Tech Briefs Magazine - December 2023 - 28

Imaging
photocathode had to be sensitive to the
photons emitted as UV light. This design
makes our technique a stand-alone system
that can be easily integrated into various
experimental platforms, " said Liang.
Taking the picture is only the first half
of the job - it also has to be reconstructed.
To do this, the researchers developed
a new algorithm, more efficient than
standard algorithms, via their collaboration
with Boston University. Its strength
comes from a division of tasks. Rather
than solve the reconstruction problem
as a lump, the algorithm divides the reconstruction
into smaller problems that
it tackles individually.
With the innovations in both hardware
and software, UV-CUP has an imaging
speed of 0.5 trillion frames per
second. It produces videos with 1,500
frames in large format. As a light-speed
imager, UV-CUP sees flying UV photons
in real time.
Even though it is the fastest camera
in the world, the device can still be improved.
For example, the chosen photocathodes
have limited efficiency, so
researchers want to explore other types
of materials. Regarding reconstruction,
Liang said that the algorithm has greatly
improved the quality, but that it still
takes quite a long time. To increase its
speed, he is collaborating with Professor
Tiago Falk, also from INRS, on using artificial
intelligence to improve it.
The device developed through this
international collaboration will be sent
to the research laboratory SOLEIL
Synchrotron in France to visualize
physical phenomena. It could capture
laser-plasma generation, a phenomenon
that is essential for deducing certain
properties of materials, and UV
fluorescence, which is important in
medical imaging to identify biomarkers
linked to diseases.
For
more information,
communications@inrs.ca.
Optimal Information About the Invisible
A way to specifically modify the laser beam so that it delivers exactly the desired information
even in a complex, disordered environment.
TU Wien, Vienna, Austria
L
aser beams can be used to precisely
measure an object's position or
velocity. Normally, however, a clear,
unobstructed view of this object is
required - and this prerequisite
is not always satisfied. In biomedicine,
for example, structures are
examined that are embedded in an
irregular, complicated environment.
There, the laser beam is deflected,
scattered, and refracted, often making
it impossible to obtain useful
data from the measurement.
However, researchers have now
been able to show that meaningful
results can be obtained even in such
complicated environments. Indeed,
there is a way to specifically modify
the laser beam so that it delivers exactly
the desired information even
in a complex, disordered environment
- and not just approximately,
but in a physically optimal way. Nature
does not allow for more precision with
coherent laser light. The new technology
can be used in very different fields of
application, even with different types of
waves.
" You always want to achieve the best
possible measurement accuracy - that's
a central element of the natural sciences, "
said Stefan Rotter from TU Wien.
" Let's think, for example, of the huge
LIGO facility, which is being used to detect
gravitational waves. There, you send
laser beams onto a mirror, and changes
in the distance between the laser and
28
When light gets deflected by a disordered structure, it becomes
difficult to estimate where the target is located. (Image:
TU Wien)
the mirror are measured with extreme
precision. " This only works so well because
the laser beam is sent through an
ultra-high vacuum. Any disturbance, no
matter how small, must be avoided.
But what can you do when you are
dealing with disturbances that cannot be
removed? Imagine a panel of glass that
is not perfectly transparent, but rough
and unpolished like a bathroom window.
Light can pass through, but not in a
straight line. The light waves are altered
and scattered, so we can't accurately see
an object on the other side of the window
with the naked eye. The situation is
quite similar when you want to examine
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tiny objects inside biological tissue:
the disordered environment disturbs
the light beam. The simple,
regular straight laser beam then becomes
a complicated wave pattern
that is deflected in all directions.
However, if you know exactly
what the disturbing environment is
doing to the light beam, you can reverse
the situation. Then it is possible
to create a complicated wave pattern,
which gets transformed into
exactly the shape needed to correct
for the disturbances, and hits right
where it can deliver the best result.
To achieve this, you don't even
need to know exactly what the disturbances
are, it's enough to first
send a set of trial waves through the
system to study how they are
changed by the system.
The researchers developed a
mathematical procedure that can then
be used to calculate the optimal wave
from this test data. It can be shown that
for various measurements there are certain
waves that deliver maximum information
such as, for example, on the spatial
coordinates at which a certain object
is located.
Take an object that is hidden behind
a turbid pane of glass: there is an optimal
light wave that can be used to
obtain the maximum amount of information
about whether the object has
moved a little to the right or a little to
the left. This wave looks complicated
Tech Briefs, December 2023
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