Kilian R. Keller

University of Luxembourg

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Co-Authors

Daniele Brida

University of Luxembourg

Jonas Allerbeck

Swiss Federal Laboratories for Materials Science and Technology

Markus Ludwig

Deutsches Elektronen-Synchrotron DESY

Aline Vanderhaegen

University of Luxembourg

Ricardo Rojas‐Aedo

University of Luxembourg

Nicolò Maccaferri

University of Luxembourg

Pirmin Schweizer

University of Luxembourg

Deep Jariwala

University of Pennsylvania

R. Rojas-Aedo

University of Luxembourg

Arne Budweg

University of Konstanz

Cooperative Institutions

University of Konstanz

University of Luxembourg

Radiation Monitoring Devices (United States)

University of Pennsylvania

Politecnico di Milano

Institut für Rundfunktechnik

Max Planck Institute of Quantum Optics

Tianjin Medical University

Brandeis University

Ludwig-Maximilians-Universität München

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Generation of Sub-20 fs Pulses at 2 µm via Degenerate Optical Parametric Amplification

Conference on Lasers and Electro-Optics (2022)

Kilian R. Keller Arne Budweg Jonas Allerbeck Daniele Brida

We present a compact two-stage optical parametric amplifier that implements ultrabroad phase-matching at degeneracy driven by a ytterbium-based laser, enabling the generation of sub-20 fs pulses at 2 µm with µJ pulse energy.

Optical parametric amplifier

Ytterbium

Degeneracy (biology)

Optical Pumping

10.1364/cleo_at.2022.jw3a.50

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CW operation of GaAs travelling wave amplifiers for X-band frequencies.

Wolfgang Frey R. Becker R.W.H. Engelmann Kilian R. Keller

Source

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Citations (2)

Avalanche Diode Low Energy X-Ray and Nuclear Particle Detector

IEEE Transactions on Nuclear Science (1986)

Michael R. Squillante R. Farrell J.C. Lund F. Sinclair G. Entine

Avalanche diodes which are sensitive enough to detect low energy x-rays and beta particles have been fabricated and tested. They operate at room temperature and their structure is based on large area avalanche photodiodes. X-ray response has been measured over the energy range of 4 keV to 26 keV. At 5.9 keV a FWHM of 10% was obtained. In addition, multi-element sensors have been fabricated. Beta particles were detected from a variety of isotopic sources including C1-36, Sr-90, C-14 and H-3. The tritium beta particles, with 5 keV average energy, were detected with a 20% counting efficiency from a calibrated source. Tritium beta particles from biological samples were also measured. The high sensitivity to low energy x-rays and beta particles makes this detector useful for many industrial, military and commercial applications, and in particular for biomedical research.

Beta particle

Particle detector

X-ray detector

Alpha particle

Particle (ecology)

BETA (programming language)

10.1109/tns.1986.4337113

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Citations (29)

Stable supercontinuum generation in water at high repetition rates

Aline Vanderhaegen Kilian R. Keller R. Rojas-Aedo Markus Ludwig Daniele Brida

Water is an effective nonlinear medium for supercontinuum (SC) generation. We demonstrate high SC signal stability through precise liquid velocity control and superior spectral broadening compared to established solids at multi-kilohertz (kHz) repetition rates.

Supercontinuum

Repetition (rhetorical device)

10.1364/cleo_si.2024.sth1c.6

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Passive Elimination of Spectrally Correlated Intensity Noise in Ultrabroadband Supercontinua from Highly Nonlinear Fibers

Conference on Lasers and Electro-Optics (2019)

Philipp Sulzer Andreas Liehl Kilian R. Keller Jeldrik Huster Cornelius Beckh

Amplitude fluctuations of pump pulses for frequency broadening by third-order processes are found to result in strong anti-correlations of spectral output components. We exploit this information to minimize intensity noise in subsequent nonlinear conversion steps.

Intensity

10.1364/cleo_si.2019.stu4l.5

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Sub-ps thermionic electron injection effects on exciton-formation dynamics at a van der Waals semiconductor/metal interface

arXiv (Cornell University) (2022)

Kilian R. Keller Ricardo Rojas‐Aedo Huiqin Zhang Pirmin Schweizer Jonas Allerbeck

Inorganic van der Waals bonded semiconductors like transition metal dichalcogenides are subject of intense research due to their electronic and optical properties which are promising for next-generation optoelectronic devices. In this context, understanding the ultrafast carrier dynamics, as well as charge and energy transfer at the interface between metals and semiconductors is crucial and yet quite unexplored. Here, we present an experimental study on how thermally induced ultrafast charge carrier injection affects the exciton formation dynamics in bulk WS2 by employing a pump-push-probe scheme, where a pump pulse induces thermionic injection of electrons from the gold substrate into the conduction band of the semiconductor, and another delayed push pulse excites direct transitions in the WS2. The transient response shows different dynamics on the sub-ps timescale by varying the delay between pump and push pulses or by changing the pump fluence, thus disclosing the important role of ultrafast hot electron injection on the exciton formation dynamics. Our findings might have potential impact on research fields that target the integration of ultrafast optics at the boundary of photonics and electronics, as well as in optically-driven CMOS and quantum technologies.

Thermionic emission

10.48550/arxiv.2202.03818

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High stability white light generation in water at multi-kilohertz repetition rates

Optics Express (2023)

Kilian R. Keller Ricardo Rojas‐Aedo Aline Vanderhaegen Markus Ludwig Daniele Brida

An efficient supercontinuum (SC) generation featuring high spectral intensity across a large bandwidth requires high peak powers of several megawatts from pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition rates, the SC generated in most materials is unstable due to thermal effects. In this work, we leverage the superior dispersion properties of water to maximize the spectral width of the SC, while avoiding stability issues due to thermal loading by means of a constant laminar flow of the liquid. This flow is controlled by a differential pressure scheme that allows to precisely adjust the fluid velocity to an optimum value for maximum stability of the SC. This approach is successfully implemented for repetition rates of 50 kHz and 100 kHz and two different pump wavelengths in the visible (VIS) and near infrared (NIR) spectral region with stability of the SC signal only limited by the driving pulses. The resulting water SC spans more than one octave covering the VIS to NIR range. Compared to established materials, such as yttrium aluminum garnet (YAG) and sapphire, the spectral bandwidth is increased by 60% and 40% respectively. Our scheme has the potential to be implemented with other liquids such as bromine or carbon disulfide (CS2), which promise even wider broadening and operation up to the mid-infrared.

Repetition (rhetorical device)

10.1364/oe.503172

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Citations (2)

Passive Elimination of Spectrally Correlated Intensity Noise in Ultrabroadband Supercontinua from Highly Nonlinear Fibers

Conference on Lasers and Electro-Optics (2019)

Philipp Sulzer Andreas Liehl Kilian R. Keller Jeldrik Huster Cornelius Beckh

Intensity

10.23919/cleo.2019.8750667

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Broadband Pulse Generation at Infrared Frequencies Based on a multi-kHz Ytterbium Amplifier

Kilian R. Keller Arne Budweg Jonas Allerbeck Daniele Brida

Two-stage optical parametric amplification enables the generation of sub-20 fs pulses at near- to mid-infrared frequencies, spanning from 1.5 to 2.5 µm (120 – 200 THz) and tunable up to 5 µm (60 THz).

Ytterbium

Optical parametric amplifier

10.1109/cleo/europe-eqec52157.2021.9542201

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High stability white light generation in water at multi-kilohertz repetition rate

arXiv (Cornell University) (2023)

Kilian R. Keller Ricardo Rojas‐Aedo Aline Vanderhaegen Markus Ludwig Daniele Brida

Efficient supercontinuum (SC) generation featuring high spectral intensity across a large bandwidth requires high peak powers of several megawatt from pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition rates, the SC generated in most materials is unstable due to thermal effects. In this work, we leverage the superior dispersion properties of water to maximize the spectral width of the SC, while avoiding stability issues due to thermal loading by means of a constant laminar flow of the liquid. This flow is controlled by a differential pressure scheme that allows to precisely adjust the fluid velocity to an optimum value for maximum stability of the SC. This approach is successfully implemented for repetition rates of 50 kHz and 100 kHz and two different pump wavelengths in the visible (VIS) and near infrared (NIR) spectral region with stability of the SC signal only limited by the driving pulses. The resulting water SC spans more than one octave covering the VIS to NIR range. Compared to established materials, such as yttrium aluminum garnet (YAG) and sapphire, the spectral bandwidth is increased by 60 % and 40 % respectively. Our scheme has the potential to be implemented with other liquids such as bromine or carbon disulfide (CS2), which promise even wider broadening and operation up to the mid-infrared.

Supercontinuum

10.48550/arxiv.2308.06636

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