Self-starting, third-harmonic mode-locked 1 GHz Nd:YLF laser

AM and FM active mode-locking methods have been utilized to generate high-quality pulse trains at high repetition rate in several laser systems, including semiconductor lasers, and erbium-doped fiber lasers. However, these techniques usually fail to produce pulse trains with long-term stability. Some forms of active stabilization are generally required for mode-locked lasers to maintain exact synchronism between the modulation frequency and the natural cavity repetition rate, which tends to drift in time owing to mechanical vibrations and thermal changes. Additionally, because the higher repetition rate makes the cavity length shorter, it is difficult when the mechanical mountings of an active mode-locker are put close to the output mirror to achieve the maximum modulation efficiency in a bulk laser system. To solve two problems in high repetition rate active mode-locking laser systems, the direct drive method and harmonic mode-locking method are useful as a solution of the synchronism and the short laser cavity. We developed a self-starting third-harmonic mode-locked bulk Nd:YLF laser operating at a 1 GHz repetition rate.