3 kW Passive-Gain-Enabled Metalized Raman Fiber Amplifier With Brightness Enhancement

Abstract

Raman fiber lasers (RFLs) are currently promising and versatile light sources for a variety of applications. So far, operations of high power and brightness-enhanced RFLs have absorbed enormous interests along with rapid progress. Nevertheless, the stable Raman lasing at high power levels remains challenged by the thermal effects. In an effort to realize more effective thermal management in high power RFLs, here we demonstrate, for the first time, an all-fiberized RFA employing metal-coated passive fiber enabling high power lasing. By employing aluminum to the cladding of graded-index (GRIN) passive fiber, the thermal abstraction of the laser devices is more sufficient to support low-temperature operation. The maximum output power reaches 3.083 kW at 1130 nm with a conversion efficiency of 78.7%. To the best of our knowledge, this is the first Raman laser generation based on metal-coated passive fiber. Meanwhile, it is also the highest power attained in the fields of all kinds of Raman lasers based on merely nonlinear gain.

Power Scaling of CW Crystalline OPOs and Raman Lasers

“…For example, in ref. [102], the metalized fiber amplifier at 1130 nm exhibited a deterioration of M 2 from 3.12 to 5.72 when the output power increased from 2.36 kW to the maximum power of 3.08 kW. The maximum BEF of 27 has been achieved in a Raman GRIN fiber amplifier at 943 W at 1130 nm [175].…”

“…Meanwhile, the output powers of OPOs and non-diamond Raman lasers are yet to approach even hundreds of watts; restricted by thermal lensing in the gain materials. The only other technology competitive enough to pursue such power gains is the fiber-based Raman lasers [98,[101][102][103][104][166][167][168][169][170][171][172][173], as evident from the figure . For constant power deposited in the crystal, crystal length, and spot size, the thermal focal length is given by the expression,…”

“…The brightness achieved by a DRL is more than three orders of magnitude than realized by a non-diamond Raman laser. On the other hand, Raman fiber lasers have displayed BE similar to DRLs [102,103,169,[173][174][175][176][177]. However, in most of these cases, the thermal load in fibers with elevating output powers have prevented the beam quality to reach to near diffraction-limited output.…”

“…An optical fiber was used as the gain medium to achieve Raman lasing in 1976 [100]. Owing to the optical confinement provided by the small core area, optical fibers proved to be efficient frequency converters producing output powers as high as 3 kW and few hundreds of watts in 1 µm and 1.5 µm range, respectively [98,[101][102][103][104]. However, the narrow optical transparency of the fiber material, small Raman shift, and the absence of resonators required for frequency doubling/tripling limited their applications [99].…”

Cladding-pumped Raman fiber laser with 0.78% quantum defect enabled by phosphorus-doped fiber

“…Up to hundreds of watt-level high-power RFLs in allfiber formats have been demonstrated by several independent groups [28][29][30][31] . By adopting a main-oscillator-power-amplifier structure, up to 3 kW RFLs have been demonstrated [32,33] . Usually, the high-power fiber lasers aforementioned have QDs of about 4%-5% based on the 13.2 THz frequency shift.…”