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Channel Modelling
Published in Z. Ghassemlooy, W. Popoola, S. Rajbhandari, Optical Wireless Communications, 2019
Z. Ghassemlooy, W. Popoola, S. Rajbhandari
The same result given by (3.77) can be obtained by substituting Aim=θbLp for the image size in Pr=PtArAim. In order to reduce the diffraction-limited beam divergence, a beam expander of the type shown in Figure 3.25, in which the diffracting aperture has been increased, can then be used. The beam expander reduces the beam divergence loss and increases the received signal power in the process.
Lasers
Published in Abdul Al-Azzawi, Photonics, 2017
Each telescope has distinct advantages for beam expansion. The advantage of the Galilean type of beam expander is well utilized in high power or pulsed laser systems. Since the beam does not come to a focus anywhere inside the beam expander’s optical path, the power density of the beam decreases. Thus, if the lenses and environment can survive the initial beam, they can survive the beam anywhere in the optical path. Although the Keplerian beam expander can give similar ratios of beam expansion, the power density at the focus of the first lens is very large. In fact, when using a high-power pulsed laser it is possible to cause a breakdown of the air in the space between the lenses. This breakdown is caused by the strong electrical field that results from focusing the beam to a small diameter, creating miniature lightning bolts.
Metal additive manufacturing using lasers
Published in Rupinder Singh, J. Paulo Davim, Additive Manufacturing, 2018
C. P. Paul, A. N. Jinoop, K. S. Bindra
In powder bed fusion (PBF) the laser beam is manipulated using moving optics. A beam expander is an optical device, composed of two lenses that produces an output beam with a near-zero divergence. It enlarges the beam diameter by selected amounts. For example, 1.6x, 2x and 2.5 times diameter of the beam are standard expansion ratio. The magnification of the beam expander can be expressed as the diameter of the output beam divided by the diameter of the input beam. Thus, it increases the working distance of a lens and allows the beam to travel a long path without divergence. Figure 2.10 presents beam manipulation in PBF using a galvanoscanner.
In-situ Laser ultrasound-based Rayleigh Wave Process Monitoring of DED-AM Metals
Published in Research in Nondestructive Evaluation, 2022
C. Bakre, T. Meyer, C. Jamieson, A. R. Nassar, E. W. Reutzel, C. J. Lissenden
Rayleigh waves are generated using a Q-switched Nd:YAG pulsed laser (Inlite III-10, Continuum, Milpitas, CA, USA). The pulse duration was 6 ns and pulse energies for broadband Rayleigh wave generation and narrowband Rayleigh wave generation were 45 mJ and 270 mJ respectively. The 7 mm diameter laser beam is first expanded using a 3X beam expander (Part # 35–099, Edmond Optics Inc., Barrington, NJ, USA), and then reflected using a mirror (Part #38–900, Edmond Optics Inc., Barrington, NJ, USA) onto the beam patterning optics at an oblique incidence of 8 degrees from the vertical. Next, the beam patterning optics create a single line illumination using a cylindrical lens (LJ1703RM-B, Thorlabs Inc., Newton, NJ, USA) or a line-arrayed illumination pattern using a slit mask. The slit mask consists of 13 slits with opening widths of 0.47 mm, pitch of 1 mm, and slit lengths of 10 mm. The pitch of the slit mask dictates the wavelength of the Rayleigh waves. Thus, a broadband pulse or a narrowband burst generated the Rayleigh waves on the specimen surface. The liftoff distance from the specimen surface for the cylindrical lens is nominally its focal length (FL = 75 mm), and the liftoff distance for the slit mask was fixed at 1 mm.
Evaluation of generalized stress intensity factors at blunt V-notch tip in polymer materials using transmitted caustics
Published in Mechanics of Advanced Materials and Structures, 2022
Wei Liu, Longkang Li, Peng Xu, Zhongwen Yue
A non-contact optical setup was used to observe the evolution of caustic patterns at the tip of blunt V-notch under different three-point-bend loading levels, which was shown in Figure 6. The optical setup consisted of a green laser (MW-GL-532: Changchun Laser Company, China), two convex lenses (with the diameter 300 mm and the focal length 1500 mm), a beam expander (LCht-3X: Edmund Optics Company, USA), a Charge-coupled Device (CCD) camera with 4024 × 3036 black-and-white pixels (MER-1220-32U3M: Daheng Imaging Company, China), an electronic universal testing machine, and a computer. The light beams emitted from the green laser were expanded by the beam expander, and passed through the first convex lenses, then condensed by the second convex lenses and finally received by the CCD camera. Here, the power of the green laser was 70 mW to ensure that the specimen was uniformly and brightly illuminated, and the spatial resolution was 3.67 × 10−3 mm/pixel in all cases. In this setup, the distance between the specimen plane and the reference plane was z0 = 1000 mm, the distance between the two supports was W = 140 mm. The universal testing machine was positioned in the middle of these two convex lenses.
Enhanced outer peaks in turbulent boundary layer using uniform blowing at moderate Reynolds number
Published in Journal of Turbulence, 2022
Gazi Hasanuzzaman, Sebastian Merbold, Vasyl Motuz, Christoph Egbers
This is also used for the calculation of the fringe spacing () and the dimension of measurement volume. Therefore, resulting beam diameter () at the exit of the beam expander is the product of inlet beam diameter and expander ratio. The LDA system also includes receiving optics connected to a burst spectrum analyser (BSA, Dantec Dynamics Inc.) and a traverse system (Isel Germany AG) with three-dimensional motion for precise positioning of the integrated transmitting and receiving optics. With the present traverse system, minimum step size of 0.0063 mm (less than the size of viscous length scale at maximum Reynolds number) was achievable. Hasanuzzaman et al. [17] have discussed in detail the present LDA setup.