Analysis of Research Progress of High Power Fiber Raman Laser

Compared with traditional solid-state lasers and chemical lasers, fiber lasers have the advantages of good beam quality, small size, high conversion efficiency, and convenient thermal management. At present, the output laser power of high-power rare-earth ion-doped fibers has increased by leaps and bounds. In June 2009, IPG used a 1018nm laser to pump a single ytterbium-doped fiber and obtained a single-mode laser output of about 10kW. In 2010, IPG applied for a patent for a 20kW-class fiber laser system with different wavelengths. Due to the influence of the absorption and emission spectrum of rare earth ions, the wavelength of the laser output by the stimulated amplification method in the fiber is limited. It is difficult to obtain lasers in some special-purpose bands such as the wavelength of 1018nm using this doped ion stimulated amplification method. . However, the fiber Raman amplification method is another important way to obtain fiber laser. Compared with the stimulated amplification method of doped ions, it has a wider gain bandwidth and lower amplification noise characteristics, and can obtain various special wavelengths. The laser has been extensively studied.　　The fiber Raman amplification method is based on the stimulated Raman scattering (SRS) effect generated by the laser in the fiber, which transfers the energy of the pump light to the Stokes light. The Raman gain spectrum in the fiber is often wider, so its biggest advantage is the variability of the output laser wavelength, which can obtain wavelengths that are difficult to obtain in rare-earth ion-doped fibers, such as 1018, 1480 nm lasers and so on. In fact, the use of this technology can obtain transparent lasers of any wavelength in the fiber, and it is also suitable for many other astronomical, medical and industrial applications that have special requirements for laser wavelengths.　　The Raman frequency shift produced by different fiber matrices is different. According to the different matrix materials, Raman fibers can be roughly divided into two types: germanium silicon fiber and phosphorous silicon fiber. Compared with germanium silicon fiber (Raman frequency shift is about 440cm-1), the main advantage of phosphorous silicon fiber is that it has a larger Raman frequency shift (about 1330cm-1). Only a few cascades are needed to obtain the laser output of the required wavelength, but there are disadvantages of relatively high optical loss and low Raman gain. Regarding the cascaded fiber Raman laser, Zhou Xiaojun and others introduced its development in detail. Nicholson et al. used the cascaded silicon germanium fiber Raman laser to obtain a high power output of 1480 nm laser of 81W. In addition, the Raman amplification method is also an important way to obtain the output of high-power narrow-linewidth lasers. High-power narrow-linewidth lasers are widely used in photoelectric sensing, lidar, spectroscopy and other fields. At the same time, they are used in coherent synthesis and spectral synthesis. And research fields such as frequency conversion require narrow linewidth lasers with special wavelengths, high power, and high beam quality. Therefore, it is of great significance to study the narrow linewidth fiber Raman amplifier (NL-FRA).