Pyramid Schemes & Piston Dreams

For about a year, Laird, Alex H., and I have been putting together the protoype-High Contrast Adaptive Optics Testbed (P-HCAT). P-HCAT sent half of the simulated GMT pupil to the “Holey Mirror” which, as the name suggests, is a mirror with a hole in it.

Holey Mirror

The holey mirror is able to simulate a piston differential with a piezo-controlled mirror sticking through the hole. This light was sent into MagAO-X and the PyWFS was used to sense piston. The next phase of the project was adding post-doc Sebastiaan Haffert’s Holographic Dispersed Fringe Sensor into MagAO-X. This 1″ optic is able to interfere each segment of the GMT pupil with another then disperse them so we can back out the piston differentials. We got some very interesting results we plan on sharing in some upcoming papers!

P-HCAT aligned, not sending light into MagAO-X through the hole in the wall, but rather to a Basler science camera via a fold mirror

The next step is to convert P-HCAT into simply HCAT. This new and improved version will have a concept known as the “parallel DM.” This involves sending the entire GMT pupil onto a reflective 6-sided pyramid, a hexpyramid, which will send the light to 6 separate deformable mirrors. The central segment will pass through a hole in the center of the pyramid.


Manufacturing a hexpyramid with a central hole is no small feat. We are super excited to finally have our hexpyramid in the lab and ready to play with. This week we put it in front of an interferometer to check surface quality. To mount an optic this complex you need to be creative to say the least. See our makeshift mount below. We are happy to note the pyramid is very photogenic – it doesn’t have a bad side!

Hexpyramid mounted in front of interferometer

Piston Control is a fantastic mode of risk reduction for the Giant Magellan Telescope and we are so happy we get to be a part of this effort!

Zweetkamertje—or—Congratulations Dr. Van Gorkom!

Our Dutch postdoc Sebastiaan Haffert has taught us many important terms (like “We at Toilet Duck recommend Toilet Duck!”), but the one most relevant today is zweetkamertje. As explained by Atlas Obscura, this is the “sweating room” where Ph.D. candidates in Leiden await the results of their doctoral exams.

This draft is being written (in part) during the sweating period of Kyle Van Gorkom’s Ph.D. defense.

But let’s back up a bit: Today, a pandemic-appropriate number of masked people filed in to Meinel 812 (and a much larger people joined online) to see Kyle Van Gorkom defend his Ph.D. research in adaptive optics. The view was excellent, but Jhen and Daewook had eyes only for Kyle.

Some pretty sweet mountains, you might say.

Mr. Van Gorkom (as he was then known) regaled us with tales of deformable mirror characterization and modeling. Battles won, vibrational modes damped, etc. (We will not talk about the IrisAO.)

The room was then closed for the committee to thoroughly examine him. We waited. Some of us blogged. Then, after some ritual hazing questioning, he was presented to us: Dr. Kyle Van Gorkom, Ph.D.!

A toast was called for.

The final test of the candidate is whether they can open a bottle of champagne. We are happy to report that he passed this as well, despite Susana’s evident skepticism.

And, after some initial difficulties, a toast was had! Congratulations, Dr. Kyle Van Gorkom!

Song of the Day

“Someday” by The Strokes

Orbital Mechanics Trivia

As a viscacha, integral and differential calculus are beyond me. However, it does seem to be spring again here in the southern hemisphere, and my calendar indicates it has been one full year since the last October 14th we saw.

(I’d double-check my facts with some of the cientificos, but I haven’t seen them in a couple years. I hope they’re doing okay.)

This means that the Earth has completed one more turn about the Sun, and the P.I. is a year older and wiser. In celebration of his wisdom, please enjoy P.I. utterances, available where-ever fine quotes are sold.

Song of the day

“Hard to Kill” by Bleached

Happy 5 Year Anniversary, CACTI!

Today is the Autumnal Equinox, the official end of summer and the start of autumn in the northern hemisphere. Autumn doesn’t really mean much here in Tucson, except our days of constant 100+F heat is waning down. (This does not barricade me from getting a PSL.) A more important date is 8 days away on September 30, which is the end of monsoon season in Tucson. Currently, we are at the 3rd wettest monsoon season this summer, a welcome break from last year’s missing monsoons.

Accumulated precipitation record for Tucson 2021. According to National Weather Service, this is the 3rd wettest monsoon summer in Tucson history! (Plot: National Weather Service)

While the Autumnal Equinox is a pretty neat phenomena that can be explained by any Astronomy graduate student at Steward Observatory, we have an additional event deserving a celebration: today is the 5th year anniversary of the arrival of the CACTI testbed in the XWCL!

For the uninitiated, CACTI stands for Comprehensive Adaptive optics and Coronagraph Test Instrument. CACTI is XWCL’s AO simulator testbed where we can tack on and swap components for testing and developing projects (particularly for many of XWCL’s optics graduate students’ PhD dissertations).The initial incarnation of CACTI was used to develop Kelsey’s dissertation on Linear Dark Field Control. The current version of CACTI began as the AO simulator of Lauren’s 3PyWFS dissertation project. At the moment, CACTI is serving several projects such as my laboratory demonstration for a cubesat laser guide star, Alex R’s demo of the differential Optical Transfer Function WFS, Sebastiaan and Meghan’s optical differential wavefront sensor, and Avalon’s Basler camera characterization. CACTI has endless capabilities, with only physical space and laboratory time as the limits.

To celebrate CACTI’s 5 year anniversary, let’s take a walk down memory lane to see CACTI’s evolution.

The CACTI table was moved from room N431 to the XWCL space in room 265. It was this instance where we learned we could not use regular movers for relocating an optical table. Instead, we required riggers who have access to a crane to lift and move the optical table. Though Jared was absent for much of the moving process picking up a pallet with Alex R, Dr. Kelsey Miller was able to record some of the process.

Sept 22, 2016: CACTI now in 265, horray! (Photo: Dr. Kelsey Miller)

To prepare CACTI’s table placement, we used masking tape to set up locations where the table legs would be positioned such that the table would be balanced when craned down. However, no matter how well we measured and allocated tolerance regions, some table legs needed to go elsewhere.

Sept 22, 2016: A legend in the making, never to be forgotten.

These days, when you walk into XWCL, it’s packed to the brim. Some walking areas are only wide enough for a computer rack to pass through. It’s hard to believe that once upon a time, the XWCL consisted of the CACTI optical table, a few desks, and a bunch of shelves. It was also a time when Beast still did stuff.

Over the course of a year, the XWCL room started filling up more and more. This includes CACTI’s journey of upgrades. The first major CACTI facelift was the BMC 1K’s new air pressure chamber. Justin worked diligently through many different designs. The first prototype was a tupperware with a hole cut out for a window chamber. It eventually converged to the current chamber, custom built with holes for cable routing and an entrance for pumping in dry air.

In summer 2017, CACTI was graced with a new addition: the Zygo Verifire Fizeau interferometer. It was promptly parked onto CACTI, along with the first and only Windows machine in XWCL.

June 27, 2017: The Zygo Verifire is free for use for all CAAO-related projects.

The Zygo Verifire has been an interesting learning experience. Beyond measuring and characterizing deformable mirrors, flat mirrors, and various LBTI hardware, it has bricked twice. Alex R and I tried to hook up the Zygo computer to the internet, only to brick the software because the ethernet port was for communicating between the interferometer and computer. We spent 2 hours on the phone with a Zygo engineer, who eventually stepped us through fixing the settings so we could connect the Zygo computer to the internet. Kyle, Kelsey, and I discovered together one afternoon that the Zygo uses Basler cameras. We installed our Basler cameras’ software on the Zygo machine, only for the software to stop working because the installation overwrote the required Zygo version. Luckily, we were able to revert to a recent, old Windows version state and undo our errors. Despite these unexpected inconveniences, the Zygo Verifire has been the backbone to very important work.

Sept 20, 2017: How to fix the Zygo. (Photo: Alex Rodack)

Soon enough, a new neighbor moved in next to CACTI: MagAO-X! After passing PDR in May 2017, MagAO-X began building in XWCL. The first thing assembled was the portable clean room, which arrived in July 2017.

July 26, 2017: Alex R (left) and Dr. Kelsey Miller (right) showcasing the newly built portable clean room. (Photo: Dr. Jared Males)

The arrival of the clean room meant moving furniture around in the lab.

July 14, 2017: Dr. Justin Knight shows us there is plenty of space behind the shelves for storage. (Photo: Alex Rodack)

From the get-go, the MagAO-X cleanroom was designed for portability that could fit above CACTI with minimal fuss. Early on, we identified the air ducts and lights needed to be moved and replaced so the clean room can properly fit above CACTI. That was something that got fixed.

The next major CACTI upgrade was installing blackout curtains around the table. This helps considerably when an experiment is light sensitive. The curtains have allowed simultaneous non-CACTI laboratory work with the ceiling lights on while minimizing external source disturbance during data collection. Along the way, we learned that a top curtain was essential for an occasional ceiling pipe leak. We store all the DM drivers at the top shelf that a water leak on these electronics will destroy them. These electronics are not easily replaceable, particularly the IrisAO driver!

Oct 20, 2017: MagAO-X cleanroom with legs in foreground, CACTI with full blackout curtains in background.
Nov 14, 2019: Two years later, the air duct construction has its moment to shine. The adjusted ducts and lights, and the cleanroom moved over CACTI while MagAO-X and the team are in Chile. (Photo: Alex Rodack)

In 2019, Lauren and I designed an upgraded CACTI with custom lambda/10 OAP mirrors. In December 2019, we received the new OAPs and dismantled the original CACTI. We began building the new CACTI in January 2020. However, the pandemic hit halfway through our build process. Nevertheless, Lauren heroically trucked on and completed building CACTI in summer 2020 just in time to integrate the 3PyWFS from HartSci. In May 2021, Dr. Lauren Schatz finished her PhD using CACTI and the 3PyWFS was shipped out a month later.

Sept. 22, 2021: CACTI in its current form

CACTI continues to get lots of action in the lab. Open spaces on the testbed get used for small testing experiments. I’ve since added a secondary source to CACTI for my laboratory demonstration of LGS. Alex R and I have worked out a procedure for swapping the IrisAO segmented DM in and out of a pupil plane that can be done solo in less than 1 hour. Joseph, Lauren, and I wrote CACTI’s testbed operation entry in the MagAO-X handbook as a localized resource for users, to which I update regularly. Since CACTI utilizes a customized version of the MagAO-X control code, it also has the capability of being operated remotely. There are a few limitations though, such as the IrisAO DM driver power button requiring a physical button push.

Despite XWCL and CACTI’s evolution through the years, there remains one constant: the masking tape continues to hang out underneath the table leg.

Sept. 22, 2021: Masking tape under CACTI table leg. The excess has been cut off since the fateful placement 5 years ago, but it’s still there if you look closely.

Happy 5th anniversary, CACTI! Here’s to many more years of new development, more dissertations to feed into, and everlasting masking tape under the table legs.

With lots of love,

Jhen and Alex R

Song of the day

Given the focus on the desert (CACTI,  rain, and Tucson), and our love for a connection to space/astronomy, we pick a song by Tucson’s own Calexico, who have been making their unique brand of “desert noir” rock since the mid 90’s. This particular song was picked by Rep. Gabby Giffords to be played in space on June 13, 2008, on the Space Shuttle Discovery as the wake up call for the crew including her husband (and current AZ Senator) Mark Kelly.

Calexico, “Crystal Frontier”

And let us never forget, at XWCL,

The XWCL motto

Desert Hackberry Pie: A Perilous Quest

This is a recipe post in the traditional internet style.

Part I: The Rains

We have had a fairly incredible monsoon season. It just keeps raining and raining here in Tucson, and everything around us is enjoying it. Since this is a science blog, we should start with evidence for these assertions.

The plot shows our last 2.8 years of rain according to our backyard rain gauge. This year, we have had two months which individually exceed all of 2020. Combined those two months exceed all of 2019. And it might not be over.

My house is at the outlet of Ventana Canyon, and the Ventana Wash runs through our backyard. These next two videos are from a game camera we use to monitor the various goings on back there. The first one shows one of our neighborhood bobcats trotting by, with the wash down to just a trickle:

We can go several months at a time with at least some water flowing. Since the Bighorn Fire last year, the flow has gotten exceptionally strong at times due to the increased runoff. Next is just a day or so after the bobcat video, showing what happens after an inch of rain falls in the canyon (same camera, same spot):

Now all of this rain has led to an abundance of rainbows and a wonderful lushness to our desert foliage.

The view towards Sabino Canyon. At left is a big old Mesquite Tree, right (light green) is a very happy Palo Verde tree. In the middle of the frame is the star of this blog post: a thicket of Desert Hackberry.

Part II: The Hackberry

We have two big bushes, and one thicket with several bushes, of Desert Hackberry. Here’s a view from the back of the thicket in the previous snap:

I’ll send you over to the Arizonensis page to learn more about the natural history of this plant. The main takeaway is that you can eat the berries, but I also noticed the butterflies. I actually witnessed the butterfly combat described, and hanging out around the thicket was lovely:

You can hear the running water in the background.

This is the first year we even noticed the berries, and we have TONS. So of course I decided to start picking and, well, we’ll get to that.

Hackberry harvesting. Note the toes.

The above picture shows the fruits of my labor, mid-harvest. This much takes about 30 minutes. We have a saying in our house: “Everything outside wants to kill you, even the plants.” The hackberry is no exception. Thorny, and the berries tend to be embedded behind small twigs and the thorns.

So I ended up spending about 4 hours on labor day afternoon, sun on my back, butterflies flitting about (and fighting), the wash running next to me, picking hackberries. It was wonderful!

Part III: The Guardian

After my wonderful nature-full day, I decided to do a little maintenance in the back yard. The Hackberry thicket tends to get a little overgrown, and I have trimmed it back a few times to keep the lower parts under control. This time I also had in mind that I was now an expert Hackberry picker, and wanted to optimize things.

So I grabbed my big pruning shears and my nata tool and set to work. I had gotten a good chunk out, and was getting down low to go under to cut from the inside out a bit. I stuck the shears in to get a big branch and . . . MONKEY BRAIN CIRCUITS ENGAGED. JUMP JUMP JUMP was the response from my brain as my highly tuned image processing CNN took over when my eyes focused on this:

The biggest freaking diamondback I have yet to interact with personally. Hackberries for scale, and to document how long she was there!

She (I’m going with she) is absolutely gorgeous, and please note just how well camouflaged. And gorged! Her mid region (under the head) looks very bulging, so I’m guessing one of the bunnies that triggers the trail camera frequently is no more. She was also super chill, no rattle, just flicked the tongue and watched.

Here’s the thing: I was within 1 meter of her for several hours. My bare, flip-flopped feet were maybe closer depending on the lay of various branches. She never made a peep, and could have easily struck many times. I feel like I was judged worthy. Or maybe she was just too sleepy to care…

Interlude and Song of the Day

Part IV: The Pie (Finally)

So after all that picking, I next had to clean. Luckily it turns out Hackberries sink. So a water bath for about 1 cup at a time allows lots of the twig and leaf matter to float and be strained out. They are also just large enough that a standard slotted spoon works as a strainer. Perhaps the most tedious part was berry-by-berry inspection to get residual stems off.

After all that, I had a little more than 4 cups of Desert Hackberries!

My harvest.

Now what to do? The internet was not super helpful. Some discussion of foraging and eating them while hiking, a few hints at making energy bars and wine, but nothing really satisfying.

The berries have a hard pit, but you can crunch it and eat it. The taste is complicated: sweet, but with a sort-of green apple + green tea aftertaste or bite (I’m not sure that’s right, but it’s hard to describe). I decided that I wanted to get the pits out, and after a bit of kitchen lab work, found that our food processor handled this perfectly:

in motion

and a salad strainer worked perfectly to drain:


and in the end about 4 cups of berries made 2.25 cups of berry pulp:

The juice that was worth it

Well great. Now we have 2.25 cups of Hackberry pulp but still no clear direction. So we decided to try a blueberry pie recipe because what the hell. It was a bit of a meander, I document it here for posterity.

2.25 cups Desert Hackberry pulp (about 4 cups whole berries)

1/3 cup granulated sugar

2 tbsp tapioca flour to thicken (or corn starch)

1/3 tsp salt (cut in half next time)

1/3 tsp cinnamon (tasted like too much before baking, maybe ok after. TBC)

1 tbsp lemon juice. this is common in blueberry pie, but did NOT work here.

1/3 cup granulated sugar (to counteract the lemon juice)

Note: error bars on the above quantities are estimated at +/- 5% unless otherwise specified.

This will fill one small pie pan:

Finally, I dotted the pie with 1 tbsp of butter chopped into flakes. Then baked at 375 for 50 minutes. And here’s the result:

That’s supposed to be a Saguaro.

Verdict: it was ok! We had a friend over, the one who first told us about Hackberries in fact!, and went for it `a la mode. Vaguely pumpkin pie in texture and smell. The cinnamon was a little overdone. The main challenge is to figure out what to do with the green-apple/green-tea aftertaste I described in the fresh berries. I’ve decided that, based on the lemon juice mistake, that the issue might be being to acidic. So note for next time: try adding some baking soda to knock it down.

Plan for next time is to: (1) inspect under all bushes thoroughly and (2) make small batches in ramekins to experiment with different buffers and spices.


It’s now been a couple days and I’m eating the last piece. Also my fingers have started to heal from the thorns, but a few splinters are still working their way out. The pie is still good. I def think the baking soda is worth a shot. I feel like I’m on to something, this might be the pumpkin pie of the Sonoran Desert!

I’ve also been thinking about the snake, a lot. That was quite a scare, and frankly I’m still a bit jumpy outside. But also, we interact with them fairly often up here in the hills. I encounter them when on runs, crossing our driveway, and we had one in our compost bin once. Only one time have I heard the rattle, and that was from a baby that I was chasing away from our front door with a looooooong pole. There’s this idea that rattlesnakes are evolving to rattle less, but I’m skeptical. She wasn’t scared and not rattling because I might hurt her, she just didn’t care. I leave you with this link, and note that “peaceful sighting” is a great way to describe this: Are rattlesnakes evolving to rattle less, or losing their rattles?