115 114 Principal Scientist Profiles Stefan Nolte Stefan Nolte Principal Scientist Profiles PROFESSOR OF EXPERIMENTAL PHYSICS/ LASER PHYSICS, INSTITUTE OF APPLIED PHYSICS Prof. Nolte is the head of the Ultrafast Optics group at the Institute of Applied Physics and Deputy Director of the Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Jena. He is a member of the executive board of the Abbe School of Photonics, a fellow of the Max Planck School of Photonics, and a member of the Center of Medical Optics and Photonics (CeMOP). In December 2013, he has been awarded the Federal German President‘s Award for Innovation in Science and Technology together with Bosch and Trumpf for transferring ultrashort pulse laser processing into industrial mass production. STEFAN NOLTE RESEARCH AREAS The research topic of Prof. Nolte is ultrashort laser pulses inclucing ultrashort pulse micromachining and material modification for industrial and medical applications, areas where he is engaged in since the field’s inception in the mid-1990s. Current research interests include: • Linear and nonlinear interaction of light and matter • Micro- and nanostructuring by ultrashort laser pulses • Ultrashort pulse laser cutting and welding • 3D-volume structuring of glasses and crystals • Fiber and volume Bragg gratings • Linear and nonlinear optics in discrete systems • Additive manufacturing using ultrashort laser pulses • Applications of ultrashort lasers in ophthalmology • Nonlinear spectroscopy TEACHING FIELDS Stefan Nolte is teaching courses ranging from fundamental aspects of physics to state-of-the-art research. He is also responsible for the ASP optics training laboratory, including labwork internships. He gives courses in Atomic and Molecular Physics and Ultrafast Optics. RESEARCH METHODS The laboratories led by Prof. Nolte are equipped with a wide variety of lasers, handling equipment and characterization technology. These include: • High repetition rate ultrashort pulse laser systems (7 fs to 20 ps) including wavelength conversion (300 nm to 10 µm), and average powers up to 500 W • High-precision positioning and laser scanner systems • Equipment for sample preparation and characterization (optical microscopes, electron microscope, Raman microscope, etc.) • Characterization of spectral and spatial properties of micro- and nanostructured samples • Characterization of nonlinear spatio-temporal dynamics RECENT RESEARCH RESULTS The Ultrafast Optics group has extensive capabilities to precisely structure virtually any material on a micrometer scale. This includes the defined modification of the optical properties within the volume of transparent materials, which is e.g. used to realize complex coupled waveguide array structures of various three-dimensional geometries. Its potential is exploited for tailoring the flow of light in artificially structured glass. By combining this with the localized generation of so-called nanogratings acting as artificial birefringent structures, integrated optical quantum gates can be realized for quantum optical operations [1]. In addition, we use ultrashort laser pulses to inscribe highly periodic structures into transparent materials. This way we are able to realize Bragg gratings in various fibers, which can be used as efficient fiber-integrated laser mirrors withstanding even highest powers [2]. In addition, the inscription of aperiodic fiber Bragg gratings allows for a precise spectral filtering as required e.g. in astrophotonic applications [3]. When this technique is extended to bulk material, volume Bragg gratings can be generated. We recently managed to inscribe such highly efficient gratings into fluoride glasses, targeting applications as lasers or hyperspectral imaging in the mid-infrared spectral range [4]. For optimizing the laser processing, a detailed spatio-temporal analysis of the laserglass interaction is essential [5]. Apart from structuring and ablation, we apply ultrashort laser pulses for additive manufacturing. The high peak power of these pulses allows to process a large variety of different materials. Currently, we focus on copper, glass as well as lightweight alloys. Here, the ultrashort pulse duration results in extremely fast heating and cooling cycles, allowing e.g. the laser powder bed fusion of hypereutectic alloys [6]. A promising spectroscopic approach for the process analysis of chemical reactions is the coherent anti-Stokes Raman scattering using femtosecond laser pulses (fs-CARS). The short pulse durations enable the excitation of molecular states of a gas, before detrimental molecular collisions take place. This feature makes fs-CARS ideally suited for thermometry and gas concentration measurements under high temperature and high pressure conditions. We recently investigated twobeam fs/ps CARS for effective concentration and temperature measurements in gas mixtures [7]. LASER-WRITTEN INTEGRATED OPTICS DEEP INSIDE SILICON Silicon is the backbone of today’s semiconductor industry. Despite electronics, silicon photonics plays an increasing role due to the large interest of integrating photonic and electronic devices on the same chip. However, conventional approaches are limited to the surface resulting in 2D planar photonic solutions. Recently, we directly inscribed highly localized single mode waveguides into the bulk of crystalline silicon by using infrared ultrashort laser pulses [Kämmer et al., Laser Photonics Rev. 13, 1800268 (2019)]. Microstructural analysis revealed that defects and dislocations are induced in the crystalline matrix. The resulting strain is expected to be responsible for the positive refractive index changes of up to 5x10-3 enabling waveguiding with losses below 8.7 dB/cm [Alberucci et al., Phys. Rev. Applied 14, 024078 (2020)]. In order to demonstrate the 3D writing capabilities, a buried Y-splitter was fabricated with an exact splitting ratio of 50:50 [Matthäus et al., Opt. Express 26, 24089 (2018)]. [1] Lammers et al., Opt. Mat. Express 9, 2560 (2019). [2] Krämer et al., Opt. Lett. 45, 1447 (2020). [3] Goebel et al., Opt. Lett. 43, 3794 (2018). [4] Talbot et al., Opt. Lett. 45, 3625 (2020). [5] Bergner et al., Appl. Opt. 57, 4618 (2018). [6] Ullsperger et al., Appl. Phys A 123, 798 (2017). [7] Ran et al., J Raman Spectrosc. 50, 1268 (2019). Contact: Phone: + 49 3641 9-47820 Email: stefan.nolte@uni-jena.de
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