K. F. Mak

Compressing µJ-level pulses from 250 fs to sub-10 fs at 38-MHz repetition rate using two gas-filled hollow-core photonic crystal fiber stages

Compression of 250-fs, 1-μJ pulses from a KLM Yb:YAG thin-disk oscillator down to 9.1xa0fs is demonstrated. A kagomé-PCF with a 36-μm core-diameter is used with a pressure gradient from 0 to 40xa0bar of krypton. Compression to 22xa0fs is achieved by 1200u2009u2009fs2 group-delay-dispersion provided by chirped mirrors. By coupling the output into a second kagomé-PCF with a pressure gradient from 0 to 25xa0bar of argon, octave spanning spectral broadening via the soliton-effect is observed at 18-W average output power. Self-compression to 9.1xa0fs is measured, with compressibility to 5xa0fs predicted. Also observed is strong emission in the visible via dispersive wave generation, amounting to 4% of the total output power.

Two techniques for temporal pulse compression in gas-filled hollow-core kagomé photonic crystal fiber

We demonstrate temporal pulse compression in gas-filled kagomé hollow-core photonic crystal fiber (PCF) using two different approaches: fiber-mirror compression based on self-phase modulation under normal dispersion, and soliton effect self-compression under anomalous dispersion with a decreasing pressure gradient. In the first, efficient compression to near-transform-limited pulses from 103 to 10.6xa0fs was achieved at output energies of 10.3xa0μJ. In the second, compression from 24 to 6.8xa0fs was achieved at output energies of 6.6xa0μJ, also with near-transform-limited pulse shapes. The results illustrate the potential of kagomé-PCF for postprocessing the output of fiber lasers. We also show that, using a negative pressure gradient, ultrashort pulses can be delivered directly into vacuum.

Supercontinuum generation in the vacuum ultraviolet through dispersive-wave and soliton-plasma interaction in a noble-gas-filled hollow-core photonic crystal fiber

We report on the generation of a three-octave-wide supercontinuum extending from the vacuum ultraviolet (VUV) to the near-infrared, spanning at least 113 to 1000 nm (i.e., 11 to 1.2 eV), in He-filled hollow-core kagome-style photonic crystal fiber. Numerical simulations confirm that the main mechanism is a novel and previously undiscovered interaction between dispersive-wave emission and plasma-induced blueshifted soliton recompression around the fiber zero dispersion frequency. The VUV part of the supercontinuum, which modeling shows to be coherent and possess a simple phase structure, has sufficient bandwidth to support single-cycle pulses of 500 attosecond duration. We also demonstrate, in the same system, the generation of narrower-band VUV pulses, through dispersive-wave emission, tunable from 120 to 200 nm with efficiencies exceeding 1% and VUV pulse energies in excess of 50 nJ.

Low loss hollow optical-waveguide connection from atmospheric pressure to ultra-high vacuum

A technique for optically accessing ultra-high vacuum environments, via a photonic-crystal fiber with a long small hollow core, is described. The small core and the long bore enable a pressure ratio of over 108 to be maintained between two environments, while permitting efficient and unimpeded delivery of light, including ultrashort optical pulses. This delivery can be either passive or can encompass nonlinear optical processes such as optical pulse compression, deep UV generation, supercontinuum generation, or other useful phenomena.

Interaction between Kerr and ionization induced nonlinear fiber optics

Light-plasma interactions are explored in gas-filled photonic crystal fibers through self-compression of few-μJ pulses. Here we study the interaction between ionization-driven soliton dynamics and Kerr-based deep-UV generation.

Extremely broadband single-shot cross-correlation frequency-resolved optical gating using a transient grating as gate and dispersive element.

A cross-correlation frequency-resolved optical gating (FROG) concept, potentially suitable for characterizing few or sub-cycle pulses in a single shot, is described in which a counter-propagating transient grating is used as both the gate and the dispersive element in a FROG spectrometer. An all-reflective setup, which can operate over the whole transmission range of the nonlinear medium, within the sensitivity range of the matrix sensor, is also proposed, and proof-of-principle experiments for the ultraviolet and visible-to-near-infrared spectral ranges are reported.

Pushing the blue side of supercontinuum using photonic crystal fiber

By utilizing the versatile dispersion properties and enhanced nonlinearity of all-silica solid-core photonic crystal fiber, supercontinnum sources extending from below 400 nm up to the near-infrared have been generated (P. St.J. Russell, J. Lightwave Tech. 24, 2006, pp. 4729–4749). The spectral range is usually limited by the transmission properties of the material and alternative ways to extend the achievable wavelengths must be found. One possibility is to use exotic glass such as heavy-metal oxide, chalcogenide or fluoride-based glass. Unfortunately, the viscosity of these glasses rapidly changes with temperature and the suitable range of drawing temperature is considerably reduced compare to silica. Microstructured fibers made of such glasses are therefore extremely challenging to produce. On the other hand, they are ideal candidates for ultra-broad supercontinuum because of their very large transmission window (from ∼200nm to above 7 µm for ZBLAN). We recently successfully drew ZBLAN PCF. We will present here recent results on the generation of ultrabroad supercontinuum is such fibers.

High-field nonlinear fiber optics

Soliton compression of few-µJ fs-pulses leads to ionization in gas-filled photonic crystal fiber, and the emission of blue-shifting solitons. By pressure-tuning the dispersion we observe the transition between plasma and Kerr influenced propagation.