75 research outputs found
Observing angular deviations in light beam reflection via weak measurements
An optical analog of the quantum weak measurement scheme proved to be very
useful for the observation of optical beam shifts. Here we adapt the weak value
amplification method for the observation of the angular Goos-Hanchen shift. We
observe this effect in the case of external air-dielectric reflection, the more
fundamental case in which it occurs.We show that weak measurements allow for a
faithful amplification of the effect at any angle of incidence, even at the
Brewster angle of incidence
Orbital angular momentum induced beam shifts
We present experiments on Orbital Angular Momentum (OAM) induced beam shifts
in optical reflection. Specifically, we observe the spatial Goos-H\"anchen
shift in which the beam is displaced parallel to the plane of incidence and the
angular Imbert-Fedorov shift which is a transverse angular deviation from the
geometric optics prediction. Experimental results agree well with our
theoretical predictions. Both beam shifts increase with the OAM of the beam; we
have measured these for OAM indices up to 3. Moreover, the OAM couples these
two shifts. Our results are significant for optical metrology since optical
beams with OAM have been extensively used in both fundamental and applied
research.Comment: 7 pages, 7 figure
How orbital angular momentum affects beam shifts in optical reflection
It is well known that reflection of a Gaussian light beam ()
by a planar dielectric interface leads to four beam shifts when compared to the
geometrical-optics prediction. These are the spatial Goos-H\"{a}nchen (GH)
shift, the angular GH shift, the spatial Imbert-Fedorov (IF) shift and the
angular IF shift. We report here, theoretically and experimentally, that
endowing the beam with Orbital Angular Momentum (OAM) leads to coupling of
these four shifts; this is described by a mixing matrix.Comment: v2 Version accepted for publication in Phys. Rev.
Duality Between Spatial and Angular Shift in Optical Reflection
We report a unified representation of the spatial and angular Goos-Hanchen
and Imbert-Fedorov shifts that occur when a light beam reflects from a plane
interface. We thus reveal the dual nature of spatial and angular shifts in
optical beam reflection. In the Goos-Hanchen case we show theoretically and
experimentally that this unification naturally arises in the context of
reflection from a lossy surface (e.g., a metal).Comment: 4 pages, 3 figure
Observation of Goos-H\"{a}nchen shifts in metallic reflection
We report the first observation of the Goos-Hnchen
shift of a light beam incident on a metal surface. This phenomenon is
particularly interesting because the Goos-Hnchen shift
for polarized light in metals is negative and much bigger than the positive
shift for polarized light. The experimental result for the measured shifts
as a function of the angle of incidence is in excellent agreement with
theoretical predictions. In an energy-flux interpretation, our measurement
shows the existence of a backward energy flow at the bare metal surface when
this is excited by a polarized beam of light.Comment: The parer was published on Optics Express. The new version is
modified according to the reviewers suggestion
Time-resolved cathodoluminescence of InGaAs/AlGaAs tetrahedral pyramidal quantum structures
An original time resolved cathodoluminescence set up has been used to investigate the optical properties and the carrier transport in quantum structures located in InGaAs/AlGaAs tetrahedral pyramids. An InGaAs quantum dot formed just below the top of the pyramid is connected to four types of low-dimensional barriers: InGaAs quantum wires on the edges of the pyramid, InGaAs quantum wells on the (111)A facets and segregated AlGaAs vertical quantum wire and AlGaAs vertical quantum wells formed at the centre and at the pyramid edges. Experiments were performed at a temperature of 92K, an accelerating voltage of 10kV and a beam probe current of 10pA. The cathodoluminescence spectrum shows five luminescence peaks. Rise and decay times for the different emission wavelengths provide a clear confirmation of the peak attribution (previously done with other techniques) to the different nanostructures grown in a pyramid. Moreover, experimental results suggest a scenario where carriers diffuse from the lateral quantum structures towards the central structures (the InGaAs quantum dot and the segregated AlGaAs vertical quantum wire) via the InGaAs quantum wires on the edges of the pyramid. According to this hypothesis, we have modeled the carrier diffusion along these quantum wires. An ambipolar carrier mobility of 1400cm2/Vâs allows to obtain a good fit to all temporal dependence
Geometric Spin Hall Effect of Light at Polarizing Interfaces
The geometric Spin Hall Effect of Light (geometric SHEL) amounts to a
polarization-dependent positional shift when a light beam is observed from a
reference frame tilted with respect to its direction of propagation. Motivated
by this intriguing phenomenon, the energy density of the light beam is
decomposed into its Cartesian components in the tilted reference frame. This
illustrates the occurrence of the characteristic shift and the significance of
the effective response function of the detector.
We introduce the concept of a tilted polarizing interface and provide a
scheme for its experimental implementation. A light beam passing through such
an interface undergoes a shift resembling the original geometric SHEL in a
tilted reference frame. This displacement is generated at the polarizer and its
occurrence does not depend on the properties of the detection system. We give
explicit results for this novel type of geometric SHEL and show that at grazing
incidence this effect amounts to a displacement of multiple wavelengths, a
shift larger than the one introduced by Goos-H\"anchen and Imbert-Fedorov
effects.Comment: 6 pages, 4 figure
High spatial resolution picosecond cathodoluminescence of InGaN quantum wells
The authors have studied InxGa1-xN/GaN (x approximate to 15%) quantum wells (QWs) using atomic force microscopy (AFM) and picosecond time resolved cathodoluminescence (pTRCL) measurements. They observed a contrast inversion between monochromatic CL maps corresponding to the high energy side (3.13 eV) and the low energy side (3.07 eV) of the QW luminescence peak. In perfect correlation with CL images, AFM images clearly show regions where the QW thickness almost decreases to zero. Pronounced spectral diffusion from high energy thinner regions to low energy thicker regions is observed in pTRCL, providing a possible explanation for the hindering of nonradiative recombination at dislocations. (c) 2006 American Institute of Physics
Operating organic light-emitting diodes imaged by super-resolution spectroscopy
Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semi-conducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. This points the way towards real-time analysis of materials design principles in devices as they actually operateope
- âŠ