Ultra-broadband Generation Research Articles

Odd harmonics-enhanced supercontinuum in bulk solid-state dielectric medium.

We report on generation of ultrabroadband, more than 4 octave spanning supercontinuum in thin CaF2 crystal, as pumped by intense mid-infrared laser pulses with central wavelength of 2.4 μm. The supercontinuum spectrum covers wavelength range from the ultraviolet to the mid-infrared and its short wavelength side is strongly enhanced by cascaded generation of third, fifth and seventh harmonics. Our results capture the transition from Kerr-dominated to plasma-dominated filamentation regime and uncover that in the latter the spectral superbroadening originates from dramatic plasma-induced compression of the driving pulse, which in turn induces broadening of the harmonics spectra due to cross-phase modulation effects. The experimental measurements are backed up by the numerical simulations based on a nonparaxial unidirectional propagation equation for the electric field of the pulse, which accounts for the cubic nonlinearity-induced effects, and which reproduce the experimental data in great detail.

Deep-ultraviolet to mid-infrared supercontinuum generated in solid-core ZBLAN photonic crystal fibre

Silica-based photonic crystal fibre has proven highly successful for supercontinuum generation, with smooth and flat spectral power densities. However, fused silica glass suffers from strong material absorption in the mid-infrared (>2,500 nm), as well as ultraviolet-related optical damage (solarization), which limits performance and lifetime in the ultraviolet (<380 nm). Supercontinuum generation in silica photonic crystal fibre is therefore only possible between these limits. A number of alternative glasses have been used to extend the mid-infrared performance, including chalcogenides, fluorides and heavy-metal oxides, but none has extended the ultraviolet performance. Here, we describe the successful fabrication (using the stack-and-draw technique) of a ZBLAN photonic crystal fibre with a high air-filling fraction, a small solid core, nanoscale features and near-perfect structure. We also report its use in the generation of ultrabroadband, long-term stable, supercontinua spanning more than three octaves in the spectral range 200–2,500 nm. A low-loss ZBLAN micro-structured fibre is used to generate a supercontinuum spanning from the UV to the mid-IR (200 nm–2,500 nm). The material has high resistance even after extended operation and can withstand large spectral power densities.

Spatial modulation of the pump in the ultrabroadband dye laser with a “spatially-dispersive” resonator

The ultrabroadband nanosecond dye laser with a prism-based “spatially-dispersive” resonator, and a transverse pump being spatially modulated by Fresnel biprism, has been investigated. The influence of the lateral shift between the frequency components, the pumped zone dimension and the divergence on the laser bandwidth has been analyzed and experimentally demonstrated. The possibility to manipulate the shape of the laser spectrum by spatial modulation of the pump has been estimated. The biprism delivers a specific pump intensity distribution of the active medium, thus it compensates the lower emission cross-section in the wings of the dye gain profile and expands the laser bandwidth. Ultrabroadband generation (FWHM = 45 nm) is obtained.