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Cid Bartolomeu de Araújo: The adventures of light

Physicist from Pernambuco explains phenomena that can be used to improve optical fibers, cell phones, new materials, and lasers

Brenda Alcântara

In a recent experiment, physicist Cid Bartolomeu de Araújo aimed beams of light at groups of five to six atoms, which surprisingly lost some of their individual characteristics and started to behave as a type of aggregate called a metamolecule. In addition to discovering new properties of light and new materials, the knowledge produced in the Physics Department’s laboratories at the Federal University of Pernambuco (UFPE) helps to improve the efficiency of optical fibers and special glasses, such as those used in cell phones and photovoltaic panels, not to mention the unexpected results. Araújo was happy to see that three studies by his research group reinforced the argument that led to Italian physicist Giorgio Parisi winning the 2021 Nobel Prize in Physics.

In the 1970s, Araújo and other young physicists founded UFPE’s Physics Department, which became one of the most productive in the country in the field of nonlinear optics­—the study of the effects of high-intensity light on solids, liquids, and gases. Aged 78 and married with three children and six grandchildren, he is now retired, but he still visits the labs daily and participates in research. The book História da física no Recife (The history of physics in Recife; Cepe Editora), written by Ascendino Silva, Marcos Galindo, Osvaldo Pessoa Jr., and Wanderley Vitorino and released in December 2022, emphasizes the importance of the UFPE physics group and links it to the state’s strong scientific reputation, rooted in the work of astronomers and naturalists who arrived in the seventeenth century with the German-Dutch Count John Maurice of Nassaua (1604–1679) when the region was occupied by the Dutch.

Age 78
Field of expertise
Nonlinear optics and photonics
Federal University of Pernambuco (UFPE)
Degree in electrical engineering from UFPE, master’s and PhD in physics from the Pontifical Catholic University of Rio de Janeiro (PUC-RJ)
Published works
Author of 359 scientific articles and coauthor of 2 books published by international publishers

You were 26 years old in 1971 when you helped create UFPE’s Physics Department, one of the country’s first and still one of the most productive in the field to this day. How was it planned?
I’ll have to go back a few years to answer that. I studied electrical engineering at UFPE and then did a master’s degree in physics at PUC [Pontifical Catholic University] in Rio de Janeiro together with José Rios Leite, who is a colleague of mine to this day. The two of us and three other UFPE colleagues who were in São Paulo planned to do our doctorates outside Brazil and then return to Recife. Physicist Sérgio Mascarenhas [1928–2021] had made a proposal: “You can come back, form a research group in Recife, and get funding to carry out research.” At that time, in the early 1970s, it was relatively easy to get money for research because there was little competition. Mascarenhas, however, noted: “You need someone more experienced leading the work.” We discussed some names and he chose to invite Sérgio Rezende, who in 1970 was considered a very experienced scientist. It was only three years since he had finished his PhD at MIT [Massachusetts Institute of Technology in the USA]. He agreed to come to Recife with a plan to stay for one or two years, but he ended up liking it so much that he is still here today [see interview with Sérgio Rezende in the Conrado Wessel Prize supplement of Pesquisa FAPESP, January 2012]. One very important factor in the formation of the group was our common objective. From a scientific point of view, we focused on one area in particular: magnetic materials. And we were thus able to create an environment in which everyone spoke the same language. But it was a risk for all of us.

There was a high probability that it would not work out. At the time, very few people were doing research at UFPE and other universities in the region. And several physics groups were being formed in Campinas and São Carlos, both in the state of São Paulo. When we came to Recife, there were no laboratories or physicists in the department. Only engineers who were part-time physics professors while also working at private companies. My first job at UFPE was to design the electrical substation to power the lab. I worked on it together with an engineer from the dean’s office at UFPE. Since I had an engineering degree, I was partially responsible for the substation. Sérgio Mascarenhas and physicist Gerhard Jacob [1937–2019] sent our research plan to the CNPq [Brazilian National Council for Scientific and Technological Development] to ask for our first funding. Mascarenhas had already created other groups in São Carlos and even in Mexico, and he believed in our group’s capabilities. I was hired in 1971, before completing my PhD, which I finished at PUC-RJ in 1975, before leaving to do a postdoctorate at Harvard University shortly after. I then returned to Recife in December 1977. We got our first funding from the CNPq, but it took some time to establish the lab and start producing results. In the meantime, we tried to do a bit of theory work so that we wouldn’t be sitting around idly and to keep up-to-date on the few areas in which we were involved. At that time, most scientific journals took a long time to arrive, some less because we subscribed and they were delivered by air mail. But, in general, we received journals five to six months after they were published. It was a problem because we would start a study and then a few months later we would receive a journal and see that someone had already done what we were doing.

Does the department’s current team maintain that spirit of unity that guided your work in the early days?
Our motivation comes from working closely together and from being excited about the research, which is infectious. We try to surround ourselves with like-minded people who have the same excitement about research. To select undergraduate students, for example, one of the first questions a colleague used to ask was: “Do you know how to fix your bike?” It was a test to see if the person liked to get their hands dirty tinkering and fixing things, a very important skill in an experimental physics lab like ours.

In 1980, you and a colleague from UFPE published an article in Chemical Physics Letters proposing that two distinct molecules interacting with each other inside an organic crystal can simultaneously absorb two photons, an effect that decades later was observed in experiments. How exactly does this phenomenon occur?
This was one of the theoretical papers that Rios Leite and I worked on while we waited for our lab to be properly set up. In the simplest model of an atom, the nucleus has positive charges and the electrons that revolve around it have negative charges. When atoms are far apart, the electric field created by the charges on one atom have only a small effect on the charges of the other atom. When they are closer together, the strength of the electric field increases. What we proposed was that, at certain distances and under certain conditions, two nearby atoms can behave as a single system, as if they were a quasi-molecule. When excited by a beam of light at a certain frequency, they absorb and share the energy; part of the energy goes to one atom and part goes to the other. If they were further apart, one atom—one electron, to be more precise—would take all the energy for itself and change state from the least to most energetic state, before returning to the previous state when it emitted the energy it absorbed. When they are close together, there is an electrostatic interaction between the charges of the two atoms, which encourages the simultaneous absorption of two photons. Today, this theory seems like the kind of problem that could be taught in an advanced physics course—it is not highly sophisticated. When we first created the Physics Department at UFPE, since we did not have the money to set up labs, Rios Leite and I explored the possibility of investigating this effect in the lab, which had not yet been done in other studies. We did the calculations and published the article, which is four pages long and for years went largely ignored in the scientific literature.

Have you ever tried to demonstrate the effect experimentally?
When we managed to set up a lab, we tried to conduct the experiment but we still did not have the infrastructure needed for that kind of problem. You need two molecules or two atoms very close together so that they can interact. We tried it with sodium vapors. When we achieved the necessary experimental conditions, the two atoms joined together and formed a sodium molecule, which was no good for what we wanted to do. We tried later with a solid with rare-earth ions, but that did not work either. In around 1985, a French group achieved something very close, but the effect was only truly observed in 2002 by a Swiss-German group. They doped [enriched] an organic solid and used a probe to locate pairs of molecules that were very close but not touching, and thus observed the effect. To my surprise and Rios Leite’s, they had found our article 22 years after it was published and cited it. Their article was featured on the cover of Science magazine. In 2012, Vanderlei Bagnato’s team at USP [University of São Paulo] in São Carlos confirmed the effect in sodium vapor, but we had discussed it together beforehand. We gave a seminar there and he thought he would be able to do this kind of experiment. He did and it worked. The resulting article was published in Physical Review Letters. It was really satisfying, because he worked with a system closer to what we had imagined 32 years earlier. The effect came to be known as absorption of two photons by two atoms [TPTA]. It is a phenomenon that can be described within the broad framework of nonlinear optics. Afterwards, other groups also studied this effect from different perspectives.

Our department spawned startups that make medical equipment based on photonics

What is nonlinear optics?
It is a field, also known as nonlinear photonics, that studies the effects of high-intensity light on the various states of matter, be they solid, liquid, gas, or plasma. These materials of interest can be in the laboratory or in nature, so it is possible to study nonlinear optics in labs that simulate the atmosphere of stars, for example. From a practical point of view, the first important contribution of this field was the creation of the first laser and the understanding of how it functions in the 1960s. Then came optical fibers, which carry data and changed our lives. And from then on, applications for optics emerged in medicine, in tests that assess the luminescence [ability to emit light] of specific blood molecules, for example.

In 2013, we reported on your study on optical vortices, which we call light spirals. Has this work progressed?
It has advanced. A doctoral student who was working on it at the time, Anderson Amaral, is now a professor at UFPE. What at the time was a basic research project [see Pesquisa FAPESP issue 211] has become a mainstay. We can produce the beams with optical vortices and use them to do different experiments. The beams have angular momentum, which means that when they hit a group of electrons or molecules, they tend to make the electrons or molecules spin. A group from the US and another from China are using this means of manipulating the profile of light to generate random numbers, which are very important in the encryption of messages sent via cell phone or the internet.

With such a long career, what important moments would you highlight?
In 2021, a report by the Royal Swedish Academy of Sciences committee that nominates people for the Nobel Prize referenced three of the studies we carried out in Recife, which served to corroborate the ideas proposed by a winner of the Nobel Prize in Physics, Italian physicist Giorgio Parisi. This made me and our teammates very happy because we had no contact with the authors of the report, but they noted that our work was important in proving Parisi’s ideas. In the late 1970s, Parisi proposed a theory that explained the behavior of some magnetic materials. Other physicists in the field agreed that Parisi’s theory was correct, but the way of verifying it was very indirect. So between 2015 and 2017, using random lasers, we showed directly that his proposal was correct. That was not what we were trying to do though. We arrived at the results by chance while working together with a fellow UFPE professor: Anderson Gomes. Since we are experimental physicists, we needed support from other theoretical physicists. By coincidence, Ernesto Raposo, a younger colleague who specializes in statistical physics here at UFPE, had already studied these processes in solid state physics and helped us immensely.

Are you in touch with companies in the field of optics?
We had contact with Jarbas Castro from Opto in São Carlos for many years. The company went through some serious financial trouble, but as far as I know it has recovered now [see Pesquisa FAPESP issues nos. 162 and 227]. Besides Opto, I do not know of any other company that manufactures lasers in Brazil. Quantum Tech, based in São Paulo, made some attempts, but it went out of business after two years. There are other companies in São Paulo that use lasers to make stents [a medical device used in heart surgery], for example, but they import them. Our department spawned startups that became part of the Pernambuco Technology Institute’s incubator and developed medical equipment based on photonics, but the light-emitting diodes are also imported. It is expensive to manufacture a laser and the Brazilian market is still small. A company setting up in Brazil would have to compete internationally with established companies in the USA, France, and Germany that manufacture lasers for industrial and medical use. We contribute to the market indirectly, because we train people qualified to work at companies, not just in Brazil. Some of our former students are now working at companies in Canada, the USA, India, and China. Two of them are at nanotechnology companies, using particles prepared by chemical techniques, like what we do here. Others are now researchers at universities. We have dedicated ourselves to topics that naturally prepare students for areas interested in nanoparticles—the drug industry, for example. However, most of our graduate students have become professors and researchers at universities in Brazil and neighboring countries, as well as in North America and Europe.

You also work with other optical applications, such as metallic nanoparticles and special glasses. Can you tell us a little about that?
We study metallic nanoparticles—of silver, gold, and other metals—as a nonlinear medium that allows us to investigate, among other things, the propagation of pulses of light that move without losing its shape, known as solitons. To understand our motivation for studying solitons, consider the following: when you turn on a flashlight or an ordinary light bulb, the light does not come out like a single cylinder—it diverges, it spreads out. To study the behavior of some molecules we need unidirectional beams like solitons, since even lasers are deformed as they propagate. Solitons are optical objects with a wide range of applications, in optical fibers for example, to avoid message deformations caused by overlapping light pulses. High-frequency experimental circuits already exist, which allow a lot of information to be sent in a very short time. The behavior of metallic particles can be described by equations that help build solitons. The metallic particles are also used to build so-called random lasers, which do not have reflecting mirrors to amplify the light like conventional lasers. You can put these particles in a liquid or a solid that shines brightly [emits a lot of light] and they function as the laser mirrors.

At Harvard I learned research strategies by interacting with people who were doing cutting-edge physics research

What have you done with these particles?
In one of our most recent experiments, the results of which we published a year ago, we used these particles, which are 10 nanometers in diameter [1 nanometer is one billionth of a meter], to study the properties of atom clusters. Starting from about 1,500 to 1,700 atoms, we reduced the amount until we had clusters of just six gold atoms surrounded by other molecules. A chemist from India provided us with the samples and we analyzed them. Now we have new samples of seven to 12 copper atoms that he prepared. We have seen that as we reduce the size of the group of atoms, there are no longer any free electrons like you would see in a metallic wire. The electrons are more or less attached to each atom, and each cluster behaves as if it were a large molecule, surrounded by others, which hold the atoms together. In the past, metallic silver and gold particles were used to make stained glass windows in European cathedrals in the Middle Ages. The red glass contains gold microparticles and the green glass contains copper ones. The Lycurgus Cup, made by the Romans in 400 AD and now held by the British Museum in London, appears green when illuminated from the outside and red when a light source is placed inside it. These particles are currently being studied by nanoscience and nanotechnology scholars. Together with FATEC [São Paulo College of Technology] professor Luciana Kassab, we are building special glasses with metallic particles for use in optical fibers and sensors, providing control over color and fluorescence [light emission] in color displays, optical sensors, or even lasers that emit various colors.

In 2003, you were the first and so far the only Brazilian to receive the Galileo Galilei Medal from the International Commission for Optics (ICO). When awarding the prize, the ICO referred to your “exceptional scientific contributions produced under comparatively unfavorable circumstances.” Do these unfavorable circumstances remain?
Today they are even bigger. There is a lack of research funding and we have been through many ups and downs. At the time of Brazil’s dictatorship [1964–1985], it was relatively easy to get funding because some of the military were nationalists who understood that it was important to develop new technologies. Then we suffered a really bad period during the José Sarney and Fernando Collor de Mello administrations, when money for research just disappeared. Federal research budgets were slashed. There was a strong recovery in the first two terms of President Lula [da Silva], but the last six years of the Temer and Bolsonaro governments [2016–2022] were really bad. I hope things will improve in the coming years. Our main source of funding is the MCTI [the Brazilian Ministry of Science, Technology, and Innovation]; some international sources; and FACEPE [the Pernambuco State Research Foundation].

Why did you choose an electrical engineering course if you wanted to study physics?
At the time, they told me that it was the best course at UFPE and the one that taught the most physics and mathematics, which I had liked a lot ever since high school. The first two years laid the groundwork, with lots of physics, mathematics, and chemistry, and in the third year the more applied disciplines began. Then I realized that I did not want to study engineering, but there was still no physics course at the university. I completed my electrical engineering degree, but on the advice of some of my professors, I studied certain disciplines that were part of bachelor’s degrees in physics at other universities. After I graduated, I went to PUC-RJ. A professor had put me in touch with two physicists there—Erasmo Ferreira and Nicim Zagury, both currently at UFRJ [Federal University of Rio de Janeiro]—who told me what I should study so that I could do a graduate degree in physics there. Then, at Harvard University, I worked with Nicolaas Bloembergen [1920–2017], who was considered the father of nonlinear optics and was one of the winners of the 1981 Nobel Prize in Physics. At Harvard I learned not only the basics of the field, but also research strategies, by interacting with people working on cutting-edge physics, and I gained an understanding of how research groups work.

Did your parents support your choices?
My father thought that I was going to be a salesman like him. He had a leather and shoe store in the neighborhood of Santo Antônio in Recife’s old town. When I reached a certain age he thought I should be there with him. For a while I thought I would follow in his footsteps, but I started to disagree with the way he did business, with the dynamics of the store, and I started to think more independently, which he did not like. When I decided to study engineering, my mother supported me but my father was sad. And he was even sadder when my brother, who is three years younger, became a sociologist. Eventually my father had to sell the store because he had no one to take over the business. But I think that later he was happy with the choices we made, both me and my brother, who also became a university professor and has now retired and has been living in Rio de Janeiro for over 20 years. I retired too, but I am still a professor, I have the lab and some graduate students.

And two of your three children are also physicists?
Yes, but I already told them that it is not my fault. They work with optics too. The eldest, Luís Eduardo Evangelista de Araújo, is a professor and he has had a lab at UNICAMP’s Institute of Physics for about 20 years. The other, Renato Evangelista de Araújo, works with medical and biological laser applications in UFPE’s Electronics Department. The fact that they chose academic careers is probably the result of being so close to my colleagues and their children. We once lived near the campus and they would often come with my wife to pick me up at the end of the day. I remember Luís, aged 3 or 4, sitting in the lab and asking to turn on the laser, which he thought was beautiful. When we lived in the US, they both went to schools with great labs; it was there that Luís learned how to grow crystals. And Renato was already into electronics. I think it was during high school that both decided to study physics when we returned to Recife.

Two of my children followed an academic career because they grew up so close to my colleagues and their children

And your third son, what does he do?
Paulo Henrique Evangelista de Araujo started studying mathematics, but at the end of his second year he switched to computer science. He studied it until the third year of the course and then started a software company with two colleagues at an incubator in Recife. They had 15 employees, but after two years they had to close the company. Then he worked at Motorola in São Paulo, before deciding to study Mandarin, and the following year he went to China to study another year of Mandarin. There he opened a logistics, import, and export company, but his wife came back here and in the end he closed the company and came back too. Now he has a software company connected to Porto Digital [the technology park in Recife] and he works with photovoltaic solar energy, making use of his connections in China. All three are happy with what they do. My wife, Rubi, is a retired school principal. We live in Boa Viagem. We like the beach, but she says I am a bit of a workaholic.

Besides the beach, what other interests do you have?
Music. I studied solfeggio and singing. I was a tenor and when I was younger, in the 1960s and 1970s, I sang in the Coral do Carmo choir in Recife, the most renowned in the city at the time. It was a religious choir, but I was not religious like the other members. We sang religious music, but also international and folk songs with really interesting arrangements. The choir recorded three albums of Brazilian music and a fourth that was the soundtrack to a movie called Terra sem Deus (Land without god). It was about the cangaço social movement and was filmed here in Pernambuco in 1963. The music on the soundtrack was inspired by northeastern Brazil, polyphonic music with four voices and dissonant arrangements, which was considered advanced at the time and was in a way influenced by João Gilberto [1931–2019]. During my undergraduate degree, four colleagues and I took extra classes for two years with a Portuguese mathematical physicist called Rui Gomes, who left Porto during the [António] Salazar [1889–1970] government, moving to Argentina and then to Recife. In the 1960s and 1970s I visited his house several times. His wife, who knew that I was a tenor, asked me to sing Neapolitan songs from the time. My father also liked to sing.