Broadband Frequency Doubling Of Er-Fiber Mode-Locked Laser

Chirped pulse amplification(CPA) technique is an important technical method to generate ultra-short and ultra-intense laser pulses, and widely applied in the laser fusion fast ignition, wide spectrum diagnosis and X-ray laser field. Nevertheless, its application is limited because of the unstable seeding source. In recent years, the mode-locked fiber laser has drawn a lot of attention and gradually developed maturely, for its compact structure, high spatial beam quality, and low cost. The mode-locked erbium-doped fiber laser emits pulses with a central wavelength of 1550 nm, corresponding to frequency doubling of 775 nm of central wavelength, which is close to the wavelength of the Ti: Sapphire laser. Thus it can be applied as an alternative to the Ti: Sapphire oscillator, used as the seeding source of CPA system. And a more stable and cheaper CPA system can be obtained afterwards, which can significantly extends the field of the CPA application and commercialize it. In this paper, we worked on the broadband frequency doubling of mode-locked erbium-doped fiber laser, based on the spectrally noncritical phase-matching of BBO crystal. The research work consists of the following parts:1. A frequency doubling coupled wave equation was deduced on the basis of parameters designed for the broadband frequency conversion of mode-locked erbium-doped fiber laser. And the equation was deduced on the basis of parameter designed for the broadband frequency. And the equation was numerically solved by using the split-step Fourier method. It was analyzed in detail how the pulse width and spectral width of incident fundamental light and the thickness of the crystal affect the spectrum width and efficiency of the frequency doubled light. A standard of optimal frequency doubling crystal size was thereby proposed.2. An all-fiber mode-locked erbium-doped laser was constructed based on nonlinear polarization rotation effect. By optimizing its parameters, a femtosecond laser was obtained, with 1560 nm of wavelength, 30 nm of spectral width, 200 fs of pulse width, 80 MHz of repetition rate, and higher than 100 m W of average power. The chirped mirror was applied innovatively in compressing the light of the fiber laser amplifier stage, without appearance of side lobe in the femtosecond laser.3. Broadband frequency conversion experiment of mode-locked erbium-doped fiber laser was carried out with single BBO crystal, acquiring an output bandwidth of 16 nm. The BBO crystal was experimentally proved to be a good option to implement broadband frequency conversion of mode-locked erbium-doped fiber laser. And the standard of crystal size was also proved to be reliable.