Christopher J. Hensley

Soliton pulse compression in photonic band-gap fibers.

We report on pulse compression using a hollow-core photonic band-gap fiber filled with Xe. Output pulses with megawatt peak powers and durations of 50 fs have been generated from 120-fs input pulses. The large third-order dispersion inherent in these fibers degrades the optimal compression ratio and prevents generation of even shorter pulses. Nevertheless, for picosecond input pulses, compression to less than 100 fs is predicted.

Photonic band-gap fiber gas cell fabricated using femtosecond micromachining

Femtosecond laser drilling is used to produce a variablepressure fiber gas cell. Tightly focused laser pulses are used to produce micrometer-diameter radial channels in a hollow-core photonic band-gap fiber (HC-PBGF), and through these microchannels the core of the fiber is filled with a gas. The fiber cell is formed by fusion splicing and sealing the ends of the HC-PBGF to standard step-index fiber. As a demonstration, acetylene is introduced into an evacuated fiber at multiple backing pressures and spectra are measured.

Silica-glass contribution to the effective nonlinearity of hollow-core photonic band-gap fibers

We measure the effective nonlinearity of various hollow-core photonic band-gap fibers. Our findings indicate that differences of tens of nanometers in the fiber structure result in significant changes to the power propagating in the silica glass and thus in the effective nonlinearity of the fiber. These results show that it is possible to engineer the nonlinear response of these fibers via small changes to the glass structure.

Highly-efficient coupling of linearly- and radially-polarized femtosecond pulses in hollow-core photonic band-gap fibers

We demonstrate extremely efficient excitation of linearly-, radially-, and azimuthally-polarized modes in a hollow-core photonic band-gap fiber with femtosecond laser pulses. We achieve coupling efficiencies as high as 98% with linearly polarized input Gaussian beams and with high-power pulses we obtain peak intensities greater than 10(14) W/cm(2) inside and transmitted through the fiber. With radially polarized pulses, we achieve 91% total transmission through the fiber while maintaining the polarization state. Alternatively with azimuthally-polarized pulses, the mode is degraded in the fiber, and the pure polarization state is not maintained.

Extremely high coupling and transmission of high-powered-femtosecond pulses in hollow-core photonic

Amplified femtosecond laser pulses are coupled through a hollow-core photonic band-gap fiber with efficiencies greater than 98%. Peak power intensities greater than 1014 W/cm2 are achieved inside the fiber core.

Midinfrared frequency comb by difference frequency of erbium and thulium fiber lasers in orientation-patterned gallium phosphide

We generate over 60 mW of pulses with wavelengths from 6 to 11 micrometers by difference frequency mixing between erbium and thulium fiber amplifiers in orientation-patterned GaP with a photon conversion efficiency of 0.2. By stabilizing the repetition rate of the shared oscillator and adding a frequency shifter to one arm, the output becomes a frequency comb with tunable carrier envelope offset.

Efficient excitation of polarization vortices in a photonic bandgap fiber with ultrashort laser pulses

We experimentally investigate the excitation of radially and azimuthally polarized modes in a hollow-core photonic bandgap fiber. With radially-polarized ultrashort pulses, we achieve 91% total transmission through the fiber, including coupling losses.

Novel nonlinear processes in hollow-core photonic bandgap fibers

We present the results of several experiments in which nonlinear-optical processes are enhanced by introducing gases into the hollow core of a photonic bandgap fiber. Such fibers offer the potential of greatly enhancing nonlinear interactions

Offset-tunable, fiber-pumped frequency comb at 7–10 μm by difference frequency in orientation-patterned GaP

Midinfrared frequency combs are a promising tool for new applications in chemical imaging and sensing, as they can directly access molecular vibrations in the molecular fingerprint wavelength region [1]. Practical laser sources are moving steadily from few micrometer wavelengths further into the fingerprint region to the 10 μm region. For practical applications of midinfrared light, difference frequency generation (DFG) with well-developed fiber laser technology provides a highly-integrated, compact, and robust frequency comb source. Difference frequency generation fits naturally with fiber lasers, given the midinfrared photon energy difference between Er and Tm amplifier wavelengths. The recent availability of orientation-patterned GaP (OP-GaP) has made this much more practical, with its large transparency window, good nonlinearity, and flexibility from quasi-phase matching [2]. We use the difference frequency from Er and Tm amplifiers to generate 25 mW of midinfrared centred at 8 μm wavelength, and show that the output is a frequency comb, with a stable repetition rate and tunable carrier-envelope offset (CEO) frequency.

Broadband midinfrared from fiber laser difference frequency generation in OP-GaP

We generate 52 mW of broadband pulses at 8 μm wavelength by difference frequency generation (DFG) in orientation patterned GaP (OP-GaP). Pumping by fiber lasers is possible because of the wide transparency range of GaP. An Er fiber oscillator at 1.5 μm wavelength and 90 MHz repetition rate provides pulses for direct amplification and shifting to 1.9 μm followed by amplification in Tm doped fiber. The two beams are mixed in OP-GaP with up to 20% photon conversion efficiency. The wavelength is tunable from 5 to 11 μm by changing the crystal period or the degree of wavelength shifting. With coherent broadening, we can also generate midinfrared frequency combs with tunable carrier envelope offset frequencies.