Sequence Of Laser Pulses Research Articles

SiPM-based LiDAR with multipulse sequence modulation and multithreshold signal processing.

A light detection and range technology (LiDAR) system that enables rapid ranging under extremely low signal-to-noise ratios (SNRs) during daylight conditions based on a SiPM (silicon photomultiplier) detector is proposed. The system emits a sequence of modulated laser pulses by controlling the semiconductor laser and then processes the SiPM response signals using dynamic multithreshold. The experimental result shows that, under extremely low SNR of daylight, the system achieves a 100% success rate in continuous ranging of a low reflectivity target at 125 m, with a ranging precision of less than 20 cm and a ranging time of less than 10 µs. Our system provides a significant reference value for achieving high-speed, noise-resistant, miniaturized, practical, and low-cost LiDAR based on a SiPM.

Reduction of light shifts in a cold-atom CPT clock

Light shifts induced during atom–light interactions significantly affect the medium- and long-term frequency stability of atomic clocks. Here, we employ composite laser pulse sequences to mitigate interrogation-induced light shifts in a cold-atom coherent-population-trapping clock. We obtain the anti-symmetry error signal via modulating the local oscillator phase in the free-evolution time of Ramsey interferometry. Utilizing this signal, we employ two feedback loops to simultaneously eliminate light shifts and stabilize the clock frequency using the auto-balanced Ramsey (ABR) spectroscopy scheme. Our experimental results demonstrate that this approach can reduce the clock frequency’s sensitivity to variations in light shifts by implementing four Ramsey sub-sequences. Furthermore, we show that the ABR spectroscopy scheme enhances the long-term frequency stability of the atomic clock when the averaging time τ > 5000 s.

Switching the electrical properties of thin-film memristive elements based on GeTe by sequences of ultrashort laser pulses

Switching the electrical properties of thin-film memristive elements based on GeTe by sequences of ultrashort laser pulses

Enhancing strontium clock atom interferometry using quantum optimal control

Strontium clock atom interferometry is a promising new technology, with multiple experiments under development around the world to explore its potential for dark matter and gravitational wave detection. In these detectors, large momentum transfer using sequences of many laser pulses is necessary, and thus high-fidelity pulses are important since small errors become magnified. Quantum optimal control (QOC) is a framework for developing control pulse waveforms that achieve high fidelity and are robust against experimental imperfections. Resonant single-photon transitions using the narrow clock transition of strontium involve significantly different quantum dynamics than more established atom interferometry methods based on far-detuned two-photon Raman or Bragg transitions, which leads to new opportunities and challenges when applying QOC. Here, we study in simulation QOC pulses for strontium clock interferometry and demonstrate their advantage over basic square pulses (primitive pulses) and composite pulses in terms of robustness against multiple noise channels. This could improve the scale of large momentum transfer in Sr clock interferometers, paving the way to achieving these scientific goals.

Coherent generation and control of tunable narrowband THz radiation from a laser-induced air-plasma filament.

We report on the proof-of-principle experiment of generating carrier-envelope phase (CEP)-controllable and frequency-tunable narrowband terahertz (THz) radiation from an air-plasma filament prescribed by the beat of a temporally stretched two-color laser pulse sequence. The pulse sequence was prepared by propagating the fundamental ultrafast laser pulse through a grating stretcher and Michelson interferometer with variable inter-arm delay. By partially frequency-doubling and focusing the pulse sequence, an air-plasma filament riding a beat note was created to radiate a THz wave with primary pulse characteristics (center frequency and CEP) under coherent control. To reproduce experimental results and elucidate complex nonlinear light-matter interaction, numerical simulation has been performed. This work demonstrates the feasibility of generating coherently controlled narrowband THz wave with high tunability in laser-induced air plasma.

High-Precision PCB Topologies Formation by Selective Laser Micromachining

The paper considers possibility of using laser radiation to form and correct printed circuit topology boards through micromachining. Processes arising from the interaction of ultrashort laser pulses with processed thin-film coatings are considered. The dependence of the effect of a variable sequence of laser pulses on the quality of the formed holes in coating is presented. Experimental data on the selection of optimal exposure modes of femtosecond radiation on a multilayer coating for selective ablation are presented. Femtosecond laser micromachining allows the precision formation of topological contours, regardless of treated coating type, its thermal and electric conductive properties.

Influence of femtosecond laser pulse sequence on the morphology and roughness of titanium surface micro-patterns

The geometry of the medical titanium surface micro pattern, the micro- and nanostructures within the pattern, and the roughness of the structure are key parameters affecting the integration of the implant surface with the bone tissue. The femtosecond laser is an effective method for surface modification of implants, but achieving effective control of the depth of the pattern and the inner surface topography and roughness is a crucial processing challenge. In this study, the evolution of ablation pit morphology with process parameters was analyzed to establish the correspondence between process parameters and the ablation mechanism. A femtosecond laser pulse sequence method is proposed to increase the machining depth from 24 μm to 38 μm while reducing the surface roughness from Sa = 2.2 μm to Sa = 0.5 μm by regulating the liquid phase migration as well as the thermal phase change process without affecting the processing efficiency. And the surface roughness can be reduced from Sa = 2.2 μm to <0.1 μm with appropriate pulse sequence parameters.

Uncovering Transport Mechanisms in Perovskite Materials and Devices with Recombination-Induced Action Spectroscopies

Although valuable insights are derived from conventional spectroscopic approaches, the understanding of a photovoltaic device’s operation mechanisms can be limited in ex situ measurements. For example, the signals measured in transient absorption experiments reflect the concentrations and extinction coefficients of all photoexcited species in a material regardless of functional relevance. Elimination of such ambiguities has motivated the development of various “action spectroscopy” techniques in which the response of a photovoltaic device to a sequence of laser pulses is directly detected. The class of action spectroscopies described in this Perspective leverages recombination-induced nonlinearities to distinguish lossy (fluorescence) and productive (photocurrent) processes within the active layers of photovoltaic cells. Although recombination processes are problematic in alternate approaches for conducting action spectroscopies, our experiments show that this type of nonlinearity can be exploited to reveal transport mechanisms on nanosecond time scales. Applications to mixtures of layered perovskite quantum wells are presented to demonstrate signatures of energy funneling and long-range carrier drift in photovoltaic devices.

Nonadiabatic wave packet dynamics and predissociation resonances in sodium hydride.

Vibrational wave packet dynamics provides an opportunity to explore the energy landscape and the population transfer between nonadiabatically coupled excited electronic states. Here the coupled nonadiabatic dynamics of the C1Σ+ and D1Σ+ states of sodium hydride (NaH) in the gas phase in the adiabatic picture is studied, using a sequence of ultra-fast laser pulses in the femtosecond region. Emergence of different population dynamics and dissociation probabilities is shown by carefully choosing the pulse wavelength, duration and time-shift between the pulses, exciting the molecule from the ground X1Σ+ state via the immediate A1Σ+ state. Quantum dynamics simulations were performed in the adiabatic picture, avoiding the adiabatic to diabatic transformation. Predissociation resonances, i.e. vibrational states with finite lifetimes, arise due to nonadiabatic couplings between bound and continuum states. Here accurate resonance energies and widths are computed providing further insight into the dissociation dynamics.

Optical two-dimensional coherent spectroscopy of cold atoms.

We report an experimental demonstration of optical two-dimensional coherent spectroscopy (2DCS) in cold atoms. The experiment integrates a collinear 2DCS setup with a magneto-optical trap (MOT), in which cold rubidium (Rb) atoms are prepared at a temperature of approximately 200 µK and a number density of 1010 cm-3. With a sequence of femtosecond laser pulses, we first obtain one-dimensional second- and fourth-order nonlinear signals and then acquire both one-quantum and zero-quantum 2D spectra of cold Rb atoms. The capability of performing optical 2DCS in cold atoms is an important step toward optical 2DCS study of many-body physics in cold atoms and ultimately in atom arrays and trapped ions. Optical 2DCS in cold atoms/molecules can also be a new avenue to probe chemical reaction dynamics in cold molecules.

Coherent dynamics in a five-level atomic system

The coherent control of multi-partite quantum systems presents one of the central prerequisites in state-of-the-art quantum information processing. With the added benefit of inherent high-fidelity detection capability, atomic quantum systems in high-energy internal states, such as metastable noble gas atoms, promote themselves as ideal candidates for advancing quantum science in fundamental aspects and technological applications. Using laser-cooled neon atoms in the metastable 3P2 state of state 1s 22s 22p 53s (LS-coupling notation) (Racah notation: 2 P 3/23s[3/2]2) with five m J -sublevels, experimental methods for the preparation of all Zeeman sublevels |m J ⟩ = |+2⟩, |+1⟩, |0⟩, |−1⟩, |−2⟩ as well as the coherent control of superposition states in the five-level system |+2⟩, …, |−2⟩, in the three-level system |+2⟩, |+1⟩, |0⟩, and in the two-level system |+2⟩, |+1⟩ are presented. The methods are based on optimized radio frequency and laser pulse sequences. The state evolution is described with a simple, semiclassical model. The coherence properties of the prepared states are studied using Ramsey and spin echo measurements.

Study of the adiabatic passage in tripod atomic systems in terms of the Riemannian geometry of the Bloch sphere

We present an analysis of the stimulated Raman adiabatic passage (STIRAP) processes based on the methods of differential geometry. The present work was inspired by an excellent article by Shore et al (Unanyan et al 1999 Phys. Rev. A 59 2910). We demonstrate how a purely geometric interpretation of the adiabatic passage in quantum tripod systems as a Riemannian parallel transport of the dark state vector along the Bloch sphere allows describing the evolution of the system for a given sequence of Stokes, pump and control laser excitation pulses. In combination with the Dykhne–Davis–Pechukas adiabaticity criterion and the minimax principle for circles on a sphere, this approach allows obtaining the analytical form of the optimal laser pulse sequences for a high fidelity tripod fractional STIRAP. In contrast to the conventional STIRAP in Λ-systems, the Gaussian approximations of the optimal laser pulse sequences allow reaching the infidelity of 10−7 for the adiabaticity parameter of 300 without noticeable oscillatory or other detrimental effects on population transfer accuracy.

Exciton Controlled-NOT Gate Using Coupled Quantum Dots in Carbon Nanotube

A four-level system is a prerequisite for the controlled-NOT (CNOT) gate and is realized with excitons confined in the coupled quantum dots (QDs). The coupled QDs are fabricated by chemically bonding the collagen model peptides to a single-walled carbon nanotube. An interdot exciton–exciton interaction and an exciton four-level system based on it are confirmed through photoluminescence measurements. Rabi oscillations of the exciton populations are observed, which allow the manipulations of the exciton four-level system with designed laser-pulse sequences. The tests on whether the exciton four-level system operates as a CNOT gate are conducted, and the quantum process fidelity is estimated to be approximately 0.7–0.8. The SWAP operation is also demonstrated by employing the CNOT gate three times.

The Efficacy of Fractional CO2 Laser in the Treatment of Genitourinary Syndrome of Menopause: A Large Prospective Observational Study

Background: Genitourinary syndrome of menopause (GSM) majorly caused by the physiological decline in estrogen, affects up to 90% of menopausal women. Hormonal therapy seems to be an effective treatment, often not executable for contraindication or patient’s low compliance to local or systemic medical therapy. Fractional CO2 laser therapy is an emerging and effective choice for women affected by vulvo-vaginal atrophy (VVA), promoting collagen regeneration and improving blood flow of the vaginal mucosa and elasticity of tissues. Methods: Ninety-two menopausal Patients affected by vulvo-vaginal atrophy (VVA) were considered for the present prospective observational study. All women were treated with Fractional CO2 laser Lumenis AcuPulse in a fractionated sequential mode laser pulse. Patients were requested to complete questionnaires regarding the Female Sexual Functional Index (FSFI), Female Sexual Distress Scale (FSDS) and severity of Most Bothersome Symptoms (MBS) at baseline (T0) and at three-month following three-treatment-sessions (T1). Results: Data indicated a significant improvement of MBS (vaginal itching (p &lt; 0.0001), post-coital vaginal bleeding (p &lt; 0.002), vaginal dryness (p &lt; 0.0001), dyspareunia (p &lt; 0.0001) and dysuria (p &lt; 0.0001), higher Vaginal Health Index Score (VHIS) (4.1 ± 1.21; 95% CI = 3.84–4.35) and reduces pH (–0.53 ± 0.24; 95% CI = 0.48–0.58) after CO2 laser treatment. A significantly improvement of FSFI Total score (p &lt; 0.0001) and FSDS (p &lt; 0.0001) have been demonstrated. Conclusions: Fractional CO2 laser improves vaginal health as well as signs and symptoms associated with GSM, while significantly elevating quality of life and sexual functionality among postmenopausal symptomatic women.

Efficient ion acceleration by multistaged intense short laser pulses

We present a computational study of laser-driven ion acceleration that optimizes a combination of target transparency and extended field acceleration at moderate relativistic intensity. Our scheme applies two sequential laser pulses irradiating a thin target foil along the same direction: The first pulse drives a rapid expansion of the target, while the second one drives a quasistatic electric field in the expanding target with increasing electron temperature. In our particle-in-cell simulations we observe proton peak energies and numbers enhanced by factors of up to 3 compared with regular target-normal sheath acceleration.Received 6 October 2020Accepted 4 May 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L032003Published 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-energy-density plasmasLaser driven ion accelerationAccelerators & BeamsPlasma PhysicsParticles & Fields

Calculating Multidimensional Optical Spectra from Classical Trajectories

Multidimensional optical spectra are measured from the response of a material system to a sequence of laser pulses and have the capacity to elucidate specific molecular interactions and dynamics whose influences are absent or obscured in a conventional linear absorption spectrum. Interpretation of complex spectra is supported by theoretical modeling of the spectroscopic observable, requiring implementation of quantum dynamics for coupled electrons and nuclei. Performing numerically correct quantum dynamics in this context may pose computational challenges, particularly in the condensed phase. Semiclassical methods based on calculating classical trajectories offer a practical alternative. Here I review the recent application of some semiclassical, trajectory-based methods to nonlinear molecular vibrational and electronic spectra.

Preparation of vibrational quasi-bound states of the transition state complex BrHBr from the bihalide ion BrHBr.

Efficient strategies that allow the preparation of molecular systems in particular vibrational states are important in the application of quantum control schemes to chemical reactions. In this paper, we propose the preparation of quasi-bound vibrational states of the collinear transition state complex BrHBr, from vibrational states of the bihalide ion BrHBr-, that favor the bond selective breakage of BrHBr. The results shown complement the investigation that we reported in a previous paper, [A. J. Garzón-Ramírez, J. G. López and C. A. Arango, Int. J. Quantum Chem., 2018, 24, e25784], in which we demonstrated the feasibility of controlling the bond selective decomposition of the collinear BrHBr using linear combinations of reactive resonances. We employed a dipole moment surface, calculated at the QCISD/d-aug-cc-pVTZ level of theory, to simulate the interaction of the BrHBr- ground vibrational state with heuristically optimized sequences of ultrashort infrared linear chirped laser pulses to achieve a target vibrational state, resulting from expanding a chosen linear combination of reactive resonances of BrHBr in terms of vibrational eigenstates of BrHBr-. The results of our simulations show final states that capture the most relevant features of the target state with different levels of description depending on the sequence of laser pulses employed. We also discuss ways of improving the description of the target state and possible limitations of our approach.

Phonon-mediated many-body quantum entanglement and logic gates in ion traps

The high-fidelity multi-ion entangled states and quantum gates are the basis for trapped-ion quantum computing. Among the developed quantum gate schemes, Mølmer-Sørensen gate is a relatively mature experimental technique to realize multi-ion entanglement and quantum logic gates. In recent years, there have also been schemes to realize ultrafast quantum entanglement and quantum logic gates that operate outside the Lamb-Dicke regime by designing ultrafast laser pulse sequences. In such a many-body quantum system, these entanglement gates couple the spin states between ions by driving either the phonon energy level or the motional state of the ion chain. To improve the fidelity of quantum gates, the modulated laser pulses or the appropriately designed pulse sequences are applied to decouple the multi-mode motional states. In this review, we summarize and analyze the essential aspects of realizing these entanglement gates from both theoretical and experimental points of view. We also reveal that the basic physical process of realizing quantum gates is to utilize nonlinear interactions in non-equilibrium processes through driving the motional states of an ion chain with laser fields.

Quantum Computing with Exciton Qubits in Colloidal Semiconductor Nanocrystals

The present work evaluates the feasibility of quantum computing with exciton qubits in coupled colloidal semiconductor nanocrystals (NCs). A strategy for manipulating two-qubit states of colloidal NC hetero-dimers is described. We show that a sequence of laser pulses with the same photon energy can bring excitonic states of a nanocrystal hetero-dimer into entanglement and perform arbitrary qubit rotations (quantum gates). Our simulations of a realistic two-particle assembly of CdSe/CdS core/shell NCs demonstrate that such two-qubit gate operations can be driven by optical parametric oscillators with a theoretical error of 0.1%. A strategy for upscaling two-qubit hetero-dimers to N-qubit exciton gates in semiconductor NC assemblies is discussed.

Full-color photon-counting single-pixel imaging

We propose and experimentally demonstrate a high-efficiency single-pixel imaging (SPI) scheme by integrating time-correlated single-photon counting (TCSPC) with time-division multiplexing to acquire full-color images at an extremely low light level. This SPI scheme uses a digital micromirror device to modulate a sequence of laser pulses with preset delays to achieve three-color structured illumination, then employs a photomultiplier tube into the TCSPC module to achieve photon-counting detection. By exploiting the time-resolved capabilities of TCSPC, we demodulate the spectrum-image-encoded signals, and then reconstruct high-quality full-color images in a single round of measurement. Based on this scheme, strategies such as single-step measurement, high-speed projection, and undersampling can further improve imaging efficiency.