Study On The Properties Of Near Infrared Dual-wavelength All-solid-state Laser

Monochromaticity is one of the basic characteristics of laser. Usually only a single wavelength can oscillate in a laser and other wavelengths were restrained. However, in many important applications, such as detection, laser display, medical instrumentation, lidar, precision laser spectroscopy, nonlinear frequency conversion and scientific research, we need a laser emission dual-or multi-wavelength simultaneously. Benefited by much more energy levels, obvious inhomogeneous broadening effect, gas laser is more likely to realize multiple wavelength operation; All solid-state dual-wavelength lasers own compact structure, small volume, and the wave bands it covered are close to practical application. For the past few years, all solid state dual-or multi-wavelength laser has become one of the popular research subject on the international.There are two methods for dual-wavelength laser generation. The first method is nonlinear frequency conversion (such second harmonic generation, sum frequency generation, difference frequency generation, Raman frequency shift). In most cases, this method needs strict phase matching, thus the structure and design are both relatively complex. The second one is based on the energy splitting of the active ions. It needs to select transitions between different energy levels of the active ions or different Stark levels within the same energy levels. This method has a simple structure, wide application, but the design is relatively complex. Corresping to the second method, laser operations at1.06μm+1.3μm、1.06μm+0.9μm、1.32μm+1.34μm have been investigated with Nd:YAG crystal or Nd:YVO4as laser medium, belonging to the combination of the three transitions at4F3/2�'4I9/2、4F3�'4I11/2、4F3/2�'4I13/2,or combination of different components within the4F3/2�'4I13/2transition.Nd3+is one of the trivalent rate earth ions used in laser application firstly, and it remains by the most important element in this group.Nd ion belongs to four-level system and its energy level structure varies only slightly from one host to another. The effect of the crystal field is treated as a perturbation on the free-ion levels. Compared with spin-orbit and electrostatic interactions among the4f electrons, the perturbation is small.The primary change in the energy levels is a splitting of each of the free-ion levels in many closely spaced levels caused by the Stark effect of the crystal field. Different energy levels were generated by the different combination of orbital angular momentum and spin anglar momentum.By selecting appropriate crystals and designing suitable cavity, simultaneously dual-or even multi-wavelength laser operation can be achieved.This dissertation emphasized on the phenomenon of near-infrared dual-or multi-wavelength laser physics of Nd-doped laser gain medium, including laser crystals and laser ceramic, involving isotropic medium and crystals with senior, intermediate and low symmetry.It focused on the the combination of different components within the4F3/2�'4I11/2transition around1μm, including usual and unusual laser output. The main laser gain medium in this dissertation includes Nd:YAG crystal,Nd:YAG ceramic and Nd:GGG crystal in higher category; Nd:GdVO4crystal、Nd:YVO4crystal and Nd:LiGd (MoO4)2crystal in intermediate category;Nd:LYSO crystal in lower category.The main contents of this dissertation include:1.Aiming at the important requirements of dual-wavelength all-solid-state laser for blood detection, we proposed the design scheme of1074and1112nm dual-wavelength laser and realized an efficient laser diode end-pumped continuous-wave dual-wavelength Nd:YAG crystal laser operating at1074and1112nm simultaneously, for the first time to our knowledge. The maximum output power was3.15W, including2.2W1074nm laser, and1W1112nm laser, with an optical conversion efficiency of23.6%.This dual-wavelength laser is an important source for detecting carbon monoxide poisoning by simple frequency doubling.2. Aiming at the research status of multi-wavelength laser used in laser display with compact structure, simple design and low cost, combing with the high gain coefficient of Nd:YAG ceramic, we proposed the design ideas of direct output multi-wavelength laser with Nd:YAG ceramic. Using one polished end face of the ceramic as the output coupler directly, we realized1064、1319、1338nm tri-wavelength output laser without coating process.The total maximum output power was3.2W, including2.2W1064nm laser, and1W1319&1338nm laser, corresponding to an optical conversion efficiency of30%.We proposed the design scheme of RGB three-fundamental-color lasers based on the tri-wavelength laser by further nonlinear frequency conversion.3.We studied the1.11μm laser output of Nd:GGG crystal,realized the dual-wavelength operation at1106and1110nm.We discussed its emission mechanism and dynamics process, as well as the application of this dual-wavelength laser. Difference frequency generation of this dual-wavelength laser can generate1.17THz coherent radiation.Besides, by frequency-doubling or sum-frequency, yellow-green laser around555nm can be obtained.The human eye macula is most sensitve for the555nm yellow-green light.4.We studied the1083nm laser output of Nd:GdVO4crystal and Nd:YVO4cystal.1083nm laser is important in helium magnetometers.We realized1083nm single-wavelength continuous wave and pulsed operation with Nd:GdVO4crystal,obtaining10.1W output power, which was the highest to the best of our knowledge and pulsed output with111μJ pulse energy、77ns pulse width and1.44kW highest peak power. By using an output coupler suitable for dual-wavelength operation, at a pump power of16.1W, the output powers of1083and1063nm were2.0and2.2W, respectively. We discussed the important application in helium magnetometers and the treatment of facial telangiectasia.5.Nd:LiGd(MoO4)2is a new laser crystal, belonging to tetragonal system.We characterized the anisotropic of its laser behavior. We calculated the stimulated emission cross-section on the principal axis at1061and1068nm and provided the theoretical study of simulating on the spatial distribution of the two wavelengths. We discussed the anisotropic laser output of Nd:LiGd(MoO4)2crystals with different orientations and found out the angle at which the two wavelength has similar proportion.Proposing the new thought of controlling emission wavelength by crystal anisotropy. 6. Nd:LYSO crystal belongs to monoclinic system.We demonstrated an811nm LD end-pumped Nd:LYSO laser at1075and1079nm and discussed the mechanism.The maximum output power was702mW corresponding to an optical conversion efficiency of27.7%and a slope efficiency of37.0%.It provides reference for the multiple wavelength laser output based on crystals with low symmetry.