72 research outputs found
Near-field diffraction of fs and sub-fs pulses: super-resolutions of NSOM in space and time
The near-field diffraction of fs and sub-fs light pulses by nm-size slit-type
apertures and its implication for near-field scanning optical microscopy (NSOM)
is analyzed. The amplitude distributions of the diffracted wave-packets having
the central wavelengths in the visible spectral region are found by using the
Neerhoff and Mur coupled integral equations, which are solved numerically for
each Fourier's component of the wave-packet. In the case of fs pulses, the
duration and transverse dimensions of the diffracted pulse remain practically
the same as that of the input pulse. This demonstrates feasibility of the NSOM
in which a fs pulse is used to provide the fs temporal resolution together with
nm-scale spatial resolution. In the sub-fs domain, the Fourier spectrum of the
transmitted pulse experiences a considerable narrowing that leads to the
increase of the pulse duration in a few times. This imposes a limit on the
simultaneous resolutions in time and space.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
Diffraction-free subwavelength-beam optics
Diffraction is a fundamental property of light propagation. Owing to this
phenomenon,light diffracts out in all directions when it passes through a
subwavelength slit.This imposes a fundamental limit on the transverse size of a
light beam at a given distance from the aperture. We show that a
subwavelength-sized beam propagating without diffractive broadening can be
produced in free space by the constructive interference of multiple beams of a
Fresnel source of the respective high-refraction-index waveguide. Moreover, it
is shown that such a source can be constructed not only for continuous waves,
but also for ultra-short (near single-cycle) pulses. The results theoretically
demonstrate the feasibility of completely diffraction-free subwavelength-beam
optics, for both continuous waves and ultra-short pulses. The approach extends
operation of the near-field subwavelength-beam optics, such as near-field
scanning optical microscopy and spectroscopy,to the "not-too-distant" field
regime (0.5 to about 10 wavelengths).Comment: 4 figure
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