Abstract
In this paper, we experimentally investigated the extreme frequency shift in high-power Raman fiber laser (RFL). The RFL was developed by using a pair of fiber Bragg gratings with fixed and matched central wavelength (1120 nm) combined with a piece of 31-m-long polarization maintaining (PM) passive fiber adopted as Raman gain medium. The pump source was a homemade high-power, linearly polarized (LP) wavelength-tunable master oscillator power amplifier (MOPA) source with ${\sim}25~\text{nm}$ tunable working range (1055–1080 nm). High-power and high-efficiency RFL with extreme frequency shift between the pump and Stokes light was explored. It is found that frequency shift located within 10.6 THz and 15.2 THz can ensure efficient Raman lasing, where the conversion efficiency is more than 95% of the maximal value, 71.3%. In addition, a maximum output power of 147.1 W was obtained with an optical efficiency of 71.3%, which is the highest power ever reported in LP RFLs to the best of our knowledge.
Highlights
Raman fiber laser (RFL) can theoretically achieve emission at almost arbitrary wavelength with the help of proper pump wavelength[1]; the emission range of RFL is much broader than lasers based on rare earth-doped fibers
The results indicate that the Stokes frequency downshifted from the pump frequency by 10.6 to 15.2 THz can operate with high power and high efficiency
We report an experimental investigation on the extreme frequency shift between the pump wavelength and Raman wavelength in a high-power linearly polarized (LP) RFL
Summary
Raman fiber laser (RFL) can theoretically achieve emission at almost arbitrary wavelength with the help of proper pump wavelength[1]; the emission range of RFL is much broader than lasers based on rare earth-doped fibers. It is well known that the Raman gain in silica fibers extends over a large frequency range up to 40 THz[23]. The frequency shift between pump wavelength and Raman wavelength is approximately 13.2 or 14.7 THz corresponding to the double-peak structure of Raman gain spectrum for silica fiber[23, 24]. The frequency shift between the pump light and target Raman light is usually designed to be well matched to fulfill the peaks of Raman gain spectrum.
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