Carrier-envelope phase effects on the strong-field photoemission of electrons from metallic nanostructures

Sharp metallic nanotapers irradiated with few-cycle laser pulses are emerging as a source of highly confined coherent electron wavepackets with attosecond duration and strong directivity. The possibility to steer, control or switch such electron wavepackets by light is expected to pave the way towards direct visualization of nanoplasmonic field dynamics and real-time probing of electron motion in solid state nanostructures. Such pulses can be generated by strong-field induced tunneling and acceleration of electrons in the near-field of sharp gold tapers within one half-cycle of the driving laser field. Here, we show the effect of the carrier-envelope phase of the laser field on the generation and motion of strong-field emitted electrons from such tips. This is a step forward towards controlling the coherent electron motion in and around metallic nanostructures on ultrashort length and time scales

Real-time observation of dissipative soliton formation in nonlinear polarization rotation mode-locked fibre lasers

Formation of coherent structures and patterns from unstable uniform state or noise is a fundamental physical phenomenon that occurs in various areas of science ranging from biology to astrophysics. Understanding of the underlying mechanisms of such processes can both improve our general interdisciplinary knowledge about complex nonlinear systems and lead to new practical engineering techniques. Modern optics with its high precision measurements offers excellent test-beds for studying complex nonlinear dynamics, though capturing transient rapid formation of optical solitons is technically challenging. Here we unveil the build-up of dissipative soliton in mode-locked fibre lasers using dispersive Fourier transform to measure spectral dynamics and employing autocorrelation analysis to investigate temporal evolution. Numerical simulations corroborate experimental observations, and indicate an underlying universality in the pulse formation. Statistical analysis identifies correlations and dependencies during the build-up phase. Our study may open up possibilities for real-time observation of various nonlinear structures in photonic systems

Analysis of laser radiation using the Nonlinear Fourier transform

Modern high-power lasers exhibit a rich diversity of nonlinear dynamics, often featuring nontrivial co-existence of linear dispersive waves and coherent structures. While the classical Fourier method adequately describes extended dispersive waves, the analysis of time-localised and/or non-stationary signals call for more nuanced approaches. Yet, mathematical methods that can be used for simultaneous characterisation of localized and extended fields are not yet well developed. Here, we demonstrate how the Nonlinear Fourier transform (NFT) based on the Zakharov-Shabat spectral problem can be applied as a signal processing tool for representation and analysis of coherent structures embedded into dispersive radiation. We use full-field, real-time experimental measurements of mode-locked pulses to compute the nonlinear pulse spectra. For the classification of lasing regimes, we present the concept of eigenvalue probability distributions. We present two field normalisation approaches, and show the NFT can yield an effective model of the laser radiation under appropriate signal normalisation conditions

Efficient and accurate modeling of electron photoemission in nanostructures with TDDFT

We derive and extend the time-dependent surface-flux method introduced in [L. Tao, A. Scrinzi, New J. Phys. 14, 013021 (2012)] within a time-dependent density-functional theory (TDDFT) formalism and use it to calculate photoelectron spectra and angular distributions of atoms and molecules when excited by laser pulses. We present other, existing computational TDDFT methods that are suitable for the calculation of electron emission in compact spatial regions, and compare their results. We illustrate the performance of the new method by simulating strong-field ionization of C60 fullerene and discuss final state effects in the orbital reconstruction of planar organic molecules

Single-Pixel Fluorescence Spectroscopy Using Near-Field Dispersion for Single-Photon Counting and Single-Shot Acquisition

Time-resolved sensing of fluorescence quanta provides exceptionally versatile information–including access to nanoscopic structure, chemical environment and nonclassical behavior of quantum emitters. Combined spectro-temporal information is typically obtained using spatial dispersion with photoelectron imaging such as streak-cameras or position-sensitive counting and, alternatively, sequential filtering with single-pixel detectors. However, such schemes require complex, expensive and low-sensitivity detectors or rely on scanning acquisition. Here, we demonstrate a single-pixel implementation of fluorescence emission spectroscopy entirely in the temporal domain compatible with (a) time-correlated single-photon counting (TCSPC) and (b) high-speed single-shot detection. Harnessing the near-field regime of the Time-Stretch Dispersive Fourier Transformation (TS-DFT), we encode spectral information via chromatic dispersion into temporal signals, and we demonstrate the retrieval of entwined information via a direct deconvolution using prior knowledge. Addressing high optical throughput for extended emitters, we introduce a high-bandwidth graded-index multimode fiber for TS-DFT. As proof-of-concept, we present rapid single-shot optical thermometry based on quantum-dot luminescence. Given its high speed, efficiency, and simplicity, we foresee broad applications for fast hyperspectral confocal fluorescence microscopy, low-light sensing, and high-throughput spectral screening

Terabit sampling system with photonic time-stretch analog-to-digital converter

The detection of rapid dynamics in diverse physical systems is traditionally very difficult and strongly dominated by several noise contributions. Laser mode-locking, electron bunches in accelerators and optical-triggered phases in materials are events that carry important information about the system from which they emerge. To under- stand the underlying dynamics of complex systems often large numbers of single-shot measurements must be acquired continuously over a long time with extremely high temporal resolution. Ultrafast real-time instruments allow the acquisition of large data sets, even for rare events, in a relatively short time period. The real-time measurement of fast single-shot events with large record lengths is one of the most challenging problems in the fields of instrumentation and measurement. In this contribution, the novel ultra-fast and continuous data sampling system THERESA using photonic time-stretch is presented and its performance is discussed. The pro- posed data acquisition system is based on the latest ZYNQ Radio Frequency System on Chip (ZYNQ-RFSoC) family from Xilinx, which combines an array of fast (GS/s) multi-channel Analog-to-Digital Converters (ADCs) with a Field Programmable Gate Array (FPGA) and a multi-core ARM processor in a single heterogeneous programmable device. The stretched pulse is sampled in parallel by 16 wideband sampling channels operating in time-interleaving mode. The sampled data is transferred by a 100 Gb Ethernet data link to the Data Acquisition (DAQ) compute node for further analysis. The combination of both, the photonic time-stretch and the fast sampling system, is capable of sampling short pulses with femtosecond time resolution. Applications of the new system, hardware implementation and the commissioning of the first system for the electron bunch diagnostics are presented