5 research outputs found
On the normality of -ary bent functions
Depending on the parity of and the regularity of a bent function from
to , can be affine on a subspace of dimension
at most , or . We point out that many -ary bent
functions take on this bound, and it seems not easy to find examples for which
one can show a different behaviour. This resembles the situation for Boolean
bent functions of which many are (weakly) -normal, i.e. affine on a
-dimensional subspace. However applying an algorithm by Canteaut et.al.,
some Boolean bent functions were shown to be not - normal. We develop an
algorithm for testing normality for functions from to . Applying the algorithm, for some bent functions in small dimension we
show that they do not take on the bound on normality. Applying direct sum of
functions this yields bent functions with this property in infinitely many
dimensions.Comment: 13 page
Wave Front Sensing and Correction Using Spatial Modulation and Digitally Enhanced Heterodyne Interferometry
This thesis is about light. Specifically it explores a new way
sensing the spatial distribution
of amplitude and phase across the wavefront of a propagating
laser. It uses spatial
light modulators to tag spatially distinct regions of the beam, a
single diode to collect
the resulting light and digitally enhanced heterodyne
interferometry to decode the phase
and amplitude information across the wavefront. It also
demonstrates how using these
methods can be used to maximise the transmission of light through
a cavity and shows
how minor aberrations in the beam can be corrected in real time.
Finally it demonstrate
the preferential transmission of higher order modes.
Wavefront sensing is becoming increasingly important as the
demands on modern interferometers
increase. Land based systems such as the Laser Interferometer
Gravitational-Wave
Observatory (LIGO) use it to maximise the amount of power in the
arm cavities during
operation and reduce noise, while space based missions such as
the Laser Interferometer
Space Antenna (LISA) will use it to align distant partner
satellites and ensure that the
maximum amount of signal is exchanged. Conventionally wavefront
sensing is accomplished
using either Hartmann Sensors or multi-element diodes. These are
well proven
and very effective techniques but bring with them a number of
well understood limitations.
Critically, while they can map a wavefront in detail, they are
strictly sensors and
can do nothing to correct it.
Our new technique is based on a single-element photo-diode and
the spatial modulation
of the local oscillator beam. We encode orthogonal codes
spatially onto this light and use
these to separate the phases and amplitudes of different parts of
the signal beam in post
processing. This technique shifts complexity from the optical
hardware into deterministic
digital signal processing. Notably, the use of a single analogue
channel (photo-diode,
connections and analogue to digital converter) avoids some
low-frequency error sources.
The technique can also sense the wavefront phase at many points,
limited only by the
number of actuators on the spatial light modulator in contrast to
the standard 4 points
from a quadrant photo-diode. For ground-based systems, our
technique could be used to
identify and eliminate higher-order modes, while, for space-based
systems, it provides a
measure of wavefront tilt which is less susceptible to low
frequency noise.
In the future it may be possible to couple the technique with an
artificial intelligence
engine to automate more of the beam alignment process in
arrangements involving multiple
cavities, preferentially select (or reject) specific higher order
modes and start to reduce
the burgeoning requirements for human control of these complex
instruments