(Picture Credit: Tim Kramer, RUB) 

Clara Saraceno

Full Professor at the Ruhr University Bochum, Germany

High-power ultrafast moves into the Terahertz

Ultrafast laser-driven broadband Terahertz light sources are nowadays ubiquitous tools in many scientific fields, enabling researchers to control and probe an immense variety of low energy phenomena in condensed matter and other systems. They are also being increasingly deployed in industrial settings for inspection and non destructive testing: THz waves "see through" optically opaque objects, and can provide rich spectroscopic information at a glance. While techniques to generate short, broadband THz pulses using ultrafast laser pulses and nonlinear conversion techniques have seen continuous performance progress in the last few years, their average power has traditionally moved comparatively slowly, which has prevented many of these fields from blooming. On the other hand, the increasing availability and enormous performance progress of ultrafast Ytterbium-based lasers providing multi-100-W to kilowatt average-power levels has opened up the area of high average power, laser-driven THz sources: recent results reaching average power levels in the THz domain approaching the watt-level, opening the door to a multiplicity of new and old research areas to be re-visited. We review recent progress in the generation of high-average power THz-pulses, current technological challenges in scaling THz average power, and applications areas that could potentially benefit from these novel sources.

About the Speaker

Clara Saraceno is a full professor at the Ruhr University Bochum, Germany. She was born in 1983 in Argentina. In 2007 she completed a Diploma in Engineering and an MSc at the Institut d’Optique Graduate School, Paris France. She first worked as an engineering trainee at Coherent Inc. Santa Clara, California, until 2008. She then completed a PhD in Physics at ETH Zürich in 2012 where she carried out research on high-power ultrafast disk lasers. From 2013-2014, she worked as a Postdoctoral Fellow at the University of Neuchatel and ETH Zürich, Switzerland, where she worked on high-flux XUV generation via high harmonics generation. In 2016, she received a Sofja Kovalevskaja Award of the Alexander von Humboldt Foundation and became Associate Professor of Photonics and Ultrafast Science in the Electrical Engineering Faculty at the Ruhr University Bochum, Germany, followed by a full professorship in the same university since 2020. 
Prof. Saraceno’s research interests are in the development of high-power ultrafast laser systems and their application in driving secondary sources via nonlinear optics. One of her current main research areas is THz technology and spectroscopy, where her group aims to achieve high average power level broadband THz radiation.
She has received a number of prizes and awards including the ETH Medal for Outstanding PhD thesis (2013), the European Physical Society Quantum Electronics and Optics Division PhD prize in applied aspects (2013), the Sofja Kovalevskaja Award of the Alexander von Humboldt (2016), an ERC Starting Grant (2018), the SPIE Harold E. Edgerton Award for High-speed Optics (2024) and an ERC Consolidator Grant (2024). She was elected Fellow of Optica (formerly the Optical Society) in the 2022 class.

LinkedIn: Clara Saraceno

Arie den Boef

Corporate Fellow at ASML, Part-time full professor at Vrije Universiteit Amsterdam, Part-time group leader of the “Computational Imaging” group at ARCNL, The Netherlands

Digital Holographic Microscopy in overlay metrology for the semiconductor industry

Device density in semiconductor chips continues to increase through many innovations. For example, high-NA EUV lithography enables the printing of smaller features that allow more devices in a smaller area. In addition, many innovations are taking place in the area of 3D device integration where devices are stacked on each other.
Manufacturing state-of-the-art chips with sufficient yield requires good control of many process steps during manufacturing. Overlay, for example, is a critical parameter in chip manufacturing. Overlay describes the lateral mis-alignment between 2 overlapping layers in a device. Any misalignment (=overlay error) can result in significant yield loss and overlay must therefore be controlled to the 1 nm level. These levels of control need accurate and robust overlay metrology.
Overlay is often measured on dedicated targets using optical microscopy. However, robustly achieving sub-nanometer precision requires near-perfect microscopic imaging conditions which drives the need for high-quality imaging optics with very low aberration levels. Technically this is possible, but it leads to complex and costly optical imaging systems. In order to keep metrology costs to acceptable levels there is a need for a microscopy approach that achieves the sub-nanometer precision levels in a more cost-efficient way.
The ARCNL research institute is exploring Digital Holographic Microscopy (DHM) as a possible future option for overlay metrology. In our DHM concept we image an overlay target on a camera using low-cost high-NA optics with only a few lens elements. The resulting image is aberrated but DHM is able to computationally correct for aberrations and therefore offers near-perfect imaging in a cost-effective way.
This talk will present an overview of the status of our research on DHM. We will explain the underlying concept and present some first experimental data that demonstrate the potential benefit for overlay metrology. Moreover, we will also present potential solutions to some of the challenges that come with DHM like vibration sensitivity.

About the Speaker

Arie den Boef is a Corporate Fellow at ASML where he is involved in research on optical wafer metrology. He joined ASML in 1997 and since 2016 he is also a part-time full professor at the Vrije Universiteit in Amsterdam and a part-time group leader of the “Computational Imaging” group at the Advanced Research Center for Nano Lithography in Amsterdam (ARCNL).
From 1995 till 1997 he worked at Philips Optical Storage as a System Engineer for optical recording systems. From 1992-1995 he was at Philips Medical Systems working on Magnetic Resonance Imaging. Before joining Medical Systems Arie was at Philips Research Laboratories from 1979 – 1992 where he was involved in laser diode characterization and research on optical measurement systems for industrial inspection.
Arie received a B.Sc. degree in electrical engineering in 1985 from the Eindhoven Polytechnic Institute and a Ph.D. degree in 1991 from the department of Physics from the University of Twente, The Netherlands. The topic of his Ph.D. thesis was “Scanning Force Microscopy using Optical Interferometry”.

Pablo Artal

Full Professor of Optics at the University of Murcia, Spain

Two-photon infrared vision

Although human vision is traditionally confined to the visible spectrum, recent research has revealed that pulsed near-infrared (NIR) light can be perceived as visible due to two-photon absorption (TPA) in the photoreceptors. This nonlinear optical process enables infrared photons to effectively stimulating the visual pigments in a manner similar to conventional visible-light absorption. This expands our understanding of retinal physiology and opens new possibilities for both fundamental and applied vision research. In this presentation, I will discuss our recent investigations into TPA-mediated vision, including its impact on visual acuity and color perception. Our experimental studies demonstrate that visual resolution under TPA conditions is comparable to that of normal visible-light vision, achieved by scanning a pulsed NIR beam across the retina to form letter stimuli. Furthermore, our psychophysical experiments reveal that perceived hues shift predictably with increasing NIR wavelength (880 to 1100 nm) and radiant power (10 to 30 µW), transitioning from reddish-purple to blue, green, and yellow-green. These findings provide novel insights into the intensity-dependent interplay between single-photon (1P) and two-photon (2P) absorption processes in human vision. Beyond its fundamental implications, TPA vision presents exciting clinical and technological opportunities. It offers a potential method for retinal diagnostics that circumvents ocular opacities. Additionally, the development of TPA-based RGB displays could revolutionize display technologies. This presentation will provide an overview of our key findings, the methodologies employed, and the broader impact of TPA vision research and applications.

About the Speaker

Pablo Artal studied physics at the University of Zaragoza (Spain) and completed his PhD at the Instituto de Óptica (CSIC) in Madrid. He pursued postdoctoral research at Cambridge University (UK) and the Institut d’Optique in Orsay, France, before securing a permanent research position at the Instituto de Óptica. In 1994, he became the first full Professor of Optics at the University of Murcia, where he founded the Laboratorio de Óptica. His research focuses on the optics of the eye and retina, as well as the development of optical and electronic imaging techniques for vision, ophthalmology, and biomedicine. He has published over 400 peer-reviewed papers (h-index:87), holds more than 30 international patents, and has co-founded two spin-off companies. He has received numerous prestigious awards, including the Edwin H. Land Medal (2013), the King Jaime I Award in New Technologies (2015), the Spanish National Research Award “Juan de la Cierva” (2018), the Edgar D. Tillyer Award (2019), and the 2021 medal of the Spanish Royal Physics Society. A Fellow of Optica (OSA), ARVO, EOS, and SPIE, he continues to contribute significantly to both fundamental and applied optics.

Nathalie Picqué

Director at the Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Professor of Physics at the Humboldt University of Berlin, Germany

Frequency Comb Interferometry

Optical frequency combs have revolutionized time and frequency metrology by providing rulers in frequency space that measure large optical frequency differences and/or straightforwardly link microwave and optical frequencies. Such combs enable precision laser spectroscopy, tests of fundamental physics and provide the long-missing clockwork mechanism for optical clocks.

While frequency combs have become key to research areas such as attosecond science, or calibration of astronomical spectrographs, one of the most successful applications beyond their original purpose has been dual-comb interferometry. An interferometer can be formed using two frequency combs of slightly different line spacing. Dual-comb interferometers without moving parts are fundamentally different from any other type of interferometers: they perform direct frequency measurements, without geometric limitations to resolution. They outperform state-of-the-art devices in an increasing number of fields including spectroscopy and three-dimensional imaging, offering unique features such as frequency measurements, accuracy, precision, speed. This talk will provide a short introduction to optical frequency combs and will survey dual-comb interferometry and its latest exciting developments.

About the Speaker

Nathalie Picqué is a Director at the Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (Berlin, Germany) and a Professor of Physics at the Humboldt University of Berlin. She has been previously a research group leader at the Max-Planck Institute of Quantum Optics (Garching, Germany) and a research scientist with the Centre National de la Recherche Scientifique (CNRS) at Orsay (France). She received her doctoral degree in Physics from Université Paris-Saclay (France) in 1998. Her research interests are in the areas of optics and molecular physics, more particularly in interferometry, precision spectroscopy and laser technology. Her research focuses on exploring new ideas that involve laser frequency combs and on applying these novel concepts to metrology, molecular spectroscopy, holography and chip-scale sensing. Nathalie Picqué has received several awards, including the 2021 Gentner-Kastler Prize in Physics, the 2022 Breakthrough in Physical Sciences of the Falling-Walls Foundation and the 2024 William F. Meggers Award.