45 research outputs found
Femtosecond laser microfabricated devices for biophotonic applications
Femtosecond Laser DirectWriting has emerged as a key enabling technology
for realising miniaturised biophotonic applications offering clear advantages
over competing soft-lithography, ion-exchange and sol-gel based fabrication
techniques. Waveguide writing and selective etching with three-dimensional
design flexibility allows the development of innovative and unprecedented
optofluidic architectures using this technology. The work embodied in this
thesis focuses on utilising the advantages offered by direct laser writing in
fabricating integrated miniaturised devices tailored for biological analysis.
The first application presented customised the selective etching phenomenon
in fused silica by tailoring the femtosecond pulse properties during the writing
process. A device with an embedded network of microchannels with a
significant difference in aspect-ratio was fabricated, which was subsequently
applied in achieving the high-throughput label-free sorting of mammalian
cells based on cytoskeletal deformability. Analysis on the device output cell
population revealed minimal effect of the device on cell viability.
The second application incorporated an embedded microchannel in fused
silica with a monolithically integrated near-infrared optical waveguide. This
optofluidic device implemented the thermally sensitive emission spectrum
of semiconductor nanocrystals in undertaking remote thermometry of the
localised microchannel environment illuminated by the waveguide. Aspects
relating to changing the wavelength of illumination from the waveguide were
analysed. The effect of incorporating carbon nanotubes as efficient heaters
within the microchannel was investigated. Spatio-thermal imaging of the
microchannel illuminated by the waveguide revealed the thermal effects to
extend over distances appreciably longer than the waveguide cross-section.
On the material side of direct laser writing, ultra-high selective etching is
demonstrated in the well-known laser crystal Nd:YAG. This work presents
Nd:YAG as a material with the potential to develop next-generation optofluidic
devices
Ultrafast laser inscription of mid-IR directional couplers for stellar interferometry
We report the ultrafast laser fabrication and mid-IR characterization (3.39
microns) 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. A series of couplers were inscribed with different interaction
lengths, and we demonstrate power splitting ratios of between 8% and 99% for
mid-IR light with a wavelength of 3.39 microns. These results clearly
demonstrate that ultrafast laser inscription can be used to fabricate high
quality evanescent field couplers for future applications in astronomical
interferometry.Comment: 4 pages, 4 figure
Three-dimensional microstructuring of yttrium aluminum garnet crystals for laser active optofluidic applications
The following article appeared in Applied Physics Letters 103.4 (2013): 041101 and may be found at http://scitation.aip.org/content/aip/journal/apl/103/4/10.1063/1.4816338We demonstrate three-dimensional microstructuring in a neodymium doped yttrium aluminum garnet (Nd:YAG) crystal. Spatially well-defined hollow microstructures deeply embedded within the material are shown to result from the creation of a pre-damage state within the Nd:YAG crystal network that is validated using luminescence and Raman analyses of the structures. This opens up the potential of fabricating next-generation optofluidic devices in optical gain materialsFinancial support from the Spanish Ministerio de Educación under the Programa de Movilidad de Recursos Humanos del Plan Nacional de IþDþi 2008/2011 for abroad postdoctoral researchers. This work was also supported by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (Project S2009/MAT- 1756) and by the Spanish Ministerio de Educación y Ciencia (MAT2010-16161
Observation of a localized flat-band state in a photonic Lieb lattice
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.Comment: Accepted for publication in Physical Review Letter
Modulation-assisted tunneling in laser-fabricated photonic Wannier-Stark ladders
We observe Wannier-Stark localization in curved photonic lattices, realized
using arrays of evanescently coupled optical waveguides. By correctly tuning
the strength of inter-site coupling in the lattice, we observe that
Wannier-Stark states become increasingly localized, and eventually fully
localized to one site, as the curvature of the lattice is increased. We then
demonstrate that tunneling can be successfully restored in the lattice by
applying a sinusoidal modulation to the lattice position, an effect that is a
direct analogue of photon-assisted tunneling. This precise tuning of the
tunneling matrix elements, through laser-fabricated on-site modulations, opens
a novel route for the creation of gauge fields in photonic lattices.Comment: 5 pages. Comments are welcom
Optimisation of ultrafast laser assisted etching in fused silica
Observations of runout distances combined with velocity measurements suggest that “major” dry-mixed avalanches show a scale invariance to the total drop height HSC. This is in accordance to the proposed upper-limit envelope of the maximum velocity by McClung and Schaerer (2006). The observations are also supported by a simple scaling analysis using a simple mass block model on cycloidal and parabolic tracks (Gauer, 2018b), concluding Umax~ gHSC/2 . In this supplementary paper, a simple mass block model is presented that includes basic observations of major dry-mixed avalanches, such as mass entrainment and deposition, and that reflects this scale invariance. Almost all model parameters can principally be observed in the field. Model results are compared with a series of avalanche observations of runout and velocity and match well, considering that the model is a first order approximation