Search

Mid-infrared (MIR) pulsed lasers operating in the ∼3 μm region play a crucial role in various applications, including molecular spectroscopy, ultrafast molecular imaging, and laser-assisted surgery. Despite recent advancements in MIR gain platforms, a notable technological challenge remains in the absence of an effective optical Q-switch. Here, a remarkable optical Q-switch in the 3 μm region based on a Dirac semimetal PtTe2 saturable absorber is realized. By modulating the surface state of PtTe2, the pulsed laser exhibited an increase in average power, escalating from 521 to 588 mW, accompanied by a significant decrease in pulse width from 368 to 187 ns. Nondegenerate pump–probe measurements showed that the recombination rate of the photocarrier in thinner PtTe2 nanoplates was effectively accelerated, primarily attributed to the substantial increase in surface state density, leading to better saturable absorption performance. As the thickness of the PtTe2 nanoplates decreases, the nonsaturable loss decreases from 12% to 3%, while the modulation depth increases from 6% to 12%. The enhanced ultrafast nonlinear absorption enables flexible modulation of saturation absorption parameters, which endows high-performance MIR pulsed laser generation. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a SESAM mode-locked Tm:CaYLuAlO4 (a-cut) laser in the 2-μm spectral range. A birefringent filter (BF) is employed to shift the emission wavelength above 2 μm to support the stable mode locking through avoiding the structured water vapor absorption. Pulses as short as 288 fs are generated with a central wavelength of 2037 nm and an average power of 166 mW at a repetition rate of ~ 77.6 MHz. Moreover, wavelength tunable femtosecond laser with a tuning range from 2031.8 to 2081.1 nm is realized simply by rotating the birefringent filter around its surface normal. This work experimentally shows that birefringent filter is a simple and low-cost way to support the stable mode locking of Tm-bulk femtosecond lasers with an emission peak in the water vapor absorption region. [ABSTRACT FROM AUTHOR]

In this paper, an acousto-optic (AO) Q-switch based on α-BaTeMo2O9 (α-BTM) crystal is designed and further applied to generate a laser pulse at 639 nm for the first time. The α-BTM AO Q-switch demonstrates a large diffraction angle of 0.93° and a high diffraction efficiency of 85% at 639 nm. In the experiment, a maximum AO Q-switched output power of 362 mW is achieved at a repetition rate of 30 kHz, under a maximum absorbed pump power of 3.60 W, corresponding to a slope efficiency of 15.2%. With transmittance of T = 3%, the shortest Q-switching pulse width of 54.7 ns is generated at a repetition rate of 1 kHz. Meanwhile, the beam quality factor M2 of the above laser is measured, presenting the magnitude of 1.14 at both x and y directions. Our findings indicate that α-BTM AO Q-switch could act as an excellent switching device at 639 nm which may help to explore potential applications in the visible field. [ABSTRACT FROM AUTHOR]

To shed light on the association between restless leg syndrome (RLS) and anxiety in Parkinson's disease (PD) population. This was a case-control study including 129 PD participants with and without anxiety who presented to the Aerospace Center Hospital in Beijing, China. Anxiety was evaluated by using the Beck Anxiety Index score. RLS was assessed using the minimal diagnostic criteria of the International Restless Legs Study Group and RLS symptom frequency and treatment. We then examined the relationship between RLS and anxiety by logistic regression models and subgroup as well as interaction analyses. The proportion of RLS in PD with anxiety was significantly higher in the PD without anxiety (p < 0.001). The multivariate logistic regression models indicated that PD participants with RLS had a 5.98-fold higher risk of anxiety in PD than those without RLS (OR, 6.98; 95% CI, 2.77–17.59). Subgroup analyses indicated that PD with RLS tended to be associated with a greater risk of anxiety in all stratified subgroups (adjusted ORs >1). Furthermore, the interaction analyses revealed no interactive role in the association between RLS and anxiety. The present case-control study suggests that RLS is an independent risk factor for anxiety in PD patients. Early attention and targeted treatment for RLS may be necessary for mood management in PD. Larger prospective cohort studies are wanted to validate these findings. [ABSTRACT FROM AUTHOR]

Laser polishing (LP) is an effective method to improve the surface quality of an additively manufactured nickel-based alloy. In this paper, the in-situ laser polishing (ILP) experiment is performed on the selective laser melting (SLM) IN718 samples. The white light interferometer is used to test the three-dimensional surface profile and surface roughness of samples. The results show that the surface quality of as-SLMed samples by ILP is improved. In particular, the surface roughness is decreased by 33.5%. To reveal the mechanism of ILP, a three-dimensional numerical model is established based on the finite volume method (FVM). The model can accurately simulate the mesoscopic scale physical phenomena when the laser interacts with the metal. The temperature field, the melt pool flow, and the evolution of the surface morphology during the ILP process are predicted using this model. The mechanism of ILP is revealed based on the dynamics of the molten pool. The contribution of capillary and thermocapillary forces to the reduction of bulge curvature at different stages is studied. Furthermore, the effect of ILP power on the surface quality is investigated, and the mechanism of bulges and depressions on the track surface during high-power ILP is revealed. [ABSTRACT FROM AUTHOR]