24-mJ, 2-kHz pulse generation with a Q-switched Nd:YAG laser oscillator and fiber amplifier hybrid system

摘要

With the emergence of large-mode-area fiber and cladding pump technique, output power of rare-earth doped fiber lasers are grown rapidly in recent years. However, "bulk solid-state-laser" is still a choice of geometry in high-pulse-energy regime. Scaling of pulse energy with a fiber-based system is limited mainly due to damage threshold, nonlinear effect, and energy dissipation induced by ASE (Amplified Spontaneous Emission). To overcome these issues, various systems have been reported so far. The approaches by fiber-based amplifier scheme could be divided into two groups from the viewpoint of seed pulse: (1) pulsed laser diode or pulsed-laser-diode-pumped fiber laser, (2) Q-switched solid-state laser. In first approach, complex multi-stage amplifier is indispensable because of relatively weak laser diode seed pulse. We considered the second approach is better adapted to our target, industrial, high-energy, and high-repetition-rate material processing application. Since, established Q-switched solid-state-laser technique enables flexible and reliable pulse waveform and repetition-frequency control, a monolithic fiber laser system allows highly-efficient amplification. The experimental apparatus was consisted of an in-house Q-switched Nd:YAG rod laser oscillator and a Yb-doped fiber amplifier (Fig. 1). As a result, we obtained an average output power of 48 W with a typical clean Q-switched pulse waveform at a repetition rate of 2 kHz. The corresponding pulse duration time was 150 ns (FWHM). This is, to our knowledge, the highest pulse energy obtained with a solid-state-laser oscillator and a fiber-based amplifier scheme.