Nonlinear ultrafast fiber amplifiers

A pulsed laser apparatus comprising:

• an input coupler configured to receive pumping light from one or more pumping light sources and a seed pulse from a seed pulse generator;
• and
• a doped optical fiber that exhibits normal dispersion, has an input port coupled to the input coupler at a first end to receive the pumping light and the seed pulse and to amplify the seed pulse to form an amplified pulse propagating in the doped optical fiber that exits a second end of the doped optical fiber as an output pulse,
• wherein:
• along a first length of the doped optical fiber, a pulse spectrum of the amplified pulse broadens due to a fiber nonlinearity in the doped optical fiber, and
• in an extended portion of the doped optical fiber beyond the first length, the pulse output from the first length is shifted in wavelength towards longer wavelengths and broadened in both spectral and temporal domains to form the output pulse output by the second end of the doped optical fiber.