Infrared laser-absorption sensing for combustion gases

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

We present the first detailed demonstrations of octave-spanning SC generation in all-normal dispersion photonic crystal fibers (ANDi PCF) in the visible and near-infrared spectral regions. The resulting spectral profiles are extremely flat without significant fine structure and with excellent stability and coherence properties. The key benefit of SC generation in ANDi PCF is the conservation of a single ultrashort pulse in the time domain with smooth and recompressible phase distribution. For the first time we confirm the exceptional temporal properties of the generated SC pulses experimentally and demonstrate their applicability in ultrafast transient absorption spectroscopy. The experimental results are in excellent agreement with numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking. To our knowledge, we present the broadest spectra generated in the normal dispersion regime of an optical fiber.

Coherent octave spanning near-infrared and visible supercontinuum generation in all-normal dispersion photonic crystal fibers.

We demonstrate supercontinuum generation in a photonic crystal fiber with all-normal group velocity dispersion. Pumping a short section of this fiber with compressed pulses from a compact amplified fiber laser generates a 200 nm bandwidth continuum with typical self-phase-modulation characteristics. We demonstrate that the supercontinuum is compressible to a duration of 26 fs. It therefore has a high degree of coherence between all the frequency components, and is a single pulse in the time domain. A smooth, flat spectrum spanning 800 nm is achieved using a longer piece of fiber.

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Coherent supercontinuum generation in photonic crystal fiber with all-normal group velocity dispersion.

Tomographic absorption spectroscopy for the study of gas dynamics and reactive flows

We report the first double-nested antiresonant hollow core fiber. The fiber matches the loss of commercial solid core fibers in the C-band (0.174 dB/km) and fundamentally improves it (0.22 dB/km) in the O-band.

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0.174 dB/km Hollow Core Double Nested Antiresonant Nodeless Fiber (DNANF)

We report the use of a dispersed supercontinuum generated in an all-normal-dispersion fibre to record low-noise spectra from atmospheric molecules at least an order of magnitude faster than has been previously reported. Supercontinuum generation in standard, anomalous dispersion photonic-crystal fibres is inherently connected with large pulse-to-pulse fluctuations resulting in detrimental consequences for high resolution spectroscopy if temporal averaging is not permitted. Replacing the standard photonic-crystal fibre (PCF) with a specially designed all-normal dispersion PCF we find that a substantially superior noise performance is achieved and present its use for high repetition rate absorption spectroscopy where spectra covering hundreds of nm in spectral bandwidth can be captured of gases at hundreds of kHz repetition rates.

/pdf/ultra-high-repetition-rate-absorption-spectroscopy-with-low-3gr1rhit61.pdf

Ultra-high repetition rate absorption spectroscopy with low noise supercontinuum radiation generated in an all-normal dispersion fibre

We report the coherent spectral broadening of the output of a mode-locked VECSEL emitting 455 fs pulses at 1007 nm in the normal-dispersion regime. Subsequent compression of the fiber outputs using a transmission grating compressor produced 1.56 GHz trains of 150 fs pulses at 270 mW average power or 220 fs pulses at 520 mW average power. The system approaches the performance needed for a pump for coherent supercontinuum generation.

/pdf/gigahertz-pulse-source-by-compression-of-mode-locked-vecsel-tn1c1y372n.pdf

Gigahertz pulse source by compression of mode-locked VECSEL pulses coherently broadened in the normal dispersion regime.

We describe supercontinuum generation in a short photonic crystal fiber with all-normal group velocity dispersion. We observe a 200 nm broad self phase modulation spectrum, which is expected to have high temporal coherence.

/pdf/all-normal-dispersion-photonic-crystal-fiber-for-coherent-2e2c8b0akf.pdf

L. E. Hooper

Papers

Coherent supercontinuum generation in photonic crystal fiber with all-normal group velocity dispersion.

0.174 dB/km Hollow Core Double Nested Antiresonant Nodeless Fiber (DNANF)

Ultra-high repetition rate absorption spectroscopy with low noise supercontinuum radiation generated in an all-normal dispersion fibre

Gigahertz pulse source by compression of mode-locked VECSEL pulses coherently broadened in the normal dispersion regime.

All-normal dispersion photonic crystal fiber for coherent supercontinuum generation