A method of generating ultrashort pulses with wavelengths greater than 2 m comprising a short pulse diode laser or fiber laser operating at a wavelength of 1 m or greater with a pulse width of 10 ps or greater, one or more amplification stages to increase the peak power of the pulsed source, a nonlinear fiber stage whereby the dispersion of the nonlinear fiber is anomalous at the pulsed source wavelength such that the fiber breaks up the pulse into a series of sub-ps pulse train through modulation instability which may be seeded by spontaneous noise which are then wavelength shifted in one or more stages by soliton self frequency shift in anomalous dispersion fiber or Raman in normal dispersion fiber and amplified in one or more stages to generate a high peak power ultrashort pulse (<1 ps) source at a wavelength of 2.4 m or greater.

In an example, a tandem pumped fiber amplifier may include a seed laser, a first section coupled to an output of the seed laser, and a second section coupled to an output of the first section. The first section may operate as an oscillator, and may receive pump light from one or more diode pumps, and may the first section may be arranged to convert the one or more diode pumps into a tandem pump. The second section may operate as a power amplifier, and may include a length of a single or plural active core fiber. The tandem pumped fiber amplifier may be arranged to mitigate spectral broadening related to four-wave mixing.

An active waveguide including active and passive rods which have respective polymeric claddings mechanically and optically coupled to one another so as to define a side pumping scheme. One or a plurality of elements are embedded in one of or both active and passive rods and have a refractive index lower than the lowest of refractive indices of the respective active and passive rods at at least 1*10.sup.3. The MM core of the active rod includes inner and outer concentric regions with a concentration of light emitters in the outer region being lower than that of the inner region at more than 50% and, a radius of the inner region being at most 92% of that of the outer region. The unabsorbed pump light at the output of the active waveguide constitutes less than 1% of the delivered pump light which in combination with the refractive index of the the embedded elements and selectively doped core regions contribute to laser efficiency of at least 86%.