R. R. Thomson

Heriot-Watt University, Edinburgh, SCT, United Kingdom

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Publications (98)130.31 Total impact

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    ABSTRACT: We show experimentally how a non-diffracting state can be excited in a photonic Lieb lattice. This lattice supports three energy bands, including a perfectly flat middle band, which corresponds to an infinite effective mass with zero dispersion. We show that a suitable optical input state can be prepared so as to only excite the flat band. We analyse, both experimentally and theoretically, the evolution of such photonic flat-band states, and show their remarkable robustness, even in the presence of disorder.
    12/2014;
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    ABSTRACT: We present an ultrafast laser inscribed-four-port spatial mode-multiplexing/de-multiplexing device based on photonic-lanterns. The device demonstrates waveguide propagation loss of ~1 dB/cm and input dependant insertion losses between 4.18 dB and 4.73 dB at 780 nm
    Photonics 2014: 12th International Conference on Fiber Optics and Photonics; 11/2014
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    ABSTRACT: It is possible to significantly improve the performance of astronomical spectroscopy by taking the Point Spread Function from a near diffraction-limited telescope and reformatting it using photonic technologies. This can improve the stability of a conventional instrument or provide an interface to single mode instruments developed for the telecommunications industry. We compare different options for reformatting and interfacing with different types of instruments and examine them using set metrics. We then examine the relative merits for instruments that could be developed for astronomy.
    SPIE Astronomical Telescopes + Instrumentation; 07/2014
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    ABSTRACT: We report picosecond laser welding of similar and dissimilar materials based on plasma formation induced by a tightly focused beam from a 1030 nm, 10 ps, 400 kHz laser system. Specifically, we demonstrate the welding of fused silica, borosilicate, and sapphire to a range of materials including borosilicate, fused silica, silicon, copper, aluminum, and stainless steel. Dissimilar material welding of glass to aluminum and stainless steel has not been previously reported. Analysis of the borosilicate-to-borosilicate weld strength compares well to those obtained using similar welding systems based on femtosecond lasers. There is, however, a strong requirement to prepare surfaces to a high (10-60 nm Ra) flatness to ensure a successful weld.
    Applied Optics 07/2014; 53(19):4233-4238. · 1.69 Impact Factor
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    ABSTRACT: We report the ultrafast laser fabrication and mid-IR characterization (3.39 µm) of four-port evanescent field directional couplers. The couplers were fabricated in a commercial gallium lanthanum sulphide glass substrate using sub-picosecond laser pulses of 1030 nm light. Straight waveguides inscribed using optimal fabrication parameters were found to exhibit propagation losses of ⇠ 0.8 dB·cm 1 . A series of couplers were inscribed with di↵erent interaction lengths, and we demonstrate power splitting ratios of between 8% and 99% for mid-IR light with a wavelength of 3.39 µm. These results clearly demonstrate that ultrafast laser inscription can be used to fabricate high quality evanescent field couplers for future applications in astronomical interferometry. OCIS codes: (130.2755) Glass waveguides; (140.3390) Laser materials processing; (220.4000) Mi-crostructure fabrication. Astronomical optical instruments that utilize pho-tonic concepts [1], such as integrated optical waveguides [2–7], Bragg-gratings [8, 9] and laser frequency combs [10, 11], have the potential to revolutionize astronomy in a plethora of di↵erent areas. One such area is stellar interferometry which, by combining the light gathered by multiple widely spaced telescopes, enables imaging of celestial objects with extremely high spatial resolution (sub milli-arcsecond [12–14]), well beyond that realisti-cally achievable using a single telescope. To image an object using a telescope interferometer array is a highly non-trivial task. The collected light must first be transported to a central location using vacuum delay lines. A high-speed fringe tracker is also necessary to correct for path length changes due to at-mospheric conditions. Once at the central location, the transported light must be coherently combined using a beam-combining instrument [15] which analyses the mutual coherence between the light from each pair of telescopes in the array. In 1996, Kern et al. [16] pro-posed that integrated optic (IO) waveguide technologies could provide an inherently stable and scalable platform for beam combination. Since then, IO beam combin-ers [6, 17–20] have been utilized in a variety of lead-ing interferometric beam combination instruments, such as the PIONIER beam combination instrument for the ⇤ a.arriola@hw.ac.uk
    Optics Letters 06/2014; 39(17). · 3.39 Impact Factor
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    ABSTRACT: Spectroscopy is a technique of paramount importance to astronomy, as it enables the chemical composition, distances and velocities of celestial objects to be determined. As the diameter of a ground-based telescope increases, the point-spread-function (PSF) becomes increasingly degraded due to atmospheric seeing. A degraded PSF requires a larger spectrograph slit-width for efficient coupling and current spectrographs for large telescopes are already on the metre scale. This presents numerous issues in terms of manufacturability, cost and stability. As proposed in 2010 by Bland-Hawthorn et al, one approach which may help to improve spectrograph stability is a guided wave transition, known as a "photonic-lantern". These devices enable the low-loss reformatting of a multimode PSF into a diffraction-limited source (in one direction). This pseudo-slit can then be used as the input to a traditional spectrograph operating at the diffraction limit. In essence, this approach may enable the use of diffraction-limited spectrographs on large telescopes without an unfeasible reduction in throughput. We (and others) have recently demonstrated that ultrafast laser inscription can be used to realize "integrated" photonic-lanterns, by directly writing three-dimensional optical waveguide structures inside a glass substrate. This paper presents our work on developing ultrafast laser inscribed devices accept and reformat multimode light into a diffraction-limited slit.
    SPIE Astronomical Telescopes + Instrumentation 2014, Montreal (Canada); 06/2014
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    ABSTRACT: In this paper we report the fabrication and mid-infrared characterization (λ = 3.39 µm) of evanescent field directional couplers. These devices were fabricated using the femtosecond laser direct-writing technique in commercially available Gallium Lanthanum Sulphide (GLS) glass substrates. We demonstrate that the power splitting ratios of the devices can be controlled by adjusting the length of the interaction section between the waveguides, and consequently we demonstrate power splitting ratios of between 8% and 99% for 3.39 µm light. We anticipate that mid-IR beam integrated-optic beam combination instruments based on this technology will be key for future mid-infrared astronomical interferometry, particularly for nulling interferometry and earth-like exoplanet imaging.
    SPIE Astronomical Telescopes + Instrumentation 2014, Montreal (Canada); 06/2014
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    ABSTRACT: Due to their high efficiency and broad operational bandwidths, volume phase holographic gratings (VPHGs) are often the grating technology of choice for astronomical instruments, but current VPHGs exhibit a number of drawbacks including limits on their size, function and durability due to the manufacturing process. VPHGs are also generally made using a dichromated gelatin substrate, which exhibits reduced transmission at wavelengths longer than ~2.2 µm, limiting their ability to operate further into the mid-infrared. An emerging alternative method of manufacturing volume gratings is ultrafast laser inscription (ULI). This technique uses focused ultrashort laser pulses to induce a localised refractive index modification inside the bulk of a substrate material. We have recently demonstrated that ULI can be used to create volume gratings for operation in the visible, near-infrared and mid-infrared regions by inscribing volume gratings in a chalcogenide glass. The direct-write nature of ULI may then facilitate the fabrication of gratings which are not restricted in terms of their size and grating profile, as is currently the case with gelatine based VPHGs. In this paper, we present our work on the manufacture of volume gratings in gallium lanthanum sulphide (GLS) chalcogenide glass. The gratings are aimed at efficient operation at wavelengths around 1 µm, and the effect of applying an anti-reflection coating to the substrate to reduce Fresnel reflections is studied.
    SPIE Astronomical Telescopes + Instrumentation 2014, Montreal (Canada); 06/2014
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    ABSTRACT: A key requirement for astronomical instruments in next generation Extremely Large Telescopes (ELTs) is the development of large-aperture Integral Field Units (IFUs) that enable the efficient and spatially contiguous sampling of the telescope image plane for coupling stellar light onto a spectrometer. Current IFUs are complex to fabricate and suffer from stray light issues, which limits their application in high-contrast studies such as exoplanet imaging. In this paper, we present our work on the development of freeform microlens arrays using the rapidly maturing technique of ultrafast laser inscription and selective wet chemical etching. Using the focus spot from a femtosecond laser source as a tool with an essentially unrestricted "tool-path", we demonstrate that it is possible to directly write the surface of a lenslet in three dimensions within the volume of a transparent material. We further show that high surface quality of the lenses can be achieved by using an oxy-natural gas flame to polish the lens surface roughness that is characteristic of the post-etched structures. Using our technique, the shape and position of each lenslet can be tailored to match the spatial positioning of a two-dimensional multimode fiber array, which can be monolithically integrated with the microlens array.
    SPIE Astronomical Telescopes + Instrumentation, Montreal (Canada); 06/2014
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    ABSTRACT: We report on the development and testing of the building blocks of a possible compact heterodyne setup in the mid-infrared, which becomes particularly relevant for flight instrumentation. The local oscillator is a Quantum Cascade Laser (QCL) source at 8.6 µm operable at room temperature. The beam combination of the source signal and the local oscillator will occur by means of integrated optics for the 10 µm range, which was characterized in the lab. In addition we investigate the use of superlattice detectors in a heterodyne instrument. This work shows that these different new components can become valuable tools for a compact heterodyne setup.
    SPIE Astronomical Telescopes + Instrumentation 2014, Montreal (Canada); 06/2014
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    ABSTRACT: We present a 57 channel spatial multiplexer consisting of 19 separate 3-port photonic lanterns arranged in a hexagonal array. An average insertion loss of 0.92 dB was measured across all ports with 0.1 dB uniformity.
    Optical Fiber Communication Conference; 03/2014
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    ABSTRACT: The spectral resolution of a dispersive spectrograph is limited by the width of the entrance slit. This inherently means that astronomical spectrographs trade-off throughput with spectral resolving power. Recently, optical guided-wave transitions known as 'photonic-lanterns' have been proposed to circumvent this trade-off, by enabling the efficient reformatting of multimode light into a pseudo-slit which is highly multimode in one axis, but diffraction-limited in the other. Here, we demonstrate the successful reformatting of a telescope point-spread-function into such a slit using a three-dimensional integrated optical waveguide device, which we name the 'photonic-dicer'. Using the CANARY Adaptive-Optics system on the William Herschel Telescope, and broadband celestial light between 1350 nm and 1550 nm, the device exhibits throughputs of 19.5%, 10.5% and 9.0%, under closed-loop, open-loop and tip-tilt modes of operation respectively. This work clearly demonstrates that integrated photonic technologies can facilitate new astronomical instruments with higher spectral resolution and increased efficiency.
    02/2014;
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    ABSTRACT: We report on the ultrafast laser inscription (ULI) of volume phase gratings inside gallium lanthanum sulphide (GLS) chalcogenide glass substrates. The effect of laser pulse energy and grating thickness on the dispersive properties of the gratings is investigated, with the aim of improving the performance of the gratings in the mid-infrared. The grating with the optimum performance in the mid-infrared exhibited a 1st order absolute diffraction efficiency of 61% at 1300 nm and 24% at 2640 nm. Based on the work reported here, we conclude that ULI is promising for the fabrication of mid-infrared volume phase gratings, with potential applications including astronomical instrumentation and remote sensing. This paper was published in Optical Materials Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-3-10-1616. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
    Optical Materials Express 09/2013; 3(10):1616-1624. · 2.92 Impact Factor
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    ABSTRACT: We have delivered picosecond and femtosecond pulses with peak powers of 15.3 MW and 0.95 MW respectively through a hollow-core Negative Curvature Fibre and thereby demonstrated the suitability of fibre-delivered beam in precision micro-machining applications.
    Workshop on Specialty Optical Fibers and their Applications; 08/2013
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    ABSTRACT: This the copy of a presentation given by David Lee at the National Astronomy Meeting in St. Andrews on 2 July 2013. Abstract: The aim of Astrophotonics is to develop high performance astronomical instrumentation which is both more compact and lower cost than existing instrumentation. Astrophotonics uses optical building blocks provided by photonics devices that were originally developed for the telecommunications industry but their design is now being modified and enhanced for use in future astronomical instruments. The reliable manufacture of this technology has recently been made possible by the technique of ultrafast laser inscription, whereby a high power laser beam is used to directly write photonics structures, such as diffraction gratings, within glass substrates. We will provide an overview of the various Astrophotonics optical devices being developed at Heriot-Watt University and STFC using the manufacturing technique of laser inscription. We will present preliminary results of laser inscribed fibre coupling systems and diffraction gratings and an overview of other systems being developed. Finally we will show how these photonics building blocks can be linked together to form a high performance miniature astronomical spectrograph. Ultimately our aim is the production of a spectrometer on a chip which will form the basis of instruments providing high multiplex observing capability.
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    David Lee, Robert R. Thomson, Colin R. Cunningham
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    ABSTRACT: This is a copy of the power point presentation given by David Lee at the Astronomical Instrumentation conference in Amsterdam (2012).
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    ABSTRACT: We present an evanescent-field device based on a right-angled waveguide. This consists of orthogonal waveguides, with their points of intersection lying along an angled facet of the chip. Light guided along one waveguide is incident at the angled dielectric-air facet at an angle exceeding the critical angle, so that the totally internally reflected light is coupled into the second waveguide. By depositing a nanotube film on the angled surface, the chip is then used to mode-lock an Erbium doped fiber ring laser with a repetition rate of 26 MHz, and pulse duration of 800 fs.
    Applied Physics Letters 01/2013; 103(22):221117-221117-5. · 3.52 Impact Factor
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    ABSTRACT: We report passive mode-locking of an Er-doped fiber laser using carbon nanotubes deposited on the facet of a right-angle optical waveguide.
    Lasers and Electro-Optics Pacific Rim (CLEO-PR), 2013 Conference on; 01/2013
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    ABSTRACT: Recent results from our work using ultrafast laser writing to fabricate waveguides and on-chip devices inside sulphide chalcogenide glasses are presented in this paper. Low loss single-mode (SM) and multi-mode (MM) waveguide arrays were successfully laser fabricated, for the first time to our knowledge, for operation in the whole near-IR (NIR) to mid- IR (MIR) range (1 to 11 μm wavelengths). These waveguides are demonstrated to have numerical apertures (NA) which can exceed NA=0.2, therefore also allowing for low bend losses as well as direct coupling to QC lasers. We also demonstrate the control over the waveguide mode field diameters (MFDs) (at 1/e2) by changing the waveguide core sizes and index contrasts, achieving typical values of 44 μm at 10.6 μm, down to 6 μm for telecom 1.55 μm light. The optical nonlinear properties of these waveguides have also been preliminarily investigated. Using a femtosecond (fs) optical parametric amplifier system, the optical nonlinearity of bulk gallium lanthanum sulphide (GLS) glass was first measured at 2.5 μm. The upper limits for the nonlinear properties of the laser modified material could be estimated based upon the nonlinear spectral broadening of a 2.5 μm fs pulse train coupled into SM waveguides. Further work includes the demonstration of on-chip three dimensional (3D) beam combiners for the MIR range (10.6 μm in this work), for near future implementation in astronomical observatories for stellar interferometry.
    Proc SPIE 09/2012;
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    ABSTRACT: It is shown that grisms, a grating and prism combination, are a simple way to achieve chromatic control in 3D multi-plane imaging. A pair of grisms, whose separation can be varied, provide a collimated beam with a tuneable chromatic shear from a collimated polychromatic input. This simple control permits the correction of chromatic smearing in 3D imaging using off-axis Fresnel zone plates and improved control of the axial profile of a focussed spot in multi-photon experiments.
    Optics Express 08/2012; 20(18):20705-14. · 3.55 Impact Factor

Publication Stats

485 Citations
130.31 Total Impact Points

Institutions

  • 2005–2012
    • Heriot-Watt University
      • • Department of Physics
      • • School of Engineering and Physical Sciences
      Edinburgh, SCT, United Kingdom
  • 2009–2011
    • University of St Andrews
      • School of Physics and Astronomy
      Saint Andrews, SCT, United Kingdom