We report on a passively mode-locked Nd : LuVO4 laser using a type saturable absorber of tungsten disulfide (WS2) fabricated by chemical vapor deposition method. At the pump power of 3.3 W, 1.18-W average output power of continuous-wave mode-locked laser with optical conversion efficiency of 36% was achieved. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser based on WS2. The repetition rate of passively mode-locked pulse was 80 MHz with the pulse energy of 14.8 nJ. Our experimental results show that WS2 is an excellent type of saturable absorber.
Third-harmonic generation (THG) with high output power based on the type-I phase-matching La2CaB10O19 (LCB) crystal was investigated in yz plane (θ=48.7°, φ=90°), in which direction the effective nonlinear coefficient (deff) of LCB is 0.7, much larger than the previous reports in other direction. The maximum output power we obtained at 355 nm was as high as 11.5 W, and the beam quality was measured to 1.47 in x direction and 2.56 in y direction. The angular bandwidth and temperature bandwidth in this direction were measured, which are larger than the previous reports also.
A high-power high efficiency picosecond (ps) 355 nm ultraviolet (UV) laser was reported based on the nonlinear optical crystal of type-I phase-matching La2CaB10O19 (LCB) which possesses the characteristic of non-hygroscopicity. The high-power third harmonic generation was successfully achieved from a 1064 nm ps fundamental laser. The maximum output power of 7.81 W of 355 nm UV laser was obtained from 35.2 W 1064 nm ps laser (80 MHz repetition rate, 10 ps pulse width) with optical conversion efficiency of 22.2%. The experimental results show that the LCB crystal has a promising prospect in generating high-power high efficiency UV laser.
During the process of laser ranging, the interaction between the target and the laser beam has the close relationship with the light scattering characteristic of the target surface, which can be characterized by the bidirectional reflectivity distribution function (BRDF). This paper discusses the effects of target reflective characteristics by the BRDF model and the Lambertian model. The BRDF is definited by surface parameters, such as surface roughness, correlation lengths and refractive index, incident angle and wavelength, which the Lambertian model does not include the detailed properties of the target. The results show BRDF is more precise than Lambertian model in factual environment. The main work is the research on calculating and comparing the minimal detectable power of laser rangefinder obtained the two models under different incident angles and surface roughness. The angular dependence of the BRDF is related to the microscopic properties of the surface. It showS that when the surface roughness increases the detectable power decreases rapidly. Modeling and simulation of the typical target shape of parabolic is provided in this paper on the bases of the BRDF and the LRCS is calculated. According the above study, it will provide some fruitful reference for further parameters choice of laser rangefinders and laser radar.
We have proposed a metallic dipole-ellipsoid-bagel nanostructure for the generation of high harmonics via two-color laser field. Comparing with the case of the one-color field, this nanostructure enables a broader bandwidth and smoother harmonic spectra under the condition of the two-color incidence field, which is in favor of the generation of extreme-ultraviolet (XUV) radiation and isolated attosecond pulses. Numerical techniques are employed to optimize nanoantennas and attain enhanced plasmonic field. The electromagnetic properties of this nanostructure is fully analyzed and discussed. The nanostructure support the highest enhancement fact of 2500 for both of 800-nm and 1500-nm incidence, and effectively enhance the field intensity exceed 103 in the volumn of 50×50×50 nm3.This nanostructure would benefit for the generation of high-harmonic, extreme-ultraviolet (XUV) radiation via plasmonic enhanced filed in a two-color multi-cycle laser field. This work would have potential application in the ultra-sensitive color sensor and the source of isolated attosecond pulses via multicycle laser.
During the process of laser propagation in free space, energy attenuation is brought by atmospheric medium. One of the major problems about laser propagation is that atmospheric component does not remain constant within the whole altitude band. So working out the relatively accurate attenuation coefficient is a research interest of many researches for several years. On this basis of analysis of the atmospheric component distributing characteristic, simple and practical simulate approach was given to meet the needs of laser rangefinder. The main work is the research on 1.06μm YAG laser transmission characteristics in the atmosphere, and the atmosphere loss of the mathematical model is investigated. The paper discussed the influence of atmospheric attenuation on ranging ability of laser rangefinder and analyzed the atmospheric attenuation theoretical. It showed that when the attenuation coefficient γ increases the detectable distance decreases rapidly. In the condition of three transmission modes, which are ground-to-ground mode, ground-to-air mode and air-to-air mode, the relationships between atmospheric transmittance and different visibility, different zenith angle were analyzed. Minimal detectable power of laser rangefinder represents ranging ability in above-mentioned three different modes was formulated with atmospheric transmittance. Based on the results, we can adjust the experimental parameters and achieve more desirable results. It has positive influence for the design of laser rangefinder.
In this paper, we investigated the characteristic of radar target, the spherical and the pyramidal missile warheads, and compared the RCS and performance of the targets with and without the cover of the plasma metamaterials. Numerical simulation is obtained by the numerical calculation Finite-difference time-domain method (FDTD). The parameters of plasmonic structures as a metamaterial cloak was designed and optimized. The relationship between the parameters of the cloak and the corresponding electromagnetic characteristic of the target are analyzed by the simulation and discussion in broadband radar signals. After optimization, the plasma cover could attenuate 40 dBsm of the radar cross section (RCS) of the targets maximally. The result shows that the anomalous phenomenon of cloaking and stealth effects induced by plasma materials for the radar target, which might have potential application of military affairs.
We have theoretically investigated and optimized a nano-periodical highly-efficient blazed grating, which is used as an outcoupler for extreme-ultraviolet (XUV) radiation. The rigorous coupled-wave analysis (RCWA) with S matrix method is employed to optimize the parameters of the grating. The grating is designed to be etched on top layers of IR reflector, performs as a highly-reflective mirror for IR light and highly-efficient outcoulper for XUV. The diffraction efficiency of -1 order of this XUV outcoupler is greater than 20% in the range near 60 nm, which allows high resolution spectroscopy of the 1s-2s transition in He+ at around 60 nm with extreme precision. The theoretical calculations are verified by the experimental results.
We theoretically investigate utilizing the enhanced plasmonic fields in metallic nanostructures. Numerical techniques are employed to optimize nanoantennas to attain the enhanced plasmonic fields up to 270. In the volume of 15 × 15 × 30 nm3 in nanoantenna, the intensity could be enhanced to 1014 W/cm2 for high harmonic generation (HHG). Optimal conditions for the production of MHz isolated attosecond pulse of 140 attosecond via HHG have been identified. These findings open up the possibility for the development of a compact source of ultrashort XUV pulses with MHz repetition rates. our simulations indicate a potential route towards the temporal shaping of the plasmonic near-field and in turn the generation of single attosecond pulses. Such XUV sources, which may operate at MHz repetition rate, could find applications in high-precision spectroscopy and for spatio-time-resolved measurements of collective electron dynamics on nanostructured surfaces. Moreover, the asymmetric cross nanoantennas is proposed to control the polarizations and select the wavelengths via varying the ratio of nanoantennas and generate the XUV pulse in both polarized direction.
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