Fig. 1. Experimental setup of 2.15 μm all-fiber gas Raman laser. (a) Configuration of system; (b) spectrum of seed laser; (c) transmittance spectrum of long-period fiber grating

Fig. 2. Experimental results. (a) Measured transmission loss spectrum of hollow core fiber; (b) microscopic view of cross-section of hollow-core fiber; (c) enlarged view of Splice 2

Fig. 3. Spectrum results. (a) Spectrum varying with pump power; (b) fine spectrum of pump laser; (c) fine spectrum of Raman laser with central wavelength of 2043.6 nm; (d) fine spectrum of Raman laser with central wavelength of 2147.1 nm

Fig. 4. Raman laser power, residual pump laser power and optical-to-optical conversion efficiency varying with coupled pump power. (a) Raman laser power; (b) residual pump laser power; (c) optical-to-optical conversion efficiency

Fig. 5. Power varying with coupled pump power under different pulse widths. (a) Raman laser; (b) residual pump laser

Fig. 6. Pulse train and pulse profile. (a)-(c) Pulse train; (d)-(f) pulse profile