All-fiber widely tunable ultrafast laser source for multimodal imaging in nonlinear microscopy.

In this Letter, we present an all-fiber, easy-to-use, wavelength-tunable, ultrafast laser, based on soliton self-frequency shifting in an Er-doped polarization-maintaining very large mode area fiber. The system is tunable over 370 nm, starting at 1620 nm, with an average power of up to 1.5 W that emits 120 fs short laser pulses directly out of the fusion-spliced fiber without using bulky pulse compression optics. The output is subsequently frequency doubled to a wavelength range covering 810 nm up to almost 1000 nm with more than 500 mW average power and 120 fs pulse width. Having a polarization extinction ratio better than 40 dB and a M2 of 1.1, the fully computer-controlled laser system presents a robust and compact laser source. These parameters make the laser perfectly suited for multimodal imaging in nonlinear microscopy.