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Current New Applications of Laser Plasmas
Published in Leon J. Radziemski, David A. Cremers, Laser-Induced Plasmas and Applications, 2020
Allan A. Hauer, David W. Forslund, Colin J. McKinstrie, Justin S. Wark, Philip J. Hargis, Roy A. Hamil, Joseph M. Kindel
Several authors (Guenther and Bettis, 1978; Woodworth et al, 1982; Woodworth et al., 1984; Guenther and Bettis, 1985; Humphreys et al, 1985) have observed the effect of laser pulse length on switch delay and jitter. With an IR-laser trigger source, the pulse-length dependency is quite distinct. The switch delay and jitter become quite large as soon as the switch delay exceeds the laser pulse length. The UV-laser-trigger data do not always show this very abrupt increase in jitter and delay when the laser pulse terminates before switch closure (Woodworth et al., 1984). Recent UV-laser trigger experiments (Hamil and Smith, 1983) performed at 3 MV across an 11 cm gap showed that laser pulse length effects can be minimized. These unpublished experiments achieved lower jitter and delay with a short 2 nsec long pulse than with a 20 nsec long pulse of equal energy. Additional factors, such as laser beam quality, laser pulse shape, spark formation time, switch geometry, and f-number of the optical system, appear to be important in determining the performance of UV-laser-triggered spark gaps.
Photoacoustic Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
The principle of PA spectroscopy is the detection of the fraction of light that is converted into heat. That means that photoacoustics is a competitive effect to fluorescence. The fraction of energy that is emitted as fluorescence light does not contribute to the local warming, hence it does not generate a PA signal. It has to be stated that even in the theoretical case of 100% fluorescence quantum efficiency, i.e., when for each incoming photon one fluorescence photon is emitted, the energy difference between vibrational excited levels on the S1 state and the S1 ground state is converted into heat, which generates a PA signal. Hence, the PA effect is suitable for the quantification of fluorescence quantum efficiencies. The application of OT and PA techniques for these measurements dates back to the late 1970s (Auzel, Meichenin et al., 1979). Usually, modulated optothermal spectrometry is employed rather than pulsed excitation (Adams, Highfield et al., 1981; Rodriguez, Nunez et al., 1994; Ristovski and Dramicanin, 1997). Beyond experimental simplicity, the main advantage of the pulsed laser source is the possibility to employ a wavelength-tunable OPO laser system, which can be easily tuned to essentially any visible and NIR wavelength between 420 nm and about 2.5 µm, without affecting the laser beam quality, allowing for quantum efficiency measurements at any of these wavelengths.
Introduction to Laser Beam Profiling
Published in Barat Ken, Laser Safety Tools and Training, 2017
There are many laser applications in which the beam profile is of critical importance. Because the beam profile is important, it is usually necessary to measure it to ensure that the proper profile exists. For some lasers and applications this may only be necessary during design or fabrication of the laser. In other cases, it is necessary to monitor the laser profile continuously during the process. For example, scientific laser applications often force the laser to its operational limits, and continuous or periodic measurement of the beam profile is necessary to ensure that the laser is still operating as expected. Some industrial laser applications require periodic beam profile monitoring to eliminate scrap produced when the laser beam quality degrades. In medical laser applications, the practitioner often does not have the capability to tune the laser. The laser manufacturer measures the beam profile in the design phase to ensure that the laser provides reliable performance at all times and is responsible for guaranteeing that the spatial beam profile remains stable. However, there are medical uses of lasers, such as photorefractive keratotomy (PRK), for which periodic checking of the beam profile can considerably enhance the reliability of the operation. PRK is an example of laser beam shaping, a process by which the irradiance of the laser beam is changed along its cross section. For this laser beam shaping to be effective, it is necessary to be able to measure the degree to which the irradiance pattern or beam profile has been modified by the shaping medium.
Doubly Q-switched tape casting YAG/Nd:YAG/YAG ceramic laser
Published in Journal of Modern Optics, 2018
Yufei Ma, Ying He, Zhenfang Peng, Renpeng Yan, Xudong Li, Xin Yu, Yao Tong, Lin Ge, Jiang Li, Frank K. Tittel
In the absence of an AO Q-switch and Cr4+:YAG, continuous-wave (CW) laser operation was implemented with three kinds of output couplers which had transmissions of 10, 15 and 20%, respectively. The measured results are shown in Figure 2. The absorption efficiency of the pump beam was about 90%. We can see from Figure 2 that with increasing absorbed pump power the CW output power increased as well. A maximum CW output power of 3.88 W was obtained at an absorbed pump power of 12.5 W when an output coupler with transmission of 15% was used, which resulted in a slope efficiency of 35%. The laser beam quality factor M2 was measured by a 90/10 traveling knife-edge method in the far field at this condition and it was found to be 1.42. For output couplers with transmission of 10 and 20%, the slope efficiency was 32 and 32%, respectively.