| 1. |
- Harth, A., et al.
(författare)
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Few-cycle high-repetition rate OPCPA for multiphoton PEEM towards atto-PEEM
- 2016
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Ingår i: International Conference on Ultrafast Phenomena, UP 2016. - 9781943580187 ; Part F20-UP 2016
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Konferensbidrag (refereegranskat)abstract
- We present a few-cycle high-repetition rate optical parametric amplifier for multiphoton PEEM experiments on semiconductor nanowires. This parametric amplifier is also used for the generation of high-order harmonics at 200kHz for future atto-PEEM experiments.
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| 2. |
- Guo, Chen, et al.
(författare)
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Phase control of attosecond pulses in a train
- 2018
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:3
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast processes in matter can be captured and even controlled by using sequences of few-cycle optical pulses, which need to be well characterized, both in amplitude and phase. The same degree of control has not yet been achieved for few-cycle extreme ultraviolet pulses generated by high-order harmonic generation (HHG) in gases, with duration in the attosecond range. Here, we show that by varying the spectral phase and carrier-envelope phase (CEP) of a high-repetition rate laser, using dispersion in glass, we achieve a high degree of control of the relative phase and CEP between consecutive attosecond pulses. The experimental results are supported by a detailed theoretical analysis based upon the semi-classical three-step model for HHG.
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| 3. |
- Heyl, C. M., et al.
(författare)
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A nozzle for high-density supersonic gas jets at elevated temperatures
- 2018
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 89:11
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Tidskriftsartikel (refereegranskat)abstract
- We present the development of a gas nozzle providing high-density gas at elevated temperatures inside a vacuum environment. Fused silica is used as the nozzle material to allow the placement of the nozzle tip in close proximity to an intense, high-power laser beam, while minimizing the risk of sputtering nozzle tip material into the vacuum chamber. Elevating the gas temperature increases the gas-jet forward velocity, allowing us to replenish the gas volume in the laser-gas interaction region between consecutive laser shots. The nozzle accommodates a 50 μm opening hole from which a supersonic gas jet emerges. Heater wires are used to bring the nozzle temperature up to 730 °C, while a cooling unit ensures that the nozzle mount and the glued nozzle-to-mount connection is kept at a temperature below 50 °C. The presented nozzle design is used for high-order harmonic generation in hot gases using gas backing pressures of up to 124 bars.
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| 4. |
- Heyl, C. M., et al.
(författare)
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Noncollinear optical gating - A method for intra-cavity single attosecond pulse generation?
- 2019
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Ingår i: Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. - 9781467374750
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Konferensbidrag (refereegranskat)abstract
- The process of high-order harmonic generation requires laser intensities around 1014 W/cm2, most easily reached with laser pulses of high energy, thus implicitly limiting the repetition rate of attosecond sources. A route towards multi-MHz attosecond sources relies on HHG inside a passive enhancement cavity [1]. Although successfully demonstrated for attosecond pulse trains, the generation of single attosecond pulses (SAPs) inside a cavity remains an unsolved challenge, mainly limited by dispersion management and out-coupling problems. We recently proposed a new gating concept for SAP generation [2], noncollinear optical gating (NOG) which has the potential to facilitate SAP gating and efficient out-coupling at once. Similar to the recently introduced attosecond lighthouse [3] NOG employs attosecond angular streaking [4] and combines this concept with noncollinear HHG, proposed earlier [5] as out-coupling method for intra cavity HHG.
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| 5. |
- Lorek, Eleonora, et al.
(författare)
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High-Order Harmonic Generation and Plasmonics
- 2015
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Ingår i: Nano-Structures for Optics and Photonics : Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion - Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion. - Dordrecht : Springer Netherlands. - 9789401791328 - 9789401791335 ; , s. 531-531
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Bokkapitel (refereegranskat)abstract
- Attosecond pulses allow for imaging of very fast processes, like electron dynamics. Stockman et al. suggested to use these pulses in connection with a Photoemission electron microscope (PEEM) to study the ultrafast dynamics of plasmons (Stockman et al. Nat Photonics 1:539–544, 2007). For efficient plasmon studies, the repetition rate of the attosecond pulses used needs to be higher than a few kHz (Mikkelsen et al. Rev Sci Instrum 80:123703, 2009). Attosecond pulses are produced in a process called high-order harmonic generation (HHG) (Paul et al. Science 292(5522):1689–1692, 2001; Ferray et al. J Phys B At Mol Opt Phys 21:L31–L35, 1988). In HHG, a strong laser field allows an electron to tunnel out, get accelerated and recombine with a high kinetic energy resulting in extreme ultraviolet attosecond pulses. The large intensity needed to drive the process normally limits the repetition rate of the laser to a few kHz. Using a tight focusing scheme (Heyl et al. Phys Rev Lett 107:033903, 2011; Vernaleken et al. Opt Lett 36:3428–3430, 2011), we, however, generate harmonics at a repetition rate of 200 kHz, both with a commercial turn-key laser and with an advanced laser system. Suitable nanostructures for a strong field enhancement are produced in-house and the field enhancement is studied with PEEM in a non-time resolved manner. With high-order harmonics produced at a high repetition rate, we hope to be able to follow also the ultrafast dynamics of plasmons in these structures (Mårsell et al. Ann der Phys 525:162–170, 2013).
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| 6. |
- Manschwetus, B., et al.
(författare)
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Two-photon double ionization of neon studied with intense attosecond pulse trains
- 2016
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Ingår i: International Conference on Ultrafast Phenomena, UP 2016. - 9781943580187 ; Part F20-UP 2016
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Konferensbidrag (refereegranskat)abstract
- We focused an intense attosecond pulse train into a neon gas target and observed Ne2+ resulting from two-photon double ionization. By modifying the photon spectrum we find that the process is dominated by the sequential ionization via the Ne+ ion.
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| 7. |
- Manschwetus, B., et al.
(författare)
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Two-photon double ionization of neon using an intense attosecond pulse train
- 2016
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Ingår i: Physical Review A. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 93:6
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Tidskriftsartikel (refereegranskat)abstract
- We present a demonstration of two-photon double ionization of neon using an intense extreme ultraviolet (XUV) attosecond pulse train (APT) in a photon energy regime where both direct and sequential mechanisms are allowed. For an APT generated through high-order harmonic generation (HHG) in argon we achieve a total pulse energy close to 1μJ, a central energy of 35 eV, and a total bandwidth of ∼30 eV. The APT is focused by broadband optics in a neon gas target to an intensity of 3×1012Wcm−2. By tuning the photon energy across the threshold for the sequential process the double ionization signal can be turned on and off, indicating that the two-photon double ionization predominantly occurs through a sequential process. The demonstrated performance opens up possibilities for future XUV-XUV pump-probe experiments with attosecond temporal resolution in a photon energy range where it is possible to unravel the dynamics behind direct versus sequential double ionization and the associated electron correlation effects.
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| 8. |
- Porat, G., et al.
(författare)
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Phase-matched extreme-ultraviolet frequency-comb generation
- 2019
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Ingår i: Ultrafast Optics XII. - 1996-756X .- 0277-786X. - 9781510635128 ; 11370, s. 94-95
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Konferensbidrag (refereegranskat)abstract
- Extreme ultraviolet (XUV) laser radiation is commonly produced via high-harmonic generation (HHG) in gases. The lasers that drive this process typically operate at low pulse repetition rates (<100 kHz). Under these operating conditions, the plasma generated by each laser pulse clears the generation volume before the next pulse arrives. Therefore, each laser pulse interacts with fresh plasma-free gas, where phase-matching facilitates efficient HHG. However, applications requiring high counting statistics or frequency-comb precision make high repetition rates (>10 MHz) necessary. Unfortunately, at high repetition rates, plasma accumulates in the XUV generation region and prevents phase-matching, resulting in low HHG efficiency. We use high-temperature gas mixtures to increase the gas translational velocity, thus reduce plasma accumulation and facilitate phase-matching. We experimentally achieve phase-matched HHG at a repetition rate of 77 MHz, generating record power of ~2 mW at 97 nm and ~0.9 mW at 67 nm.
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| 9. |
- Reid, Derryck T., et al.
(författare)
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Roadmap on ultrafast optics
- 2016
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Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 18:9
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Tidskriftsartikel (refereegranskat)abstract
- The year 2015 marked the 25th anniversary of modern ultrafast optics, since the demonstration of the first Kerr lens modelocked Ti:sapphire laser in 1990 (Spence et al 1990 Conf. on Lasers and Electro-Optics, CLEO, pp 619-20) heralded an explosion of scientific and engineering innovation. The impact of this disruptive technology extended well beyond the previous discipline boundaries of lasers, reaching into biology labs, manufacturing facilities, and even consumer healthcare and electronics. In recognition of such a milestone, this roadmap on Ultrafast Optics draws together articles from some of the key opinion leaders in the field to provide a freeze-frame of the state-of-the-art, while also attempting to forecast the technical and scientific paradigms which will define the field over the next 25 years. While no roadmap can be fully comprehensive, the thirteen articles here reflect the most exciting technical opportunities presented at the current time in Ultrafast Optics. Several articles examine the future landscape for ultrafast light sources, from practical solid-state/fiber lasers and Raman microresonators to exotic attosecond extreme ultraviolet and possibly even zeptosecond x-ray pulses. Others address the control and measurement challenges, requiring radical approaches to harness nonlinear effects such as filamentation and parametric generation, coupled with the question of how to most accurately characterise the field of ultrafast pulses simultaneously in space and time. Applications of ultrafast sources in materials processing, spectroscopy and time-resolved chemistry are also discussed, highlighting the improvements in performance possible by using lasers of higher peak power and repetition rate, or by exploiting the phase stability of emerging new frequency comb sources.
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