High-Power Continuous-Wave Directly-Diode-Pumped Fiber Raman Lasers

Abstract

We describe novel fiber Raman lasers pumped directly by spectrally combined high power multimode laser diodes at ∼975 nm and emitting at ∼1019 nm. With a commercial multimode graded-index fiber, we reached 20 W of laser output power with a record slope efficiency of 80%. With an in-house double-clad fiber, the beam quality improved to M 2 = 1.9, albeit with lower output power and slope efficiency due to higher fiber loss. We believe this is the first publication of a fiber Raman laser cladding-pumped directly by diodes.

Femtosecond Red and Near-Infrared Lasers Due to Cascaded-Raman-Assisted Four-Wave Mixing in a Nonlinear Yb-Doped Fiber Amplifier

“…This overcame the gain saturation, and resulted in compression of the pulse duration. Besides, in our experiment for the nonlinear LMA fiber, group velocity dispersion (GVD) in high-order modes could compensate for material group velocity mismatch, when fundamental and parametric waves were propagating with different modes [10,20]. Thus, efficient nonlinear parametric amplification was achieved.…”

High-brightness all-fiber Raman lasers directly pumped by multimode laser diodes

“…First direction continues the study initiated in Ref. [5] with a focus on the opportunities of high-quality beam generation using fiber Bragg gratings (FBGs) as cavity mirrors [7][8][9][10] , whereas second one aims at high-power capabilities based on freespace pump coupling and bulk mirrors cavity [4,11,12] . In the last case, up to 154 W power is obtained at ∼1020 nm [12] , but Raman output at this wavelength is not as interesting, because higher power and narrower linewidth are available from YDFLs [13,14] .…”

Simulations of multiwavelength cladding pumping of high-power fiber Raman amplifiers

“…For power scaling, pumping with multimode laser diodes has recently been demonstrated in multimode as well as doubleclad (DC) fibers. 1,2 This approach combines the well-established and well-controlled fabrication, the potentially high resilience to photodarkening, and the high damage threshold of "passive" high-silica fibers (e.g., germanosilicate fibers) with the simplicity of high-power, direct-diode laser pumping, the brightness enhancement enabled by DC fibers, and the advantages of SRS such as wavelength-agility, immunity to high-energy self-Q-switching, and nonlocal gain saturation. 3 However, SRS is a relatively weak process, so high diode brightness and pump intensity are required to reach sufficient Raman gain.…”

“…This can be analyzed in terms of a figure of merit (FoM), given by the induced peak Raman gain relative to the background loss, i.e., I P g R ðν peak Þ∕α, where I P is the pump intensity, g R (ν) is the Raman gain coefficient, ν peak is the frequency shift to the Raman gain peak, and α is the fiber background loss, which for simplicity is sometimes assumed to be the same for pump and signal. It was found that a value of the FoM of at least five 1 was needed for efficient conversion in an ideal cavity, whereas a higher value would be required in laser cavities and amplifiers with excess loss or high gain. Today's continuouswave (cw) diode lasers can provide 140 to 200 W of output power at 0.9 to 1 μm from a 105-μm core pigtail at an NA of 0.15.…”