RESUMO
An all-fiber amplification of highly chirped dissipative solitons (DSs) by stimulated Raman scattering in a standard passive fiber with continuous-wave pumping is demonstrated for the first time to our knowledge. DSs with a duration of 20 ps and a repetition rate of 15.6 MHz at a wavelength of 1275 nm are amplified by a pump wave at 1205 nm. On-off Raman gain dependence on the amplifier length and pump power, as well as the pumping configuration, are experimentally studied. Uniform amplification has been achieved with a net gain of 10 dB resulting in a pulse energy of 13 nJ at backward pumping. Further Raman amplification is limited by emerging the next Stokes component. The output pulses are compressed by a factor of 50 down to a duration of 400 fs. As a result, the peak power reached the level of 9 kW. The demonstrated scheme can be a simple and robust alternative to the widely used parametric amplification of chirped pulses outside the dopant amplification band, and the resulting pulses can be used in multiphoton microscopy and other applications.
RESUMO
Raman lasing in a graded-index fiber (GIF) attracts now great deal of attention due to the opportunity to convert high-power multimode laser diode radiation into the Stokes wave with beam quality improvement based on the Raman clean-up effect. Here we report on the cascaded Raman generation of the 2nd Stokes order in the 1.1-km long GIF with 100-µm core directly pumped by 915-nm diodes. In the studied all-fiber scheme, the 1st Stokes order is generated at 950-954 nm in a linear cavity formed at GIF ends by two fiber Bragg gratings (FBGs) securing beam quality improvement from M2 ≈ 30 to M2 ≈ 2.3 due to special transverse structure of FBGs. The 2nd Stokes wave is generated either in linear (two FBGs) or half-open (one FBG) cavity with random distributed feedback via Rayleigh backscattering. Their comparison shows that the random lasing provides better beam quality and higher slope efficiency. Nearly diffraction limited beam (M2 ≈ 1.6) with power up to 27 W at maximum gain (996 nm), and 17 W at the detuned wavelength of 978 nm has been obtained, thus demonstrating that the 2nd-order random lasing in diode-pumped GIF with FBGs provides high-efficiency high-quality beam generation in a broad wavelength range within the Raman gain spectral profile.
RESUMO
An external-cavity generation of powerful ultrashort pulses in an all-fiber scheme by using a new type of phosphosilicate polarization maintaining fiber is investigated. The phosphorus-related Stokes shifted Raman pulse near 1.3 microns is observed. Optimization of Stokes output spectrum depending on pump pulse duration (chirp), energy and output coupling ratio of the cavity is performed. As result, the output energy of highly-chirped pulses compressible to 570 fs reaches 1.6 nJ.
