222 research outputs found
Towards Hollow-Core-Fiber Delivery of Broadband Mid-Infrared Light for Remote Spectroscopy
No full textWe describe progress towards fiber-delivered broadband mid-IR light for multi-species spectroscopy in inaccessible environments. Water and HCl are resolved after propagating 3-μm light through five meters of hollow-core fiber, illustrating the technique's potential.</p
Hollow-Core-Fibre-Delivered Attenuated Total Internal Reflection Heterodyne Spectroscopy
No full textAttenuated total internal reflection Fourier-transform infrared (ATR-FTIR) spectroscopy is a commonly used modality for measuring the spectra of highly absorbing liquids and solids. Previously, we combined broadband OPO-based mid-IR spectroscopy [1] with the use of a non-resonant hollow-core fibre (HCF) [2] to demonstrate heterodyne detection in a way that achieved common mode rejection of absorption features unique to the fibre transmission path [3]. We now extend this approach to enable simple, fibre-delivered ATR spectroscopy
Hollow-Core-Fiber Delivery of Broadband Mid-Infrared Light for Remote Spectroscopy
No full textHigh-resolution multi-species spectroscopy is achieved by delivering broadband 3–4-μm mid-infrared light through a 4.5-meter-long silica-based hollow-core optical fiber. Absorptions from H37Cl, H35Cl, H2O and CH4 present in the gas within the fiber core are observed, and the corresponding gas concentrations are obtained to 5-ppb precision using a high-resolution Fourier-transform spectrometer and a full-spectrum multi-species fitting algorithm. We show that by fully fitting the narrow absorption features of these light molecules their contributions can be nulled, enabling further spectroscopy of C3H6O and C3H8O contained in a Herriott cell after the fiber. As a demonstration of the potential to extend fiber-delivered broadband mid-infrared spectroscopy to significant distances, we present a high-resolution characterization of the transmission of a 63-meter length of hollow-core fiber, fully fitting the input and output spectra to obtain the intra-fiber gas concentrations. We show that, despite the fiber not having been purged, useful spectroscopic windows are still preserved which have the potential to enable hydrocarbon spectroscopy at the distal end of fibers with lengths of tens or even hundreds of meters
Supercontinuum generation in orientation-patterned gallium phosphide
Get PDFA supercontinuum from the blue/green to the red is generated by pumping orientation-patterned
gallium phosphide crystal by femtosecond pulses from Yb:fibre laser. Experimentally, the supercontinuum is generated by focusing 32 nJ 100 fs pulses at 1040 nm into the OPGaP crystal,
to a focus of w0=25 µm. Using a nonlinear envelope equation model developed in this work,
a combine action of χ
(2)
and χ
(3) nonlinearities is shown to be the origin of the supercontinuum generation. The modelling implies that high-order parametric gain pumped by the secondharmonic light of the laser and seeded by self-phase-modulated sidebands is responsible. The
results represent the first time a visible supercontinuum has been generated in a bulk material
using a low-energy high-repetition rate femtosecond laser
Yb-based femtosecond oscillators for high-power amplification
Get PDFMotivated by the industrial requirement for multi-100-W sub-ps pulses, this thesis describes the development of a high-average-power master-oscillator power-amplifier (MOPA) based on seeding an Yb:YAG planar waveguide amplifier using an Yb-based modelocked oscillator operating at 1030 nm. The scope of the research presented includes both the development of the seed oscillators and of the high-power amplifier.
Two end pumped Yb:KYW oscillators were demonstrated, one with Brewster-Brewster crystal geometry and another with a novel plane-Brewster crystal, permitting a simple pumping arrangement and which provided superior efficiency than Brewster-Brewster geometry. In both oscillators, one or more Gires-Tournois interferometer (GTI) mirrors were used in the cavity to compensate for the large amount of positive dispersion from the crystal. Both systems were modelocked using semiconductor saturable absorber mirrors. The oscillators demonstrated here produced amongst the highest average powers reported from end-pumped systems to date, generating up to 4.5 W in the nearinfra-red region in the form of 500-fs pulses, with a repetition frequency of 53 MHz.
The study of oscillator performance was extended to include a comparison between Yb:KYW and Yb:YAG lasers constructed in similar configurations, both based on plane-Brewster crystal geometries and dispersion compensated using GTI mirrors. The Yb:YAG system provided 700-fs pulses, compared to 500-fs pulses obtained using Yb:KYW, with the average power produced being 2.88 W for Yb:YAG, and 2.42 W for Yb:KYW, despite significantly better CW performance being observed with Yb:YAG. Due to their near-infrared wavelengths, high average powers and sub-ps pulse durations, both systems showed potential as seed lasers for high-power Yb:YAG amplifiers.
A MOPA system was developed around an Yb:YAG planar waveguide amplifier seeded by the Yb:KYW femtosecond laser based on a Brewster-Brewster crystal geometry and operating at 53 MHz repetition frequency. With single-sided pumping and five passes of the gain waveguide, the Yb:YAG amplifier provided 700-fs pulses with average powers of 50 W at 1030 nm. With the extension to double-sided pumping and the use of toroidal mirrors to achieve seven passes, the amplifier produced 780-fs pulses with average powers of 255 W. A numerical simulation of the amplifier identified gain narrowing as the dominant pulse-shaping mechanis
Novel sources of near- and mid-infrared femtosecond pulses for applications in gas sensing, pulse shaping and material processing
Get PDFIn this thesis the design, construction process and the performance of two femtosecond
optical parametric oscillators and one second–harmonic generation femtosecond
pulse shaper is described. One oscillator was applied to gas sensing
while potential applications of other devices are outlined.
ATi:sapphire oscillator was used to pump a periodically–poled lithium niobate–
based optical parametric oscillator. This signal–resonant device was configured
to produce broadband idler pulses tunable in the range of 2.7–3.4 μm. This wavelength
coverage was matched to the ν3 optical absorption band of methane, and
Fourier–transform spectroscopy of a CH4:N2 mixture was implemented by employing
a mid–IR silica photonic bandgap fibre simultaneously as a gas cell and
an optical waveguide. Methane sensing below a 1% concentration was demonstrated
and the main limiting factors were identified and improvements suggested.
Another optical parametric oscillator was demonstrated which was pumped
by a commercial Yb:fibre master oscillator/power amplifier system and was based
on a periodically–poled lithium niobate crystal. The signal was tunable between
1.42–1.57 μm and was intended as a source for a subsequent project for waveguide
writing in silicon. The oscillator was a novel long–cavity device operating
at 15 MHz. The 130 nJ pump pulse energies allowed for 21 nJ signal pulses at
a pump power of 2 W. The performance of the oscillator was characterised via
temporal and spectral measurements and the next steps of its development are
outlined.
Finally a pulse shaper based on second harmonic generation in a grating–
engineered periodically–poled lithium niobate crystal was demonstrated. Pulses
from a 1.53 μm femtosecond Er:fibre laser were compressed and then used as the
input to the shaper. The performance of the shaper was tested by performing
cross–correlation frequency–resolved optical gating measurements on the output
second harmonic pulses and this confirmed the successful creation of multiple
pulses and other tailored shapes including square and chirped pulses, agreeing
well with theoretical calculations
Mid-infrared dual comb spectroscopy with asynchronous optical parametric oscillators
Get PDFDual-comb spectroscopy (DCS) is a novel approach that uses asynchronous broadband coherent sources to achieve Fourier-transform-like spectroscopy but with no moving parts and at kHz acquisition rates. To date, fully resolved and accurate dual-comb spectrometers have been demonstrated in the near-infrared and applied to broadband spectroscopy for precise measurement of molecular centerlines, spectral lidar, and greenhouse gases from the near- to mid-IR.
This thesis describes DCS with asynchronous optical parametric oscillators and explores their applications in rapid, high-resolution broadband spectroscopy in the mid-infared. Initially a dual-comb spectrometer was designed with two identical optical parametric oscillators (OPOs) pumped by two identical Yb:fibre lasers and its stability performance was characterized measuring relative intensity noise. First experiments were accomplished by using free-running independent MgO:PPLN based OPOs with a repetition-rate difference of 500 Hz, achieving resolutions of 0.2 cm-1 across a wavelength range 3.1 to 3.5 μm; an absolute wavelength calibration technique was employed to allow registration and averaging of consecutively acquired dual-comb spectra. Then experiments were repeated with a dual-comb source for the spectral fingerprint region based on a pair of entirely free-running OPOs, each pumped by a 1-µm femtosecond laser and utilizing the new gain medium orientation-patterned gallium phosphide (OPGaP) to produce broadband idler pulses tunable from 6–8 µm. Methane absorption spectroscopy in the deep infrared region was demonstrated with the same wavelength calibration approach for both dual-comb spectrometers, leading to a high quality and low-noise absorbance measurement with spectral coverage simultaneously spanning the methane P, Q and R branches in good agreement with the Hitran database
Kerr-mediated symmetry breaking of counterpropagating light in microresonators
Get PDFNonlinear Optics has been a source of surprises for physicists for almost a century
comprising both fundamental physics and real-world applications. To access optical
nonlinearities, significant light intensities are required; thus nonlinear optics often
involves a resonant cavity to amplify the light intensity. Microresonators have proven
to be an ideal platform for this kind of experiment since the cavity mode area can be
as small as a few µm2 and their high Q-factor traps light for many round trips while
more light is coupled in. Also, light interacts with the nonlinear material, of which
the resonator is made, for the whole round trip. However, the interaction between
counter-propagating light in microresonators is still a relatively unexplored field.
This thesis reports on the first observation of Kerr-induced spontaneous symmetry breaking in a microresonator, whereby light can circulate in only one direction
inside the resonator. I develop a theoretical model describing the steady-state solutions and the dynamics of how the symmetry-broken regime responds to the input
changes. I show experimentally how the symmetry breaking can be used to realise all-optical isolator, circulators, memories and logic gates. These devices, based
on the Kerr-nonreciprocity, represent a promising alternative for the realisation of
integrated all-optical passive photonics circuits
Continuous Ultraviolet to Blue-Green Astrocomb
Get PDFThe characterization of Earth-like exoplanets and precision tests of
cosmological models using next-generation telescopes such as the ELT will
demand precise calibration of astrophysical spectrographs in the visible
region, where stellar absorption lines are most abundant. Astrocombs--lasers
providing a broadband sequence of ultra-narrow, drift-free, regularly spaced
optical frequencies on a multi-GHz grid--promise an atomically-traceable,
versatile calibration scale, but their realization is challenging because of
the need for ultra-broadband frequency conversion of mode-locked infrared
lasers into the blue-green region. Here, we introduce a new concept achieving a
broad, continuous spectrum by combining second-harmonic generation and
sum-frequency-mixing in an aperiodically-poled MgO:PPLN waveguide to generate
gap-free 390-520 nm light from a 1 GHz Ti:sapphire laser frequency comb. We
lock a low-dispersion Fabry-Perot etalon to extract a sub-comb of bandwidth
from 392-472 nm with a spacing of 30 GHz, visualizing the thousands of
resulting comb modes on a high resolution cross-dispersion spectrograph.
Complementary experimental data and simulations demonstrate the effectiveness
of the approach for eliminating the spectral gaps present in
second-harmonic-only conversion, in which weaker fundamental frequencies are
suppressed by the quadratic \{chi}^((2)) nonlinearity. Requiring only ~100 pJ
pulse energies, our concept establishes a practical new route to broadband
UV-visible generation at GHz repetition rates.Comment: 14 pages; 4 figure
ANDES, the high-resolution spectrograph for the ELT: a 30 GHz UB-band astrocomb from 390–470 nm
No full textNext generation extreme precision radial velocity (EPRV) instruments such as the ANDES spectrograph of the Extremely Large Telescope will require an unprecedentedly high-precision calibration approach, particularly in the UB band region in which the most dense stellar absorption lines are present. For this purpose, astrocombs delivering thousands of atomically referenced, evenly-spaced calibration lines across a broad spectrum have the potential to be ideal calibration sources. Here, we report a novel and effective approach to generating a laser frequency comb with a multi- GHz mode spacing covering a broad wavelength range in the UB band. The approach is based on nonlinear mixing between near-infrared ultrafast laser pulses in a MgO:PPLN waveguide. The generated 1-GHz comb, spanning 390–520 nm, was filtered to a 30 GHz sub-comb using a low-dispersion Fabry-Perot etalon. The resultant UB-band astrocomb was then captured on a lab-built cross-dispersion echelle-prism spectrograph, demonstrating well resolved comb lines across the etalon bandwidth of 392–472 nm
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