| 1. |
- Vacher, Morgane, et al.
(author)
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Transition dynamics in two-photon ionisation
- 2017
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 19:11
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Research review (peer-reviewed)abstract
- We review various aspects of photoemission dynamics in the case of two-photon ionisation. We first recall the definition of a transition phase specific to two-photon transitions. Numerical experiments on model atoms are used to show how the group delay associated with the transition phase is actually representative of the early dynamics of the detected photoelectron wave packets. Then we address the question of measuring these transition delays using a standard interferometric technique of experimental attosecond physics, so-called rabbit . Finally, we outline different reinterpretations of rabbit giving access to the more fundamental scattering dynamics affecting any photoemission processes.
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| 2. |
- Andersson, Magnus, et al.
(author)
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Optimizing active and passive calibration of optical tweezers
- 2011
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 13:4
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Journal article (peer-reviewed)abstract
- To obtain quantitative information from optical trapping experiments it is essential to perform a precise force calibration. Therefore, sources of noise should be pinpointed and eliminated. Fourier analysis is routinely used to calibrate optical trapping assays because it is excellent for pinpointing high frequency noise. In addition, Allan variance analysis is particularly useful for quantifying low frequency noise and for predicting the optimal measurement time. We show how to use Allan variance in combination with Fourier analysis for optimal calibration and noise reduction in optical trapping assays. The methods are applied to passive assays, utilizing the thermal motion of a trapped particle, and to active assays where the bead is harmonically driven. The active method must be applied in assays where, for example, the viscoelastic properties of the medium or the size or shape of the trapped object are unknown. For measurement times shorter than the optimal calibration time the noise is larger in active than in the passive assays. For times equal to or longer than the optimal measurement time, though, the noise on passive and active assays is identical. As an example, we show how to quantify the influence on measurement noise of bead size and chamber geometry in active and passive assays.
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| 3. |
- Finetti, P., et al.
(author)
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Optical setup for two-colour experiments at the low density matter beamline of FERMI
- 2017
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 19:11
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Journal article (peer-reviewed)abstract
- The low density matter beamline of the free electron laser facility FERMI is dedicated to the study of atomic, molecular and cluster systems, and here we describe the optical setup available for two-colour experiments. Samples can be exposed to ultrashort pulses from a Ti:Sapphire source (fundamental, or second or third harmonic), and ultrashort light pulses of FERMI in the EUV/soft x-ray region with a well-defined temporal delay, and negligible jitter (<10 fs) compared to the pulse durations (40–100 fs). Detection schemes available include electron, ion and optical spectroscopy. The majority of experiments using this apparatus are pump-and-probe, where either wavelength can be pump or probe, but the system is also useful for other techniques, such as multi-photon spectroscopy, cross-correlation measurements and alignment of molecules in space.
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| 4. |
- Song, Yi, et al.
(author)
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Efficient coupling between dielectric and hybrid plasmonic waveguides by multimode interference power splitter
- 2011
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 13:7, s. 075002-
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Journal article (peer-reviewed)abstract
- Multimode interference power splitters based on hybrid plasmonic waveguides are investigated theoretically. Balanced power splitting is achieved in designed 1 × 3 and 1 × 2 power splitters between a silicon-on-insulator waveguide and several hybrid plasmonic waveguides, with total transmission efficiencies at 76.1% and 78.3% at the wavelength of 1550 nm, respectively.
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| 5. |
- Song, Yi, et al.
(author)
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Subwavelength hybrid plasmonic nanodisk with high Q factor and Purcell factor
- 2011
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 13:7, s. 075001-
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Journal article (peer-reviewed)abstract
- Optical nanodisk resonators based on a hybrid plasmonic waveguiding geometry areinvestigated theoretically in the wavelength range of 1200–2000 nm with their radii varyingfrom 320 to 1000 nm. Due to the fact that a hybrid plasmonic structure can efficiently confinelight in a deep-subwavelength mode volume with a relatively low propagation loss, thenanodisks designed exhibit simultaneously a high Q factor and a high Purcell factor. For ahybrid plasmonic nanodisk with the radius of 1000 nm, a Q factor of 819 and a Purcell factor of1827 are achieved at the telecommunication wavelength of 1558 nm.
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| 6. |
- Yan, Wei, 1983-, et al.
(author)
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Generalized nihility media from transformation optics
- 2011
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 13:2
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Journal article (peer-reviewed)abstract
- Nihility media in the previous literature are usually understood as media with epsilon = mu = 0. Transformation optics opens a new perspective for capturing the essence of such media. From this perspective, we generalize the definition of nihility media as transformation media derived from volumeless geometrical elements. A volumeless geometrical elements can be either a point (P), a line (L), or a surface (S). Their corresponding transformation media are therefore called P-, L-, or S-type nihility media, respectively. The previous defined nihility media with epsilon = mu = 0 is a special case under the P-type nihility media. The constructions of nihility media by metamaterials are discussed. The eigenfields in different types of nihility media are derived. The interactions between an externally incident wave and a slab of nihility media in a free space background are analyzed. Furthermore, we discuss compensated bilayers composed of nihility media. It is shown that for a slab of P-type nihility media, a normally incident wave can perfectly transmit through, while all obliquely incident waves are completely blocked; for a slab made of L-type nihility media, both normally and obliquely incident waves can transmit with some reflections, which can be eliminated by adding a compensating L-type nihility media; for a slab of S-type nihility media, all field components can perfectly transmit through.
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| 7. |
- Bashinov, A. V., et al.
(author)
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Towards attosecond-scale highly directed GeV gamma-ray sources with multipetawatt-class lasers
- 2017
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In: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 19:11
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Journal article (peer-reviewed)abstract
- We consider a possibility of constructing a gamma-ray source based on the multibeam configuration of a multipetawatt laser system which we simulate using a converging dipole wave. It is shown that such a configuration of fields allows the generation of gamma radiation with narrow directivity of about 1 mrad in the form of pulse trains or isolated pulses on the attosecond timescale. The influence of quantum electrodynamic cascade development on the parameters of generated gamma bursts is studied.
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| 8. |
- Dahlström, Jan Marcus, et al.
(author)
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Attosecond transient absorption of a bound wave packet coupled to a smooth continuum
- 2017
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In: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 19:11
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Journal article (peer-reviewed)abstract
- We investigate the possibility of using transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In a recent work, we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy-independent of the atomic structure-with maximal photoemission at all kinetic energies given a wave packet with zero relative phase (Pabst and Dahlstrom Phys. Rev. A 94 13411 (2016)). Here, we perform numerical propagation of the time-dependent Schrodinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at a zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smooth -pi/2 shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are also found in helium. Our finding is surprising, because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.
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| 9. |
- Harth, Anne, et al.
(author)
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Compact 200 kHz HHG source driven by a few-cycle OPCPA
- 2018
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In: Journal of Optics (United Kingdom). - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:1
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Journal article (peer-reviewed)abstract
- We present efficient high-order harmonic generation (HHG) based on a high-repetition rate, few-cycle, near infrared (NIR), carrier-envelope phase stable, optical parametric chirped pulse amplifier (OPCPA), emitting 6 fs pulses with 9 μJ pulse energy. In krypton, we reach conversion efficiencies from the NIR to the extreme ultraviolet (XUV) radiation pulse energy on the order of ∼10-6 with less than 3 μJ driving pulse energy. This is achieved by optimizing the OPCPA for a spatially and temporally clean pulse and by a specially designed high-pressure gas target. In the future, the high efficiency of the HHG source will be beneficial for high-repetition rate two-colour (NIR-XUV) pump-probe experiments, where the available pulse energy from the laser has to be distributed economically between pump and probe pulses.
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| 10. |
- Mauritsson, Johan, et al.
(author)
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Emerging attosecond technologies
- 2018
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In: Journal of Optics (United Kingdom). - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:11
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Journal article (peer-reviewed)abstract
- The quest for fundamental scientific knowledge triggers technological advancement. This has been particularly true for attosecond science in recent years: we assisted in the development of many new approaches - both experimentally and theoretically - that will have a high impact, not only on atomic and molecular physics, but also on optical technology. This special issue collects several of these contributions.
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