Valeriy Yashchuk aims to make the binary pseudo-random calibration tool (BPR) the internationally recognized standard for thorough characterization of a broad spectrum of measuring tools in the spatial frequency domain. Others might be stymied by technical challenges or find it daunting to convince scientists around the world to agree on one standard, but Yashchuk is accustomed to roadblocks and finding creative solutions to overcome them. At this year’s ALS User Meeting, the Users’ Executive Committee recognized Yashchuk, senior staff scientist and ALS program lead for metrology, for his “contribution to the development of a precision surface measurement technology critical for advanced x-ray optical systems.”
As a teenager in USSR, Yashchuk won the physics and math competition of the northwest region of the Soviet Union, which granted him admission to the Physical Mathematical Boarding School of Leningrad University at age 14. His early acumen seemed to set a course for the rest of his life, and indeed, after graduation from university, Yashchuk worked in the Nuclear Physics Institute (NPI) in Leningrad (now St. Petersburg) for almost 20 years. However, the fall of the Soviet Union also collapsed the research program and funding streams, and having no salary at the NPI for three months, Yashchuk worked four jobs to be able to feed his family. Then, he joined Dmitry Budker’s group in the UC Berkeley physics department. Although Yashchuk was no longer working in nuclear physics, he was able to apply his experience and knowledge in super-high-accuracy measurements to a new field of experiments in atomic physics and magnetometry, which eventually brought him to the ALS.
“At the interview, they asked why I was switching from making fundamental measurements,” Yashchuk recalled. “I told them that it doesn’t matter what you’re measuring in physics—it’s always the same problems of random noise, systematic errors, and drifts you have to solve.”
During the interview process, Yashchuk realized that he could apply his knowledge of binary pseudo-random techniques to a variety of ALS metrology tools and beamlines. His method calibrates metrology instruments over both the entire spatial and spatial frequency dynamic range, allowing high-confidence measurements in the instrument transfer function (ITF). It uses test samples that are sets of two physical parameters, such as binary heights, or two materials with different physical properties, such as x-ray or electron transmission, distributed according to a pseudo-random pattern. “Valeriy’s recent work has led to an improvement in the absolute accuracy of x-ray optics measurements by a factor of 30,” said Photon Science Development Group Lead Ken Goldberg.
“The most important and unique application is to the instrumental transfer function calibration of x-ray microscopes,” said Argonne National Laboratory Senior Physicist Lahsen Assoufid. Not only have BPR multilayer samples been used to calibrate ALS Beamlines 6.1.2 and 184.108.40.206, “the Advanced Photon Source at ANL has already used similar samples for resolution characterization,” Assoufid said.
Yashchuk’s peers confirm the broad impacts of his work. Kazuto Yamauchi, professor of precision science and technology and applied physics at Osaka University, acknowledged Yashchuk’s contributions to the evaluation of precision x-ray optical devices, and said, “He has achieved results worthy of a world leader.”
“The method has been applied to improve the calibration of interferometers, optical microscopes, scanning and transmission electron microscopes, scanning probe and atomic force microscopes, and x-ray microscopes,” explained Alexei Erko, professor of physics at Freie Universität Berlin. These improved calibrations have benefited nanoscience and fabrication, semiconductors, and more.
Recognition of BPR has also come in the form of a patent, R&D 100 award, and support from the DOE and NASA STTR/SBIR Programs. Yashchuk’s collaborators include small businesses like HighRI Optics and Rochester Scientific and government agencies like NIST. In fact, upon receiving the Halbach Award, Yashchuk was quick to credit his collaborators as well. He acknowledged Wayne McKinney, Peter Takacs, Sergey Babin, Raymond Conley, Keiko Munechika, Simon Rochester, Erik Anderson, Weilun Chao, Ulf Griesmann, Ian Lacey, Carlos Pina-Hernandez, and Allen Roginsky as key partners in developing and applying the BPR technique.
With input from academia, government labs, and industry, as well as applications across multiple light sources, it does not seem so outlandish a goal for BPR calibration to be recognized as an international standard after all.
When asked what has driven him to pursue international standardization, Yashchuk responded, “Everyone wants to leave a legacy behind.” He added, “I would be glad if people are using it.”
Klaus Halbach was a senior staff scientist at LBNL who pioneered the development of undulators using permanent magnets, and other innovations in accelerator physics. Even though he retired from LBNL in 1991, he remained active in lab projects and student training until his death in 2000.