High power, high repetition rate, 700 – 850 nm pulsed laser

High power, linearly polarized, picosecond pulsed lasers with wavelength tuning from 700 to 850 nm and repetition rates in the range of 0.5 to 3 GHz are required as photoinjector sources in polarized electron beams used in advanced nuclear physics research. Commercially available mode-locked 775-nm lasers generate, via frequency doubling of mode-locked Erbium fiber lasers, low average powers in the range of 100 mW, a repetition rate of 10’s MHz, and no wavelength tuning. In this SBIR program, an innovative method is proposed to demonstrate a robust, high power, linearly polarized, tunable pulsed laser that generates over 10-W average power, 20-ps pulses at a 0.5-GHz repetition rate wavelength tunable from 700 to 850 nm. First, a 20-ps linearly polarized 1064-nm seed laser with a repetition rate of 0.5 GHz will be built by gain switching a 1064-nm diode laser. Second, a novel all-fiber-based, linearly polarized, Yb-doped fiber amplifier system will be built to boost the seed laser to over 100-W of average power with a repetition rate of 0.5 GHz. Third, nonlinear frequency doubling based on LBO crystal will be used to yield a 50-W, picosecond, green laser at 532 nm. Lastly, a synchronously-pumped optical parametric oscillator (SPOPO) utilizing an LBO crystal will be used to generate a greater than 10-W average power, 0.5-GHz repetition rate, pulsed laser with tunability from700 to 850 nm. In Phase I, a 20-ps linearly polarized 1064-nm seed laser with a repetition rate of 0.5-GHz, will be developed. A novel all-fiber based linearly polarized fiber pre-amplifier and mid-amplifier will be built to boost the 1064-nm seed laser to over 1-W average power with excellent long term stability. Frequency doubling and SPOPO will be designed and modeled. The innovation incorporated into this program is the use of a gain switching diode technique plus a novel all fiber based fiber amplifier system to achieve a reliable and robust high power picosecond laser with a tunable wavelength from 700 – 850 nm and optimized repetition rate from 0.5 to 3 GHz which is impossible to achieve via mode-locking technology. In addition, the pulsewidth of the proposed laser can be scaled up to 50-ps and the repetition rate can be adjusted down to 20 MHz if required. The laser proposed in this program will play a critical role in the improvement of DoE accelerator applications and will leverage into advanced micro-machining applications for commercial manufacturing. Commercial Applications and other Benefits: The laser development proposed will meet DOE’s need for a polarized beam source used in photoinjector applications for their accelerators. The laser proposed here has the potential to be widely used in precise material processing and micromachining. It will also provide opportunities in scientific research and instrumentation such as a replacement for Ti: Sapphire lasers currently used in many research institutes.