Optical Logic Gate Devices Using Mach–Zehnder Interferometer based on the Electro-optic Effect
Published in IETE Technical Review, 2021
Manish Kumar, Ajay Kumar, Sumit Kumar Jindal, Sanjeev Kumar Raghuwanshi
Similarly, the gain is the photoconductor gain G can be represented by where, the carrier lifetime to the carrier transit time . However, the gain has adjusted by applying suitable operating parameters. The photoconductors using the co-planar strip-lines can be useful and effective in the short electric pulse, which can be easily used for the electro-optic effect based integrated MZI switches. The techniques can provide sub-picosecond resolution. The high-speed photoconductors are used, which is available at the variety of wavelength, ranging from 1.65 () to 0.4 ().
Recent progress on the surface finishing of metals and alloys to achieve superhydrophobic surfaces: a critical review
Published in Transactions of the IMF, 2021
Ali Raza Shaikh, Jian Qu, Minchen Zhou, Christian K. Y. Mulbah
The nanosecond laser, also known as nanolaser, is the most common type of q-switched pulsed lasers. The high peak power and short pulse width of this laser make it well suited for a wide range of applications such as LIBS (laser-induced breakdown spectroscopy), marking, and laser design. Recently, He et al.98 used nanosecond laser ablation to create a fine groove mesh and ethanol-assisted low-temperature annealing contributed to an SHS. The maximum WCA was found to be 161° and the surface has ultra-high adhesion. A picosecond laser emits pulses of light at durations ranging from a picosecond to some tens of picoseconds. Hence, it also falls into the category of ultrafast lasers or ultrashort pulse lasers. Long et al.99 prepared SHS on Cu substrate by picosecond laser. Laser-induced periodic pico-second nanostructures were modified with triethoxyoctylsilane, and the maximum WCA was 153.9° ± 3.2° with ultra-high adhesion.
Selective laser ablation of CFRP composite to enhance adhesion bonding
Published in Materials and Manufacturing Processes, 2019
Ramkumar Sathiyamurthy, Muthukannan Duraiselvam
Laser-based surface preparation provided district advantage over all mechanical techniques by being the non-contact type and also offer no tool wear and eliminating the necessity of secondary cleaning method. Because of available and low cost of operation, CO2 lasers were the first to be used for polymer composite processing.[15] But due to the thermal energy of radiation thermomechanical degradation will occur in the material[3,16,17] In CFRP, due to the huge difference in thermal properties of carbon fibers and resin matrix, a large heat-affected zone (HAZ) will form due to which the integrity of the composite will be compromised by degrading carbon fiber and matrix interface.[18] Degradation due to thermal effects can be minimized by employing a pulsed laser source and increasing scanning speed.[19] Various types of laser sources were experimented for HAZ by Herzog et.al[18] experimented using various laser sources and stated that tensile strength has an inverse relationship with HAZ dimensions. He obtained 0.6, 1.2 and 1.4 mm for pulsed Nd:YAG, continuous wave Nd:YAG and CO2 respectively. Many researchers have[20–22] explained that picosecond lasers can minimize the material damage and joint degradation by effectively reducing heat input to the material.