Research On Blue Laser Diode Directly Pumped Pr:YLF Oscillator

Visible laser has been applicated widely in astronomy,environmental detection,holographic technology,laser display,medical treatment,fine processing,information storage and other fields.At present,methods of realizing laser at visible band are mainly semiconductor laser and nonlinear frequency conversion.In recent years,using blue laser diode(LD)as the pump source,visible laser generated by all-solid-state laser technology has become an emerging research direction.Among them,the praseodymium-doped laser crystal has absorbtion band at blue and broad emittion band covering blue,green,orange,red and other visible wavelengths,which is an important laser material for blue-pumped all solid-state laser.In this thesis,theoretical simulations and experiments were carried out on the blue-LD directly pumped praseodymium-doped solid-state laser.The main research contents and innovative achievements of the paper are as follows.1.Due to the serious divergence and poor beam quality of the blue light LD,we designed two beam-shaping schemes to improve the beam quality.Experimental results of two schemes were compared,including shaping effects,intracavity mode matching condition,laser output and loss of the crystal in the cavity,to optimize beam shaping.Based on the comprision,a combination of an aspheric lens and a cylindrical lens was used to realize the collimation and shaping of the blue LD,which was employed as the pump source for the subsequent continuous and mode locking experiments.2.The Pr:YLF crystal was directly pumped by blue LD to realize the visible continuous laser operation.The influence of the pump wavelength on the absorption of the Pr:YLF crystal and the laser output was analyzed.According to the polarization characteristics of the Pr:YLF crystal,continuous laser operated at 721 nm and 640 nm was achieved.The highest output power of 640 m W was obtained at the 721 nm under 2.5 W pumping,with light-tolight conversion efficiency reached 30%.The tuning range of continuous wave was tested.Laser operated at 605 nm,698 nm and 721 nm were realized under π polarization while 607 nm and 640 nm were realized under σ polarization.In addition,to increase the intracavity pump power,a double-ended pumping structure was used and an output power of 800 m W was obtained at 721 nm,which is beneficial for the subsequent mode-locking experiments of Pr:YLF crystals.3.Self-mode-locking operated at 721 nm and 640 nm were realized by using four-mirror cavity,the output power and repetition rate were 160 m W at 79 MHz and 130 m W at 75 MHz,respectively.According to the Kerr-lens mode locking technology and the principle of dispersion compensation,four types of mode-locking cavity structure were designed,and the intra-cavity laser mode,stable region and Kerr sensitivity were simulated.Among the four types,the dual-crystal dual-pump confocal cavity showed great possibility to achieve Kerr-lens mode locking of Pr:YLF crystals.