Few-cycle all-fiber supercontinuum laser for ultrabroadband multimodal nonlinear microscopy.

Temporally coherent supercontinuum sources constitute an attractive alternative to bulk crystal-based sources of few-cycle light pulses. We present a monolithic fiber-optic configuration for generating transform-limited temporally coherent supercontinuum pulses with central wavelength at 1.06 µm and duration as short as 13.0 fs (3.7 optical cycles). The supercontinuum is generated by the action of self-phase modulation and optical wave breaking when pumping an all-normal dispersion photonic crystal fiber with pulses of hundreds of fs duration produced by all-fiber chirped pulsed amplification. Avoidance of free-space propagation between stages confers unequalled robustness, efficiency and cost-effectiveness to this novel configuration. Collectively, the features of all-fiber few-cycle pulsed sources make them powerful tools for applications benefitting from the ultrabroadband spectra and ultrashort pulse durations. Here we exploit these features and the deep penetration of light in biological tissues at the spectral region of 1 µm, to demonstrate their successful performance in ultrabroadband multispectral and multimodal nonlinear microscopy.

Detection and elimination of pulse train instabilities in broadband fibre lasers using dispersion scan.

We use self-calibrating dispersion scan to experimentally detect and quantify the presence of pulse train instabilities in ultrashort laser pulse trains. We numerically test our approach against two different types of pulse instability, namely second-order phase fluctuations and random phase instability, where the introduction of an adequate metric enables univocally quantifying the amount of instability. The approach is experimentally demonstrated with a supercontinuum fibre laser, where we observe and identify pulse train instabilities due to nonlinear propagation effects under anomalous dispersion conditions in the photonic crystal fibre used for spectral broadening. By replacing the latter with an all-normal dispersion fibre, we effectively correct the pulse train instability and increase the bandwidth of the generated coherent spectrum. This is further confirmed by temporal compression and measurement of the output pulses down to 15 fs using dispersion scan.

Simulations of the gain profile and performance of a diode side-pumped QCW Nd:YAG laser.

A design of a diode side-pumped Nd:YAG laser module and simulations of the gain distribution inside the active medium are presented in this paper. The code is based on a nonsequential ray-tracing Monte Carlo method for the light generated by the laser diodes. The fluorescence image of the active medium was analyzed in order to compare it with the simulations, which were found to be in good agreement with experimental data. The laser was tested in QCW mode and provided a maximum average power of 220 W while maintaining constant energy per pulse in the 100-1000 Hz range.

Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings.

In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.