Hello, and thanks for viewing our poster–in-person or virtual–from
the 2021 AGU Fall Meeting. This page holds videos, extra images, a PDF
of the poster itself, excess snark, late-breaking or on-request
additions… It’s like iPosters, but easy to use!
Please note that, due to a very crowded convention center WiFi and
the possibility of phones on cellular data, these videos have been set
to not preload.
###Poster
Take home your very own "screen resolution" copy of
the
poster! Sorry, no free pens. Maybe next year.
###Wavelength throwdown ####10.6 μm laser They’re a common sight in
architecture modeling studios, makerspaces, and other workshops: Universal
Laser Systems’ laser cutters, which use a CO2
laser—emitting around 100 watts of 10.6 μm light—to etch glass and cut
thin sheets of plastic, wood, and cardboard. Which inevitably raises the
question: what could they do to ice?
Well, they can behead tiny ice cores. To be precise: tap-water ice
cylinders ~15 mm in diameter, held in acrylic forms (laser-cut on the
same machine!) over a glass meltwater-catching plate. This video was
taken in slow motion by a somewhat focus-challenged camera sitting on
the cutting bed.
A second slice, this time shown at normal speed by a camera looking
through the laser cutter’s glass lid. This ice sample was toted to the
cutter in a liquid nitrogen cooler, which cuts down on the melting but
also causes aggressive frosting. The blue-tipped glass slide serves as a
sacrificial beam stop.
The extremely short penetration depth of this long-wavelength light is
demonstrated by cutting a Minnesota M logo out of a flat disc of ice a
few millimeters thick.
####1.07 μm laser Okay, so 10.6 μm laser light can quickly and
precisely slice through ice. Problem is, it cannot be efficiently
carried by the glass optical fibers so well-developed by the telecom
industry–materials such as polycrystalline AgCl can transmit it, but
very lossily and at hundreds of dollars for each fragile meter–and is
produced by physically large sources involving gas-filled glass tubes.
Compare this to the 1.07 μm wavelength’s stunningly effective fiber
transmission—retaining well over 80% of initial power over a
kilometer—and a wealth of economical high-power fiber lasers.
We have this past summer acquired a 1.07 μm fiber laser with a 1 kW
power capability, jointly supported by NSF and DE-JTO/ONR, and have just
begun seeing what it can do.
Lots of people wonder what a 1 kW laser source looks like. Ours is not
very mad-sciencey, and more like a nicely-portable 4U server. The fiber
optic cable delivering the laser emerges from the rear of this unit. The
bigger thing at the bottom of the rack is a water-cooling unit for
room-temperature environments.
A rectangular rod of tap-water ice, about 1 inch on each side, is moved
downward at 2.5 mm/sec through a 550 W beam of 1.07 μm CW laser light.
The ice starts out somewhere north of -20 °C and is experimented on in
room temperature, which doesn’t help limit the rate of meltwater
production.
We use inexpensive webcams with laser-reflecting filters for monitoring
the experiment (while we, the operators, hide behind a big
laser-blocking object, just in case a scattered beam strays where it
shouldn’t.) This camera doesn’t do any favors for image quality, but it
does get views from interesting angles, such as looking (almost) back
into the laser.. Bonus: this sensor sees the near-infrared laser as a
purplish light.
Another webcam shot, this time looking downward from the top of the
vertical motion stage that moves the ice sample downward to cross the
cutting beam.
###Wedges and… not wedges
A prototype two-axis motion rig—one rotation stage and one linear
stage—carves a wedge out of a short 3" diameter tap-water ice core.
Video is 15x actual speed, because the rig is a bit wobbly. It’s a work
in progress…
All work and no play makes Jack a dull motion rig, so here’s the same
setup carving a UMN logo. Video is 10x actual speed.
The resulting logo, lovingly if unskillfully photographed. The cutting
rig used just one focusing lens here due to current space constraints,
which are being addressed alongside the wobbliness.
###LN2, ice, and acoustic sensors If brittle ice will not
come to the lab, then we must bring the lab to the brittle ice—or just
make some tap-water ice brittle. Applying an extreme temperature
gradient to an artificial core using liquid nitrogen, plumbed through a
hollow center channel molded into the sample, seems to very effectively
create fractures.
Remember playing with these little buzzer/microphone parts as a kid?
They’re baaaaaack! Two piezoelectric transducers, facing opposite
directions, frozen into an artificial ice core in its PVC mold.
A tap-water core, frozen in a mold that puts a hollow channel down its
center axis, develops internal fractures over several minutes as its
cavity is flooded with liquid nitrogen. This kills the ice core. 🦀
Video is 15x actual speed.
Data from two Pt1000 resistive temperature devices (RTDs) frozen into a
tap-water core, one within 0.5 inches from the wall of the core’s center
channel and the other about 1 inch farther away, read a ~30 °C radial
temperature difference upon filling the channel with liquid nitrogen.
(Unfortunately these RTDs were placed without the aid of our new
3D-printed freeze-in holders, so their positions are only approximately
known.)
###3D printed parts
Some of our rapidly-proliferating custom lab accessories, designed and
3D-printed in-house at UMN.
You might have noticed a number of black plastic parts holding our
samples, mounting our laser collimator, getting frozen into our
tap-water cores… You get the drift. We designed and 3D printed these
parts to meet our needs, and if any of them look like they might meet
your needs, then our parts are your parts! (Think of this as
swag.) We’ve uploaded a few to YouMagine, a site
for open-source 3D print designs. If you’re looking for one that isn’t
there, just ask!
Technical note: we print most of our parts from Markforged Onyx, a nylon material with
micro carbon fiber bits and optional Kevlar reinforcement layers.
Without the reinforcement, Onyx is a lot less rigid than most PLA/PETG
printing materials; many of our designs take advantage of this
flexibility, so we don’t often test them in different materials. If you
do, please let us know how they work out!
