Using laser irradiation to remove contaminants from soil is an emerging soil remediation method. The model used in this paper is based on local thermal non-equilibrium, using a carrier gas to simulate the recovery of contaminant gases. Numerical simulations are employed to study the temperature field, the evaporation and condensation of moisture, and the transport of gases within the soil under laser irradiation. The results show that continuous wave laser irradiation can rapidly bring both the gas and solid temperatures in unsaturated porous media to conditions suitable for separating most organic contaminants from the soil. Within the effective influence range of the laser, the phase change of water and the gas's transport speed are enhanced. This model can provide a theoretical basis for laser soil remediation or the interaction between lasers and unsaturated porous media.
We report the high repetition frequency dual-wavelength pulse laser output of Pr3+:YLF at 604 and 639 nm. We discuss the relationship between the threshold powers of the dual-wavelength laser with the insertion of a Fabry-Perot etalon and numerically solve the corresponding four-level rate equations. Based on the results, we designed and conducted the experimental research. Then we obtained dual-wavelength pulse laser output at different repetition frequencies. When the repetition frequency is 40 kHz and the maximum absorbed pump power is 2.723 W, the output power at 604 and 639 nm are 27 and 25 mW, respectively. This study provides a simplest method for direct output of dual-wavelength visible pulsed laser.
In this paper, a laser diode with a center wavelength of 444nm is used as the pump source. Based on the pre-laser mode selection technology, combined with the F-P etalon technology for auxiliary mode selection, a single-longitudinal-mode pulse laser with a center wavelength of 639.7nm is developed. In the experiment, a stable single-longitudinal-mode laser output under high energy injection is realized by optimizing the parameters of the laser insertion element. When the output power of the pump source is 10.8W and the repetition rate is 20kHz, the maximum single-longitudinal-mode output pulse energy is 10.25μJ, the peak power is 170W, and the pulse width is 77.66ns.
Green-red (500nm-660nm) laser is widely used in laser projection, laser color display, lithography and laser communication. It is a relatively simple and effective method to obtain the green, orange and red laser from Pr3+:YLF crystal pumped by blue laser diode (LD). In this paper, the influence of output mirror with different transmittance and different curvature radius on the output power of green laser is analyzed. The green laser is achieved with the maximum output power of 960mW at 522nm, when the full pumping current is 2.269A, the absorption power of a-cut Pr3+:YLF crystal is 7.44W.
At present, the research on hollow light mostly focuses on the near-infrared invisible light band, however, with the development of space light field and nonlinear optics, the nonlinear frequency conversion process of hollow light is also paid attention to, but most of them are focused on the theoretical level of frequency transformation, and few hollow light frequency conversion with realizability and applicability is available. In this paper, the visible hollow light conversion from 1064 nm to 532 nm is realized by using the conical refraction of biaxial crystal and a novel technical scheme based on the plane concave cavity structure and combining with nonlinear frequency conversion. The gain medium Nd:YVO4 is pumped by 808 nm LD, and LBO I phase matching is used for intra-cavity frequency doubling. When the pump power is 10.49W, 532nm hollow light output is 0.067W; finally, when the pump power is 23.09W, the maximum output power of 532nm hollow light is 1.146W, and the maximum light-to-light conversion efficiency of 1064nm-532nm is 27.4%. During the experiment, the cone refraction led to the formation of the 532nm hollow spot was observed, and the output performance of the 532nm hollow light was analyzed. The experimental scheme in this paper has the advantages of simple structure, low maladjustment sensitivity and high mechanical stability, which is conducive to frequency conversion in resonant cavity. It provides a novel and effective technical means for obtaining hollow light in visible light band, and broadens the application of hollow light in quantum computing and communication.
A dual-wavelength alternately Electro-Optic (EO) Q-switched output laser operating at 1064 and 1319nm is demonstrated. The mathematical model describing the operation mechanism of alternately Q-switched output of dual-wavelength laser was put forward, and the principle of the dual-wavelength laser alternately Q-switched output was analyzed. When the full pumping current of Nd:YAG (A) crystal is 90 A and that of Nd:YAG (B) crystal is 70 A, alternating dual-wavelength pulsed lasers are achieved with a delay of 200μs at the pulse repetition frequency (PRF) of 10 Hz under the voltage on RTP crystals of 1000V. The results show that the experimental results were consistent with the theory, which proved the correctness of the theory of dual-wavelength laser alternately Q-switched laser.
We develop a theoretical model of multimode rate equation that accurately describes mode evolution mechanism of prelase Q-switched Pr3+:YLF single longitudinal mode (SLM).The theoretical simulation process explained each part of the operation and experimental phenomenon in the pre-lase process effectively.We identify that there is an optimal parameter for the two step signal of acoustic-optic modulator which determines the stability of SLM output.Our theoretical model can be applied to most solid-state lasers, and offer theoretical references for the design and construction of experimental facilities, which is significant for future research.Up to now, there is still not a complete theory to accurate description of prelase Q-switching technology. Moreover, there have been no reported about directly emitting Q-switched SLM laser in the visible region.
For the asymmetric plane-plane cavity, the influence of cavity length as a variable factor on the thermal lens diopter, dynamic stable zone, and modes selection in the stable zone is discussed. The relationship between the length of the cavity and the width of the dynamic stability zone is pointed out. The influence of the ratio of the long arm to the short arm on the degree of separation of the various oscillation modes is indicated. A suitable pump operating point for modes selection is indicated. A end-pump Nd:YVO4 cavity with different long arms is built up for modes selection experimentally, the fundamental mode and hollow beam (TEM01+TEM10) output are observed in the experiments, which are concordant with the theoretical predictions.
In this paper, a new kind of long distance detection source-- hollow double-half
Gaussian laser beams is put forward. By use of modified Cassegrain optics system, we obtained
hollow beams with special light distribution-parallel hollow double-half Gaussian laser beams,
the intensity distribution of this kind of hollow beams is zero at all the hollow area and is
maximum at inner margin, so forms double half-Gaussian beams, and the inner and the outer
diameters of the hollow beams are controllable. The analytical equation of propagation and
transformation of the hollow laser beams in free space was deduced. The simulation shows that
the intensity exhibits three-dimensional trap distribution in the near-field, while the double
half-Gaussian hollow beams turns into solid laser beams when propagating a certain distance,
which shows the characteristic of self-focus. By use of the characteristic of self-focus of the
double half-Gaussian hollow beams, we can realized the self-gating long distance detection to the
small object even if in the condition of lower laser power. The technology will be applied broadly
in the near years.
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