| 1. |
- Bruder, Lukas, et al.
(författare)
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Generation and compression of 10-fs deep ultraviolet pulses at high repetition rate using standard optics
- 2021
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Ingår i: Optics Express. - 1094-4087. ; 29:16, s. 25593-25604
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Tidskriftsartikel (refereegranskat)abstract
- The generation and characterization of ultrashort laser pulses in the deep ultraviolet spectral region is challenging, especially at high pulse repetition rates and low pulse energies. Here, we combine achromatic second harmonic generation and adaptive pulse compression for the efficient generation of sub-10 fs deep ultraviolet laser pulses at a laser repetition rate of 200 kHz. Furthermore, we simplify the pulse compression scheme and reach pulse durations of ≈10 fs without the use of adaptive optics. We demonstrate straight-forward tuning from 250 to 320 nm, broad pulse spectra of up to 63 nm width, excellent stability and a high robustness against misalignment. These features make the approach appealing for numerous spectroscopy and imaging applications.
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| 2. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Understanding radiative transitions and relaxation pathways in plexcitons
- 2021
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Ingår i: Chem. - : Elsevier BV. - 2451-9308 .- 2451-9294. ; 7:4, s. 1092-1107
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Tidskriftsartikel (refereegranskat)abstract
- Molecular aggregates on plasmonic nanoparticles have emerged as attractive systems for the studies of polaritonic light-matter states, called plexcitons. Such systems are tunable, scalable, easy to synthesize, and offer sub-wavelength confinement, all while giving access to the ultrastrong light-matter coupling regime, promising a plethora of applications. However, the complexity of these materials prevented the understanding of their excitation and relaxation phenomena. Here, we follow the relaxation pathways in plexcitons and conclude that while the metal destroys the optical coherence, the molecular aggregate coupled to surface processes significantly contributes to the energy dissipation. We use two-dimensional electronic spectroscopy with theoretical modeling to assign the different relaxation processes to either molecules or metal nanoparticle. We show that the dynamics beyond a few femtoseconds has to be considered in the language of hot electron distributions instead of the accepted lower and upper polariton branches and establish the framework for further understanding.
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| 3. |
- Kolesnichenko, Pavel V., et al.
(författare)
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Fully symmetric dispersionless stable transmission-grating Michelson interferometer
- 2020
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Ingår i: Optics Express. - 1094-4087. ; 28:25, s. 37752-37757
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Tidskriftsartikel (refereegranskat)abstract
- Michelson interferometers have been routinely used in various applications ranging from testing optical components to interferometric time-resolved spectroscopy measurements. Traditionally, plate beamsplitters are employed to redistribute radiation between the two arms of an interferometer. However, such an interferometer is susceptible to relative phase fluctuations between the two arms resulting from vibrations of the beamsplitter. This drawback is circumvented in diffraction-grating-based interferometers, which are especially beneficial in applications where highly stable delays between the replica beams are required. In the vast majority of grating-based interferometers, reflective diffraction gratings are used as beamsplitters. Their diffraction efficiency, however, is strongly wavelength dependent. Therefore transmission-grating interferometers can be advantageous for spectroscopy methods, since they can provide high diffraction efficiency over a wide spectral range. Here, we present and characterize a transmission grating-based Michelson interferometer, which is practically dispersion-free, has intrinsically high symmetry and stability and moderate throughput efficiency, and is promising for a wide range of applications.
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| 4. |
- Vogelsang, Jan, et al.
(författare)
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Coherent Excitation and Control of Plasmons on Gold Using Two-Dimensional Transition Metal Dichalcogenides
- 2021
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:6, s. 1607-1615
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Tidskriftsartikel (refereegranskat)abstract
- The hybrid combination of two-dimensional (2D) transition metal dichalcogenides (TMDs) and plasmonic materials open up novel means of (ultrafast) optoelectronic applications and manipulation of nanoscale light-matter interaction. However, control of the plasmonic excitations by TMDs themselves has not been investigated. Here, we show that the ultrathin 2D WSe2 crystallites permit nanoscale spatially controlled coherent excitation of surface plasmon polaritons (SPPs) on smooth Au films. The resulting complex plasmonic interference patterns are recorded with nanoscale resolution in a photoemission electron microscope. Modeling shows good agreement with experiments and further indicates how SPPs can be tailored with high spatiotemporal precision using the shape of the 2D TMDs with thicknesses down to single molecular layers. We demonstrate the use of WSe2 nanocrystals as 2D optical elements for exploring the ultrafast dynamics of SPPs. Using few-femtosecond laser pulse pairs we excite an SPP at the boundary of a WSe2 crystal and then have a WSe2 monolayer wedge act as a delay line inducing a spatially varying phase difference down to the attosecond time range. The observed effects are a natural yet unexplored consequence of high dielectric functional values of TMDs in the visible range that should be considered when designing metal-TMD hybrid devices. As the 2D TMD crystals are stable in air, can be defect free, can be synthesized in many shapes, and are reliably positioned on metal surfaces, using them to excite and steer SPPs adds an interesting alternative in designing hybrid structures for plasmonic control.
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| 5. |
- Wittenbecher, Lukas, et al.
(författare)
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Correction of Fabry-Pérot interference effects in phase and amplitude pulse shapers based on liquid crystal spatial light modulators
- 2019
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Ingår i: Optics Express. - 1094-4087. ; 27:16, s. 22970-22982
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Tidskriftsartikel (refereegranskat)abstract
- Broadband femtosecond laser pulses manipulated by pulse shapers based on a liquid crystal spatial light modulator (LC-SLM) inevitably experience periodic spectral distortions due to Fabry-Perot interference effects within the LC-SLM. We present a method, applicable to phase and amplitude pulse shapers based on dual LC-SLMs, that enables the calibration and suppression of the undesired spectral intensity modulations in a non-iterative fashion. We demonstrate that the method considerably improves the amplitude shaping fidelity of phase and amplitude pulse shapers without compromising the phase shaping properties.
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| 6. |
- Wittenbecher, Lukas
(författare)
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Time-Resolved Photoemission Electron Microscopy: Development and Applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Time-resolved photoemission electron microscopy (TR-PEEM) belongs to a class of experimental techniquescombining the spatial resolution of electron-based microscopy with the time resolution of ultrafast opticalspectroscopy. This combination provides insight into fundamental processes on the nanometer spatial andfemto/picosecond time scale, such as charge carrier transport in semiconductors or collective excitations ofconduction band electrons at metal surfaces. The high spatiotemporal resolution also offers a detailed view of therelationship between local structure and ultrafast photoexcitation dynamics in nanostructures and nanostructuredmaterials, which is beneficial in exploring new materials and applications in opto-electronics and nano-optics.This thesis describes the investigation of ultrafast photoexcitation dynamics in metal- and III-V semiconductornanostructures using TR-PEEM. We investigate hot carrier cooling in individual InAs nanowires where we findevidence that electron-hole scattering strongly contributes to the intra-band energy relaxation of photoexcitedelectrons on a sub-picosecond time scale and we observe ultrafast hot electron transport towards the nanowiresurface due to an in-built electric field. We demonstrate the combination of TR-PEEM with optical time-domainspectroscopy to enable time- and excitation frequency-resolved PEEM imaging. The technique is applied to GaAssubstrates and nanowires. TR-PEEM is further used to investigate localized and propagating surface plasmonpolaritons. We explore the optical properties of disordered, porous gold nano-particles (nanosponges). Using TRPEEM,we can resolve several plasmonic hotspots with different resonance frequencies and lifetimes within singlenanosponges. We also explore excitation and temporal control of surface plasmon polaritons by means of singlelayeredcrystals of the transition metal dichalcogenide WSe2.In addition, this thesis includes developments in ultrafast optics, aiming to expand the capabilities of the TR-PEEMsetup. We present a setup for generating tunable broadband ultraviolet (UV) laser pulses via achromatic secondharmonic generation. The setup is suitable for operation at high repetition rates and low pulse energies due to its highconversion efficiency. Further, we describe a transmission grating-based interferometer for the generation of stable,phase-locked pulse pairs. Pulse shaping based on liquid crystal technology allows accurate control over the temporalshape of femtosecond laser pulses. We characterize Fabry-Perot interferences affecting the accuracy of such pulseshapers, and we demonstrate a calibration scheme to compensate for these interference effects.
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| 7. |
- Wittenbecher, Lukas, et al.
(författare)
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Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires
- 2021
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:1, s. 1133-1144
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Tidskriftsartikel (refereegranskat)abstract
- Hot electron relaxation and transport in nanostructures involve a multitude of ultrafast processes whose interplay and relative importance are still not fully understood, but which are relevant for future applications in areas such as photocatalysis and optoelectronics. To unravel these processes, their dynamics in both time and space must be studied with high spatiotemporal resolution in structurally well-defined nanoscale objects. We employ time-resolved photoemission electron microscopy to image the relaxation of photogenerated hot electrons within InAs nanowires on a femtosecond time scale. We observe transport of hot electrons to the nanowire surface within 100 fs caused by surface band bending. We find that electron-hole scattering substantially influences hot electron cooling during the first few picoseconds, while phonon scattering is prominent at longer time scales. The time scale of cooling is found to differ between the well-defined wurtzite and zincblende crystal segments of the nanowires depending on excitation light polarization. The scattering and transport mechanisms identified will play a role in the rational design of nanostructures for hot-electron-based applications.
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| 8. |
- Zhong, Jin Hui, et al.
(författare)
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Nonlinear plasmon-exciton coupling enhances sum-frequency generation from a hybrid metal/semiconductor nanostructure
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The integration of metallic plasmonic nanoantennas with quantum emitters can dramatically enhance coherent harmonic generation, often resulting from the coupling of fundamental plasmonic fields to higher-energy, electronic or excitonic transitions of quantum emitters. The ultrafast optical dynamics of such hybrid plasmon–emitter systems have rarely been explored. Here, we study those dynamics by interferometrically probing nonlinear optical emission from individual porous gold nanosponges infiltrated with zinc oxide (ZnO) emitters. Few-femtosecond time-resolved photoelectron emission microscopy reveals multiple long-lived localized plasmonic hot spot modes, at the surface of the randomly disordered nanosponges, that are resonant in a broad spectral range. The locally enhanced plasmonic near-field couples to the ZnO excitons, enhancing sum-frequency generation from individual hot spots and boosting resonant excitonic emission. The quantum pathways of the coupling are uncovered from a two-dimensional spectrum correlating fundamental plasmonic excitations to nonlinearly driven excitonic emissions. Our results offer new opportunities for enhancing and coherently controlling optical nonlinearities by exploiting nonlinear plasmon-quantum emitter coupling.
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