Intense Light Pulses Research Articles

Unlocking Coherent Control of Ultrafast Plasmonic Interaction

AbstractStriking a metallic nanostructure with a short and intense pulse of light excites a complex out‐of‐equilibrium distribution of electrons that rapidly interact and lose their mutual coherent motion. Due to the highly nonlinear dynamics, the photo‐excited nanostructures can generate energetic photons beyond the spectrum of the incident beam, where the shortest pulse duration is traditionally expected to induce the greatest nonlinear emission. Here, these photo‐induced extreme ultrafast dynamics are coherently controlled by spectrally shaping a sub‐10 fs pulse within the timescale of coherent plasmon excitations. Contrary to the common perception, it is shown that stretching the pulse to match its internal phase with the plasmon‐resonance increases the second‐order nonlinear emission by >25%. The enhancement is observed only when shaping extreme‐ultrashort pulses (<20 fs), thus signifying the coherent electronic nature as a crucial source of the effect. A detailed theoretical framework that reveals the optimal pulse shapes for enhanced nonlinear emission regarding the nanostructures’ plasmonic‐resonances is provided. The demonstrated truly‐coherent plasma control paves the way to engineer rapid out‐of‐equilibrium response in solids state systems and light‐harvesting applications.

Ultrashort laser-driven dynamics of massless Dirac electrons generating valley polarization in graphene

We identify and describe how intense short light pulses couple to massless Dirac fermions in two-dimensional systems. The ensuing excitation dynamics exhibits unusual scaling with the wavelength of the light due the linear dispersion of the band structure and the fact that light coupling is efficient only close to the Dirac points. We exploit these features to achieve valley polarization of more than 70 % with simple pulse shapes. Quantitative results are given for pristine graphene.

Photon Emission from Hollow Ions Near Surfaces

Ions with multiple inner-shell vacancies frequently arise due to their interaction with different targets, such as (intense) light pulses, atoms, clusters or bulk material. They are formed, in addition, if highly charged ions approach surfaces and capture electrons at rather large distances. To explore the interaction of such hollow ions and their subsequent relaxation, photon spectra in different frequency regions have been measured and compared to calculations. To support these and related measurements, we here show within the framework of the Jena Atomic Calculator (Jac) how (additional) electrons in outer shells modify photon emission and lead to characteristic shifts in the observed spectra. Further, for highly charged Ar ions in KLm(m=1…8) configurations, we analyze the mean relaxation time for their stabilization into the different ground configurations. These examples demonstrate how a powerful and flexible toolbox such as Jac will be useful (and necessary) in order to model the photon and electron emission of ions as they occur not only near surfaces but also in astro-, atomic and plasma physics.

Solving time-dependent Schrödinger equation in momentum space with application to strong-field problems

We present a numerical method to solve the time-dependent Schrödinger equation (TDSE) in momentum representation (p-space). We show that the method is practically useful and easier than the coordinate space (r-space) method when continuous states are involved. For a single-active electron (SAE) atom, the numerically complete eigenset can be accurately constructed in p-space by quadrature method which bypasses the singularities in the Coulombic kernel. Although there is an ingenious Lande subtraction for dealing with the singularity but is not straightforward. We formulate the time marching algorithms for an SAE atom in linearly polarized (LP) laser pulse and in circularly polarized (CP) pulse, respectively. We show calibrations to literature results to justify the formulations. Argon in a resonant and a nonresonant CP pulse are investigated and show distinct properties from the case of tunneling regime. Together with the currently available powerful graphics processing unit (GPU) for massively parallel computing, the p-space method could provide a useful alternative tool for some problems such as atoms in intense light pulses.

Past Forward: The Nobelist’s First Laser

When George Porter arrived at the University of Cambridge in 1945 as a Ph.D. student, he found the equipment remarkably primitive. Students had to build their own oscilloscopes! To conduct his research—detecting the short-lived molecules known as free radicals—Porter pieced together a setup that included a surplus army searchlight powered by a surplus diesel engine. After seeing flash lamps at a Siemens factory, he decided to modify his approach, replacing the continuous light source with short, intense pulses of light. With his flash photolysis technique, Porter was able to capture reactions lasting mere milliseconds. To study even faster reactions, though, he needed a faster light source, for which he’d have to wait. The ruby laser, invented in 1960, was the ideal solution. Porter used this one to record nanosecond-scale reactions. Flash photolysis is still used to study semiconductors, nanoparticles, and photosynthesis, among other things. For their work on high-speed, lightdriven chemical reactions, Porter; his Ph.D. adviser, Ronald G.W. Norrish; and Manfred Eigen shared the 1967 Nobel Prize in Chemistry.

Intense laser matter interaction in atoms, finite systems and condensed media: recent experiments and theoretical advances

This special issue of the European Journal of Physics: Special Topics entitled “Intense Laser Matter Interaction in Atoms, Finite Systems and Condensed Media” published a set of 21 articles aiming to put in perspective this burgeoning area of science, application and technology. The invention of chirped pulse amplification by Strickland and Mourou, which led to their Nobel prizes in 2018, has ushered in a new era in photon–matter interaction where coherent intense light pulses in the optical and infrared domains play a central role. This development has not only called in creative experimental methods, but has demanded new theoretical approaches working in the non-perturbative and highly nonlinear regimes of light–matter interaction. Both for fundamental physics as well as key applications these have played an essential role. Key pillars of this subject, captured in this collection, are laser-induced nanometer-scale plasmas ignited in unsupported nanoparticles, laser-based particle acceleration taking advantage of unprecedented field gradients, the generation of high-order harmonics opening up attosecond science and ultrafast X-ray spectroscopy, and the generation of terahertz pulses for time-domain spectroscopy of new materials.

Mixed-Halide Perovskite Film-Based Neuromorphic Phototransistors for Mimicking Experience-History-Dependent Sensory Adaptation.

Sensory adaptation is an essential function for humans to live on the earth. Herein, a hybrid synaptic phototransistor based on the mixed-halide perovskite/organic semiconductor film is reported. This hybrid phototransistor achieves photosensitive performance including a high photoresponsivity over 4 × 103 A/W and an excellent specific detectivity of 2.8 × 1016 Jones. Due to the photoinduced halide-ion segregation of the mixed-halide perovskites and their slow recovery properties, the experience-history-dependent sensory adaptation behavior can be mimicked. Moreover, the light pulse width, intensity, light wavelength, and gate bias can be used to regulate the adaptation processes to improve its adaptability and perceptibility in different environments. The CsPbBrxI3-x/organic semiconductor hybrid films produced by spin coating are beneficial to large-scale fabrication. This study fabricates a novel solution-processable light-stimulated synapse based on inorganic perovskites for mimicking the human sensory adaptation that makes it possible to approach artificial neural sensory systems.

Diffraction-limited coherent wake emission

The plasma mirror is a relativistic optical element that under certain irradiation conditions generates intense attosecond extreme-ultraviolet light pulses, in a process known as coherent wake emission (CWE). CWE has been previously characterized by its high spatial divergence, originating from an intrinsic intensity-dependent phase accumulation. In this Letter, we show that the transverse variations of the plasma expansion can completely cancel the CWE intrinsic phase. Accordingly, we experimentally demonstrate nearly diffraction-limited CWE with unprecedented divergence, under 6 mrad. We validate our analytical model with particle in cell simulations. This understanding facilitates the development of plasma mirrors as applicable ultraviolet light sources.Received 9 March 2021Accepted 5 August 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L032059Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh intensity laser-plasma interactionsHigh-order harmonic generationPhysical SystemsRelativistic plasmasAtomic, Molecular & OpticalPlasma Physics

First-principles simulation of intense single-cycle ultrashort light pulses interacting with diamond: Comparison study in attosecond and femtosecond regimes

The interaction of intense single-cycle ultrashort (0.1 to 9 fs) light pulses with diamond crystal and thin film is simulated, combining the dependent Kohn-Sham equation with the Maxwell equations. Distinct features are observed depending on the duration of the pulse. In the diamond crystal, maximum energy transfer from light pulse is observed with a pulse duration 0.3 fs. In this case, the phase of current density $J(t)$ coincides with that of the electric field $E(t)$. For the incident pulse of duration 0.1 fs, most of the light will transmit on passing the thin film. But for the pulse of duration 0.5 fs, there is more reflection than transmission. For light pulses of durations 7 and 9 fs in diamond crystal, traditional nonlinear behavior of energy transfer are observed. Interestingly, for the attosecond pulse, there is a linear scaling behavior with the pulse intensity below ${10}^{16}\phantom{\rule{4pt}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ on the one hand and an unusual linear dynamic interference response behavior with the pulse width, determined by the interference of the different quantum pathways, on the other hand.

Macroscopic, layered onion shell like magnetic domain structure generated in YIG films using ultrashort, megagauss magnetic pulses

Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simulations show that the giant magnetic field pulses create ultrafast terahertz (THz) spin waves and a snapshot of these fast-propagating spin waves is stored as the layered onion shell shaped domains in the YIG film. Typically, information transport via spin waves in magnonic devices occurs in the gigahertz regime, where devices are susceptible to thermal disturbances at room temperature. Our intense laser light pulse—YIG sandwich target combination, paves the way for room temperature table-top THz spin wave devices, operating just above or in the range of the thermal noise floor. This dissipation-less device offers ultrafast control of spin information over distances of few hundreds of microns.

Unconventional light-induced states visualized by ultrafast electron diffraction and microscopy

Exciting electrons in solids with intense light pulses offers the possibility of generating new states of matter through nonthermal means and controlling their macroscopic properties on femto- to picosecond timescales. One way to manipulate a solid is by altering its lattice structure, which often underlies the electronic, magnetic and other phases. Here, we review how structures of solids are affected by photoexcitation and how their ultrafast dynamics are captured with time-resolved electron diffraction and microscopy. Specifically, we survey how a strong light pulse has been used to tailor the nonequilibrium characteristics to yield on-demand properties in various material classes. In the existing literature, four main routes have been exploited to control material structures: (i) phase competition, (ii) electronic correlations, (iii) excitation of coherent modes, and (iv) defect generation. In this review, we discuss experiments relevant to all four schemes and finish by speculating about future directions.

Nonequilibrium charge-density-wave order beyond the thermal limit

The interaction of many-body systems with intense light pulses may lead to novel emergent phenomena far from equilibrium. Recent discoveries, such as the optical enhancement of the critical temperature in certain superconductors and the photo-stabilization of hidden phases, have turned this field into an important research frontier. Here, we demonstrate nonthermal charge-density-wave (CDW) order at electronic temperatures far greater than the thermodynamic transition temperature. Using time- and angle-resolved photoemission spectroscopy and time-resolved X-ray diffraction, we investigate the electronic and structural order parameters of an ultrafast photoinduced CDW-to-metal transition. Tracking the dynamical CDW recovery as a function of electronic temperature reveals a behaviour markedly different from equilibrium, which we attribute to the suppression of lattice fluctuations in the transient nonthermal phonon distribution. A complete description of the system’s coherent and incoherent order-parameter dynamics is given by a time-dependent Ginzburg-Landau framework, providing access to the transient potential energy surfaces.

Photonic Curing of Nickel Oxide Transport Layer and Perovskite Active Layer for Flexible Perovskite Solar Cells: A Path Towards High-Throughput Manufacturing

High-throughput roll-to-roll (R2R) manufacturing of perovskite solar cells (PSCs) is currently limited by thermal processes that take tens of minutes each, translating to impractically long annealing tools at high web speeds. In addition, PSCs are usually made with metal oxide transport layer materials that require high temperatures for thermal annealing. Here, we demonstrate the fabrication of PSCs using photonic curing, instead of thermal annealing, to convert NiOx directly from sol-gel precursors for hole transport layers and to crystallize methylammonium lead iodide (MAPbI3) active layers on flexible Willow® Glass substrates. Photonic curing uses short, intense pulses of light to process materials at a high speed, hence it is compatible with R2R manufacturing. We achieved power conversion efficiencies (PCEs) of 11.7% in forward-scan and 10.9% in reverse-scan for PSCs made with photonic cured NiOx and MAPbI3 films. Furthermore, both NiOx and MAPbI3 films could be processed with a single photonic curing pulse, with a web speed of 5.7 m/min, and still produce PCEs comparable to thermally annealed control samples. Based on the single-pulse photonic curing condition for each film, we project a web speed of 26 m/min, laying a pathway to high-throughput production of perovskite solar modules.

Non-linear light emission of inorganic protonic diodes, H+LEDs

H+LEDs are light emitting devices based on a protonic p–n junction; now with no organic polymers. The unique are non-linear optical effects: collimated light beams and stimulated Raman scattering (SRS), observed while generating intense light pulses.

P.765 The role of N-acetyl-D-glucosamine kinase in protecting proteinopathies

This study evaluates the potential of continuous wave Ultraviolet C light (UV-C) and broad-spectrum intense pulsed light (in this study referred to as High Intensity Light Pulses, HILP) for the inactivation of pathogens of public concern in powdered infant formula (PIF) producers. To achieve this goal a sequential set of experiments were performed, firstly in clear liquid media, secondly on the surface of spherical beads under agitation and, finally in PIF. L. innocua was the most sensitive microorganism to both technologies under all conditions studied with reductions exceeding 4 log10 cycles in PIF. In the clear liquid medium, the maximum tolerance to light was observed for C. sakazakii against UV-C light and for B. subtilis spores against HILP, with a fluence of approximately 17 mJ/cm2 required for a 1 log10 cycle inactivation (D value) of each species. In PIF it was possible to inactivate >99% of the vegetative cell populations by HILP with a fluence of 199 mJ/cm2 and of B. subtilis spores by doubling the fluence. By contrast, for UV-C treatments a fluence of 2853 mJ/cm2 was needed for 99.9% reduction of C. sakazakii, which was the most light-resistant microorganism to UV-C. Results here obtained clearly show the potential for light-based interventions to improve PIF microbiological safety.

Formation of dispersive shock waves in a saturable nonlinear medium.

We use the Gurevich-Pitaevskii approach based on the Whitham averaging method for studying the formation of dispersive shock waves in an intense light pulse propagating through a saturable nonlinear medium. Although the Whitham modulation equations cannot be diagonalized in this case, the main characteristics of the dispersive shock can be derived by means of an analysis of the properties of these equations at the boundaries of the shock. Our approach generalizes a previous analysis of steplike initial intensity distributions to a more realistic type of initial light pulse and makes it possible to determine, in a setting of experimental interest, the value of measurable quantities such as the wave-breaking time or the position and light intensity of the shock edges.

Influence of voltage and distance on quality attributes of mixed fruit beverage during pulsed light treatment and kinetic modeling

AbstractThe study investigates the influence of pulsed light (PL) processing parameters on quality of mixed fruit beverage followed by kinetic modeling. The attributes tested were aerobic mesophiles (AM), yeast and mold (YM) counts, polyphenol oxidase (PPO) and peroxidase (POD) activity, color change (ΔE*), browning index (ΔBI), antioxidant capacity (AOC), and ascorbic acid (AA) content at varying voltage (1.8–2.4 kV), the number of pulses (2–187), and distance (2.4–9.6 cm). Weibull model described the PL inactivation rate of AM and YM and nth order kinetic model estimated the inactivate rate of PPO, POD, and AA. The maximum inactivation of PPO, POD, and AA content were 41, 51, and 36%, respectively. At the most severe PL condition, ΔE* was 6.4, ΔBI was 5.6 with 14% increment in phenolics. A secondary kinetic model adequately predicted the ratio of rate constant and fluence‐based rate (k/kF) for PPO, YM, and AA correlating voltage (V) and lamp distance (x). PL‐induced pasteurization of the beverage is possible at the fluence rate of 17.42 W/cm2 for 3 min.Practical ApplicationsExposing the food material to a high intensity pulsed light (PL) is a nonthermal way of food preservation for the shelf‐life extension. The potential of PL treatment (PLT) has been explored for a mixed fruit beverage in terms of its microbial, enzymatic, and nutritional quality. An optimized PLT condition is proposed to obtain a microbially safe fruit beverage along with a minimal loss in bioactive compounds. Subsequently, the kinetic data related to microbial and enzyme inactivation and degradation of vitamins will help in deciding the process parameters like treatment time, lamp voltage, and sample distance from the light source. The secondary kinetic model will eventually help to design a robust PL process condition for similar fruit beverages to obtain a microbiologically safe product with a minimal loss in vitamins.

Controlling energy transfer from intense ultrashort light pulse to crystals: A comparison study in attosecond and femtosecond regimes

The energy exchange between photons and electrons has been investigated theoretically by ab initio approach based on time-dependent density functional theory. Using diamond as a concrete example, three types of resonance and cancellation in the transfer of energy are theoretically observed, that allows one to gain a useful independent insight into the interaction processes of attosecond light pulses with matter. Our results demonstrate the linearity in energy transfer from intense attosecond light pulses to solids, in contrast to the nonlinearity in energy transfer from intense femtosecond light pulses to solids as expected from the conventional point of view, opening new perspectives for attoscience.

Advanced characterization of an optical fibre sensor system based on an MPPC detector for measurement of X-ray radiation in clinical linacs

A reliable, accurate and in-vivo dosimetry system for measuring the radiation dose and profiling the X-ray beam during radiotherapy is reported. Its dynamic range is investigated using an accurately controlled pulsed light emitting diode (LED) system. Highly resolved temporal analog and digital signals were captured from the analog and digital outputs of a multi-pixel photon counter (MPPC) detector when exposed to the LED system. The photon distribution of a low intensity pulsed LED light source was observed and is found to obey a Poisson distribution with changing light intensity. The average number of photons was obtained using the digital MPPC output signals which in turn allowed the appropriate intensity of the light source to be determined for the correct light exposure conditions for the detector. The average analog output voltage over a single 3 μs pulse is determined to indicate the intensity of the detected light. The MPPC detector output analog signal is limited to a narrow range (0.6 V–1.4 V) to ensure adequate signal detection level (the lower limit) and prevention of entry into saturation (the upper limit) which also corresponds to a digital output signal range (in counts). An average photon number range of 3–7 for the digital output signal is established, which leads to the establishment of a unique and constant photon number to average output voltage ratio of 4.64 ± 0.10. Experimental results show that the establishment of this ratio is significant as adherence to it ensures the correct exposure conditions of the MPPC and speeds up the measurement cycle in the clinical setting.

Applications of Pulsed Light Decontamination Technology in Food Processing: An Overview

Consumers of the 21st century tend to be more aware and demand safe as well as nutritionally balanced food. Unfortunately, conventional thermal processing makes food safe at the cost of hampering nutritional value. The food industry is trying to develop non-thermal processes for food preservation. Pulsed light (PL) is one such emerging non-thermal food processing method that can decontaminate food products or food contact surfaces using white light. Exposure to intense light pulses (in infrared, visible, and ultraviolet (UV) regions) causes the death of microbial cells, rendering the food safe at room temperature. PL technology is an excellent and rapid method of disinfection of product surfaces and is increasingly being used for food surfaces and packaging decontamination, enabling the minimal processing of food. This paper aims to give an overview of the latest trends in pulsed light research, discuss principles of pulse generation, and review applications of various PL systems for the inactivation of microorganisms in vitro, in various food products, and on food contact surfaces. Effects of PL on food quality, challenges of the process, and its prospects are presented.