We demonstrate an alternative light source for CARS microspectroscopy based on a fiber laser and a photonic crystal fiber. The light source simultaneously delivers a picosecond pump pulse at 1033.5 nm and a frequency shifted femtosecond Stokes pulse, tunable from 1033.5 nm to 1400 nm. This corresponds to a range 0 - 2500
cm-1, so that Raman-active vibrations in this frequency range can be probed. The spectral resolution is 5 cm-1,
given by the spectral width of the pump pulse. The frequency range that can be probed simultaneously is 200
cm-1-wide, given by the spectral width of the Stokes pulse. The achievable average powers are 50 mW for the
pump and 2 mW for the Stokes pulse. The repetition rate is 35 MHz. We demonstrate the capability of this
light source by performing CARS microspectroscopy and comparing CARS spectra with Raman spectra.
The recent development of photonic bandgap fibers with solid cores enables the construction of dispersion
compensated all-fiber ultrashort mode-locked fiber lasers. Solid-core photonic bandgap fibers (SC-PBG) can
be spliced to standard fibers with relative low loss and negligible Fresnel reflection due to the matching indexes
of the cores. The fibers can provide significant anomalous dispersion with low nonlinearity and are therefore
ideal for dispersion compensation in ultrafast fiber lasers. We demonstrate the use of a SC-PBG fiber for intra
cavity dispersion compensation in an ytterbium based mode-locked fiber laser. The limitations on pulse duration
due to the relative high third order dispersion of the SC-PBG fiber are discussed.
We report on a high power, high-energy femtosecond fiber source based on direct amplification of parabolic pulses from an environmental stable passively mode-locked fiber oscillator in an Yb-doped single-polarization photonic crystal fiber. The system delivers a pulse energy of 1.2 μJ (21 W average power) at a repetition rate of 17 MHz and a pulse duration of 240 fs in a linearly polarized beam with diffraction-limited quality. The special pulse shape allows for the generation of high quality femtosecond pulses beyond nonlinearity limits, which is confirmed by numerical simulations.
We report on the observation of both single pulse and bound states of an environmentally stable all-polarization maintaining (PM) mode-locked laser based on a saturable absorber. The laser operates in the self-similar regime, and parabolic pulse spectra were obtained. The pulses could externally be compressed to 212 fs (single pulse) and 248 fs (bound states). Results of a numerical model are also presented. The model reveals important information about the criteria for obtaining pulses with parabolic temporal shape.
In this work a new model based on the work with new double-clad Yb-doped photonic crystal fibers is presented. The model describes the effect of a coupling between core modes and cladding modes, causing a loss of power out of the core. The model agrees well with an experimental observed asymmetry in the output powers from the two ends of a pumped fiber due to pump depletion and the core-cladding coupling. A method to estimate the core-cladding coupling is included. The magnitude of the coupling depends on the geometry of the fiber. If an asymmetry is introduced between the coupling for the two orthogonal linear polarization directions, an polarization creating mechanism is predicted. This feature is investigated for a fiber where the asymmetric loss has been implemented by manufacturing the fiber to have an asymmetric transverse geometry.