Course brings advances in use of lasers to São Paulo

Event held with FAPESP’s support was designed to strengthen Brazil’s capacity in advanced photonics, which currently drives a market worth US$530 billion worldwide.

By José Tadeu Arantes  |  Agência FAPESP – Advances in the field of optics have been so fast and have produced such surprising results that even outstanding master’s students or PhD researchers are unlikely to know much about what is happening at the cutting edge of their research area.

This is the thinking that motivated the organization of the São Paulo School of Advanced Science (SPSAS) on Frontiers in Lasers and their Applications, which took place on July 16-27, 2018, at the Energy & Nuclear Research Institute (IPEN) in São Paulo, Brazil.

Chaired by Niklaus Ursus Wetter, a senior researcher at IPEN and a professor at the University of São Paulo (USP), the event was supported by FAPESP through its SPSAS program. It assembled some of the most renowned researchers in the field as well as graduate students from various parts of the world.

“We designed this meeting to strengthen Brazil’s capacity in advanced photonics, which currently drives a market worth US$530 billion worldwide,” Wetter told Agência FAPESP.

“We brought leading researchers in their respective areas to tell students all about the state of the art in the various dimensions of optics, from the basic science to its multiple applications.”

The scope of the event encompassed light generation, amplification, modulation, emission, transmission, detection and processing. The applications discussed ranged from environmental monitoring to aerospace technology and from nanomachining to medicine. Training scientists, incubating startups and fostering innovation in the field were desirable medium-term consequences.

FAPESP has invested heavily in advanced optics research activities and facilities. Scientific Director Carlos Henrique de Brito Cruz participated in the opening of the SPSAS at IPEN, where he informed the audience of researchers and students of the types of support offered by FAPESP to people interested in study or career opportunities in São Paulo State.

Ultrafast lasers, a subarea highlighted at the event, have become a topic of major interest because of their capacity to produce the briefest and most powerful phenomena known to mankind.

“The term ultrafast refers to the temporal duration of the laser pulses,” Wetter explained. “We can currently achieve pulses lasting 5 femtoseconds [5x10^-15 s], which corresponds to five thousandths of a trillionth of a second, but there have been pulses lasting one or two orders of magnitude less, between 10^-16 s and 10^-17 s. So by operating a laser with an energy of one millijoule (1 mJ) per pulse, which isn’t a great deal, and compressing this energy into a time interval of 5 femtoseconds, we can generate as much as 10¹⁹ W at the laser focus. That’s equivalent to 10 million times more power than can be generated by all the world’s power stations together.”

The machine that can produce all this power is not a giant device like the Large Hadron Collider (LHC) at CERN on the Franco-Swiss border but rather an apparatus that can be placed on a laboratory bench.

“Ultrafast lasers can produce so much power that with only a little more, it would be possible to create matter in a controlled manner,” Wetter said. “By focusing a laser in a vacuum, we could separate that vacuum into electrons and positrons, for example. That would be like going back to what happened a fraction of a second after the Big Bang.”

These extremely powerful lasers are seen as potential sources of proton beams, which are increasingly used in cancer treatment.

However, they have new uses even now. “One application is the creation of time and frequency standards that are three orders of magnitude more precise than those made possible by existing atomic clocks. We can define one second with 18-digit precision,” Wetter said.

Random lasers

Multiphoton ablation is another application that derives from the interaction between ultrafast lasers and matter. This is a nonthermal process that can achieve very-high-precision cutting, with resolutions on the order of hundreds of nanometers, without otherwise affecting the material.

Conventional cutting processes always heat up the material, changing its properties at the edges of the cut. Cutting with an ultrafast laser, however, leaves the properties of interest intact.

The various kinds of laser technology have practically unlimited applications, from the modification of metal structures – creating highly liquid-repellent materials or, by contrast, materials that retain oil in microcavities to prevent attrition and wear of parts – to three-dimensional prospecting for pollution aerosols in areas spanning kilometers.

“A very interesting new field is that of random lasers, which can be used to study light propagation in a diffuse medium, such as an aspirin pill, for example,” Wetter said. “Besides investigation of the material itself via analysis of the rebounding light, the phenomenon can be used to achieve new optical effects, such as light imprisonment, in which the light beam becomes trapped inside the material indefinitely.”

Another new field is laser beam structuring, which consists of giving photons an angular momentum so that they turn to and fro in circular, triangular, square or hexagonal trajectories. This technique can be used to build metamaterials with noteworthy optical properties, such as negative refraction or invisibility.

Specialists who deal with these and other phenomena at the world’s advanced centers attended the SPSAS on Frontiers in Lasers and their Applications.

The following participants came from abroad: Cefe Lopez, Institute of Materials Science of Madrid, Spain; John Girkin, Durham University, UK; Jorge Rocca, Colorado State University, USA; Rui Vilar, IST, Lisbon Technical University, Portugal; Takashige Omatsu, Chiba University, Japan; Thomas Südmeyer, University of Neuchâtel, Switzerland; and Volker Freudenthaler, Ludwig Maximilian University of Munich, Germany.