99 research outputs found
Four-dimensional light shaping: manipulating ultrafast spatio-temporal foci in space and time
Spectral dispersion of ultrashort pulses allows simultaneous focusing of
light in both space and time creating so-called spatio-temporal foci. Such
space-time coupling may be combined with existing holographic techniques to
give a further dimension of control when generating focal light fields. It is
shown that a phase-only hologram placed in the pupil plane of an objective and
illuminated by a spatially chirped ultrashort pulse can be used to generate
three dimensional arrays of spatio-temporally focused spots. Exploiting the
pulse front tilt generated at focus when applying simultaneous spatial and
temporal focusing (SSTF), it is possible to overlap neighbouring foci in time
to create a smooth intensity distribution. The resulting light field displays a
high level of axial confinement, with experimental demonstrations given through
two-photon microscopy and non-linear laser fabrication of glass
Polarization based modulation of splitting ratio in femtosecond laser direct written directional couplers
This work characterizes a phenomenon in direct laser written directional
couplers where the splitting ratio for output light is dependent on the input
polarization state. In general, for laser written waveguides, different
coupling strengths exist for different polarization states of the input light.
If the linear polarization state of the input light is not aligned with one of
the symmetry axes of the system, an additional amplitude beating is imposed on
the transfer of light in directional couplers of different interaction length.
We present results for in-plane and out of plane directional couplers, which
are supported by theoretical analysis. These new results provide insights for
understanding and controlling polarization properties of directional couplers
and larger photonic circuits
High resolution structural characterisation of laser-induced defect clusters inside diamond
Laser writing with ultrashort pulses provides a potential route for the
manufacture of three-dimensional wires, waveguides and defects within diamond.
We present a transmission electron microscopy (TEM) study of the intrinsic
structure of the laser modifications and reveal a complex distribution of
defects. Electron energy loss spectroscopy (EELS) indicates that the majority
of the irradiated region remains as bonded diamond.
Electrically-conductive paths are attributed to the formation of multiple
nano-scale, -bonded graphitic wires and a network of strain-relieving
micro-cracks
Planar polymer waveguides with a graded-index profile resulting from intermixing of methacrylates in closed microchannels
Graded-index waveguides are known to exhibit lower losses and considerably larger bandwidths compared to step-index waveguides. The present work reports on a new concept for realizing such waveguides on a planar substrate by capillary filling microchannels (cladding) with monomer solution (core). A graded-index profile is obtained by intermi xing between the core and cladding material at the microchannel interface. To this end, various ratios of methyl methacrylate (MMA) and octafluoropentyl methacrylate (OFPMA) were evaluated as starting monomers and the results showed that the polymers P50:50 (50:50 MMA:OFPMA) and P0:100 (100% OFPMA) were suitable to be applied as waveguide core and cladding material respectively. Light guiding in the resulting P50:50/P0:100 waveguides was demonstrated and the refractive-index profile was quantified and compared with that of conventional step-index waveguides. The results for both cases were clearly different and a gradual refractive index transition between the core and cladding was found for the newly developed waveguides. Although the concept has been demonstrated in a research environment, it also has potential for upscaling by employing drop-on-demand dispensing of polymer waveguide material in pre-patterned microchannels, for example in a roll-to-roll environment
Antimony thin films demonstrate programmable optical non-linearity
The use of metals of nanometer dimensions to enhance and manipulate
light-matter interactions for a range of emerging plasmonics-enabled
nanophotonic and optoelectronic applications is an interesting, yet not highly
explored area of research outside of plasmonics1,2. Even more importantly, the
concept of an active metal, i.e. a metal that can undergo an optical
non-volatile transition has not been explored. Nanostructure-based applications
would have unprecedented impact on both the existing and future of optics with
the development of active and nonlinear optical tunabilities in single
elemental metals3-5. Compared to alloys, pure metals have the material
simplicity and uniformity; however single elemental metals have not been viewed
as tunable optical materials, although they have been explored as viable
electrically switchable materials. In this paper we demonstrate for the first
time that antimony (Sb), a pure metal, is optically distinguishable between two
programmable states as nanoscale thin films. We then show that these states are
stable at room temperature, and the states correspond to the crystalline and
amorphous phases of the metal. Crucially from an application standpoint, we
demonstrate both its optoelectronic modulation capabilities as well as speed of
switching using single sub-picosecond (ps) pulses. The simplicity of depositing
a single metal portends its potential for use in applications ranging from high
speed active metamaterials to photonic neuromorphic computing, and opens up the
possibility for its use in any optoelectronic application where metallic
conductors with an actively tunable state is important
Quantifying distortions in two-photon remote focussing microscope images using a volumetric calibration specimen
This Document is Protected by copyright and was first published by Frontiers. All rights reserved. it is reproduced with permission.Remote focussing microscopy allows sharp, in-focus images to be acquired at high speed from outside of the focal plane of an objective lens without any agitation of the specimen. However, without careful optical alignment, the advantages of remote focussing microscopy could be compromised by the introduction of depth-dependent scaling artifacts. To achieve an ideal alignment in a point-scanning remote focussing microscope, the lateral (XY) scan mirror pair must be imaged onto the back focal plane of both the reference and imaging objectives, in a telecentric arrangement. However, for many commercial objective lenses, it can be difficult to accurately locate the position of the back focal plane. This paper investigates the impact of this limitation on the fidelity of three-dimensional data sets of living cardiac tissue, specifically the introduction of distortions. These distortions limit the accuracy of sarcomere measurements taken directly from raw volumetric data. The origin of the distortion is first identified through simulation of a remote focussing microscope. Using a novel three-dimensional calibration specimen it was then possible to quantify experimentally the size of the distortion as a function of objective misalignment. Finally, by first approximating and then compensating the distortion in imaging data from whole heart rodent studies, the variance of sarcomere length (SL) measurements was reduced by almost 50%.Medical Research Council (MRC)Engineering and Physical Sciences Research Council (EPSRC)Biotechnology and Biological Sciences Research Council (BBSRC)British Heart Foundation Centre of Research Excellence, Oxfor
Laser-written tunable liquid crystal aberration correctors
In this Article, we present a series of novel laser-written liquid crystal (LC) devices for aberration control for applications in beam shaping or aberration correction through adaptive optics. Each transparent LC device can correct for a chosen aberration mode with continuous greyscale tuning up to a total magnitude of more than 2π radians phase difference peak to peak at a wavelength of λ = 660 nm. For the purpose of demonstration, we present five different devices for the correction of five independent Zernike polynomial modes (although the technique could readily be used to manufacture devices based on other modes). Each device is operated by a single electrode pair tuned between 0 and 10 V. These devices have potential as a low-cost alternative to spatial light modulators for applications where a low-order aberration correction is sufficient and transmissive geometries are required
Laser engineering nanocarbon phases within diamond for science and electronics
Diamond, as the densest allotrope of carbon, displays a range of exemplary material properties that are attractive from a device perspective. Despite diamond displaying high carbon–carbon bond strength, ultrashort (femtosecond) pulse laser radiation can provide sufficient energy for highly localized internal breakdown of the diamond lattice. The less-dense carbon structures generated on lattice breakdown are subject to significant pressure from the surrounding diamond matrix, leading to highly unusual formation conditions. By tailoring the laser dose delivered to the diamond, it is shown that it is possible to create continuously modified internal tracks with varying electrical conduction properties. In addition to the widely reported conducting tracks, conditions leading to semiconducting and insulating written tracks have been identified. High-resolution transmission electron microscopy (HRTEM) is used to visualize the structural transformations taking place and provide insight into the different conduction regimes. The HRTEM reveals a highly diverse range of nanocarbon structures are generated by the laser irradiation, including many signatures for different so-called diaphite complexes, which have been seen in meteorite samples and seem to mediate the laser-induced breakdown of the diamond. This work offers insight into possible formation methods for the diamond and related nanocarbon phases found in meteorites
Laser writing of individual atomic defects in a crystal with near-unity yield
Atomic defects in wide band gap materials show great promise for development
of a new generation of quantum information technologies, but have been hampered
by the inability to produce and engineer the defects in a controlled way. The
nitrogen-vacancy (NV) color center in diamond is one of the foremost
candidates, with single defects allowing optical addressing of electron spin
and nuclear spin degrees of freedom with potential for applications in advanced
sensing and computing. Here we demonstrate a method for the deterministic
writing of individual NV centers at selected locations with high positioning
accuracy using laser processing with online fluorescence feedback. This method
provides a new tool for the fabrication of engineered materials and devices for
quantum technologies and offers insight into the diffusion dynamics of point
defects in solids.Comment: 16 pages, 8 figure
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