Development of High-power Visible Lasers Based on Fiber Laser and Nonlinear Frequency Conversion

Abstract

High-power visible lasers play a critical role in various fields, including industrial applications, medical treatments, basic research, and defense systems. However, it is hard to directly generate high power beam in such wavelength range from traditional solid-state laser systems. In addition, as the wavelength get shorter, it brings more technical challenges for generation. In this thesis, developments of high-power visible lasers based on optical fiber and nonlinear frequency conversion are presented, targeting wavelengths of 532 nm and 420 nm. For 532 nm beam generation, 33.84 W, single-mode 1064 nm fiber laser was developed and employed as a pump source for second harmonic generation (SHG). Using a type I noncritical phase-matching (NCPM) condition with a Lithium Triborate (LBO), the 532 nm beam with an average power of 11.3 W, a repetition rate of 4 MHz, a pulse width of 28.46 ns, and a conversion efficiency of 33.39% was generated. For the generation of 420 nm beam, single-mode 1260 nm Raman fiber laser was used as a pump source. Using a Bismuth Triborate (BIBO) nonlinear crystal, the 1260 nm beam was frequency-doubled to 630 nm, and both 630 nm and residual 1260 nm beams were combined in the another nonlinear crystal. Separate experiments were conducted with LBO and Potassium Titanyl Phosphate (KTP) as nonlinear crystal. As a result, the 420 nm beam with an average power of 1.17 W, conversion efficiency of 1.6 %, a repetition rate of 9.17 MHz, a pulse width of 30.9 ns and was generated by LBO while KTP generated the 420 nm beam with an average power of 0.47 W, a conversion efficiency of 2.46 %, a repetition rate of 9.24 MHz, a pulse width of 34.7 ns. Equipped with high power, the visible lasers developed in this research are anticipated to meet the increasing demands for laser sources across various applications.