The Research On Visible Laser Characteristics Of Blue LD Directly Pumped Laser Gain Medium

Visible lasers are electromagnetic waves in the wavelength range of 380-780nm,which can be directly perceived by the human eye.Visible lasers have a wide range of applications not only in everyday life but also in medical,microscopic,communication,industrial,and scientific research fields.In recent years,with the rapid development of laser diode（LD）technology,research solutions based on blue LD pumped Pr³⁺-doped laser crystals for visible laser output have gained much attention.This solution is of great importance for the miniaturi zation of visible solid-state lasers,as it can achieve multiple wavelengths of visible laser output without the need for nonlinear optical transformation,and has a compact and straightforward laser cavity structure with high output efficiency.This thesis addresses the new requirements for the development of visible lasers,based on laser technologies such as Q-switching,mode-locking,and mode selecting,and guided by theoretical analysis,systematic research work on the laser output characteristics of the designed visible lasers has been carried out.Based on the selection of different optical modulation devices,successfully realizing high-performance continuous lasers,short pulse lasers,ultrashort pulse lasers,and vortex lasers in the visible band.This research work is a reference for designing high-performance continuous,pulsed,and vortex lasers in the visible band.The main research elements of this thesis are as follows.1.The absorption and emission properties of Pr:YLF crystals were introduced and the main factors affecting the output power of continuous lasers were analyzed using the four-energy level rate equation theory.The thermal lens focal length of the crystal and the changes in the oscillating laser beam radius in the cavity were analyzed.By optimizing the laser cavity length and the transmittance of the output mirror,continuous laser output of blue LD-pumped Pr:YLF crystal lasers at wavelengths of 522 nm,607 nm,639 nm,and 721 nm were successfully achieved,with corresponding maximum average output powers of 0.69 W,0.72 W,1.56 W,and 1.10 W respectively.2.By using electro-optical Q-switching technology,a KD^*P crystal was used as the optical modulation device,and the blue LD-pumped Pr:YLF crystal electro-optically Q-switched visible laser was achieved for the first time with a 200 mm linear cavity length and pressurized Q-switching operation.The shortest pulse duration,maximum pulse energy,and maximum peak power at 100 Hz repetition frequency were 137 ns,260μJ,and 1.90 k W respectively.3.By employing the passive Q-switching technique,we carried out research work on saturable absorber（SA）-based short-pulse lasers in the visible wavelength band.The saturable absorption properties of few-layer Nb₂C nanosheets and few-layer Ti₃CN MXene were investigated using the open Z-scan technique.It was also applied to visible lasers as SA and successfully achieved visible pulsed laser output.In the Nb₂C SA-based short pulse lasers,the shortest pulse width was 109 ns at 639nm.In the short pulse laser based on Ti₃CN SA,the shortest pulse width was 74 ns at 607 nm.4.By utilizing the passive mode-locking technique,the visible ultrashort pulse laser output of blue LD-pumped Pr:YLF crystal using the prepared 2D Ti₃CN and Pd Se₂ has been studied.The cavity design was optimized according to the mode-locked laser theory,and the stability of the mode-locked laser cavity and the variation of the beam radius were investigated using thermal lens theory and ABCD matrix theory.Based on the Ti₃CN saturable absorber mirror（SAM）,we successfully realized a 73.1 MHz red passive mode-locked ultrashort pulse laser with the shortest pulse width of 30 ps.Based on Pd Se₂ SA,we successfully realized a red passively mode-locked ultrashort pulse laser at 80.3 MHz with the shortest pulse width of 35ps.5.By applying the laser mode selecting technique,the visible vortex continuous laser and vortex pulsed laser outputs of blue LD-pumped Pr:YLF crystal were investigated.Based on blue LD pumping Pr:YLF crystal,the vortex visible continuous laser output at four wavelengths was successfully achieved by rational design of the cavity structure and doughnut-shaped pumping technique.By using Co:MALO crystal as SA,we have also achieved visible vortex pulsed lasers at 607nm and 639 nm with the shortest pulse width of 58 ns and 34 ns respectively.