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Lasers and Their Emission Characteristics
Published in F.J. Duarte, Tunable Laser Optics, 2017
Optically pumped ionic solid-state lasers include the well-known Nd laser that can exist either in a crystalline or in a glass host. These lasers are very well suited to be configured in various cavity arrangements, including unstable resonator arrangements, which yield single-transverse-mode emission. The linewidth of a TEM00 laser at 1064 nm is typically 15–30 GHz (Chesler and Geusic 1972). Frequency doubling using nonlinear crystals, intracavity or extracavity, yields efficient conversion into the visible. Originally, these lasers were excited using flashlamp pumping; however, diode laser pumping has become rather pervasive. Commercially available diode laser-pumped Nd:YAG lasers can yield tens of watts at prfs in the kilohertz regime. Individual laser pulse lengths can be in the 10–15 ns range. Ionic gain media, in crystalline hosts, has also lased in the CW regime.
T
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
traveling wave amplifier field component in the direction of propagation. Also known as TE-wave or H-mode. transverse electromagnetic (TEM) referring to fields or waves in which both the electric and magnetic fields have nonzero vector components only in the plane perpendicular (transverse) to a specified axis, usually a coordinate axis. In a TEM wave, the electric and magnetic fields are perpendicular to each other and to the direction of propagation. transverse electromagnetic mode electromagnetic wave propagation mode in which electric and magnetic fields are transverse to the direction of propagation (i.e., no radial field components). TEM mode propagation is a characteristic of antenna radiation in the far-field and of transmission-line propagation below the cutoff frequency of the higher order modes. transverse electromagnetic wave the electric and magnetic field components along in the direction of propagation are zero. Abbreviated TEM wave. transverse excitation laser pumping process in which the pump power is introduced into the amplifying medium in a direction perpendicular to the direction of propagation of the resulting laser radiation. transverse magnetic (TM) referring to fields or waves in which the magnetic field has nonzero vector components only in the plane perpendicular (transverse) to a specified axis, usually a coordinate axis. transverse magnetic wave the wave solutions with zero magnetic field component in the direction of propagation. Also known as TM wave and E-modes. transverse mode term used in referring to the transverse structure or indices of the mode of a laser oscillator. transverse mode-locking forcing the transverse modes of a laser to be equally spaced in frequency and have a fixed phase relationship; useful for obtaining a scanning output beam oscillator. transverse resonance a technique used in order to find the modes of closed waveguides. trap (1) in microelectronics, an imperfection in a semiconducting material that can capture a free electron or hole. (2) in computers, a machine operation consisting of a hardware-generated interrupt or subroutine call that is invoked in the case of some error condition, for example, encountering an unimplemented instruction code in the instruction stream. See also exception. TRAPATT diode acronym for trapped plasma avalanche transit time, a microwave diode that uses a high field generated electron-hole plasma and the resulting diffusion of these carriers to the contacts to create a microwave negative resistance, used as high power, high efficiency RF power sources. trapezoidal pattern a signal produced on an oscilloscope by applying an amplitude modulated signal to the horizontal input and the modulating signal to the vertical input. By measuring the maximum and minimum height of the resulting trapezoid, the modulation index may be obtained. trapped wave See bound mode.
Transparent nanofluids with high thermal conductivity for improved convective thermal management of optoelectronic devices
Published in Experimental Heat Transfer, 2022
Hao Xu, Chao Chang, Jingyi Zhang, Jiale Xu, Huanbei Chen, Huaixin Guo, Benwei Fu, Chengyi Song, Wen Shang, Peng Tao, Tao Deng
Figure 2 schematically shows the working principle of the convective thermal management of solid-state laser rod. The surfaces of Au NPs are capped by negatively-charged citrate ligands. The citrate-stabilized Au NPs are repelling each other when they are in close contact, thus they are homogeneously dispersed within the water coolant. The small particle size and homogenous dispersion of Au NPs allow the 808-nm laser pumping light to penetrate through the nanofluid coolant and excite the laser crystal rod, which generates the 1064-nm laser beam transmitting along the axis direction. The added Au NPs significantly increase the apparent thermal conductivity of the coolant, thereby enhancing the heat transfer from the lasering rod to the flowing coolant. The Brownian movement of the added Au NPs also enhances the convection heat transfer within the coolant. Through the combined mechanisms, the transparent high-thermal-conductivity Au nanofluids improve the heat dissipation capacity of the convective thermal management system without affecting the normal operation of the solid-state laser.
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.
Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr3Y(PO4)3:Yb3+/Ln3+ phosphors (Ln=Ho, Er, Tm)
Published in Science and Technology of Advanced Materials, 2019
Weigang Liu, Xuejiao Wang, Qi Zhu, Xiaodong Li, Xudong Sun, Ji-Guang Li
Figure 5(a) shows the UC luminescence spectra of Yb3+/Ho3+ codoped Sr3Y(PO4)3 under varying excitation power, where the four groups of emission bands centered at ~485 nm (blue, negligible), 545 nm (green, weak), 657 nm (red, overwhelmingly strong) and 767 nm (red in NIR, weak) can be assigned to 5F3→5I8, 5F4/5S2→5I8, 5F5→5I8 and 5I4→5I8 transitions of Ho3+ [9–12], respectively. Raising excitation power from 1.00 to 3.00 W did not produce any new emission but successively improved the intensity of the existing luminescence. The CIE chromaticity coordinates of UC luminescence gradually drifted from orange [(0.5503,0.4318)] to orange-red [(0.6235,0.3676)] with increasing excitation power (Figure 4(d) and Table S2), which is due to the gradually larger red to green intensity ratio (I657/I545, Figure S3(b)). Under 2.00 W laser pumping, the phosphor exhibits a vivid and strong orange-red emission visible to naked eyes, as shown by the inset in Figure 4(d).