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1.	Eriksson, Emma, 1980, et al. (författare) A microfluidic system in combination with optical tweezers for analyzing rapid and reversible cytological alterations in single cells upon environmental changes 2007 Ingår i: Lab on a chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 7:1, s. 71-76 Tidskriftsartikel (refereegranskat)abstract We report on the development of an experimental platform where epi-fluorescence microscopy and optical tweezers are combined with a microfluidic system to enable the analysis of rapid cytological responses in single cells. The microfluidic system allows two different media to be merged in a Y-shaped channel. Microscale channel dimensions ensure purely laminar flow and, as a result, an environmental gradient can be created between the two media. Optical tweezers are used to move a single trapped cell repeatedly between the different environments. The cell is monitored continuously by fluorescence microscopy during the experiment. In a first experiment on yeast (Saccharomyces cerevisiae) we observed changes in cell volume as the cell was moved between environments with different osmolarity. This demonstrated that the platform allowed analysis of cytological alterations on a time scale shorter than 0.2 s. In a second experiment we observed the spatial migration of the Yap1p transcription factor fused to GFP as a cell was moved from an environment of low to high oxidative capacity. The system is universal allowing the response to numerous environmental changes to be studied on the sub second time scale in a variety of model cells. We intend to use the platform to study how the age of cells, their progression through the cell cycle, or their genetic landscape, alter their capacity (kinetics and amplitude) to respond to environmental changes.
2.	Goksör, Mattias, 1975, et al. (författare) Analysis of molecular diffusion in ftsK cell-division mutants using laser surgery 2003 Ingår i: Embo Reports. - 1469-221X. ; 4:9, s. 867-871 Tidskriftsartikel (refereegranskat)
3.	Aguilar, A., et al. (författare) Double photodetachment from the Cl[-]ion 2004 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 69:2 Tidskriftsartikel (refereegranskat)abstract The correlated process involving the photodetachment of two electrons from the [Formula Presented] ion has been investigated over the photon energy range 20–45 eV. In the experiment, a beam of photons from the Advanced Light Source (ALS) was collinearly merged with a counterpropagating beam of [Formula Presented] ions from a sputter ion source. The [Formula Presented] ions produced in the interaction region were detected, and the normalized signal was used to monitor the relative cross section for the reaction. An absolute scale for the cross section was established by measuring the spatial overlap of the two beams and by determining the efficiency for collection and detection of the [Formula Presented] ions. The overall magnitude and shape of the measured cross section for this process agrees well with an R-matrix calculation. The calculation identifies the dominant mechanism leading to the production of the [Formula Presented] ion as being a direct nonresonant process involving the ejection of a pair of electrons from the valence shell. Less important is the indirect nonresonant process that involves the production and decay of core-excited and doubly excited states of the Cl atom in an intermediate step. Direct and indirect resonant mechanisms involving the excitation of a single [Formula Presented] core electron or more than one valence electron of the [Formula Presented] ion were found to be insignificant in the energy range studied.
4.	Aleman, A., et al. (författare) Phase and frequency-resolved microscopy of operating spin Hall nano-oscillator arrays 2024 Ingår i: NANOSCALE HORIZONS. - 2055-6756 .- 2055-6764. Tidskriftsartikel (refereegranskat)abstract Coherent optical detection is a powerful technique for characterizing a wide range of physical excitations. Here, we use two optical approaches (fundamental and parametric pumping) to microscopically characterize the high-frequency auto-oscillations of single and multiple nano-constriction spin Hall nano-oscillators (SHNOs). To validate the technique and demonstrate its robustness, we study SHNOs made from two different material stacks, NiFe/Pt and W/CoFeB/MgO, and investigate the influence of both the RF injection power and the laser power on the measurements, comparing the optical results to conventional electrical measurements. To demonstrate the key features of direct, non-invasive, submicron, spatial, and phase-resolved characterization of the SHNO magnetodynamics, we map out the auto-oscillation magnitude and phase of two phase-binarized SHNOs used in Ising machines. This proof-of-concept platform establishes a strong foundation for further extensions, contributing to the ongoing development of crucial characterization techniques for emerging computing technologies based on spintronics devices. An efficient platform to perform phase imaging and individual nano-addressing for application in novel SHNO-based computing devices.
5.	Alemán Hérnandez, Felipe Ademir, et al. (författare) Frequency comb enhanced Brillouin microscopy 2020 Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 28:20, s. 29540-29552 Tidskriftsartikel (refereegranskat)abstract Brillouin light scattering (BLS) microscopy is a well established and powerful technique to study acoustic and magnetic excitations in the frequency domain with sub-micron spatial resolution. Many other spectroscopic techniques have benefited from the introduction of femtosecond laser sources to optically pump and stimulate the sample under investigation. In BLS microscopy, the use of femtosecond lasers as the excitation source introduces several challenges, primarily since the measured frequency shift is small and the signal levels are weak due to the low duty cycle of typical femtosecond lasers. Here we present a method to evade these challenges. A strong enhancement of the weak scattering amplitude on selected modes is observed by pumping the sample with a high repetition rate frequency comb laser source. The laser beam can be focused to the diffraction limit, providing a micron pumping area. We can thus preserve the innate high frequency and spatial resolution of BLS microscopy. Furthermore, we are able to induce a point-like source of mode-selected elementary excitations which propagate away from the pumping spot. We conclude that we have demonstrated frequency comb pumped BLS microscopy as an attractive tool for studies of ultrafast induced laser dynamics directly in the frequency domain. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
6.	Andersson, Pontus, 1971, et al. (författare) Isobar Selective Laser Photodetachment In Trace Element Analysis 2009 Ingår i: AIP Conference Proceedings. ; 1104 Konferensbidrag (refereegranskat)abstract We are investigating the possibility to use laser photodetachment of negative ions as an isobaric selective filter in accelerator mass spectrometry (AMS). If successful, this method can be used to obtain higher sensitivity realized through better selectivity by suppression of molecular and/or elemental isobaric interference in different investigations using ultra rare isotopes in the 10−13 range and below.
7.	Andersson, Pontus, 1971, et al. (författare) Nearly complete isobar suppression by photodetachment 2010 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 1089-7550 .- 0021-8979. ; 107:2 Tidskriftsartikel (refereegranskat)abstract The efficiency of selective suppression of negative ions by photodetachment in a gas-filled radio frequency quadrupole ion cooler was investigated with a new detection method. A neodymium doped yttrium aluminum garnet laser beam at 1064 nm was used to remove Co− ions in the radio frequency quadrupole cooler and the remaining ions were then probed by photodetachment and neutral particle detection. More than 99.99% suppression of the Co− ions was observed. Under identical conditions, only 20% of a Ni− beam was suppressed. The results demonstrate that this isobar suppression technique can lead to nearly complete elimination of certain isobaric contaminants in negative ion beams, opening up new experimental possibilities in nuclear and atomic research and accelerator mass spectrometry.
8.	Andersson, Pontus, 1971, et al. (författare) Observation of the 2S1/2 metastable state in Pt− 2009 Ingår i: PHYSICAL REVIEW A. - 1050-2947. ; 79, s. 022502 - Tidskriftsartikel (refereegranskat)abstract We have experimentally investigated the structure of the Pt− ion using laser photodetachment threshold spectroscopy. The experiment was conducted using a collinear laser-ion beam apparatus, in which the residual atoms created in the photodetachment process were detected. A p-wave threshold was observed in the photo- detachment spectrum at an energy of 6851͑13͒ cm−1. We conclude that this onset originates from a photode- tachment transition in which the initial state of Pt− is the previously unobserved 5d106s 2S1/2 state and the ﬁnal state of Pt is the 5d96s 3D3 ground state. The excitation energy of the 2S1/2 state is determined to be 10 289͑13͒ cm−1. This value can be compared with a multiconﬁguration Dirac-Fock calculation performed by Thøgersen et al. ͓Phys. Rev. Lett. 76, 2870 ͑1996͔͒, which yielded an excitation energy of 11 301 cm−1. Our data show no indication of the presence of any other state of Pt−. We conclude that the structure of the Pt− ion is now fully known.
9.	Andersson, Pontus, 1971, et al. (författare) Radiative lifetimes of metastable states of negative ions 2006 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622 .- 2469-9926 .- 2469-9934. ; 73, s. 032705- Tidskriftsartikel (refereegranskat)abstract We present a technique for measuring the radiative lifetimes of metastable states of negative ions that involves the use of a heavy-ion storage ring. The method has been applied to investigate the radiative decay of the np(3) P-2(1/2) levels of Te-(n=5) and Se-(n=4) and the 3p(3) D-2 state of Si- for which the J=3/2 and 5/2 levels were unresolved. All of these states are metastable and decay primarily by emission of E2 and M1 radiation. Multi Configuration Dirac-Hartree-Fock calculations of rates for the transitions in Te- and Se- yielded lifetimes of 0.45 s and 4.7 s, respectively. The measured values agree well with these predicted values. In the case of the D-2 state of Si-, however, our measurement was only able to set a lower limit on the lifetime. The upper limit of the lifetime that can be measured with our apparatus is set by how long the ions can be stored in the ring, a limit determined by the rate of collisional detachment. Our lower limit of 1 min for the lifetime of the D-2 state is consistent with both the calculated lifetimes of 162 s for the D-2(3/2) level and 27.3 h for the D-2(5/2) level reported by O'Malley and Beck and 14.5 h and 12.5 h, respectively, from our Breit-Pauli calculations.
10.	Andersson, Pontus, 1971, et al. (författare) Selective detection of 13C by laser photodetachment mass spectrometry 2008 Ingår i: Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms. ; 266, s. 3667-3673 Tidskriftsartikel (refereegranskat)
11.	Andersson, Pontus, 1971, et al. (författare) The electron affinity of phosphorus 2007 Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. ; 40:20, s. 4097-4107 Tidskriftsartikel (refereegranskat)
12.	Athanasakis-Kaklamanakis, M., et al. (författare) Radiative lifetime of the A 2Π1/2 state in RaF with relevance to laser cooling 2024 Ingår i: PHYSICAL REVIEW A. - 2469-9926 .- 2469-9934. ; 110:1 Tidskriftsartikel (refereegranskat)abstract The radiative lifetime of the A (2)Pi(1/2) (v = 0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Gamma = 2.86(8) . 86(8) x 107 7 s-1 - 1 are of relevance to the laser cooling of RaF via the optically closed A (2)Pi(1/2) <- X (2)Sigma(1/2) transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 P 3 / 2 state in Fr to be 83(3) ns, in agreement with literature.
13.	Athanasakis-Kaklamanakisa, Michail, et al. (författare) Voltage scanning and technical upgrades at the Collinear Resonance Ionization Spectroscopy experiment 2023 Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS. - 0168-583X .- 1872-9584. ; 541, s. 86-89 Tidskriftsartikel (refereegranskat)abstract To optimize the performance of the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at CERN-ISOLDE, technical upgrades are continuously introduced, aiming to enhance its sensitivity, precision, stability, and efficiency. Recently, a voltage-scanning setup was developed and commissioned at CRIS, which improved the scanning speed by a factor of three as compared to the current laser-frequency scanning approach. This leads to faster measurements of the hyperfine structure for systems with high yields (more than a few thousand ions per second). Additionally, several beamline sections have been redesigned and manufactured, including a new field-ionization unit, an electrostatic bend with a larger deflection angle, and improved ion optics. The beamline upgrades are expected to yield an improvement of at least a factor of 5 in the signal-to-noise ratio by avoiding the use of high-power lasers (which yield non-resonantly produced ions) and providing time-of-flight separation between the resonant ions and the collisional background.
14.	Awad, Ahmad, et al. (författare) Femtosecond laser comb driven perpendicular standing spin waves 2022 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:1 Tidskriftsartikel (refereegranskat)abstract We study femtosecond laser comb driven sustained and coherent spin wave (SW) generation in Permalloy films over a thickness range of d = 40-100 nm. A simple rapid demagnetization model describes the dependence of the observed SW intensity on laser power for all film thicknesses. In the thicker films, we observe laser comb excited perpendicular standing spin waves up to the third order and to 18 multiples of the 1 GHz laser repetition rate. Our results demonstrate the versatility of femtosecond combs as contact-less SW point sources over a wide range of film thickness and type of SW modes.
15.	Bae, A. J., et al. (författare) Juggling with Light 2019 Ingår i: Physical Review Letters. - 0031-9007. ; 122:4 Tidskriftsartikel (refereegranskat)abstract We discovered that when a pair of small particles is optically levitated, the particles execute a "dance" whose motion resembles the orbits of balls being juggled. This motion lies in a plane perpendicular to the polarization of the incident light. We ascribe the dance to a mechanism by which the dominant force on each particle cyclically alternates between radiation pressure and gravity as each particle takes turns eclipsing the other. We explain the plane of motion by considering the anisotropic scattering of polarized light at a curved interface.
16.	Bergues, B., et al. (författare) Photodetachment in a strong laser field: An experimental test of Keldysh-like theories 2007 Ingår i: Physical Review A. - 1050-2947. ; 75:6 Tidskriftsartikel (refereegranskat)
17.	Bergues, B., et al. (författare) Reply to "Comment on 'Photodetachment in a strong laser field: An experimental test of Keldysh-like theories' " 2008 Ingår i: Physical Review A. ; 77 Tidskriftsartikel (refereegranskat)
18.	Blahins, J., et al. (författare) Operating a cesium sputter source in a pulsed mode 2020 Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 91:2 Tidskriftsartikel (refereegranskat)abstract A scheme is presented for pulsing of a cesium sputter negative ion source by periodically switching on and off the high voltage driving the sputtering process. We demonstrate how the pulsed ion beam can be used in combination with a pulsed laser (6 ns pulse length) that has a 10 Hz repetition rate to study the photodetachment process, where a negative ion is neutralized due to the absorption of a photon. In such experiments, where the ion beam is used only for a small fraction of the time, we show that the pulsed mode operation can increase the lifetime of a cathode by two orders of magnitude as compared with DC operation. We also investigate how the peak ion current compares with the ion current obtained when the source is run in a DC mode. We find that the peak current in the pulsed mode is strongly dependent on the ion species. In some cases, we observed a strong enhancement, whereas others showed only a moderate enhancement, or even a decrease, in the peak current. We conclude that the pulsed mode operation can be of great value when the negative ion to be investigated requires cathodes that have short lifetimes, expensive materials, or those with relatively small ion beam yields, in the latter case limited to elements with large enhancement factors. Published under license by AIP Publishing.
19.	Borglin, Johan, 1986, et al. (författare) Annular Beam Shaping in Multiphoton Microscopy to Reduce Out-of-Focus Background 2017 Ingår i: International Journal of Spectroscopy. - : Hindawi Limited. - 1687-9449 .- 1687-9457. Tidskriftsartikel (refereegranskat)abstract Despite the inherent spatial confinement of multiphoton processes that arises from focusing through an objective, the maximum imaging depth in conventional multiphoton microscopy is ultimately limited by noise from out-of-focus fluorescence. This is particularly evident when imaging beyond shallow depths in highly scattering tissue as increased laser powers are necessary. The out-of-focus signal originates from multiphoton processes taking place primarily at shallow depths and deteriorates contrast and limits imaging depth. In this paper, annular laser beams are explored as a concept to reduce this background signal in multiphoton microscopy. The approach is theoretically verified by data from simulations and proof of principle is demonstrated on a custom-built experimental multiphoton microscopy platform. Annular laser beams were created by adopting wavefront control using a spatial light modulator and implemented for imaging tissue phantoms simulating turbid media and human skin ex vivo. The signal-to-background ratios were calculated and compared to images acquired with a traditional, filled-aperture Gaussian beam. Experiments in tissue phantom show an improvement in signal-to-background ratio of about 30% when using annular beam illumination in comparison to Gaussian illumination at specific depths. When laser power is not the limiting factor, this approach is expected to provide even greater benefits.
20.	Borglin, Johan, 1986, et al. (författare) Improving multiphoton microscopy using annular beam shaping, focusing on imaging of human skin 2014 Ingår i: Multiphoton Microscopy in the Biomedical Sciences XIV: 2-4 February 2014, San Francisco, California, United States. Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 8948 Konferensbidrag (refereegranskat)abstract Multiphoton fluorescence microscopy (MPM) is a method for high resolution, non-invasive investigations of biological tissue. The aim of introducing an annular shaped laser beam is to reduce the ouf-of-focus generated background signal improving imaging of light scattering tissue such as human skin. Simulations show that 50% of the beam radius can be blocked, while preserving the shape of the point spread function. Initial experiments performed on a phantom consisting of fluorescein and fluorescent beads embedded in agar by using a custom built MPM-set up show that by introducing a simple beam blocker to create an annular beam, the background signal is reduced with approximately 5%. Future work will include optimizing the set up, and creating phantoms with more light scattering properties. © 2014 SPIE.
21.	Bäckström, Erik, 1983-, et al. (författare) Storing keV negative ions for an hour : The lifetime of the metastable 2P1/2 level in 32S− 2015 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:14 Tidskriftsartikel (refereegranskat)abstract We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p 5 P 2 o 1/2 →3p 5 P 2 o 3/2 spontaneous radiative decay in S − 32 to be 503±54 sec . This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10 −14 mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ from the only available theoretical prediction.
22.	Chartkunchand, C, et al. (författare) Measuring the 2D3/2 Ni− excited state lifetime in DESIREE 2015 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635 Konferensbidrag (refereegranskat)abstract Experimental studies of the radiative lifetime of the sole excited state in the nickel anion are presented. Beams of Ni− stored in DESIREE at cryogenic temperatures were subject to photodetachment at different photon energies and the resulting neutrals collected. Preliminary analysis of the decay in neutral production yields a radiative lifetime of approximately 15 seconds for the 3d94s2 2D3/2 excited state.
23.	Chartkunchand, K. C., et al. (författare) Lifetimes of bound excited states of Pt- 2017 Ingår i: Journal of Physics: Conference Series, Vol. 875, no. 022051. - : IOP Publishing. - 1742-6588. Konferensbidrag (refereegranskat)abstract Measurements of the radiative lifetimes of the two excited states of the platinum anion Pt- are presented. Pt- ions stored in the cryogenic ion storage ring DESIREE were photodetached at different photon wavelengths and the resulting yield of neutral Pt measured as a function of time was recorded. Analysis of the neutral decay curves show a 2.54 +/- 0.10 s lifetime for the higher-lying 5d(10)6(s) S-2(1/2) excited state and a lifetime in the range of 50-200 ms for the lower- lying 5d(9)6(s)(2) D-2(3/2) excited state. This is the first study to report the lifetime of a bound anion excited state with an electron configuration different from that of the anion ground state.
24.	Chartkunchand, Kiattichart C., et al. (författare) Radiative lifetimes of the bound excited states of Pt- 2016 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 94:3 Tidskriftsartikel (refereegranskat)abstract © 2016 American Physical Society.The intrinsic radiative lifetimes of the 5d106sS1/22 and 5d96s2 D3/22 bound excited states in the platinum anion Pt- have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d106s S1/22 state was measured to be 2.54±0.10s, while only a lifetime in the range of 50-200 ms could be estimated for the 5d96s2 D3/22 fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.
25.	Chen, Hongshan, et al. (författare) The electronic structure of HfF5- and WF5- 2011 Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 511:4-6, s. 196-200 Tidskriftsartikel (refereegranskat)
26.	Chorey, Devashish, et al. (författare) Simultaneous imaging of CH, C2, and temperature in flames using a DSLR camera and structured illumination 2023 Ingår i: Applied Optics. - 1559-128X. ; 62:14, s. 3737-3746 Tidskriftsartikel (refereegranskat)abstract Measurement of chemical species and temperature mapping in flames is essential to understanding the combustion process. Multiple cameras are conventionally employed for measurement in such scenarios making the experi-mental setup not only cost-intensive but also challenging. To circumvent this, structured illumination (SI)-based methods are reported for multispecies chemiluminescence (CL) imaging using a single camera. In this paper, we demonstrate four-channel SI-based imaging for simultaneous snapshot CH* and C*2 CL imaging and two-color pyrometry for temperature profiles in a butane diffusion flame. We demonstrate our approach using individual species and multiple species imaging. Taking the advantage of the axisymmetric nature of the flame, the Abel trans-form is performed on the line-of-sight averaged images to obtain deconvoluted images. The deconvoluted maps of temperature are compared with the temperature data obtained by using a physical thermocouple probe. (c) 2023 Optica Publishing Group
27.	Collins, G F, et al. (författare) Electron-impact fragmentation of Cl-2(-) 2005 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:4, s. 042708- Tidskriftsartikel (refereegranskat)abstract A merged beam technique has been used to investigate the fragmentation of the Cl-2(-) ion in collisions with electrons over an energy range of 0-200 eV. We have measured absolute cross sections for detachment, detachment plus dissociation and dissociation processes. Over the energy range studied, the dominant breakup mechanism is dissociation. Dissociation is relatively enhanced in the e(-)+Cl-2(-) collision system due to the suppression of the normally dominant detachment process, as a result of the large difference between the equilibrium internuclear distances of the Cl-2 and Cl-2(-) ground state potential curves. A prominent structure is observed just above the threshold in the Cl-+Cl+e(-) dissociation channel. It is proposed that the structure is a resonance associated with production and rapid decay of an excited state of the doubly charged Cl-2(-) ion. A plausible mechanism for production of the di-anionic state based on an excitation plus capture process is suggested.
28.	Covington, A. M., et al. (författare) Inner-shell photodetachment from the K- ion 2007 Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:5, s. 935-942 Tidskriftsartikel (refereegranskat)
29.	Davis, V. T., et al. (författare) Photo-double detachment from the F- ion 2005 Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 38:14, s. 2579-2589 Tidskriftsartikel (refereegranskat)
30.	de Andres Gonzalez, Aitor, 1992-, et al. (författare) Vacuum laser acceleration of electrons injected from nanotips 2023 Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350345995 - 9798350346008 Konferensbidrag (refereegranskat)abstract Vacuum laser acceleration (VLA) is a paradigm that utilizes the strong fields of focused laser light to accelerate electrons in vacuum. Despite its conceptual simplicity and a large existing collection of theoretical studies, realizing VLA in practice has proven remarkably challenging due to the difficulties associated with efficient injection: the electrons to be accelerated must be pre-energized and temporally compressed below an optical half-cycle before timely entering the rapidly oscillating fields of the laser. Therefore, only a handful of experiments have been published up to date, and a knowledge gap remains [1-3].
31.	Diehl, C., et al. (författare) Ion optical design of a collinear laser-negative ion beam apparatus 2011 Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:5 Tidskriftsartikel (refereegranskat)abstract An apparatus for photodetachment studies on atomic and molecular negative ions of medium up to heavy mass (M ≃ 500) has been designed and constructed. Laser and ion beams are merged in the apparatus in a collinear geometry and atoms, neutral molecules and negative ions are detected in the forward direction. The ion optical design and the components used to optimize the mass resolution and the transmission through the extended field-free interaction region are described. A 90° sector field magnet with 50 cm bending radius in combination with two slits is used for mass dispersion providing a resolution of M/ΔM≅800 for molecular ions and M/ΔM≅400 for atomic ions. The difference in mass resolution for atomic and molecular ions is attributed to different energy distributions of the sputtered ions. With 1 mm slits, transmission from the source through the interaction region to the final ion detector was determined to be about 0.14%.
32.	Einarsson, Jonas, et al. (författare) Periodic and aperiodic tumbling of microrods advected in a microchannel flow 2013 Ingår i: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 224:10, s. 2281-2289 Tidskriftsartikel (refereegranskat)abstract We report on an experimental investigation of the tumbling of microrods in the shear flow of a microchannel (dimensions: 40 mm x 2.5 mm x 0.4 mm. The rods are 20-30 mu m long and their diameters are of the order of 1 mu m. Images of the centre-of-mass motion and the orientational dynamics of the rods are recorded using a microscope equipped with a CCD camera. A motorised microscope stage is used to track individual rods as they move along the channel. Automated image analysis determines the position and orientation of a tracked rod in each video frame. We find different behaviours, depending on the particle shape, its initial position, and orientation. First, we observe periodic as well as aperiodic tumbling. Second, the data show that different tumbling trajectories exhibit different sensitivities to external perturbations. These observations can be explained by slight asymmetries of the rods. Third, we observe that after some time, initially periodic trajectories lose their phase. We attribute this to drift of the centre of mass of the rod from one to another streamline of the channel flow.
33.	Einarsson, Jonas, et al. (författare) Tumbling of asymmetric microrods in a microchannel flow 2016 Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 28:1 Tidskriftsartikel (refereegranskat)abstract We describe results of measurements of the orientational motion of glass microrods in a microchannel flow, following the orientational motion of particles with different shapes. We determine how the orientational dynamics depends on the shape of the particle and on its initial orientation. We find that the dynamics depends so sensitively on the degree to which particle axisymmetry is broken that it is difficult to find particles that are sufficiently axisymmetric so that they exhibit periodic tumbling ("Jeffery orbits"). The results of our measurements confirm earlier theoretical analysis predicting sensitive dependence on particle shape and its initial orientation. Our results illustrate the different types of orientational dynamics for asymmetric particles predicted by theory.
34.	Eklund, M., et al. (författare) Orbital alignment in atoms generated by photodetachment in a strong laser field 2013 Ingår i: Physical Review A. - 1050-2947. ; 88:2 Tidskriftsartikel (refereegranskat)abstract A pump-probe laser scheme is employed to investigate orbital alignment and its dynamics in the ground state of laser-generated neutral atoms. The alignment is initiated by electron photodetachment of an atomic negative ion in a strong laser pulse. The electron density distribution in the ground state of the residual atom is probed by means of strong-field ionization in a second laser pulse at a delayed time. The principle of the probe method relies on the fact that the portion of the electron density distribution oriented along the laser polarization axis constitutes the ionization yield in the high-energy jets of emitted electrons. A systematic study is carried out on C, Si, and Ge atoms, which possess two electrons in an open p shell. A pronounced temporal modulation in the yield of high-energy electrons is observed for C and Si, revealing a periodic spatial rearrangement of the electron density distribution in these atoms. Its period is defined by the beat between the J = 1 and J = 2 spin-orbit components of the ground state.
35.	Ellmann, A, et al. (författare) Radiative lifetime of a bound excited state of Te- 2004 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 92:25, s. 253002- Tidskriftsartikel (refereegranskat)abstract We report on the first experimental study of the lifetime of a bound excited state of a negative ion. A new experimental technique was developed and used to measure the radiative lifetime of the 5p(5) P-2(1/2) level of Te-. The experiment was performed in a magnetic storage ring, where a laser beam was applied along one of the straight sections. In the experiment the population of the excited J=1/2 level was probed each time the Te- ions passed through the laser field. A decay curve was built up by sampling the population of the excited level of the Te- ions as a function of time after injection into the ring. A multiconfiguration Dirac-Hartree-Fock calculation was performed in conjunction with the experiment. The calculation yielded a radiative lifetime of 0.45 s, in excellent agreement with the measured value of 0.42(5) s.
36.	Enger, Jonas, 1966, et al. (författare) Optical tweezers applied to a microfluidic system 2004 Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 4, s. 196-200 Tidskriftsartikel (refereegranskat)abstract We will demonstrate how optical tweezers can be combined with a microfluidic system to create a versatile microlaboratory. Cells are moved between reservoirs filled with different media by means of optical tweezers. We show that the cells, on a timescale of a few seconds, can be moved from one reservoir to another without the media being dragged along with them. The system is demonstrated with an experiment where we expose E. coli bacteria to different fluorescent markers. We will also discuss how the system can be used as an advanced cell sorter. It can favorably be used to sort out a small fraction of cells from a large population, in particular when advanced microscopic techniques are required to distinguish various cells. Patterns of channels and reservoirs were generated in a computer and transferred to a mask using either a sophisticated electron beam technique or a standard laser printer. Lithographic methods were applied to create microchannels in rubber silicon (PDMS). Media were transported in the channels using electroosmotic flow. The optical system consisted of a combined confocal and epi-fluorescence microscope, dual optical tweezers and a laser scalpel.
37.	Eriksson, Emma, 1980, et al. (författare) A microfluidic device for reversible environmental changes around single cells using optical tweezers for cell selection and positioning 2010 Ingår i: Lab Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 10:5, s. 617-625 Tidskriftsartikel (refereegranskat)abstract Cells naturally exist in a dynamic chemical environment, and therefore it is necessary to study cell behaviour under dynamic stimulation conditions in order to understand the signalling transduction pathways regulating the cellular response. However, until recently, experiments looking at the cellular response to chemical stimuli have mainly been performed by adding a stress substance to a population of cells and thus only varying the magnitude of the stress. In this paper we demonstrate an experimental method enabling acquisition of data on the behaviour of single cells upon reversible environmental perturbations, where microfluidics is combined with optical tweezers and fluorescence microscopy. The cells are individually selected and positioned in the measurement region on the bottom surface of the microfluidic device using optical tweezers. The optical tweezers thus enable precise control of the cell density as well as the total number of cells within the measurement region. Consequently, the number of cells in each experiment can be optimized while clusters of cells, that render subsequent image analysis more difficult, can be avoided. The microfluidic device is modelled and demonstrated to enable reliable changes between two different media in less than 2 s. The experimental method is tested by following the cycling of GFP-tagged proteins (Mig1 and Msn2, respectively) between the cytosol and the nucleus in Saccharomyces cerevisiae upon changes in glucose availability.
38.	Eriksson, Emma, 1980, et al. (författare) Optical manipulation and microfluidics for studies of single cell dynamics 2007 Ingår i: Journal of Optics. A, Pure and applied optics. - 1464-4258 .- 1741-3567 .- 1361-6617. ; 9:8, s. 113-121 Tidskriftsartikel (refereegranskat)abstract Most research on optical manipulation aims towards investigation and development of the system itself. In this paper we show how optical manipulation, imaging and microfluidics can be combined for investigations of single cells. Microfluidic systems have been fabricated and are used, in combination with optical tweezers, to enable environmental changes for single cells. The environment within the microfluidic system has been modelled to ensure control of the process. Three biological model systems have been studied with different combinations of optical manipulation, imaging techniques and microfluidics. In Saccharomyces cerevisiae, environmentally induced size modulations and spatial localization of proteins have been studied to elucidate various signalling pathways. In a similar manner the oxygenation cycle of single red blood cells was triggered and mapped using Raman spectroscopy. In the third experiment the forces between the endoplasmic reticulum and chloroplasts were studied in Pisum sativum and Arabidopsis thaliana. By combining different techniques we make advanced biological research possible, revealing information on a cellular level that is impossible to obtain with traditional techniques.
39.	Forstner, O., et al. (författare) Isobar suppression in AMS using laser photodetachment 2008 Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. ; 266:19-20, s. 4565-4568 Tidskriftsartikel (refereegranskat)abstract We are investigating the possibility of using laser photodetachment of negative atomic and molecular ions as an additional isobaric selection filter in accelerator mass spectrometry. The aim of this study is to find a possibility to further improve the detection limit for long-lived heavy radionuclides at AMS facilities. We will focus on the astrophysical relevant radionuclide 182Hf, which is one of the isotopes measured with the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator) at the University of Vienna. Laser-induced isobar suppression is also of importance for radioactive-beam facilities. The present detection limit for measuring the isotope ratio 182Hf/Hf at VERA is 1×10-11. The limiting factor is the strong background of the stable isobar 182W. Currently this background is suppressed using suitable molecular ions in the injection stage. Selective laser photodetachment of the negative ions at the injector can lead to an additional suppression of the interfering isobar. Test experiments have been carried out at the negative ion laser spectroscopy setup at Göteborg University. In a small ion beam apparatus pulsed tunable laser radiation is used to measure the photodetachment cross-section of different atomic and molecular negative ions. We will present studies of the photodetachment process for various tungsten and hafnium molecules with the aim to find a selective isobaric suppression scheme using laser photodetachment spectroscopy in combination with AMS.
40.	Forstner, Oliver, et al. (författare) Reassessment of 182Hf AMS measurements at VERA 2011 Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 269:24, s. 3180-3182 Tidskriftsartikel (refereegranskat)abstract The radioisotope 182Hf (t1/2 = 8.9 Ma) is of great interest for astrophysical applications as a chronometer for the early solar system or as possible live supernova remnant on earth. However, AMS measurements of 182Hf are seriously influenced by the presence of the stable isobar 182W, which cannot be separated at typical AMS energies. Previous studies revealed a possible suppression of 182W against 182Hf by extracting the negatively charged pentafluoride from the ion source, leading to a detection limit for 182Hf/180Hf in the order of 10−11. However, this suppression behavior is in contrast to theoretical calculations of the electron affinity and recent measurements using SIMS instruments, where the achieved suppression cannot be reproduced. The aim of our study is to determine the effects of ion source background as well as further investigate the suppression of tungsten against hafnium by extracting negatively charged fluoride ions from different sample materials. The previously reported suppression factor of about 6000 could be increased to 36000 by careful tuning of the ion source using HfF4 as sample material. The trend of the theoretical electron affinities could be reproduced using atomic tungsten and hafnium instead of HfF4 as sample material. This supports the assumption that the major contribution of the tungsten background is not sputtered from the target matrix but comes from somewhere else in the ion source. Measurements from the second ion source show a higher background of tungsten and a lower suppression factor, i.e. careful design of the ion source is crucial. Moving the sputter beam over the target surface extending over the wheel holding the targets revealed the highest tungsten background was detected outside the sputter target position. Further investigations are necessary to locate the origin of the tungsten background in the ion source. Possible sources are the material used for the ion source construction or contaminations in the cesium used for sputtering.
41.	Forstner, O., et al. (författare) The ILIAS project for selective isobar suppression by laser photodetachment 2015 Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 361, s. 217-221 Tidskriftsartikel (refereegranskat)abstract Laser photodetachment is the process when the extra electron of a negative ion is removed by means of laser radiation. This can happen only if the photon energy is larger than the electron affinity of the ion. The process can be used in mass spectrometry to selectively suppress unwanted isobars, provided that the electron affinity of the unwanted isobar is lower than that of the isobar under investigation.At the Ion Laser InterAction Setup (ILIAS) at the University of Vienna laser photodetachment of negative atomic and molecular ions is studied and its applicability for selective isobar suppression in accelerator mass spectrometry (AMS) is evaluated. The setup provides mass separated beams of negative ions with energies up to 30 keV. Negative ions are produced in a Middleton type cesium sputter ion source, mass selected and overlapped with a strong continuous wave laser beam. In order to extend the interaction time of ions and laser, the ion beam is decelerated to thermal energies in a gas-filled radio frequency quadrupole cooler. For an appropriate choice of the photon energy, unwanted isobars are neutralized while the isobar of interest is unaffected and remains negatively charged.A description of the ILIAS setup and results from the commissioning phase of the RFQ cooler are presented. Up to 8% ion beam transmission could be achieved after a recent redesign of the extraction system. Furthermore first results of photodetachment experiments of 63Cu− within the RFQ cooler are presented.
42.	Fries, Johan, et al. (författare) Spinning and tumbling of micron-sized triangles in a micro-channel shear flow 2018 Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 30:3 Tidskriftsartikel (refereegranskat)abstract We report on measurements of the angular dynamics of micron-sized equilaterally triangular platelets suspended in a micro-channel shear flow. Our measurements confirm that such particles spin and tumble like a spheroid in a simple shear. Since the triangle has corners, we can observe the spinning directly. In general, the spinning frequency is different from the tumbling frequency and the spinning is affected by tumbling. This gives rise to doubly periodic angular dynamics. © 2018 Author(s).
43.	Friese, M. E. J., et al. (författare) Optically driven micromachine elements 2001 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:4, s. 547-549 Tidskriftsartikel (refereegranskat)abstract We report on a proof of principle demonstration of an optically driven micromachine element. Optical angular momentum is transferred from a circularly polarized laser beam to a birefringent particle confined in an optical tweezers trap. The optical torque causes the particle to spin at up to 350 Hz, and this torque is harnessed to drive an optically trapped microfabricated structure. We describe a photolithographic method for producing the microstructures and show how a light driven motor could be used in a micromachine system.
44.	Fritioff, Karin, et al. (författare) Observation of an excited C2-4 ion 2004 Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 37:11, s. 2241-2246 Tidskriftsartikel (refereegranskat)abstract This paper reports an experimental investigation of the electron impact detachment of C−4. We observe structure in the electron impact cross section for detaching a single electron from a C−4 cluster anion, which we attribute to the formation and decay of the C2−4 dianion. The system is energetically unstable and very rapidly decays via double autodetachment. The energy and width of the resonance were determined to be 8.8(5) eV and 1.4(5) eV, respectively, and the resonance lies 1.5(5) eV above the ground state of the neutral system. The experiment was conducted by merging monoenergetic electron and ion beams in the heavy ion storage ring CRYRING. The detachment channel was monitored by detecting neutral C4 fragments.
45.	Fritioff, K, et al. (författare) Single and double detachment from H- 2004 Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622 .- 2469-9926 .- 2469-9934. ; 69:4, s. 042707- Tidskriftsartikel (refereegranskat)abstract Absolute cross sections for single and double detachment from H- following electron impact have been measured over a range of collision energies from the thresholds to 170 eV. The measurements were made using a magnetic storage ring. The ions in the ring were merged with a monoenergetic electron beam and neutral and positively charged fragments were detected. We cover larger energy ranges than in many of the previous experiments, and this is the first time both single and double detachment have been measured simultaneously. This allows us to present accurate ratios between the single and double detachment cross sections. On the basis of these ratio measurements we discuss possible mechanisms leading to double detachment.
46.	Galan, D., et al. (författare) A remote laboratory for optical levitation of charged droplets 2018 Ingår i: European Journal of Physics. - : IOP Publishing. - 0143-0807 .- 1361-6404. ; 39:4 Tidskriftsartikel (refereegranskat)abstract We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.
47.	Galinskiy, Ivan, et al. (författare) Measurement of particle motion in optical tweezers embedded in a Sagnac interferometer 2015 Ingår i: Optics Express. - 1094-4087. ; 23, s. 27071-27084 Tidskriftsartikel (refereegranskat)abstract We have constructed a counterpropagating optical tweezers setup embedded in a Sagnac interferometer in order to increase the sensitivity of position tracking for particles in the geometrical optics regime. Enhanced position determination using a Sagnac interferometer has previously been described theoretically by Taylor et al. [Journal of Optics 13, 044014 (2011)] for Rayleigh-regime particles trapped in an antinode of a standing wave. We have extended their theory to a case of arbitrarily-sized particles trapped with orthogonally-polarized counter-propagating beams. The working distance of the setup was sufficiently long to optically induce particle oscillations orthogonally to the axis of the tweezers with an auxiliary laser beam. Using these oscillations as a reference, we have experimentally shown that Sagnac-enhanced back focal plane interferometry is capable of providing an improvement of more than 5 times in the signal-to-background ratio, corresponding to a more than 30-fold improvement of the signal-to-noise ratio. The experimental results obtained are consistent with our theoretical predictions. In the experimental setup, we used a method of optical levitator-assisted liquid droplet delivery in air based on commercial inkjet technology, with a novel method to precisely control the size of droplets.
48.	Gatchell, Michael, et al. (författare) Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions 2014 Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488:1 Konferensbidrag (refereegranskat)abstract We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.
49.	Gatchell, Michael, et al. (författare) First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE 2014 Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488 Konferensbidrag (refereegranskat)abstract We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.
50.	Gnaser, H., et al. (författare) Spontaneous and photo-induced decay processes of WF5- and HfF5- molecular anions in a cryogenic storage ring 2022 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:4 Tidskriftsartikel (refereegranskat)abstract Spontaneous and photo-induced decay processes of HfF5- and WF5- molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13 K) and the extremely low residual gas pressure (similar to 10(-14) mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450 nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF5- anions at about 3.5 eV, above which the neutralization yield increases strongly. By contrast, HfF5- ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (similar to 5.2 eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope Hf-182 using the Hf-182-F-5(-) anion while effectively reducing the interfering stable isobar W-182 in the analyte ion (WF5-)-W-182. The radionuclide Hf-182 is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years Published under an exclusive license by AIP Publishing.

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