Research Progress on Pulsed Raman Fiber Green Laser Pointer

Recently, the research group of Feng Yan from the Shanghai Institute of Optics and Electronics has made a series of progress in the research of pulsed Raman fiber lasers. The research group used an amplified spontaneous emission green laser pointer source as a pump to achieve ultra-stable mode-locked Raman fiber laser output; a pulsed laser pump was used to achieve ultra-fast random distributed feedback Raman fiber laser output; based on a pulse pump The Pu narrow linewidth Raman fiber amplifier has successfully developed a 589nm pulsed yellow light laser with a repetition frequency of Lamor to improve the brightness of the sodium guide star.

The first advantage of Raman fiber lasers that uses stimulated Raman scattering in fibers as a gain mechanism is wavelength flexibility. In recent years, research on Raman fiber lasers has developed rapidly, the wavelength range has gradually expanded, and the output power can reach several kilowatts. If a high-performance pulsed Raman fiber green laser pointer can be obtained, its application range can be further expanded.

The efficiency and stability of CW-pumped mode-locked Raman fiber lasers are much lower than the corresponding rare-earth-doped fiber lasers. As a non-linear gain laser, the pump laser’s time-domain fluctuations caused by the vertical mode beat frequency, etc., will be directly transmitted to the laser, thereby destroying the stability of the Raman fiber laser. The research team proposed to use a more stable amplified spontaneous radiation source in the time domain as the pump to achieve a stable Raman dissipative soliton output with a pulse width of 1 ps in the 1.1 mm band, and the signal-to-noise ratio of the radio spectrum reached 85 dB. The research results were published in [Opt. Lett. 42,5162 (2017)].

Pulse pumping is an effective means to generate ultra-short-pulse Raman fiber lasers, but pulse pumping requires real-time feedback control to synchronize the pump pulse with the laser pulse in the cavity, otherwise additional noise will be introduced into the Raman pulse output. Based on this, the research group proposed a self-synchronous pumping mechanism. This mechanism uses distributed Rayleigh scattering feedback in the fiber to achieve self-matching of laser cavity length and pump pulse interval, and achieves picosecond random distributed feedback Raman fiber green laser pointers output. Using this pulse-pumped fiber laser structure, the random distributed feedback is directly characterized, and a detailed comparison between random laser and amplified spontaneous radiation is performed for the first time. The research results were published in [Laser Photon. Rev. 12, 1700326 (2018)]

Raman fiber laser technology can be used to generate the 589nm sodium guide green laser pointers required in astronomical adaptive optical systems. In order to overcome the influence of the geomagnetic field on the brightness of the sodium guide star, a repetition frequency of about 250-500 kHz (the Larmor repetition frequency depends on the strength of the local geomagnetic field) and a pulse with a narrow line width of 589 nm with a duty cycle of about 20%. The research group used a narrow line-width Raman fiber amplifier pumped by a pulsed 1120nm laser to obtain the 1178nm laser with the required pulse system. After external cavity resonance frequency doubling, it obtained a 17W Lamor heavy frequency 589nm sodium guided laser, and Successfully developed a prototype. The research results were published in [Opt. Lett. 42, 4351-4354 (2017)]. Due to the potential application of the laser in remote magnetic field detection, “Laser Focus World” reported on “Sodium guide star at Larmor frequency extends geomagnetic studies” (January 2018).