Non-Central Phase Matching Second Harmonic Generation by Using High Power Femtosecond Ytterbium-Doped Fiber Laser

Femtosecond laser has unique advantages in frequency conversion owing to broadband spectrum and ultra-high peak power. Here, the authors demonstrate the non-central phase matching second harmonic (SH) process by utilizing femtosecond ytterbium-doped fiber (YDF) laser. Numerical solution of the coupled wave equations for the process of femtosecond pulses SH indicates that the non-central phase matching is determined by the spectral broadening and frequency shift. Pumped by Watt-level 1040 nm femtosecond pluses, the period quasi-phase matching at the 1064 nm wavelength, the fundamental frequency (FF) spectrum broadened up to 34.7 nm width and red shifted about 6 nm, and the non-central phase matching SH with PPKTP crystal waveguide generates at around 523 nm. The experimental measurements confirm the theoretical predictions, and offer a deeper understanding of nonlinear optical effects. The non-central phase matching enables flexible frequency conversion with potential applications in ultrafast optics.