Studies On High Power Broadband LiF:F₂^- Color Center Lasers And Novel Waveguide Lasers

This dissertation includes two parts:One is the experimental study on LiF:F₂^-color center laser.The other is the investigations on the novel waveguide lasers.There are two types of novel waveguide lasers,one is the planar waveguide lasers;the other is single crystal fiber laser.By using color center crystal or transition metal ions doped crystal as the gain media,we can get tunable solid-state lasers.The color center laser has low threshold,can work at continous wave?CW?and Q-switched mode with good beam quality and easily realize single-longitudinal-mode operation.So it has been widely used in many fields,such as molecular spectroscopy,chemical kinetics,pollution detection,optical fiber communication and semiconductor physics.In recent years,many researchers focused on the novel waveguide lasers.The aim was to combine the traditional uniform bulk crystal and the fiber technology to achieve high-efficiency and high-power output.Traditional Nd:YAG single crystal has the advantages of high melting point,good mechanical properties,high thermal conductivity and can work stably at high power pump.The fiber laser has the advantages of high coupling efficiency,high power density,high optical efficiency,low threshold and good beam quality.So combining the two of them to form novel waveguides shows a promising approach to construct highly efficient lasers.The planar waveguide laser compromises the merits of bulk solid-state laser and fiber laser.The planar waveguide has large thermal area than bulk crystal.Compared with fiber which can only be made by glass,it can use single crystal and ceramic as materials.So the planar waveguide laser can achieve high power output with good beam quality easily.Single crystal fiber is another combination of single crystal and waveguide.This geometry is able to confine the pump beam by guiding and propagate the laser beam in free space without guiding or diffraction.Compared with the traditional glass fiber,it has high thermal conductivity,low nonlinear coefficient and high doping concentration.In this paper,by using a quasi-continous wave?QCW?diode-side-pumped acousto-optically Q-switched 1064 nm Nd:YAG laser as pump source,we study the output characteristics of the LiF:F₂^-color center laser.By using YAG/Nd:YAG/YAG ceramics planar waveguide and Nd:YAG single crystal fiber as the laser gain medium,we study the LD end pumped CW,actively Q-switched lasers experimentally.The main contents are as follows:1.A high power LiF:F₂^-color center laser is demonstrated with broadband emission.The output characteristics of the 1064 nm are firstly studied.Under the pumping current of 71 A,we obtained the maximum output power of 25.4 W with pulse duration of 70 ns at the macro pulse repetition rate of 400 Hz.And then with different output mirrors,we try to find the optimization of the color center laser cavity.The optimal result occurred at the macro repetition rate of 400 Hz with the input mirror of a curvature radius of 1000 mm and the output coupler of a reflectivity of 39%.The highest output power of up to 4.7 W was obtained under the incident 1064 nm laser power of 25.4 W,corresponding to an optical-to-optical conversion efficiency of 18.5%.The broadband emission was centered at 1142 nm with a bandwidth of 13 nm.The beam quality factors in vertical and horizontal directions were determined to be 4.7 and 4.3.2.The output characteristics of the 1064 nm YAG/Nd:YAG/YAG ceramics planar waveguide laser are researched.A 35 W fiber coupling 808 nm LD is used as pump source.For CW regime,a maximum output power of 10.4 W at a center wavelength of 1064.6 nm is obtained under an absorbed pump power of 17.4 W,corresponding to an optical-to-optical conversion efficiency of 59.8%.For acousto-optically Q-switched operation,we obtain maximum output power of 3.0 W at a pulse repetition frequency of 30 kHz,corresponding to an optical-to-optical conversion efficiency of 38.6%.The shortest pulse duration of 6.5 ns is achieved at a pulse repetition frequency of 10 kHz with peak power and pulse energy of 38.5 kW and 0.25 mJ,respectively.3.We research a high efficient and high power CW 1064 nm laser with a Nd:YAG single crystal fiber.When the absorbed pump power is 117 W.an output power of 72.3 W is obtained,corresponding to an optical-to-optical conversion efficiency of 62.8%.With a KTP crystal inserted into the cavity.the green laser power of 10 W is obtained at an absorbed pumping power of 83.5 W.4.By using Nd:YAG single crystal fiber as the gain medium,the LD end pumped CW and actively Q-switched lasers operating at 1122.6 nm are investigated.For CW regime,a maximum output power of 27.2 W is obtained under an absorbed pump power of 92.7 W,corresponding to an optical-to-optical conversion efficiency of 29.34%.For actively Q-switched operation,a maximum output power of 3.9 W is obtained at a pulse repetition frequency of 30 kHz.At a pulse repetition frequency of 10 kHz,the shortest pulse duration of 86 ns is achieved peak power and pulse energy of 4.22 kW and 0.36 mJ,respectively.The main innovations if this dissertation are as follows:1.By using a QCW diode-side-pumped acousto-optically Q-switched 1064 nm Nd:YAG laser as pump source,we study the output characteristics of the LiF:F₂^-color center for the first time.Under an incident 1064 nm laser power of 25.4 W,the highest output power of up to 4.7 W is obtained with a macro pulse repetition rate of 400 Hz and a micro pulse repetition rate of 50 kHz.The broadband emission is centered at 1142 nm with a bandwidth of 13 nm.2.The LD end-pumped high power YAG/Nd:YAG/YAG ceramic planar waveguide laser is demonstrated.It is proved that the transparent ceramic planar waveguide fabricated by a nonaqueous tape casting and solid-state reactive sintering method has excellent optical properties.For continuous wave regime,a maximum output power of 10.4 W at a center wavelength of 1064.6 nm is obtained under an absorbed pump power of 17.4 W,corresponding to an optical-to-optical conversion efficiency of 59.8%.To our best knowledge,this is the highest power and highest efficiency obtained of YAG/Nd:YAG/YAG ceramic planar waveguide laser.During AO Q-switched operation,a maximum output power of 3.0 W with an optical efficiency of 38.6%was obtained at the PRF of 30 kHz.The shortest pulse duration of 6.5 ns was obtained under the absorbed power of 7.8 W at the PRF of 10 kHz.The singlepulse energy and peak power were 0.25 mJ and 38.5 kW.3.The LD end-pumped high power 1064 nm Nd:YAG single crystal fiber laser is demonstrated.At an absorbed pumping power of 117.0 W,the maximum power of 72.3 W was obtained,with a corresponding conversion efficiency of 61.8%.To our best knowledge,this is the highest power and highest efficiency obtained of Nd:YAG single crystal fiber lasers.With a KTP crystal inserted in the cavity,the output power of 10 W is obtained under 83.5 W absorbed pumping power.4.For the first time,the LD end-pumped CW and actively Q-switched Nd:YAG single crystal fiber lasers operating at 1122.6 nm are investigated.For CW regime,a maximum output power of 27.2 W is obtained under an absorbed pump power of 92.7 W,corresponding to an optical-to-optical conversion efficiency of 29.34%.For actively Q-switched operation,a maximum output power of 3.9 W is obtained at a pulse repetition frequency of 30 kHz.At a pulse repetition frequency of 10 kHz,the shortest pulse duration of 86 ns is achieved peak power and pulse energy of 4.22 kW and 0.36 mJ,respectively.