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At present, pulse widths of passively Q-switched mid-infrared lasers at ${\sim }2.8 {\mu }\text{m}$ have been limited to be at least several hundreds of nanoseconds. In this letter, by configuring a compact laser resonator, we report on diode-pumped continuous-wave and passively Q-switched mid-infrared Er:YSGG lasers. Laser emission at 2797 nm is achieved with a maximum output power of 0.63 W and slope efficiency of 13.9% in continuous-wave mode. Using polycrystalline Fe:ZnSe as saturable absorber, the passively Q-switched operation is also realized with the narrowest pulse width of about 14.6 ns, which is believed to be the shortest pulse for passively Q-switched mid-infrared lasers. The generated maximum pulse energy and peak power are 5.05 ${\mu }\text{J}$ and 345.8 W, respectively. [ABSTRACT FROM AUTHOR]

We report on the growth and laser operation of Tm:Lu3Al5O12 (Tm:LuAG) single crystal grown via the micro-pulling-down ($\mu $ -PD) method, for the first time to the best of our knowledge. Spectral properties (absorption and fluorescence) and fluorescence lifetime of the Tm:LuAG crystal were measured at room temperature. Using a 790-nm diode laser as pump source, continuous-wave laser operation of the Tm:LuAG crystal was demonstrated with a maximum output power of 2.88 W and a slope efficiency of about 39.1% at 2016 nm. Passively $Q$ -switched laser operation was also investigated using Cr:ZnSe as saturable absorber. The maximum average output power reached about 0.53 W with the shortest pulse width of 54.3 ns and a pulse energy of $21.9~\mu \text{J}$. This letter reveals that the $\mu $ -PD technique is reliable for growing high-performance Tm3+-doped crystals for various potential applications. [ABSTRACT FROM AUTHOR]

In this letter, molybdenum ditelluride (MoTe2), a new member of the transition metal dichalcogenides family, has been characterized and fabricated as an optical modulator for the development of broadband wavelength tunable laser using a Tm3+-doped CaYAlO4crystal as a laser gain medium. The maximum average output power reaches 0.75 W with the shortest pulse width of about $0.69~\mu \text{s}$ and repetition rate of 70.9 kHz, which leads to a pulse energy of about $10.58~\mu \text{J}$ and peak power of 15.3 W. Keeping the MoTe2optical modulator inside the laser resonator and at the same time introducing an undoped YAG for wavelength tuning, wavelength tunable passively Q-switched laser operation with a wavelength range of about 112 nm has been demonstrated. This letter experimentally verifies the potential of the novel 2D material MoTe2as an optical modulator. At the same time, this letter paves the way toward the realizations of simple and compact wavelength tunable pulsed laser sources based on broadband 2D materials saturable absorbers. [ABSTRACT FROM AUTHOR]

We report on continuous-wave and passively Q-switched Tm: Y2SiO5 (YSO) crystal lasers. For continuous-wave operation, a maximum output power of 3.23 W is achieved at 1969.8 nm with slope efficiency of 34.3%. The results represent the best laser performance that ever obtained in Tm3+-doped oxyorthosilicate materials. Effective continuous-wave lasers have been also obtained at 1976.0, 1972.9, and 2044.6 nm by using differently coated output couplers. Using Cr: ZnSe saturable absorber, passively Q-switched Tm: YSO lasers are realized at 1944 and 2022 nm, for the first time to our knowledge. The maximum average output power has reached 0.74 W with pulsewidth of 78.3 ns and the corresponding pulse energy is 71.8 μJ. The present results indicate that Tm: YSO lasers could be very potential as sources for 2-μm eye safety related applications. [ABSTRACT FROM AUTHOR]

Denser deployments of heterogeneous networks (HetNets) lead to more frequent handovers, which results in a decline of user experience as well as heavy signaling overheads to the network. Therefore, the study on handover is of great importance especially in dense HetNets. In this paper, we focus on the analysis of cross-tier handover from the macro cell tier to the small cell tier, which shows the highest handover failure rate in current standards and industry studies. Using the stochastic geometry, we propose an analytical model for the cross-tier handover processes in the HetNet. Based on the derived analytical model, the closed-form expressions for the key handover performance metrics, including the handover rate, handover failure rate, and ping-pong rate, are deduced as functions of the base station density, time to trigger and user mobility. Simulation results verify the accuracy of the proposed analytical model and closed-form theoretical analyses, which provide guidance for the deployments of HetNets and corresponding handover strategies. [ABSTRACT FROM PUBLISHER]