Hello, and thanks for viewing our poster from WAIS Workshop 2021!
This page holds all the content that isn’t fit to print just
can’t be printed on a poster: videos, extra images, a PDF of the poster
itself, late-breaking or on-request additions… You know, all the
good stuff.
Please note that, in deference to the limited WiFi capacity in the
Algonkian, the videos below have been coded to not preload before the
play button is clicked.
###Poster
Take home your very own copy of
the
poster! (In “screen-resolution” PDF form—actual printout not
included.)
###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?
Our first foray to answering this question: freeze some tap water into
small cylinders of ice (~15 mm in diameter), laser-cut—on the same
machine!—some acrylic forms to hold these tiny ice cores over a glass
meltwater-catching plate, and try some cutting. 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 While 10.6 μm laser light can quickly and precisely
slice through ice, it cannot be efficiently carried by current optical
fibers and is produced by physically large sources involving gas-filled
glass tubes. This limits their usage to situations where you can bring
the ice to the laser, instead of the other way around. Fortunately for
boreholes, the 1.07 μm wavelength offers both very effective fiber
transmission 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 ONR, and have just begun seeing
what it can do.
Lots of people wonder what a 1 kW laser looks like. The answer:
disappointingly not mad-sciencey, but encouragingly
portable-looking—fits nicely in a computer server box. 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.
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.
A very similar sample cut, viewed from a different angle.
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 reflection strays where it
shouldn’t.) This camera doesn’t do any favors for image quality, but it
does allow us to get views from interesting angles, such as sitting
directly above the laser collimator. Bonus: this sensor sees the
near-infrared laser as a purplish light.
A webcam shot from the other side of the sample, looking (almost) back
into the laser.
One more 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.
A disc of ice, about 2 inches in diameter and around 5 mm thick, with a
fresh Nd:YAG laser-cut slice traveling outward from a previously
laser-drilled hole. This cut was recorded as about 1.5 mm wide, slightly
larger than the diameter of the beam, although the room-temperature
conditions around this experiment made precise measurement difficult.
###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. (We are also investigating other more complex options
to emulate brittle ice’s internal forces.)
Two Pt1000 resistive temperature devices 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 later 3D-printed freeze-in
holders, so their positions are only approximately known.)
A tap-water core, frozen in a mold that establishes a channel down its
center axis, develops internal fractures over several minutes as its
cavity is flooded with liquid nitrogen. Video is 15x actual speed.
###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! 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 bit more flexible than most
PLA/PETG printing materials; many of our designs take advantage of this
low rigidity, so we don’t often test them in different materials. If you
do, please let us know how they do!)
