Author: Warren Foster

[A peek behind the sausage factory curtain of blog ops: There was a brief moment on Friday night when I could have written this post but decided to go to sleep instead. 36 hours later, I am frenetically making up on lost time from the courtyard of a hostel in the Bellavista neighborhood of Santiago. The hostel has Wifi but doesn’t allow me to connect to Slack, so I can’t post photos of most things I’m writing about. Sorry.]

After our final dinner on the mountain, were joined by the resident electrical engineer to consult about finding a resistor for the cam LLOWFS shutter that we installed earlier this week. “I know it’s Friday evening”, Jared said, “but is it possible to do this tonight?” “Every day is the same here,” Pato replied. “Except for Sundays, when there are empanadas.”

Ninety minutes later we had a working shutter and a satisfied PI. “That’s a nice small victory at the end of the trip.” There were several frustrations, setbacks and difficulties with this engineering run. Good progress was made however across the board, and I think that all of us left the mountain feeling satisfied about the time spent through the process.

The main reason why I went to LCO this October was to overhaul the PIAA (phase induced amplitude apodization) system so that it could be used without needing alignment on-sky. The system consists of four lenses which need to be immaculately aligned with respect to each other. Relative translations of as little as 10um between lenses cause dramatic PSF degradation, meaning that previous runs required opening up the system after coupling to the telescope, and gingerly turning hand-knobs while squinting at a lagging video feed of starlight. No combination of the Thorlabs or Newport catalogues carried actuated lens assemblies that could provide this level of two-axis remote alignment, so we decided to machine picomotor interfaces into the existing cage plates that we’d been using to hold our optics. Getting the rough optomechanics to work with the old design did have some difficulties, and scientists that enjoy playing “find the shim” will see one in an unexpected place. After the system was installed and controllable with a slick new GUI, however, the stressful alignment process that used to take half a day could repeatedly dialed in within 30 minutes. It was, as Maggie said yesterday, a deeply therapeutic experience.

After finishing my work and taking some lab-data testing the extinction of the laser source, we were ready to start buttoning up the system and getting the lab ready for the observing run in some four weeks time. While Jared and Jay developed the checklist required for the first sans-PI run in MagAO-X history, I spent a thoroughly enjoyable hour cleaning the lab and organizing the piecemeal Allen key sets that had been OCD annoyances over the past week. Although I was not successful in the dream of “every key for every set”, and although our box of misfit keys continues to grow, I hope that the next run will be able to kick off with a fresh, organized start. A big part of the run turned out to be giving MagAO-X the TLC that can be often delayed by urgent actions or on-sky timelines. Maggie did excellent work in re-routing cables to clean up chaotic areas and provide a modicum of organization to an optical bench that can otherwise appear to be bursting at the seams. Although these changes may not be obvious to someone looking at the system afresh, we hope that it will lead to better, more productive and less stressful work going forward.

[Now, a brief aside for the flora of Las Campanas Observatory]

This was a very special trip for me because I thought that, when leaving the mountain in March 2023, that I wouldn’t return to LCO after graduating. Amid the satisfaction of good progress in the work here, I have equally enjoyed seeing the mountain with new eyes. Since my last time here, I’ve learned quite a lot about native Sonoran desert plants and was very interested to see similarities with the flora of LCO. The plants here cope with even harsher conditions than Tucson, and the mountain in general is very overgrazed by marauding hordes of goats. Most drought-tolerance adaptions used by Sonoran desert plant can also be seen with the plants as Las Campanas.

I’d like to highlight one LCO plant in particular that I recognized immediately from its Tucson counterparts. This is Lycium minutifolium, literally “Tiny-leaved thornbush”, that grows around the hillsides of LCO. There is a beautiful, massive specimen that grows next to the hotel rooms we usually stay at near the lodge. We have several family members of the Lycium family around in the Sonoran desert, including L. fremontii and L. berlanderi. Their fruit is related to a gogi berry (L. chinense) and is considered a “superfood” often used as a dietary supplement. The genus is in the nightshade (tomato/potato) family. They are also beloved by a huge range of birds, who eat their fruits and take shelter in their dense thickets.

The Lycium species in Tucson have several drought-tolerant characteristics including small, fleshy leaves that drop during periods of dry weather. Although the bushes seem to be covered with thorns, these are actually leafless branches that taper to points. One of the main ways to identify species in Tucson is to “shake hands” with the plant: different species have dramatically different pointy ends and leaves. Some species that grow in less stressful conditions can feel soft to the touch.

By comparison, the Lycium at LCO is a thornbush on steroids. Its leaves are an order of magnitude smaller than the Sonoran desert plants, meaning that it loses less water through transpiration. Its pointy branches can basically be considered a middle finger to the world, saying “come and try to eat me”. They are incredibly sharp and strong, even compared to the unfriendly variants that grow in Arizona. Because of this, they remain one of the only bushes that keep their leaves amid the grazing pressure from goats and donkeys. All together, the plant is a very interesting reflection of the different challenges and pressures of the Chilean desert compared to the Sonoran.

Left: L. minutifolium at LCO. Right: L. pallidium at Petrified Forest National Park

Song of the day

If you only listen to one song I ever recommend on the XWCL blog, it should be this one. It comes from my favorite album of the 2010s: “Age of Adz” by Sufjan Stevens. This song is the final track on the album, it is 25 minutes long and it is a masterpiece. Listen to it when you are driving in the car. It goes through the full range of human emotion and some day I will find a party where we can dance all the way through it. I remember listening it to the first time when I was 18, driving under the St. Johns bridge in Portland and not believing that it could change musical passages yet again. I remember listening to it while driving through eastern Maryland in Fall 2019, stuck in traffic and dancing in my seat. And now, I will remember listening to it while walking up to the cleanroom at LCO, 18 minutes deep and thinking that I need to take an extra lap so that it can finish before I get back to work. I hope you might enjoy it as well.

Walking back in the dark with Jay tonight under quiet stars, I remarked that “even though I arrived yesterday it already feels like a week, but in a good way.” Long days can do that – leaving the cleanroom at 12:00am was pushing well into our sixteenth hour of work. Time in general though has a more, ethereal quality on top of the mountain. It can be hard to remember that life continues outside of the immediate challenges of the day, and that every day before now hasn’t been just like this one.

The main goal for today was to align the LLOWFS – this is Lyot Low Order Wavefront Sensor or “YO-FUSS” using the Spanish pronunciation. When paired with a transmissive coronagraph, rejected light from the Lyot stop provides “free” photons for driving auxiliary wavefront control. The system had been roughly assembled in Tucson and we had poetic alignment instructions as courtesy of Sebastiaan Haffert and Chat-GPT:

In the lab where lasers gleam,

Align the Lyot, chase the beam.

Turn it on, ensure the light,

Hits the center, sharp and bright.

Flip the clamps, turn them around,

Old positions, stoppers found.

Pull the wheel, the system’s grace,

Install the mirror in its place.

Put it back, a careful feat,

Center Lyot, alignment neat.

Tilt the laser, shift with care,

Card in hand, another’s stare.

Lens one’s heart, its center true,

Shim stock, tilt—just right for you.

Centering near, within a mill,

Precision holds, steady still.

Lens one now done, we move ahead,

Z filter next, where paths are led.

Remove the tube, the chip exposed,

The cap now off, the system grows.

Pivot here, or pivot there,

Camera moves with patient care.

Optical feedback, guiding hand,

Or move again, the next command.

Install the tube, frosted within,

Pinholes small where light begins.

Lens to guide, align once more,

Precision sought, forever sure.

As most alignment projects go, lived experience quickly derailed from our flowery aspirations. While Jared fought down a flurry of unexpected problems that I won’t pretend to summarize, Maggie, Jay and I slogged through the full range of alignment processes and human emotion necessary to correctly focus the reflected beam onto the LLOWFS sensor.

The main difficulty in alignment came from the sheer number of things (I’m going to stick with “things” here because my gut reaction at the end of the day is to use a couple swear words but a lot of time went into each part) in the neighborhood around the Lyot wheel. Opening the panels this morning made me think of the frog that hops into lukewarm water and quickly finds itself boiled alive. When I started looking at PIAA designs in early 2022 this area was fairly crowded but manageable. Years later the optomechanics have grown layers deep and maneuvering a stubby Allen key through the optical jungle can take thirty seconds and Zen breathing techniques.

We added a mirror to the Lyot wheel to use a reflected beam for the alignment. Picomotors on the stage means that translating the wheel in x and y are quite straightforward, but using the wheel as a mirror instead of a simple aperture means that the tip and tilt in both directions became critical. The immediate descent into shim madness gave a portent of the long day in store for us.

Aside: it’s rather silly to spend much more time writing the details of our work today when it’s already late and breakfast will be served in six hours. I’m going to scatter a few photos through the post and call it sufficient. The biggest takeaway from the day though is that external challenges are always manageable with the right team around you. Despite the setbacks and technical frustrations that were part of the alignment process, problems became fun, interesting challenges when shared with the group. I appreciate doing this work on an engineering run, with no rush at night and enough time to listen to each other’s perspectives. Amid this collaboration and working in such a beautiful place, one long day makes us only more prepared for the next.

Song of the day

I had about twenty songs stuck in my head through the course of the day. When doing delicate or technical work I like to nurture their memory on repeat because I find that tends to relax the high stakes. Of the songs that I played during breaks afterwards, sitting outside the cleanroom and appreciating the warm sun, this was the only one that met the blog rule.