Single Optical Pulse Research Articles

Intrinsic Defect-Driven Synergistic Synaptic Heterostructures for Gate-Free Neuromorphic Phototransistors.

The optoelectronic synaptic devices based on two-dimensional (2D) materials offer great advances for future neuromorphic visual systems with dramatically improved integration density and power efficiency. The effective charge capture and retention are considered as one vital prerequisite to realizing the synaptic memory function. However, the current 2D synaptic devices are predominantly relied on materials with artificially-engineered defects or intricate gate-controlled architectures to realize the charge trapping process. These approaches, unfortunately, suffer from the degradation of pristine materials, rapid device failure, and unnecessary complication of device structures. To address these challenges, an innovative gate-free heterostructure paradigm is introduced herein. The heterostructure presents a distinctive dome-like morphology wherein a defect-rich Fe7S8 core is enveloped snugly by a curved MoS2 dome shell (Fe7S8@MoS2), allowing the realization of effective photocarrier trapping through the intrinsic defects in the adjacent Fe7S8 core. The resultant neuromorphic devices exhibit remarkable light-tunable synaptic behaviors with memory time up to ≈800 s under single optical pulse, thus demonstrating great advances in simulating visual recognition system with significantly improved image recognition efficiency. The emergence of such heterostructures foreshadows a promising trajectory for underpinning future synaptic devices, catalyzing the realization of high-efficiency and intricate visual processing applications.

Effect of dual-optical pulses with temporal energy distribution on laser ablation performance in in vivo zebrafish model.

A Q-switched laser system has been used in a single-pulse mode for skin melasma treatments because of instant heat deposition in the target. Despite the efficient ablation of the melanophores in the skin, the single, high-fluence pulse often causes undesirable damage to the surrounding tissue, leading to high recurrence rates. This study aims to investigate the feasibility of dual-optical pulses with a temporal energy distribution on the melasma treatment in in vivo zebrafish models in comparison to that of the single optical pulse. Based on the optical detection, the dual-optical pulses had a temporal energy distribution ratio of 4:1 and an interval of 61 μs between the two consecutive pulses. According to the histological analysis, the dual pulses removed melanophores and induced a few apoptotic nuclei with minimal recurrence. This study demonstrated that the feasibility of dual-optical pulses (energy ratio = 4:1) could enhance the laser ablation performance in vivo.

A novel technique for secure transmission of two channels using a single optical pulse position modulated signal for free space optical communication

A novel technique for secure transmission of two channels using a single optical pulse position modulated signal for free space optical communication

A Generalized Transformer-Based Pulse Detection Algorithm.

Pulse-like signals are ubiquitous in the field of single molecule analysis, e.g., electrical or optical pulses caused by analyte translocations in nanopores. The primary challenge in processing pulse-like signals is to capture the pulses in noisy backgrounds, but current methods are subjectively based on a user-defined threshold for pulse recognition. Here, we propose a generalized machine-learning based method, named pulse detection transformer (PETR), for pulse detection. PETR determines the start and end time points of individual pulses, thereby singling out pulse segments in a time-sequential trace. It is objective without needing to specify any threshold. It provides a generalized interface for downstream algorithms for specific application scenarios. PETR is validated using both simulated and experimental nanopore translocation data. It returns a competitive performance in detecting pulses through assessing them with several standard metrics. Finally, the generalization nature of the PETR output is demonstrated using two representative algorithms for feature extraction.

Simultaneous Trapping of Two Optical Pulses in an Atomic Ensemble as Stationary Light Pulses.

The stationary light pulse (SLP) refers to a zero-group-velocity optical pulse in an atomic ensemble prepared by two counterpropagating driving fields. Despite the uniqueness of an optical pulse trapped within an atomic medium without a cavity, observations of SLP so far have been limited to trapping a single optical pulse due to the stringent SLP phase-matching condition, and this has severely hindered the development of SLP-based applications. In this Letter, we first show theoretically that the SLP process in fact supports two phase-matching conditions and we then utilize the result to experimentally demonstrate simultaneous SLP trapping of two optical pulses for the duration from 0.8 to 2.0 μs. The characteristic dissipation time, obtained by the release efficiency measurement from the SLP trapping state, is 1.22 μs, which corresponds to an effective Q factor of 2.9×10^{9}. Our Letter is expected to bring forth interesting SLP-based applications, such as, efficient photon-photon interaction, spatially multimode coherent quantum memory, creation of exotic photonic gas states, etc.

Voltage Response of a Pyroelectric Detector to a Single Rectangular Optical Radiation Pulse.

In this paper, a mathematical description of the voltage response of a pyroelectric detector to a single rectangular pulse of optical radiation is presented. Mathematical procedures leading to the derivation of the dependencies describing the detector response for the cases, taking into account the duration of the radiation pulse absorbed by the detector and the relations between values of the electrical and thermal time constants of the detector, are shown in detail. The analytical results are compared and verified by experimental studies carried out using a commercially available pyroelectric detector (model PE10-S-Q) manufactured by the company Ophir. Comparison of the experimentally obtained data with analytical calculations showed good agreement.

All-fiber nonvolatile broadband optical switch using an all-optical method.

Optical switches based on phase change materials have enormous application potential in optical logic circuits and optical communication systems. Integration of all-optical switching devices with optical fibers is a promising approach for realizing practical applications in enabling the optical fiber to transmit and process signals simultaneously. We describe an all-fiber nonvolatile broadband optical switch using an all-optical method. We use a single optical pulse to modulate the phase change material deposited on the tapered fiber to achieve logical control of the transmitted light. The response time of our optical switch is 80 ns for SET and 200 ns for RESET. Our optical switches can operate in the C-band (1530-1565 nm). The optical switching contrast is 40%. Our approach paves the way for all-optical nonvolatile fiber optic communication.

QUASI-DISTRIBUTED RECIRCULATED FIBER OPTIC GASEOUS OXYGEN MEASUREMENT SYSTEM

A scheme of a quasi-distributed fiber-optic system for monitoring the oxygen concentration of the recirculation type is proposed. The principle of measurement is to register changes in the recirculation frequency of single optical pulses with periodic regeneration simultaneously at several wavelengths. The operation of the sensor is based on a change in the length of the magnetostrictive strips and the segments of optical fibers associated with them under the influence of a changing magnetic field due to the paramagnetic properties of gaseous oxygen. The numerical estimation of the measurement error has been carried out. It is shown that with a length of the sensitive element of the sensor of 1.5 m and a radius of 0.6 ... 0.7 m, it is possible to obtain a relative error of the measurement method no worse than 0.6% for pure oxygen and 2.5% for an air mixture.

Atom-Mechanical Hong-Ou-Mandel Interference

Quantum coupling between mechanical oscillators and atomic gases generating entanglement has been recently experimentally demonstrated using their subsequent interaction with light. The next step is to build a hybrid atom-mechanical quantum gate showing bosonic interference effects of single quanta in the atoms and oscillators. We propose an experimental test of Hong-Ou-Mandel interference between single phononic excitation and single collective excitation of atoms using the optical connection between them. A single optical pulse is sufficient to build a hybrid quantum-nondemolition gate to observe the bunching of such different quanta. The output atomic-mechanical state exhibits a probability of a hybrid bunching effect that proves its nonclassical aspects. This proposal opens a feasible road to broadly test such advanced quantum bunching phenomena in a hybrid system with different specific couplings.

Ultrafast coherent excitation of an ytterbium ion with single laser pulses

Experimental realizations of two qubit entangling gates with trapped ions typically rely on addressing spectroscopically resolved motional sidebands, limiting gate speed to the secular frequency. Fast entangling gates using ultrafast pulsed lasers overcome this speed limit. This approach is based on state-dependent photon recoil kicks from a sequence of counter-propagating, resonant, ultrafast pulse pairs, which can allow sub-microsecond gate speeds. Here, we demonstrate a key component of the ultrafast gate protocol, the coherent excitation of a 171Yb+ ion across the 2S1∕2-2P1∕2 transition with a single near-resonant short optical pulse at 369.53 nm. We achieve a maximum population transfer of 94(1)% using a picosecond pulsed laser that can be tuned across the 2S1∕2-2P1∕2 transition and 42.5(9)% with 190(7) GHz detuning.

Unifying femtosecond and picosecond single-pulse magnetic switching in Gd-Fe-Co

Many questions are still open regarding the physical mechanisms behind the magnetic switching in GdFeCo alloys by single optical pulses. Phenomenological models suggest a femtosecond scale exchange relaxation between sublattice magnetization as the driving mechanism for switching. The recent observation of thermally induced switching in GdFeCo by using both several picosecond optical laser pulse as well as electric current pulses has questioned this previous understanding. This has raised the question of whether or not the same switching mechanics are acting at the femo- and picosecond scales. In this work, we aim at filling this gap in the understanding of the switching mechanisms behind thermal single-pulse switching. To that end, we have studied experimentally thermal single-pulse switching in GdFeCo alloys, for a wide range of system parameters, such as composition, laser power and pulse duration. We provide a quantitative description of the switching dynamics using atomistic spin dynamics methods with excellent agreement between the model and our experiments across a wide range of parameters and timescales, ranging from femtoseconds to picoseconds. Furthermore, we find distinct element-specific damping parameters as a key ingredient for switching with long picosecond pulses and argue, that switching with pulse durations as long as 15 picoseconds is possible due to a low damping constant of Gd. Our findings can be easily extended to speed up dynamics in other contexts where ferrimagnetic GdFeCo alloys have been already demonstrated to show fast and energy-efficient processes, e.g. domain-wall motion in a track and spin-orbit torque switching in spintronics devices.

Nanotwist of aluminum with irradiation of a single optical vortex pulse

A nanoscale twisting of aluminum (Al) is demonstrated by irradiation with a single picosecond optical vortex pulse with relatively low energy near the ablation threshold, due to the orbital angular momentum (OAM) transfer effects. The twisting needle is easily transformed into a microscale non-twisting needle by only the deposition of several overlaid optical vortex pulses. Irradiation with a picosecond/nanosecond optical vortex pulse with a millijoule level pulse energy also enabled the fabrication of a microscale non-twisting needle. Such nano/microstructuring of Al provides a new physical insight for the interaction between OAM and materials, and it also offers an entirely new nano/microfabrication technique towards ultraviolet plasmonic devices.

Engineering Single-Shot All-Optical Switching of Ferromagnetic Materials.

Since it was recently demonstrated in a spin-valve structure, magnetization reversal of a ferromagnetic layer using a single ultrashort optical pulse has attracted attention for future ultrafast and energy-efficient magnetic storage or memory devices. However, the mechanism and the role of the magnetic properties of the ferromagnet as well as the time scale of the magnetization switching are not understood. Here, we investigate single-shot all-optical magnetization switching in a GdFeCo/Cu/[CoxNi1-x/Pt] spin-valve structure. We demonstrate that the threshold fluence for switching both the GdFeCo and the ferromagnetic layer depends on the laser pulse duration and the thickness and the Curie temperature of the ferromagnetic layer. We are able to explain most of the experimental results using a phenomenological model. This work provides a way to engineer ferromagnetic materials for energy efficient single-shot all-optical magnetization switching.

Analysis of ultra-short bunches in free-electron lasers

Free-electron lasers (FELs) operate at wavelengths from millimeter waves through hard x-rays. At x-ray wavelengths, FELs typically rely on self-amplified spontaneous emission (SASE). Typical SASE emission contains multiple temporal ‘spikes’ which limit the longitudinal coherence of the optical output; hence, alternate schemes that improve on the longitudinal coherence of the SASE emission are of interest. In this paper, we consider electron bunches that are shorter than the SASE spike separation. In such cases, the spontaneously generated radiation consists of a single optical pulse with better longitudinal coherence than is found in typical SASE FELs. To investigate this regime, we use two FEL simulation codes. One (MINERVA) uses the slowly-varying envelope approximation (SVEA) which breaks down for extremely short pulses. The second (PUFFIN) is a particle-in-cell simulation code that is considered to be a more complete model of the underlying physics and which is able to simulate very short pulses. We first anchor these codes by showing that there is substantial agreement between the codes in simulation of the SPARC SASE FEL experiment at ENEA Frascati. We then compare the two codes for simulations using electron bunch lengths that are shorter than the SASE slice separation. The comparisons between the two codes for short bunch simulations elucidate the limitations of the SVEA in this regime but indicate that the SVEA can treat short bunches that are comparable to the cooperation length.

Microneedle structuring of Si(111) by irradiation with picosecond optical vortex pulses

We report on comparative studies of the optical vortex-induced structures of both Si(100) and Si(111) by irradiation with a single optical vortex picosecond pulse. Furthermore, we address the effects of the total angular momentum (TAM) on the optical vortex-induced microneedle. Si(111) allows for the faster growth of the microneedle, although this impacts the monocrystallization of the needle. The TAM then forces the melted silicon to spin axially, thereby yielding an efficient accumulation of melted silicon on the substrate for microneedle formation. These results provide new fundamental insights into the interactions between optical vortex fields and irradiated materials.

Equalization of pulse timings in an excitable microlaser system with delay

An excitable semiconductor micropillar laser with delayed optical feedback is able to regenerate pulses by the excitable response of the laser. It has been shown that almost any pulse sequence can, in principle, be excited and regenerated by this system over short periods of time. We show experimentally and numerically that this is not true anymore in the long term: rather, the system settles down to a stable periodic orbit with equalized timing between pulses. Several such attracting periodic regimes with different numbers of equalized pulse timing may coexist and we study how they can be accessed with single external optical pulses of sufficient strength that need to be timed appropriately. Since the observed timing equalization and switching characteristics are generated by excitability in combination with delayed feedback, our results will be of relevance beyond the particular case of photonics, especially in neuroscience.

Integration of Tb/Co multilayers within optically switchable perpendicular magnetic tunnel junctions

This work reports the development of perpendicular magnetic tunnel junctions, based on a multilayered stack of [Tb/Co] nanolayers, in which the magnetization can be reliably toggled using a single optical pulse. The helicity-independent single-shot switching of the magnetization in the Tb/Co multilayered stack was achieved using either 60 fs-long or 5 ps laser pulses with incident fluences down to 4.7 mJ/cm2. The magnetic switching was achieved for a Co-rich composition window of the multilayer corresponding to layer thickness ratios tCo/tTb between 1.3-1.5. This was confirmed for the multilayer alone as well as for the multilayer coupled to aCoFeB electrode, with a structure consisting of CoFeB/Ta/[Tb/Co]N. The optical switching is preserved even after annealing at 250°C in magnetic tunnel junctions (MTJ) electrodes, exhibiting a tunnel magnetoresistance (TMR) of 41% and RxA value of 150 Ωμm after its integration, measured on unpatterned MTJ stacks. These results represent the first step towards the development of hybrid spintronic photonic systems with fJ switching energies.

Experimental demonstration of single-shot quantum and classical signal transmission on single wavelength optical pulse

Advances in highly sensitive detection techniques for classical coherent communication systems have reduced the received signal power requirements to a few photons per bit. At this level one can take advantage of the quantum noise to create secure communication, using continuous variable quantum key distribution (CV-QKD). In this work therefore we embed CV-QKD signals within classical signals and transmit classical data and secure keys simultaneously over 25 km of optical fibre. This is achieved by using a novel coherent displacement state generator, which has the potential for being used in a wide range of quantum optical experiments. This approach removes the need for separate channels for quantum communication systems and allows reduced system bandwidth for a given communications specification. This demonstration therefore demonstrates a way of implementing direct quantum physical layer security within a conventional classical communications system, offering a major advance in term of practical and low cost implementation.

Intertwined chiral charge orders and topological stabilization of the light-induced state of a prototypical transition metal dichalcogenide

The fundamental idea that the constituents of interacting many body systems in complex quantum materials may self-organise into long range order under highly non-equilibrium conditions leads to the notion that entirely new and unexpected functionalities might be artificially created. However, demonstrating new emergent order in highly non-equilibrium transitions has proven surprisingly difficult. In spite of huge recent advances in experimental ultrafast time-resolved techniques, methods that average over successive transition outcomes have so far proved incapable of elucidating the emerging spatial structure. Here, using scanning tunneling microscopy, we report for the first time the charge order emerging after a single transition outcome initiated by a single optical pulse in a prototypical two-dimensional dichalcogenide 1T-TaS2. By mapping the vector field of charge displacements of the emergent state, we find surprisingly intricate, long-range, topologically non-trivial charge order in which chiral domain tiling is intertwined with unpaired dislocations which play a crucial role in enhancing the emergent states’ remarkable stability. The discovery of the principles that lead to metastability in charge-ordered systems opens the way to designing novel emergent functionalities, particularly ultrafast all-electronic non-volatile cryo-memories.

First-Light Images from Low-Dispersion Spectrograph-Cum-Imager on 3.6m Devasthal Optical Telescope

A low dispersion spectrograph-cum-imager has been developed and assembled in ARIES, Nainital. The optical design of the spectrograph consists of a collimator and a focal reducer converting the f/9 beam from the 3.6-m Devasthal optical telescope to a nearly f/4.3 beam. The instrument is capable of carrying out broad-band imaging, narrow-band imaging and low-resolution ({\lambda}/{\Delta}{\lambda}<2000) slit spectroscopy in the wavelength range 350-1050 nm. A closed-cycle cryogenically cooled charge-coupled device camera, also assembled in ARIES, is used as the main imaging device for the spectrograph. The first images from the spectrograph on the telescope assert seeing-limited performance free from any significant optical aberration. An i-band image of the galaxy cluster Abell 370 made using the spectrograph shows faint sources down to ~25 mag. The quality and sensitivity of the optical spectrums of the celestial sources obtained from the spectrograph are as per the expectations from a 3.6-m telescope. Several new modes of observations such as polarimetry, fast-imaging, and monitoring of the atmospheric parameters are being included in the spectrograph. Using a test setup, single optical pulses from the Crab pulsar were detected from the telescope. The spectrograph is one of the main back-end instruments on the 3.6-m telescope for high sensitivity observations of celestial objects.