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Laser Technology
Published in Abdul Al-Azzawi, Fibre Optics, 2017
Often when a laser is used in an optical system, there is a requirement for either a larger beam or a small-beam divergence. In some cases, the size of the beam becomes critical. For example, when measuring the distance from the Earth to the Moon, a beam one metre in diameter travelling to the Moon expands to several hundreds of metres in diameter and returns to the Earth’s surface with a diameter of several kilometres. The signal returned from this expansion is millions of times smaller than the original signal, so the divergence of a laser beam needs to be reduced to produce strong and detectable signals. Reduction of the beam divergence is called beam collimation. Even in earthbound experiments, higher beam collimation is required for many applications.
Lasers
Published in Abdul Al-Azzawi, Photonics, 2017
Often when a laser is used in an optical system, there is a requirement for either a larger beam or a small beam divergence. In some cases, the size of the beam becomes critical. For example, when measuring the distance from the Earth to the Moon, a beam one metre in diameter travelling to the Moon expands to several hundred metres in diameter and returns to the Earth’s surface with a diameter of several kilometres. The signal returned from this expansion is millions of times smaller than the original signal, so the divergence of a laser beam needs to be reduced to produce strong and detectable signals. Reduction of the beam divergence is called beam collimation. Even in earth-bound experiments, higher beam collimation is required for many applications.
Free-space Optics
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
The beam quality is directly related to the product of the beam-waist radius (W0) and the half-beam divergence (ϑ): ϑω0=M2λ/π.
Optically assisted mm-wave-based multi-Gbps RoFSO transmission link under channel fading models
Published in Journal of Modern Optics, 2022
Abhishek Tripathi, Shilpi Gupta, Abhilash Mandloi, Gireesh G. Soni
The exponential demand for high-speed and real-time data service was met by the fibre optical technology; however, there is still a lack of fibre infrastructure in many places. In this situation, flexible technology is required to replace and/or extend its supplement. Currently, line of sight (LOS)-based free-space optics (FSO) is projected worldwide for use in academia, researchers, and communication service providers (CSP). Free-space optical communication (FSOC) is evolving terahertz (THz) bandwidth to satisfy gigabit’s data rate. In FSOC, the choice of 1550 nm wavelength is optimal due to low attenuation, free licensing, and compatibility with the existing photonic components. An FSO-node can be placed on the rooftop/high-rise window of multi-storey or mounted on towers without excavating subways around city-centric shopping malls and transport hubs [1]. System installation mainly uses an aligned collimated beam with minimum beam divergence for last-mile terrestrial applications.
Electrically switchable band-edge laser based on polymer-stabilized blue phase liquid crystal
Published in Liquid Crystals, 2021
De-Shan Hou, Jia-Xin Cao, Xuan Li, Ji-Liang Zhu, Wen-Ming Han
Figure 2 depicts the reflection, fluorescence, and laser emission spectra of the dye-doped PS-BPLC. The dissolved PM597 had a broad fluorescence peak from 520 nm to 630 nm [36]. The long wave edge of photonic bandgap (PBG) was made to overlap the fluorescence spectrum by controlling chiral dopant concentration. Optical excitation with the pump laser brought about a sharp and single emission peak with a full width at half maximum (FWHM) of about 2 nm near the long-wave edge of PBG, as shown in Figure 2(a). Inside the PBG, pump light was restrained due to the sudden divergence in the photon DOS, resulting in the significant gain enhancement at the band edges and then producing lasing when gain overcomes the loss [37]. The laser emission occurred because a sudden change in the intensity of the emitted light was observed, as shown in Figure 2(b). The lasing emission located at 580.9 nm with a low threshold of 0.65 μJ/pulse. The beam divergence is an important factor for the laser. The beam divergence angle of the LC laser depends on the feedback length of the cavity and cross-section area of the emission. Generally, the longer the length of the cavity, the smaller the laser beam divergence angle [24]. The dye-doped PS-BPLC kept a good stability by optimising the UV curing process. The PM597 dye is not bleached during the UV curing and laser pumping by the YAG laser because of the low UV light intensity and repetition rate of 1 Hz.
3D reconstruction of existing concrete bridges using optical methods
Published in Structure and Infrastructure Engineering, 2019
Cosmin Popescu, Björn Täljsten, Thomas Blanksvärd, Lennart Elfgren
The equipment used in this study was a long-range, RIEGL VZ-400, 3D terrestrial laser scanner (Figure 2(a)). This 3D scanner operates on the time-of-flight principle and can make measurements ranging from 1.5 m to 600 m with a nominal accuracy of 5 mm at 100 m range. It uses near-infrared laser wavelengths with a laser beam divergence of 0.3 mrad, corresponding to an increase of 30 mm of beam diameter per 100 m distance. The instrument’s maximum vertical and horizontal scan angle ranges are 100° and 360°, respectively. The raw TLS data, i.e. point clouds captured from multiple scans, were post-processed (registered and geo-referenced) using the Leica Cyclone software package, which automatically aligns the scans and exports the point cloud in various formats for further processing.