We have presented a novel substrate-based neutral atom
waveguide, based on the optical dipole force,
which combines the features of a planar far-detuned two-color evanescent
trap[156] with the ability
to confine strongly along two axes.
We utilized
the differing vertical decay lengths
of the two
bound-mode polarizations
of a submicron-sized optical waveguide near cut-off.
We have shown that only a few milliwatts of guided laser power
can create atomic potential depths K with
transverse oscillation frequencies
kHz,
a coherence time
ms and a trap minimum 200-400nm above the optical guide surface,
for Cs atoms in the
state.
Laser powers greater than ten milliwatts
can give a transverse mode spacing greater than
the temperature of a Cs MOT, opening up the single-mode waveguide regime.
The advantages of guiding optical trapping fields on a substrate include
mechanical stability and reliability, mass production and the potential for
transport along complicated paths.
We have given
some design criteria for guided-lightwave two-color
atom waveguides (chiefly the maximization of the evanescent
decay lengths, and of their normalized difference ),
and shown that a substrate of low refractive
index can be very beneficial.
We modelled in detail the trapping potentials
for a general rectangular guide of index 1.56
above a unity-index substrate, and
have shown that a realistic substrate choice of index
1.32 poses few problems to the viability of the device.
We predict that the
effect of the surface interaction is generally small, and that
coherent guiding is possible around corners of radii
mm for a
longitudinal velocity
ms
.
We also believe that the magnetic part of the potential
felt by nonzero
atoms could be used to increase the depth and oscillation
frequencies further.
This preliminary work (specifically equation (8.10)) indicates
that utilizing detunings much larger than the 15nm we
limit ouselves to
here will be very advantageous for coherent guiding.
We have only scratched the surface of the design variations
possible; for instance, equalizing the horizontal
and vertical oscillation frequencies is yet to be attempted.
The use of two polarizations is our solution to the problem
of maximizing when the detuning is very small compared to the
wavelength, but we suspect that there will exist other fruitful schemes
where these are comparable (
, very far-detuning)
and where a large
is caused simply by the different optical
cut-off conditions at the two wavelengths.
We have reserved investigation of cooling schemes for future work (although
this has already been demonstrated in an EW mirror[61]
and proposed
in EW traps[157,62]).
We believe that the
potential shapes capable of being produced by guided waves on a substrate
also include the possibility of funnel-type loading schemes and
coherent atom couplers, allowing for a complete ``integrated''
atom-optical experiment on a substrate.