1,324 research outputs found
Variable - temperature scanning optical and force microscope
The implementation of a scanning microscope capable of working in confocal,
atomic force and apertureless near field configurations is presented. The
microscope is designed to operate in the temperature range 4 - 300 K, using
conventional helium flow cryostats. In AFM mode, the distance between the
sample and an etched tungsten tip is controlled by a self - sensing
piezoelectric tuning fork. The vertical position of both the AFM head and
microscope objective can be accurately controlled using piezoelectric coarse
approach motors. The scanning is performed using a compact XYZ stage, while the
AFM and optical head are kept fixed, allowing scanning probe and optical
measurements to be acquired simultaneously and in concert. The free optical
axis of the microscope enables both reflection and transmission experiments to
be performed.Comment: 24 pages, 9 figures, submitted to the journal "Review of Scientific
Instruments
Enhanced Transmission and Reflection of Femtosecond Pulses by a Single Slit
We show that a physical mechanism responsible for the enhanced transmission
and reflection of femtosecond pulses by a single subwavelength nanoslit in a
thick metallic film is the Fabry-Perot-like resonant excitation of stationary,
quasistationary and nonstationary waves inside the slit, which leads to the
field enhancement inside and around the slit. The mechanism is universal for
any pulse-scatter system, which supports the stationary resonances. We point
out that there is a pulse duration limit below which the slit does not support
the intraslit resonance.Comment: 4 pages, 3 figure
The optimal form of the scanning near-field optical microscopy probe
A theoretical approach to determine the optimal form of the near-field
optical microscope probe is proposed. An analytical expression of the optimal
probe form with subwavelength aperture has been obtained. The advantages of the
probe with the optimal form are illustrated using numerical calculations. The
conducted calculations show 10 times greater light throughput and the reception
possibility of the more compactly localized light at the output probe aperture
which could indicate better spatial resolution of the optical images in
near-field optical technique using optimal probe.Comment: 12 pages, 6 figure
A compact fluorescence and polarization near-field scanning optical microscope
We present a transmission, fluorescence, and polarization near-field scanning optical microscope with shear-force feedback control that is small in size and simple to operate. This microscope features an ultrafine mechanical tip/sample approach with continuous manual submicron control over a range of several millimeters. The piezo-driven 12 μm x-yx-y scan range is complimented by a 4 mm coarse mechanical translation range in each direction. The construction materials used in the mechanical feedback loop have been carefully chosen for thermal compatibility in order to reduce differential expansion and contraction between the tip and sample. A unique pressure-fit sample mount allows for quick and reliable sample exchange. Shear-force feedback light is delivered to the scan head via an optical fiber so that a remote laser of any type may be used as a source. This dither light is collimated and refocused onto the tip, delivering a consistently small spot which is collected by a high numerical aperture objective. This new scan head incorporates an optical system which will permit the linearization of scan piezo response similar to a scheme used successfully with atomic force microscopy. This is designed to both overcome the piezo’s inherent hysteresis and to eliminate drift during long duration spatial scans or spectroscopic measurements at a single location. The scan head design offers added flexibility due to the use of optical fibers to deliver the dither and scan linearization light, and functions in any orientation for use in conjunction with upright or inverted optical microscopes. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70291/2/RSINAK-69-7-2685-1.pd
Extension of Bethe's diffraction model to conical Geometry: application to near field optics
The generality of the Bethe's two dipole model for light diffraction through
a subwavelength aperture in a conducting plane is studied in the radiation zone
for coated conical fiber tips as those used in near field scanning optical
microscopy. In order to describe the angular radiated power of the tip
theoretically, we present a simple, analytical model for small apertures
(radius < 40 nm) based on a multipole expansion. Our model is able to reproduce
the available experimental results. It proves relatively insensitive to cone
angle and aperture radius and contains, as a first approximation, the empirical
two-dipole model proposed earlier
Enhanced transmission versus localization of a light pulse by a subwavelength metal slit: Can the pulse have both characteristics?
The existence of resonant enhanced transmission and collimation of light
waves by subwavelength slits in metal films [for example, see T.W. Ebbesen et
al., Nature (London) 391, 667 (1998) and H.J. Lezec et al., Science, 297, 820
(2002)] leads to the basic question: Can a light be enhanced and simultaneously
localized in space and time by a subwavelength slit? To address this question,
the spatial distribution of the energy flux of an ultrashort (femtosecond)
wave-packet diffracted by a subwavelength (nanometer-size) slit was analyzed by
using the conventional approach based on the Neerhoff and Mur solution of
Maxwell's equations. The results show that a light can be enhanced by orders of
magnitude and simultaneously localized in the near-field diffraction zone at
the nm- and fs-scales. Possible applications in nanophotonics are discussed.Comment: 5 figure
Enhanced Transmission of Light and Particle Waves through Subwavelength Nanoapertures by Far-Field Interference
Subwavelength aperture arrays in thin metal films can enable enhanced
transmission of light and matter (atom) waves. The phenomenon relies on
resonant excitation and interference of the plasmon or matter waves on the
metal surface. We show a new mechanism that could provide a great resonant and
nonresonant transmission enhancement of the light or de Broglie particle waves
passed through the apertures not by the surface waves, but by the constructive
interference of diffracted waves (beams generated by the apertures) at the
detector placed in the far-field zone. In contrast to other models, the
mechanism depends neither on the nature (light or matter) of the beams
(continuous waves or pulses) nor on material and shape of the multiple-beam
source (arrays of 1-D and 2-D subwavelength apertures, fibers, dipoles or
atoms). The Wood anomalies in transmission spectra of gratings, a long standing
problem in optics, follow naturally from the interference properties of our
model. The new point is the prediction of the Wood anomaly in a classical
Young-type two-source system. The new mechanism could be interpreted as a
non-quantum analog of the superradiance emission of a subwavelength ensemble of
atoms (the light power and energy scales as the number of light-sources
squared, regardless of periodicity) predicted by the well-known Dicke quantum
model.Comment: Revised version of MS presented at the Nanoelectronic Devices for
Defense and Security (NANO-DDS) Conference, 18-21 June, 2007, Washington, US
Optical control of photon tunneling through an array of nanometer scale cylindrical channels
We report first observation of photon tunneling gated by light at a different
wavelength in an artificially created array of nanometer scale cylindrical
channels in a thick gold film. Polarization properties of gated light provide
strong proof of the enhanced nonlinear optical mixing in nanometric channels
involved in the process. This suggests the possibility of building a new class
of "gated" photon tunneling devices for massive parallel all-optical signal and
image processing.Comment: 4 pages, 4 figure
Theory of imaging a photonic crystal with transmission near-field optical microscopy
While near-field scanning optical microscopy (NSOM) can provide optical
images with resolution much better than the diffraction limit, analysis and
interpretation of these images is often difficult. We present a theory of
imaging with transmission NSOM that includes the effects of tip field,
tip/sample coupling, light propagation through the sample and light collection.
We apply this theory to analyze experimental NSOM images of a nanochannel glass
(NCG) array obtained in transmission mode. The NCG is a triangular array of
dielectric rods in a dielectric glass matrix with a two-dimensional photonic
band structure. We determine the modes for the NCG photonic crystal and
simulate the observed data. The calculations show large contrast at low
numerical aperture (NA) of the collection optics and detailed structure at high
NA consistent with the observed images. We present calculations as a function
of NA to identify how the NCG photonic modes contribute to and determine the
spatial structure in these images. Calculations are presented as a function of
tip/sample position, sample index contrast and geometry, and aperture size to
identify the factors that determine image formation with transmission NSOM in
this experiment.Comment: 28 pages of ReVTex, 14 ps figures, submitted to Phys. Rev.
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