Valeria Viteri-Pflucker, 2022 NIST Research Intern

Biography

SPS Chapter: Illinois Wesleyan University

Hello, my name is Valeria Viteri-Pflucker, and I am a recent graduate of Illinois Wesleyan University. I majored in physics and minored in mathematics, religion, and history, and plan on attending the University of Rochester this coming year to pursue a PhD in Optics. My most important involvement at my university has been the research I’ve been able to participate in. For my first two years, I conducted research with Professor Bruno deHarak studying laser-assisted free-free electron scattering and later, computationally simulating frustrated tunnel ionization in the presence of a strong femtosecond laser pulse. During my second and third years I participated in the Department of Energy’s Summer Undergraduate Laboratory Internship (SULI) where I worked with Doctor Lin Zhou on understanding the nature of the skyrmion lattice by processing Lorentz Microscopy images of these magnetic quasiparticles. My senior year I’ve worked with Professor Tian-Xiao He on an Independent Study in mathematics to first understand introductory Wavelet Analysis, and next to do research into understanding the feasibility of generalizing data that wavelet analysis can be used on to include data that is not uniformly spaced.

During my time at Illinois Wesleyan University, I’ve also participated in a lot of extracurricular activities. I’ve been highly active in SPS. This year, my school’s chapter of SPS and PME (honorary mathematics society) joined together to create a math and physics high school competition, of which I was the main coordinator. I also participate in SPIE (Society of Photo-Optical Instrumentation Engineers) where I help schedule and promote student research talks, and IEEE (Institute of Electrical and Electronics Engineers), of which I was President during this past year. In IEEE we have been building a pumpkin launcher that functions like a small scale rail gun that will be continued in the coming years. I’m also on the board of Lyrical Graffiti, a club that hosts monthly open mics and schedules to bring famous poets to my campus. I’ve also been a 4-year participant in IWU’s School of Music, participating in Wind Ensemble, pep band, opera pit, and more.

Something that has really mattered to me for this summer is to be able to do hands-on research. The majority of my time at college has been during the COVID-19 pandemic, which means most of my research had to be computational. Before I start the next step in my journey, I want to experience in-lab experimental work to know how I fit into such an environment, and have been interested in working at NIST for years.

Internship

Host: National Institute of Standards and Technology (NIST)

Project

Abstract

Gallium phosphide (GaP) is an indirect-bandgap semiconductor that is of interest for creating integrated nanophotonic devices. GaP can be used at very high powers for wavelengths above 900 nm due to its very low two-photon absorption coefficient β_2 in this regime, but precise knowledge of this as well as its optical Kerr coefficient n2 are not known. In our experiment, we use pump probe spectral interferometry to measure these coefficients as a function of wavelength. A pump pulse generates transient absorption and refractive index that is probed by a probe supercontinuum pulse. The probe is interfered with a reference beam, then measured in a spectrometer which lets us measure β_2 and n2. We normalize this data by using SiO2 as a reference material. We find reasonable agreement with a simple theoretical model and previous less precise measurements at a limited number of wavelengths.

Final Presentation

Internship Blog

Week 1: NIST!

Today is Sunday, June 5 th , 2022, and it marks the first full week of my participation in the SPS Summer Internship, working at NIST. Last Sunday I drove to Washington DC from Bloomington, Illinois, where I recently acquired a BA in physics from Illinois Wesleyan University. The move-in process at George Washington University went much easier than expected (except the parking was a bit confusing for a few days), and on my first night I did the monument walk for the first time. On Tuesday we had orientation, and my first day at NIST was Wednesday.

At NIST, my mentor is Jared Wahlstrand who works in the Nanoscale Spectroscopy Group. His research interests are primarily in time-resolved optical spectroscopy for characterization of materials. On the first day I got to see the lab he is working in, some new equipment, and around the NIST campus. I also received a lot of reading material to help me understand the set-up for the experiment and the materials being characterized.

The experiment I will be working on is a study of the organic semiconductor tetracene using different ultrafast optical techniques. Specifically, I will be working on a pump-probe study of this material. Tetracene crystals are biaxial and the polarization of light that enters the material is changed by the propagation. The goal of the experiments as I currently understand it is to isolate the polarization- dependent signal from triplet excitons that arise in the material when pumped to extract the full dielectric matrix as a function of time delay between pump and probe beams. I may also work on experiments dealing with nonlinear optical properties, which may be easier to do in the time frame I have. Since this week was introductory, more discussions need to be made in the future about what my goals within this overarching project will be.

Outside of the research I was introduced to this week, I also had a great time meeting the other interns. A few of us went out to eat together a few days ago, we went to a water park, and played games. I’m excited to explore museums in the coming weeks and experience more of the city!

Week 2: Safety Training and Lots of Events

My second week has come to a close and I am surprised by how many things I got to do this week. To begin with my work at NIST, I spent much of my week doing safety training before I begin in the lab. This includes general safety training, compressed gas safety training, personal protective equipment training, COVID-19 protocol training, and (the most important one for the lab I am in) laser safety training. I also have learned more about the organic crystal we are investigating (tetracene) and about excitons that happen in these materials. I will start next week by imaging tetracene crystals using a HyperSpectral Microscope new to NIST – once I’ve collected more information, I’m sure I will explain during a future week. I am very excited that my training is complete, and I will be able to be in the lab for the coming weeks of the internship. In addition, I got to meet the third NIST intern, Div, so now there are three of us!

Outside of this, on Thursday the intern group had an organized lunch with John Mather who won the Nobel Prize in Physics for his work on the Cosic Background Explorer Satellite. Interns asked him questions about his time in college, his advice for new scientists, has path in his career, and the projects he’s worked on. On Friday we also went to a baseball game. It was my first baseball game! The atmosphere was fun and I had a good time with other interns. Later that might a group of us went to a showing of Rocky Horror Picture Show with a shadow cast. It was my third Rocky Horror Picture Show showing, but a lot of other interns hadn’t seen the movie or been to a showing before, so it was fun to watch them experience it.

Over the weekend, I finished a project I’ve been working on for a while. I crochet a lot and started but never finished a floral backpack a year or so ago. Over the weekend I finally completed the item and have started a new one. I also started working on a piece of music with Taylor C. and Nicole who play clarinet and piano, respectively (I play flute). Today, Sunday, a group of us also went to the Spy Museum. I was a young man from Istanbul with a career in writing, sent to Guatemala to find a missing agent. Mostly I liked reading the historical exhibits, but the interactive components were interesting. I’m excited for the coming week, especially the orchestra concert and Dungeons and Dragons campaign some of the interns are trying to start.

Week 3: Music & Data Collection

This week I was working in the lab collecting data. Last week I mentioned the new Hyper Spectral microscope, which is what I used for my data collection. Essentially, we have a collection of small tetracene crystals on a clear substrate and want to figure out a method for figuring out the orientation of the crystal on the substrate. To do this, we polarize the incoming light and see how much light is transmitted at different polarization angles. The important part is we do this for each wavelength between 400 and 800 nm in 1 nm intervals to get a spectra, and we do this for each polarization angle. From this we should be able to compare the results to a simulation of what should happen, and extract orientation and thickness. I took lots of data during the beginning of the week and began the process of writing some code to extract the necessary data to compare to simulations made by my mentor, Jared Wahlstrand. The three NIST interns (Taylor, Div, and I) also went to a happy hour with my group, the Nanoscale Spectroscopy Group, where we got to meet other scientists in my group working on different projects. It was a lot of fun hearing about their experiences at NIST over time.

Outside of work, this was an important week for me because I picked out my apartment for the coming year. Starting in August I will be moving to Rochester, NY to begin my journey as a PhD student in Optics at the University of Rochester. A lot needs to be figured out before then, but the apartment process is complete. It came with lots of ups and downs, but the other interns were very supportive! I’ve also begun a long list of paperwork that needs to be completed before then, but at least it’s all been started now.

Over the weekend, a group of us went out to a place called Decades and had a lot of fun dancing, and we also went to the planned orchestra concert. I had a really good time listening to the music and running outside before the concert. My favorite song was the Funeral March, and it was fun that Justin brought a Polaroid camera to take pictures with. This morning I went to the Dupont Circle Farmer’s Market and got most of my groceries for the week as well. It was a lot of fun walking around the market with other interns. Overall, I’m excited to see what all I can get done in the following week!

Week 4: Sick Week

I had a weird week this week. On Monday I went to the beach with a few of the other interns, only to find out while there that my roommate tested positive for COVID-19. I became a bit paranoid as I had been a bit tired the past 2 days – a bit more than usual. I had a very small sore throat, but I wasn’t sure if I just choked on salt water. I got back to the dorm, and immediately took a COVID test. Every intern, including myself, tested negative. I thought nothing of it, went to work the next day having told my advisor the situation, and did some work. Throughout the day I started developing symptoms of something. I got really tired and really cold. In case I was sick, I uploaded all possible materials and slept the entire way home. I woke up the next day definitely sick with something. I proceeded to test negative 5 times in a row. However, I had a wide array of varying symptoms during the week. I thought I had a fever but the thermometer said otherwise, I lost appetite, I was incredibly tired, I had confusing sinuses, I developed a cough, I lost my throat, but all at different times. My dad had been scheduled to come see me and do things around DC during the following weekend, and the Thursday before he came, I felt substantially better and tested negative again, so my parents and I decided to clear him to come.

I was doing much better while he was here, but that’s when I developed a cough. On Saturday we went to the Air and Space Museum and the monument walk, since all other symptoms were gone, but the next day my cough got worse. I also lost my voice. I think that’s because I strained my healing throat at Astronomy on the Mall explaining my demo to people. We then did the zoo so we could be outside. It turns out walking that much is not ideal when sick, so the Monday after he was gone I felt very very tired and slept basically the entire day outside of the work I did complete. I got a surprising amount of work done during the week I was sick. I read a lot and wrote some code, as well as familiarized myself with code written by my advisor. Hopefully this week goes better. As of now it is the ten-day mark and I tested negative on two rapid tests, completing my 7^th negative COVID-19 test, so I suppose I just had a cold.

Week 5: Back to the lab

I went back to work! Having largely finished the code I needed to work on last week, this week back at NIST we have started the next phase of my internship. The lab is now equipped to perform spectroscopic interferometry experiments, so instead of only studying tetracene, we are now planning on investigating more materials. Specifically, a few indirect semiconductors and possibly a BGO crystal. For indirect semiconductors, there is a photon energy regime where photons of said energy could excite the electrons in the crystal but would need the help of a phonon to simultaneously change the momentum to make it into a possible state. Eventually when the photon energy gets high enough, it can excite the electrons on their own. We are setting up experiments on investigating the rate of two photon absorption in the regime where a photon and a phonon would be necessary, because two photons together could also excite the material without needing a phonon. In addition, as a function of light intensity, the index of refraction of the material changes. We wish to also explore that using spectroscopic interferometry. We started looking into the feasibility of these experiments during the week, and there is more to come this week!

In addition, my friend and my boyfriend came to visit me this weekend from Illinois. They arrived on Saturday and left Monday after the Fourth of July Independence Day Parade. When they first got here, we went out to eat at Residents Cafe & Bar, then did the monument walk during a thunderstorm. It was windy and wet, but the lightning and lighting was very pretty around the monuments for the duration of the outing. The next morning, we went to the National Museum of African American History and Culture for several hours and then went to Independence’s Samba at Bossa Bistro & Lounge. The samba was a live music venue showing Brazilian music, food, and cocktails, and encouraged samba dancing. I went with Justin and my friends, and we had a good time. To celebrate my boyfriend’s birthday, we made him a birthday dinner of Cajun butter steak bites with onions, fresh sweet corn we picked up from the farmer’s market that morning, avocados, crispy potato bites, and tomato slices. Some banana bread to top it off that I made with the help of Matangi. Overall, my health has been a lot better this week thankfully! In the coming week I hope to further this new path the research has taken, and I have a lot to look into as that unfolds.

Week 8: The attack of the jellies

On Saturday a bigger group of us went back to Sandy Point Beach for a day in the sun. We went in two cars, each car full, and each of us had signed up to bring an item for the midday lunch break (I brought turkey lunch meat). It was super hot out. We staked out a small collection of blankets and towels, littered with umbrellas of various size. After applying sunscreen to the group and waiting for it to dry (quite unsuccessfully as we all started sweating), we ran out into the ocean together with frisbees and balls ready to cool down. The sand was scorching hot so it was very nice to walk into the water. Within 10 minutes of being in the ocean, panic struck. Taylor O. swam over to the group, with a confused and yelping Lucy in tow. Lucy told the group something had happened, and her neck down to her chest felt like it had been burned. Since so many people were out we had ignored the jelly fish advisories on the shore, but by that point both Taylors and Lucy had been stung. We went closer to shore to collect the group and got out of the water to see what to do. You’re supposed to pee on jelly fish stings, right? Well apparently that’s not recommended but we didn’t have any vinegar. Thankfully, Taylor C. had brought a first aid kit with rubbing alcohol which is a substitute, according to Emma who read an article and was the local jelly expert. She told us they can still sting after they die, and the tentacles floating alone in the water also sting. The frightened group of us watched little children fishing jelly fish out of the water and bury them on the beach. After a while I finally got to see some swimming myself and they were very pretty. They were white/translucent, resembling blobs of snot when not clearly seen. When close to shore they became elegant blobs, pushed to the hoards of beach go-ers by the tide. The only other jelly attack was when Emma sat on one and it stung her butt. All in all, 40% of interns got jellied.

Other than that, a lot got done in the lab this week. We did some (hopefully good!) data sets taken on Friday and I’ll see what the final results look like tomorrow! I also just got back from a concert at The Anthem; I got to see Beach House with Div and Gizem. Earlier this week I had a virtual movie night with my boyfriend where I watched Green Book (for the second time). The NIST crew also successfully planned the NIST tour for the other interns! It went really smoothly I think. Currently I’m making some French toast and that’s the week.

Week 8: The attack of the jellies

On Saturday a bigger group of us went back to Sandy Point Beach for a day in the sun. We went in two cars, each car full, and each of us had signed up to bring an item for the midday lunch break (I brought turkey lunch meat). It was super hot out. We staked out a small collection of blankets and towels, littered with umbrellas of various size. After applying sunscreen to the group and waiting for it to dry (quite unsuccessfully as we all started sweating), we ran out into the ocean together with frisbees and balls ready to cool down. The sand was scorching hot so it was very nice to walk into the water. Within 10 minutes of being in the ocean, panic struck. Taylor O. swam over to the group, with a confused and yelping Lucy in tow. Lucy told the group something had happened, and her neck down to her chest felt like it had been burned. Since so many people were out we had ignored the jelly fish advisories on the shore, but by that point both Taylors and Lucy had been stung. We went closer to shore to collect the group and got out of the water to see what to do. You’re supposed to pee on jelly fish stings, right? Well apparently that’s not recommended but we didn’t have any vinegar. Thankfully, Taylor C. had brought a first aid kit with rubbing alcohol which is a substitute, according to Emma who read an article and was the local jelly expert. She told us they can still sting after they die, and the tentacles floating alone in the water also sting. The frightened group of us watched little children fishing jelly fish out of the water and bury them on the beach. After a while I finally got to see some swimming myself and they were very pretty. They were white/translucent, resembling blobs of snot when not clearly seen. When close to shore they became elegant blobs, pushed to the hoards of beach go-ers by the tide. The only other jelly attack was when Emma sat on one and it stung her butt. All in all, 40% of interns got jellied.

Other than that, a lot got done in the lab this week. We did some (hopefully good!) data sets taken on Friday and I’ll see what the final results look like tomorrow! I also just got back from a concert at The Anthem; I got to see Beach House with Div and Gizem. Earlier this week I had a virtual movie night with my boyfriend where I watched Green Book (for the second time). The NIST crew also successfully planned the NIST tour for the other interns! It went really smoothly I think. Currently I’m making some French toast and that’s the week.

Week 9: NIST Photoshoot and Frontiers in Optics

This week was a little weird for me at work. The week before was time for rapid data collection, and Monday I had to figure out how to process all of it, create the plots, and put them into an abstract for Frontiers in Optics due on Tuesday. I got it done! The tough part was that my advisor was on vacation this week, so I had to figure out a lot by myself. On Tuesday, I rehearsed my presentation and updated it so I could give it on Wednesday to the Nanoscale Spectroscopy Group. When I gave the presentation, they had a lot of ideas of ways to improve it, so I will be working on that next week. My goal for the rest of the week was to write a blog post for the NIST website. For this blog post, I needed to talk about myself, my journey in physics, my research at NIST, and my experiences this summer. I completed my rough draft on Friday titled What’s a Physicist: Summer as a Society of Physics Students Intern at NIST, focusing on my journey of understanding what a physicist does and how the SPS internship has shaped that through the diversity of posts the cohort has been in. Lots done this week! The abstract deadline was extended for the conference, so I will be adding theoretical curves to the data with Jared next week, editing my presentation (a lot), and doing a photoshoot with a photographer at NIST in the lab for the blog post.

Something fun this week was that I wanted Div and Taylor to have pictures of them at NIST before we leave for the last time (maybe) next week. I brought my camera and we took a big chunk of day out to document our experiences and the spaces we worked in, to remember. I added some of the pictures. We didn’t take pictures of me in my lab since a photographer is coming on Tuesday, and my advisor wasn’t here to make sure safety protocol was followed.

Outside of that, we played our second to last session of Dungeons and Dragons. We just found the bad guys’ layer, and Janessa was sent in alone. Survival TBD. On Saturday, Taylor and I went to the Museum of the Bible and had a fantastic time. So much to see! We also got to see a statue of Newton. After the museum (we were there for about 5 hours), we had Korean BBQ with a group of 9, then Justin took us to my very first speak easy! It was inside of a suspicious black door. We opened the title-less door to find two bouncers asking for IDs, and inside was a much classier bar than I’m used to seeing. Candles everywhere! We had a good time. Nicole brought some non-physicists in the group, and I proceeded to talk to one of them for a long time about quantum mechanics which blew their mind. That was quite fun. Today (Sunday) I went to the Museum of Natural History with Div, Taylor, and Anthony. The dinosaur exhibit was super cool, I saw some amazing taxidermy, and the stones/gems section was remarkable. Next week is the last week! Bittersweet times.

Week 10: From DC to Rochester, Thank You

The final week of the internship has come to a close and I have arrived safely in Illinois after 14 hours on the road. After all 10 weeks, I must say I had a fantastic summer. During the final week, there was a lot of finishing up to do but also a lot of preparing to say goodbyes. On August 1^st, we had our final (in-person) Dungeons and Dragons session on blankets behind the Lincoln Memorial where we got to watch the sunset. It was a very nice closing to a summer-long campaign for the group. And we finally got out of that cave we were in for the past month or so. On the 2^nd, I had a photographer come to Jared’s lab and take photographs of me for my NIST blog post, which I must revise soon. The photos turned out great and I’m very happy to have them. On the 3^rd, I had my last day at NIST. Jared planned a small going-away party where people from the group went out to eat around noon with me. Jared and I meant to try to get some work done in the lab, but we ended up talking more than working which was nice because I had things I wanted to ask about before I left. Also, finally having photos back from the photographer I finished creating my presentation which included some of these photos to give viewers a feel for what my lab looked like. The next day was the practice run for the Symposium. My talk was of course quite a bit longer than I wanted and I got fantastic feedback on what to cut and how to trim content in a way that would help the talk rather than deduct information. I practiced and edited quite a bit, and also packed most things that night. Then came the big last day. The interns gave a series of honestly fantastic talks about a wide array of topics.

Afterwards began the series of goodbyes. We all left at different times so they were scattered throughout the next 24 hours. We went back to GW and Div helped me load my car. The blue carts to help load and unload were gone! I am very thankful Div was there to help; I had way too much stuff to do alone without a cart. I essentially moved almost entirely out of my other apartment into this one and will be moving from this one to my new home in Rochester, NY in a week, so its quite a bit of stuff. After packing and throwing out any remaining food that wasn’t packable, the remaining interns had a last get-together. We sat around, played games, and talked. Eventually it was time to retire but we all just awkwardly stood around by the door to consignment (Emma & Janessa’s room) not knowing how to say goodbye. There was a group hug at one point. I don’t quite remember leaving but I won’t be forgetting the people I left.

For the last 2 summers, I participated in a Department of Energy internship program and, due to COVID-19, it was remote. I met no one during these 2 summers, and relied heavily on friends who were nowhere near me and had their own lives going on. It was lonely at times, working 50 hours a week in a room with no one to talk to. I had a lot of fun with the work I was doing (thankfully) and my cat is a wonderful work buddy (thankfully) but I didn’t realize how much more I could have gotten out of an internship program. A lot of people told me to take a break for once and relax for the summer, but I’m really glad I didn’t take that advice. I learned a lot at NIST and learned a lot about physics education from different backgrounds. I got to meet some really cool people who are going to do great things. I got to live in Washington, DC for a summer! In junior high a bunch of students took a trip to DC and I couldn’t afford it. I wanted to go for a long time and finally got the chance. I got to be an experimentalist! Overall, I had a fantastic time. In one week, I’ll be moving to start the next chapter of my life. I’m going to attend the University of Rochester to start a PhD in optics. I feel much more confidence in starting this new venture after this summer, and I’m very thankful to my advisor Jared, the other interns, and Brad for the experiences I’ve had. Thank you all for being so genuine.