22 research outputs found
On-target delivery of intense ultrafast laser pulses through hollow-core anti-resonant fibers
No full textWe report the flexible on-target delivery of 800 nm wavelength, 5 GW peak power, 40 fs duration laser pulses through an evacuated and tightly coiled 10 m long hollow-core nested anti-resonant fiber by positively chirping the input pulses to compensate for the anomalous dispersion of the fiber. Near-transform-limited output pulses with high beam quality and a guided peak intensity of 3 PW/cm² were achieved by suppressing plasma effects in the residual gas by pre-pumping the fiber with laser pulses after evacuation. This appears to cause a long-term removal of molecules from the fiber core. Identifying the fluence at the fiber core-wall interface as the damage origin, we scaled the coupled energy to 2.1 mJ using a short piece of larger-core fiber to obtain 20 GW at the fiber output. This scheme can pave the way towards the integration of anti-resonant fibers in mJ-level nonlinear optical experiments and laser-source development
Generation of deep ultra-violet pulses in hollow capillary fibres
Get PDFFemtosecond pulses in the deep ultraviolet region (DUV, 200-400 nm) are in high
demand for time-resolved studies in several fields of research such as quantum chemistry (UV photoelectron spectroscopy), material sciences (lithography in semiconductors, polymers) and biology (protein analysis, DNA sequencing, cell imaging). When
combined with external polarization control, they can provide excellent tools for chiral
molecule analysis and ultrafast magnetism studies.
A well-established route for the generation of linearly polarized pulses in the DUV has
been via frequency up-conversion in bulk materials such as nonlinear crystals or gases.
However, the former suffer from limited transmission range, narrow phase-matching bandwidths and low intensity damage thresholds while the latter require high-peak power and
provide low frequency up-conversion efficiencies. For circularly polarized pulses in the
DUV, an additional stage for polarization conversion is required, commonly implemented
by using phase retarders in the ultraviolet. This induces unwanted dispersion that compromises ultra-short duration and achromatic phase retardation.
This thesis focuses on the experimental generation of high-energy, ultrashort DUV
pulses with controlled polarization using two alternative frequency up-conversion techniques in hollow capillary fibres; four-wave mixing and resonant dispersive wave emission. Using the first technique, record-breaking energy conversion efficiency up to 50%
and large spectral bandwidths in the DUV with high pulse energy are demonstrated with
linear polarization. This scheme is then extended to achieve direct generation of DUV
pulses with circular polarization without the need for dispersive optics in the UV. Using
resonant dispersive wave emission, high energy, circularly polarized pulses tunable across
the DUV are generated when driven by circularly polarized 800 nm pulses.
These studies allow to experimentally verify the polarization-induced dynamics with
respect to fundamental science such as the angular momentum conservation and the energy scaling of nonlinearity. Although this work is focused on DUV generation, the same
techniques can be applied to other spectral regions such as the vacuum-ultraviolet (VUV,
100-200 nm) and the mid-infrared (mid-IR, 3-8 µm) by proper selection of the driving
frequencies, and can be scaled up in output energy using larger fibre systems
Broadband Ultraviolet Generation with 50% Conversion Efficiency in Hollow Capillary Fibers
Get PDFWe demonstrate broadband wavelength up-conversion (240–320 nm) based on a seeded four-wave mixing scheme in gas-filled stretched hollow-capillary fibers with 50% conversion efficiency. Our technique is scalable in energy from the nJ to mJ level
Generation of broadband circularly polarized deep-ultraviolet pulses in hollow capillary fibers
No full textWe demonstrate an efficient scheme for the generation of broadband, high-energy, circularly polarized femtosecond laser pulses in the deep ultraviolet through seeded degenerate four-wave mixing in stretched gas-filled hollow capillary fibers. Pumping and seeding with circularly polarized 35 fs pulses centered at 400 nm and 800 nm, respectively, we generate idler pulses centered at 266 nm with 27 µJ of energy and over 95% spectrally averaged ellipticity. Even higher idler energies and broad spectra (27 nm bandwidth) can be obtained at the cost of reduced ellipticity. Our system can be scaled in average power and used in different spectral regions, including the vacuum ultraviolet.</p
Strong and weak seeded four-wave mixing in stretched gas-filled hollow capillary fibers
Get PDFWe report a remarkably efficient experimental scheme for the generation of high energy ultra-short pulses by means of four-wave mixing in long stretched hollow capillary fibers filled with helium. We thoroughly investigate the role of strong and weak seeding fields in a degenerate up-conversion scheme to the deep ultraviolet. In the weak seed regime we demonstrate the tunable emission of up to 30 μJ in ultrashort pulses (~8 fs) in the 250-300 nm range, corresponding to pump energy conversion of up to 30%, from pump pulses with energies readily available from high-average power lasers. In the strong seed regime, we obtain higher pump conversion efficiencies, up to 42%, together with a spectral bandwidth supporting few femtosecond pulses and a record high deep-ultraviolet pulse energy exceeding 70 μJ. The energy can be further scaled by using stretched hollow-core fibers with larger core diameters
High-Power Ultra-Flat Supercontinuum Generation by Pumping Molecular Gas-Filled Hollow-Core Fibres in the Green
No full textSupercontinuum generation in optical fibres is a well-established route towards broadband white-light sources with high spatial coherence and brightness, as required for a variety of applications in science and industry. The use of gas-filled hollow-core anti-resonant fibres [1], allows for tight confinement of both laser pulses and gas over long interaction lengths, with broadband guidance, enabling supercontinuum generation with extreme bandwidth [2]–[4]. Access to such supercontinua has been mainly achieved by pumping in the anomalous dispersion region and driving the electronic nonlinear response (optical Kerr effect) of gases, leading to modulational instability [2] and soliton effects [3], [4]. However, the former produces spectra with low temporal coherence, while the latter require very short pump pulses (few or tens of femtoseconds). Meanwhile, pumping in the normal dispersion region can result in limited spectral broadening through self-phase modulation
Strong and weak seeded four-wave mixing in stretched gas-filled hollow capillary fibers
No full textWe report a remarkably efficient experimental scheme for the generation of high energy ultra-short pulses by means of four-wave mixing in long stretched hollow capillary fibers filled with helium. We thoroughly investigate the role of strong and weak seeding fields in a degenerate up-conversion scheme to the deep ultraviolet. In the weak seed regime we demonstrate the tunable emission of up to 30 μJ in ultrashort pulses (~8 fs) in the 250-300 nm range, corresponding to pump energy conversion of up to 30%, from pump pulses with energies readily available from high-average power lasers. In the strong seed regime, we obtain higher pump conversion efficiencies, up to 42%, together with a spectral bandwidth supporting few femtosecond pulses and a record high deep-ultraviolet pulse energy exceeding 70 μJ. The energy can be further scaled by using stretched hollow-core fibers with larger core diameters
Broadband Ultraviolet Generation with 50% Conversion Efficiency in Hollow Capillary Fibers
No full textWe demonstrate broadband wavelength up-conversion (240–320 nm) based on a seeded four-wave mixing scheme in gas-filled stretched hollow-capillary fibers with 50% conversion efficiency. Our technique is scalable in energy from the nJ to mJ level
Progress in Soliton Dynamics in Hollow Capillary Fibres
No full textPulse compression and frequency conversion are key ultrafast technologies. Few-cycle near-infrared pulses, combined with conversion across the ultraviolet to infrared, have enabled femtosecond and attosecond pump-probe experiments, advancing the field of ultrafast science. Soliton dynamics underlie a new class of technologies which can bring important new capabilities to this field [1]. They provide access to even shorter driving pulses, with sub-femtosecond and sub-cycle pulse duration produced by self-compression, while maintaining high energy and peak power. They also provide a highly efficient broadband frequency conversion technique, generating few-femtosecond,J-scale pulses, tunable across the vacuum ultraviolet to near-infrared spectrum.</p
Circularly Polarized DUV Pulses via Dispersive Wave Emission in Hollow Capillary Fibers
No full textCircularly polarized ultra-short laser pulses in the deep ultraviolet region (DUV, 200-400 nm) are commonly obtained via a two-step process requiring frequency up-conversion in nonlinear crystals followed by polarization conversion using quarter-wave plates. Due to strong dispersion in bulk media, this method suffers from limitations in phase-matching bandwidth, phase compensation and achromatic birefringence. Here, we demonstrate a direct process for the generation of ultra-short, circularly polarized DUV pulses via soliton dynamics in gasfilled stretched hollow capillary fibers [1] , driven by circularly polarized pulses centered at 800 nm. Frequency up-conversion occurs via resonant dispersive wave (RDW) emission with inherent spectral tunability (here we demonstrate 223-377 nm) through control of the gas (Ar) pressure. Our technique overcomes the limitations inherent to crystal-based approaches and allows energy up-scaling and extension to the vacuum UV (100-200 nm) and other spectral regions while permitting ultra-short duration, because the polarization conversion is performed at 800 nm, where material dispersion is low and the quality of commercial phase retarders is high.</p
