The exciton complexes in two-dimensional materials have long fascinated scientists and researchers for their mechanisms in fundamental photo-physics. And it is well established that the evolution of defect bound excitons in twodimensional semiconducting TMDs brings largely unexplored opportunities for tailoring their optoelectronic properties. Yet thus far, the properties of defect bound excitons of TMDs have been rarely investigated. In this work, the intrinsic properties of defect bound excitons in aged CVD-grown monolayer WS2 are experimentally studied by the steady-state photoluminescence measurement. Specifically, the photoluminescence mapping experiment is conducted to demonstrate the spatial distribution of the defect bound excitons, whose spectral feature is located ~0.2 eV below the neutral free Aexcitons. Additionally, the power-dependent photoluminescence experiment is applied to investigate the behavior of the defect-state photoluminescence and a significant nonlinear dependence of defect bound excitons on excitation power is revealed. Furthermore, we directly observed the disappearance of defect-state photoluminescence by exposing sample to high laser power irradiation, which can be explained by the enhanced desorption process of molecules physiosorbed on surfaces under laser irradiation. The results of our work provide a comprehensive understanding for the defect bound excitons in monolayer tungsten disulfide, which is essential in promoting the development of defect engineering about two-dimensional semiconducting TMDs and may pave the way for tailoring the performance of the optoelectronic device.
In this work, few layers of Bi2Se3 is chemically treated, in which the AuCl3 solution is used for oxidation reaction to form p-doping, and BV solution (benzyl dichloride) is put to form n-doping to change material properties. We used pumpprobe system to verify the effect of doping on Bi2Se3 materials. In addition, the nonlinear saturable absorption of the material is also controlled. Through the I-scan test, we found that the saturable absorption has diverse responses to different wavelengths and doping conditions. By doping, the Fermi level of the material can be adjusted to control the saturable absorption of the material, which can be applied to the mode-locked laser. The weakened saturable light intensity can make the mode-locked pulse easier to generate.
The plasma channel evolution tendencies are studied numerically with the change of initial conditions based on the Nonlinear Schrödinger Equation. Then, the accuracy of an optical scheme to detect the plasma density inside the filaments is certified numerically. A Gaussian beam with pulse width 50fs, radius 2.5mm ranging energy from 10mJ to 50mJ at interval of 10mJ are simulated to yield plasma channel. With the augment of energy, firstly, the beginning position of plasma channel tend to be drew back gradually whereas the end position of the channel can be putted forward in a gradient form instead of continuously. Secondly, the number of peaks add one each time when the energy increase 10mJ. Lastly, the radius of plasma channel barely changes with initial energy up from 10mJ to 50mJ. On the other hand, plasma channel produced by a Gaussian beam with pulse width 50fs, energy 50mJ ranging the radius from 2.5mm to 10mm at interval of 2.5mm are simulated. With the increase of initial beam waist, the plasma channel length becomes shorter. The channel becomes broader and broader whereas the length of the channel becomes shorter. In order to verify the rationality of the approximation, Nornaraki detecting scheme through interference of the probe laser has been tested with the numerical simulation. As a consequence, the integral of refractive index along the radius direction can be replaced by the product of average refractive index and plasma channel diameter.
The 1064nm fundamental wave (FW) and the 532nm second harmonic wave (SHW) of Nd:YAG laser have been widely applied in many fields. In some military applications requiring interference in both visible and near-infrared spectrum range, the de-identification interference technology based on the dual wavelength composite output of FW and SHW offers an effective way of making the device or equipment miniaturized and low cost. In this paper, the application of 1064nm and 532nm dual-wavelength composite output technology in military electro-optical countermeasure is studied. A certain resonator configuration that can achieve composite laser output with high power, high beam quality and high repetition rate is proposed. Considering the thermal lens effect, the stability of this certain resonator is analyzed based on the theory of cavity transfer matrix. It shows that with the increase of thermal effect, the intracavity fundamental mode volume decreased, resulting the peak fluctuation of cavity stability parameter. To explore the impact the resonator parameters does to characteristics and output ratio of composite laser, the solid-state laser’s dual-wavelength composite output models in both continuous and pulsed condition are established by theory of steady state equation and rate equation. Throughout theoretical simulation and analysis, the optimal KTP length and best FW transmissivity are obtained. The experiment is then carried out to verify the correctness of theoretical calculation result.
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