Experimental Study Of532nm Mode-locked Fiber Laser

Green laser around532nm has an important and wide application in measurement, display, communications, medical, etc. Usually532nm laser is generated by frequency doubling of1064nm laser. Fiber laser technology can get smaller waist radius, higher beam quality, higher output power, high-quality laser, and1064nm fiber laser frequency doubling to532nm laser has advantages of high efficiency, small size and easy adjustment, etc., which is now arousing more and more interest. Basing on1064nm passively mode-locked fiber laser, and using periodically poled lithium niobate (PPLN) crystal for second-harmonic generation (SHG, it means frequency-doubling), a532nm wide spectrum pulsed laser was obtained. And mode-locking fiber laser has been investigated, SHG wave output, fundamental wavelength and SHG wavelength tuning has been carried out, and so on. Experimental research work and obtained achievement are as follows:1. We experimentally studied ytterbium doped passively mode-locked fiber laser and carried out mode-locking fiber laser experimentation on a figure8cavity and a half-figure8cavity (σ cavity). The phenomena like pulse broadening and pulse division get a narrow width was discussed and analyzed, then the method of how to achieve low repetition rate, high peak power mode-locked laser was proposed;2. The SHG of1064nm fundamental wave with narrow bandwidth and broad bandwidth was studied and obtained. When the fundamental wave laser emitting out from a single mode fiber directly irradiating the PPLN crystal with a small divergence angle, the SHG wave of a broad bandwidth was obtained. The spectral characteristics and efficiency of the SHG were studied. Then, the SHG wave output to a fundamental wave of bandwidth of9.8nm, peak wavelength of1070.3nm mode-locked laser was carried out, and the SHG wave has a bandwidth of4.8nm, center wavelength of533nm pulsed, with a pulse repetition of1.3MHz;3. Based on quasi-phase-matching (QPM) technique, the SHG wavelength tuning by changing the incidence angle of the fundamental wave was experimentally studied. A wide spectrum (～60nm) mode-locked laser as the pump source, adjusting the angle of PPLN crystals, a wavelength detuned pulsed laser was obtained, when the incident angle adjusting from0°to30°, the peak wavelength of the SHG wave shifting continuously from531.6nm to536.0nm The experimental result agree to the QPM theory, and its tuning curve can be better contrasted with computer simulation results;4. For enhancing power of fundamental frequency laser and optimization of the mode-locked laser pulses, a fiber laser with large mode area (LMA) double-clad Yb-doped fiber (DC-YDF) was studied in the figure8mode-locking cavity. Finally, the mode-locked laser output power has been improved, stable mode-locked pulse with about10%slope efficiency. Next, we studied figure "8" square wave pulse mode-locked, noticing the evolving process of a gaussian pulse transforming to a square wave with increasing pump power, which can be a reference for achieving532nm square wave pulses laser.