| 1. |
- Engström, David, 1976, et al.
(författare)
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Grid-free 3D multiple spot generation with an efficient single-plane FFT-based algorithm
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:12, s. 9989-10000
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Tidskriftsartikel (refereegranskat)abstract
- Algorithms based on the fast Fourier transform (FFT) for the design of spot-generating computer generated holograms (CGHs) typically only make use of a few sample positions in the propagated field. We have developed a new design method that much better utilizes the information-carrying capacity of the sampled propagated field. In this way design tasks which are difficult to accomplish with conventional FFT-based design methods, such as spot positioning at non-sample positions and/or spot positioning in 3D, are solved as easily as any standard design task using a conventional method. The new design method is based on a projection optimization, similar to that in the commonly used Gerchberg-Saxton algorithm, and the vastly improved design freedom comes at virtually no extra computational cost compared to the conventional design. Several different design tasks were demonstrated experimentally with a liquid crystal spatial light modulator, showing highly accurate creation of the desired field distributions.
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| 2. |
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| 3. |
- Chalupsky, J., et al.
(författare)
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Characteristics of focused soft X-ray free-electron laser beam determined by ablation of organic molecular solids
- 2007
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Ingår i: Optics Express. - 1094-4087. ; 15:10, s. 6036-6043
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Tidskriftsartikel (refereegranskat)abstract
- A linear accelerator based source of coherent radiation, FLASH (Free-electron LASer in Hamburg) provides ultra-intense femtosecond radiation pulses at wavelengths from the extreme ultraviolet (XUV; lambda< 100nm) to the soft X-ray (SXR; lambda<30nm) spectral regions. 25-fs pulses of 32-nm FLASH radiation were used to determine the ablation parameters of PMMA - poly ( methyl methacrylate). Under these irradiation conditions the attenuation length and ablation threshold were found to be (56.9 +/- 7.5) nm and similar to 2 mJ center dot cm(-2), respectively. For a second wavelength of 21.7 nm, the PMMA ablation was utilized to image the transverse intensity distribution within the focused beam at mu m resolution by a method developed here.
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| 4. |
- Aquila, Andrew, et al.
(författare)
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Time-resolved protein nanocrystallography using an X-ray free-electron laser
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:3, s. 2706-2716
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
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| 5. |
- Hort, O., et al.
(författare)
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High-flux source of coherent XUV pulses for user applications
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:6, s. 8871-8883
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental results obtained at a user-oriented XUV beamline implemented at the ELI Beamlines facility. The coherent XUV radiation is produced via high harmonic generation in gases in a loose focusing geometry. The heamline is designed to be driven by 1 kHz, 100 mJ, 20 Is pulses centered at a wavelength of 830 nm. Results such as XUV spectra, beam wavefront and pulse energy obtained during the heamline commissioning with a commercial 1 kHz, 5 mJ, 40 fs laser system are presented. A unique XUV spectrometer for source characterization designed to reach a very high sensitivity is described in detail, and we demonstrate a novel technique for single shot and every shot. XUV pulse energy measurement. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
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| 6. |
- Kahnert, Michael, 1968, et al.
(författare)
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Aerosol optics model for black carbon applicable to remote sensing, chemical data assimilation, and climate modelling
- 2021
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 29:7, s. 10639-10658
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol optics models are an integral part of of climate models and of retrieval methods for global remote sensing observations. Such large-scale environmental applications place tight constraints on the affordable model complexity, which are difficult to reconcile with the considerable level of detail that is needed to capture the sensitivity of optical properties to morphological aerosol characteristics. Here, we develop a novel core-grey-shell dimer model and demonstrate its potential for reproducing radiometric and polarimetric properties of black carbon aerosols. The depolarisation is mainly sensitive to the relative size of the monomers, while the optical cross sections depend on the core-shell partitioning of black carbon. The optimum choice of these parameters is fairly stable across particle sizes and soot volume fraction, as is demonstrated by comparison with a more realistic coated aggregate model.
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| 7. |
- Kanngiesser, Franz, 1992, et al.
(författare)
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Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:25, s. 36368-36387
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties of thickly coated soot particles are sensitive to the chemical composition, thus to the refractive index of the coating material. For 58 differently sized coated soot aggregates the extinction-to-backscatter ratio (lidar ratio) and the depolarisation ratio are computed at a wavelength of 355 nm, 532 nm and 1064 nm for two different coating materials: a toluene-based coating and a sulphate coating. Additionally the Ångström exponents between 355 nm and 532 nm as well as between 532 nm and 1064 nm are calculated. The extinction-to-backscatter ratio is found to allow a distinction between the coating materials at all three wavelengths, and the depolarisation ratio allows for a distinction at 355 and 532 nm.
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| 8. |
- Kvarnström, Mats, 1974, et al.
(författare)
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Image analysis algorithms for cell contour recognition in budding yeast
- 2008
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 16:17, s. 12943-12957
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Tidskriftsartikel (refereegranskat)abstract
- Quantification of protein abundance and subcellular localization dynamics from fluorescence microscopy images is of high contemporary interest in cell and molecular biology. For large-scale studies of cell populations and for time-lapse studies, such quantitative analysiscan not be performed effectively without some kind of automated image analysis tool. Here, we present fast algorithms for automatic cell contour recognition in bright field images, optimized to the model organismbudding yeast (Saccharomyces cerevisiae). The cell contours can be used to effectively quantify cell morphology parameters as well as protein abundance and subcellular localization from overlaid fluorescence data.
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| 9. |
- Martinez Llinas, Jade, 1985, et al.
(författare)
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A Gaussian reflective metasurface for advanced wavefront manipulation
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:15, s. 21069-21082
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Tidskriftsartikel (refereegranskat)abstract
- Metasurfaces enable us to control the fundamental properties of light with unprecedented flexibility. However, most metasurfaces realized to date aim at modifying plane waves. While the manipulation of nonplanar wavefronts is encountered in a diverse number of applications, their control using metasurfaces is still in its infancy. Here we design a metareflector able to reflect a diverging Gaussian beam back onto itself with efficiency over 90% and focusing at an arbitrary distance. We outline a clear route towards the design of complex metareflectors that can find applications as diverse as optical tweezing, lasing, and quantum optics.
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| 10. |
- Odebo Länk, Nils, 1988, et al.
(författare)
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Directional scattering and multipolar contributions to optical forces on silicon nanoparticles in focused laser beams
- 2018
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087 .- 1094-4087. ; 26:22, s. 29074-29085
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles made of high index dielectric materials have seen a surge of interest and have been proposed for various applications, such as metalenses, light harvesting and directional scattering. With the advent of fabrication techniques enabling colloidal suspensions, the prospects of optical manipulation of such nanoparticles becomes paramount. High index nanoparticles support electric and magnetic multipolar responses in the visible regime and interference between such modes can give rise to highly directional scattering, in particular a cancellation of back-scattered radiation at the first Kerker condition. Here we present a study of the optical forces on silicon nanoparticles in the visible and near infrared calculated using the transfer matrix method. The zero-backscattering Kerker condition is investigated as an avenue to reduce radiation pressure in an optical trap. We find that while asymmetric scattering does reduce the radiation pressure, the main determining factor of trap stability is the increased particle response near the geometric resonances. The trap stability for non-spherical silicon nanoparticles is also investigated and we find that ellipsoidal deformation of spheres enables trapping of slightly larger particles.
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