Toward a 10-W level femtosecond erbium laser operating in the 1600 nm low gain region

1.6 µm ultrafast lasers are important in biomedical applications because the wavelength is located within an attractive biological window called the near-infrared-II (NIR-II) region. However, for erbium- or thulium-doped fibers, 1.6 μm is not their typical gain wavelength; therefore, realizing a high power femtosecond (fs) 1.6 μm laser is a challenging task. In this work, we propose a pump scheme assisted by a C-band laser. The new pump scheme can improve the gain at 1.6 μm with a mechanism originating from the re-absorption effect of the ground state and the in-band relaxation between the splitting energy levels 4I13/2b and 4I13/2a. Applying the pump scheme to the all-fiber large-mode-area (LMA) chirped pulse amplification (CPA) system, we achieve a record-high output power of ∼9.42 W, corresponding to a 262 nJ single pulse energy. The pulse duration after compression is ∼361 fs. Our approach of combining a LMA CPA system with a C-band auxiliary laser co-pumping scheme opens a way to increase the output power of an erbium-doped fiber laser by one order of magnitude in the 1600 nm region, even though this is a low gain region.