Vision of the future

From the time she was a young girl, Maria Calvo Padilla was intrigued by the natural sciences. Her mother died when she was only four and her father, a chemical engineer, raised her and her four siblings. When Calvo was 12, her father gave her two books: The Hunters of Microbes and To God from Science. Calvo was fascinated by the hidden universes and secret worlds revealed in the books, and, she says, "the fascination continues today."

When it was time to choose a career, Calvo did not have many options. "It was the '60s and Spain was a country immersed in a dictatorship and a not-so-distant civil war; many of the most brilliant scientists were exiled," she explains. The lack of options left her choosing between biology and physics. "I preferred physics," she says, "because the latter offered more options for following up on related work and because there was mathematics, which I liked as well."

Calvo is currently a professor in the department of optics at the Universidad Complutense de Madrid (UCM; Madrid, Spain), where she began as an assistant professor in 1977. For a woman in the sciences in Spain in the 1960s, the path was not an easy or direct one. "My only option was to apply for a grant to study some specialization abroad, out of Spain," says Calvo. Following graduation, she went to work at Philips (Eindhoven, The Netherlands) for a few months, where she worked on glass quality. She then applied to work in a private laboratory for glasses in Paris. The lab was associated with St. Gobain, a glass manufacturer with an emphasis on surface quality, detection of stress on glass mass, and the study of physical properties of new glasses with inorganic glass-formers. "I initiated the latter specialization, applying microhardness techniques, polarization, and various microscopy techniques," says Calvo. "I can still remember the amount of the samples I needed to polish to analyze the glass surfaces."

After two years, Calvo went to the Laboratory of Glasses of the French National Research Council (Paris, France), where she worked on a doctorate diploma, awarded by the University of Paris VI in 1971. She studied the changes induced in vitreous silica by the action of neutron radiation, a problem arising in nuclear reactors. She returned to Spain in 1972 and contacted her former professor, Armando Durán—known, along with J. M. Otero, for his discovery of night myopia—who offered her a grant to work on theoretical aspects of scattering of light by defects in isotropic media. This became the topic of her PhD dissertation, and she obtained her PhD in 1977. In 1981 she became associate professor and in 1999 was appointed professor of optics of the department.

Since 1980, Calvo has been trying to apply light scattering formalism to the study of particular inhomogeneous media such as optical waveguides and holographic gratings. She had been studying some models for developing holographic couplers and, in 1990, began to direct Pavel Cheben's PhD project. He based his thesis on applied and theoretical work to search for an optimization of holocouplers. "From the theoretical results, several anomalous mechanisms—such as splitting and angle amplification—could be predicted for very thick holographic media or be deeper modulated," Calvo explains. "We discussed the possibility of working with holographic materials other than conventional silver halide plates, gelatins, or photopolymers. The mixing of glass and photopolymer, the photopolymerizable glass, came to the surface." The prototype has high diffraction efficiency with a high refractive index modulation in films thicker than normal photopolymers; it also shows temporal stability, but Calvo concedes that "a lot of work needs to be done to improve surface quality and noise reduction for optimized applications in data storage."

Calvo is also the head of the Interdisciplinary Group for Bio-Optics Research at UCM, which focuses on applied optical techniques in biomedicine. Because of her interest in the human vision system, she also worked as a visiting researcher at the School of Optometry at the University of California, Berkeley in 1986. There, working in collaboration with Jay M. Enoch and Vasudevan Lakshminarayan, she developed models for optical photoreceptors to interpret complex visual mechanisms such as directional sensitivity. "We believe our model is a correct one, but our challenge is to develop simplified models for applications," Calvo says.

Calvo has been working with and inspiring students in optics since 1979 and collaborating with colleagues even longer. She finds that jointly discussing ideas, proposing new set-ups or new applications, looking at common achievements, and comparing results with others in a creative atmosphere is a rewarding part of her career. "These moments are invaluable and compensate for all the other troubles and worries," she says.

Calvo has two children. Her son Gabriel is also a physicist, working in nonlinear optics; her daughter Rebeca has a degree in tourism. Together they are a musical family; Calvo studied guitar and piano, but it is her son who is the talented pianist. They enjoy playing and singing American tunes such as Gershwin's greatest hits.

Still, after more than 30 years of involvement in the science community, Calvo is very concerned with the current situation of the world. "We are lucky to be working in optics, an area of science that aids global sustainable development and facilitates the interaction of our work with the current needs of people," Calvo says. In addition to her myriad commitments to students, the research community, and SPIE, she's in her first of three years as the Secretary General of the International Commission for Optics. Says Calvo: "I would like to be part, even if just a small percentage, of those who contribute to building a better world."