1700 nm and 1800 nm band tunable thulium doped mode-locked fiber lasers.

This paper presents short wavelength operation of tunable thulium-doped mode-locked lasers with sweep ranges of 1702 to 1764 nm and 1788 to 1831 nm. This operation is realized by a combination of the partial amplified spontaneous emission suppression method, the bidirectional pumping mechanism and the nonlinear polarization rotation (NPR) technique. Lasing at emission bands lower than the 1800 nm wavelength in thulium-doped fiber lasers is achieved using mode confinement loss in a specially designed photonic crystal fiber (PCF). The enlargement of the first outer ring air holes around the core region of the PCF attenuates emissions above the cut-off wavelength and dominates the active region. This amplified spontaneous emission (ASE) suppression using our presented PCF is applied to a mode-locked laser cavity and is demonstrated to be a simple and compact solution to widely tunable all-fiber lasers.

Modeling of femtosecond pulse propagation inside x-cut and z-cut MgO doped LiNbO3 anisotropic crystals.

A four-dimensional spatiotemporal nonlinear Schrödinger equation coupled with a plasma equation is solved for anisotropic crystal of MgO doped lithium niobate. The modeling is performed for x-cut and z-cut lithium niobate crystals commonly used for waveguide writing by femtosecond lasers. The effect of various parameters such as energy, duration, and polarization of the incident laser pulse on distribution of the plasma density in the vicinity of focus is studied. Our simulations reveal that the maximum plasma density in the vicinity of the focus is higher for longer pulse durations and higher pulse energies. Furthermore, it is observed that for the same peak powers of the incident pulse, the plasma density generated inside the crystal is higher for linear polarization as compared to circular polarization.

Spatially resolved laser-induced breakdown spectroscopy in methane-air diffusion flames.

A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame.