Arbitrary Pulse Shapes Research Articles

Leveraging the periodic interference condition in electro-optic modulators for picosecond pulse generation

Ultra-short optical pulses in the femtosecond and picosecond regime are typically generated using mode-locked lasers. However, in mode-locking, the pulse repetition rate is fundamentally linked to the cavity length of the laser, making it difficult to synchronize these laser pulses to other light sources. Here, we apply a pulse-on-demand approach to picosecond pulse generation with an electro-optic intensity modulator (EOM). The high, 40 GHz bandwidth of the EOM enables low picosecond pulses, however it shifts the problem of pulse generation to the electronic pulses, requiring high bandwidth electronics. In this study, we present an electro-optic operation, leveraging the periodic interference condition of intensity EOMs by operating it with rising edges at twice its V π voltage. Utilizing this method, pulse durations as short as 10.9 ps were achieved by employing a 35 ps edge from an arbitrary waveform generator. The pulses were measured directly on a high-speed oscilloscope as well as indirectly through the spectral broadening of the generated optical pulses. We employ this approach to show arbitrary pulse length generation by applying step functions with only one V π voltage, thus permitting direct pulse-on-demand generation of pulses with arbitrary pulse length, shape and repetition rate for applications in spectroscopy, sensing and nonlinear imaging.

Fast and Flexible, Arbitrary Waveform, 20-kV, Solid-State, Impedance-Matched Marx Generator

We developed a new pulsed power supply to study the influence of the high-voltage (HV) pulse shape on the generation of plasma-activated water (PAW). This article shows the design and implementation of the generator and evaluates its performance on resistive loads. The design is an improved version of the solid-state impedance-matched Marx generator (SS-IMG) concept as previously developed at Eindhoven University of Technology. The IMG concept allows for sub-nanosecond rise time pulses, to be able to create a nonthermal plasma very efficiently. A conventional SS-Marx generator (SS-Marx) circuit is taken as the starting point, and a careful implementation is made with most electrical connections analyzed as transmission lines (TLs). All these TLs are impedance-matched to each other and the load. The implemented generator is able to generate 25 ns to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> duration pulses of 20 kV up to 10-kHz repetition rate in a 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> load with about 8 ns rise time and arbitrary pulse shape. Future improvements are suggested which will increase the repetition rate and decrease the pulse rise time to the sub-nanosecond regime.

Inferring oscillator’s phase and amplitude response from a scalar signal exploiting test stimulation

The phase sensitivity curve or phase response curve (PRC) quantifies the oscillator’s reaction to stimulation at a specific phase and is a primary characteristic of a self-sustained oscillatory unit. Knowledge of this curve yields a phase dynamics description of the oscillator for arbitrary weak forcing. Similar, though much less studied characteristic, is the amplitude response that can be defined either using an ad hoc approach to amplitude estimation or via the isostable variables. Here, we discuss the problem of the phase and amplitude response inference from observations using test stimulation. Although PRC determination for noise-free neuronal-like oscillators perturbed by narrow pulses is a well-known task, the general case remains a challenging problem. Even more challenging is the inference of the amplitude response. This characteristic is crucial, e.g. for controlling the amplitude of the collective mode in a network of interacting units—a task relevant to neuroscience. Here, we compare the performance of different techniques suitable for inferring the phase and amplitude response, particularly with application to macroscopic oscillators. We suggest improvements to these techniques, e.g. demonstrating how to obtain the PRC in case of stimuli of arbitrary shape. Our main result is a novel technique denoted by IPID-1, based on the direct reconstruction of the Winfree equation and the analogous first-order equation for isostable dynamics. The technique works for signals with or without well-pronounced marker events and pulses of arbitrary shape; in particular, we consider charge-balanced pulses typical in neuroscience applications. Moreover, this technique is superior for noisy and high-dimensional systems. Additionally, we describe an error measure that can be computed solely from data and complements any inference technique.

Error budgeting for a controlled-phase gate with strontium-88 Rydberg atoms

We study the implementation of a high fidelity controlled-phase gate in a Rydberg quantum computer. The protocol is based on a symmetric gate with respect to the two qubits as experimentally realized by Levine et al [Phys. Rev. Lett. 123, 170503 (2019)], but allows for arbitrary pulse shapes with time-dependent detuning. Optimizing the pulse shapes, we introduce laser pulses which shorten the time spent in the Rydberg state by 10% and reduce the leading contribution to the gate infidelity, i.e., the decay from the Rydberg state. Remarkably, this reduction can be achieved for smooth pulses in detuning and smooth turning on of the Rabi frequency as required in any experimental realization. We carefully analyze the influence of fundamental error sources such as the photon recoil, the microscopic interaction potential, as well as the harmonic trapping of the atoms for an experimentally realistic setup based on strontium-88 atoms. We find that an average gate fidelity above 99.9% is possible for a very conservative estimation of experimental parameters.

Targeted generation of complex temporal pulse profiles

A targeted shaping of complex femtosecond pulse waveforms and their characterization is essential for many spectroscopic applications. A 4f pulse shaper combined with an advanced pulse characterization technique should, in the idealized case, serve this purpose for an arbitrary pulse shape. This is, however, violated in the real experiment by many imperfections and limitations. Although the complex waveform generation has been studied in-depth, the comparison of the effects of various experimental factors on the actual pulse shape has stayed out of focus so far. In this paper, we present an experimental study on the targeted generation and retrieval of complex pulses by using two commonly-used techniques: spatial-light-modulator (SLM)-based 4f pulse shaper and second-harmonic generation frequency-resolved optical gating (FROG) and cross-correlation FROG (XFROG). By combining FROG and XFROG traces, we analyze the pulses with SLM-adjusted complex random phases ranging from simple to very complex waveforms. We demonstrate that the combination of FROG and XFROG ensures highly consistent pulse retrieval, irrespective of the used retrieval algorithm. This enabled us to evaluate the role of various experimental factors on the agreement between the simulated and actual pulse shape. The factors included the SLM pixelation, SLM pixel crosstalk, finite laser focal spot in the pulse shaper, or interference fringes induced by the SLM. In particular, we observe that including the SLM pixelation and crosstalk effect significantly improved the pulse shaping simulation. We demonstrate that the complete simulation can faithfully reproduce the pulse shape. Nevertheless, even in this case, the intensity of individual peaks differs between the retrieved and simulated pulses, typically by 10–20% of the peak value, with the mean standard deviation of 5–9% of the maximum pulse intensity. We discuss the potential sources of remaining discrepancies between the theoretically expected and experimentally retrieved pulse.

Shape-preserving atomic pulse amplifier

Propagation of a weak probe pulse through a Λ system in a resonant gain configuration is investigated. We employ the control field intensity that permits the amplification of probe pulse during propagation, without instability at two photon resonance. Posterior to amplification, a broadened probe pulse is obtained, which retains its initial pulse shape and travels at the speed of light in vacuum without experiencing any delay, absorption, and dispersion. The salient feature of this technique lies in the fact that in addition to preserving the initial pulse shape, it also ensures stable pulse propagation after amplification. It also works for arbitrary probe pulse shapes.

Towards Arbitrary Pulse Shapes in the Terahertz Domain

Towards Arbitrary Pulse Shapes in the Terahertz Domain

Arbitrary Longitudinal Pulse Shaping with a Multi-Leaf Collimator and Emittance Exchange

Arbitrary Longitudinal Pulse Shaping with a Multi-Leaf Collimator and Emittance Exchange

Exact results on Poisson noise, Poisson flights, and Poisson fluctuations

We study non-Markovian stochastic differential equations with additive noise characterized by a Poisson point process with arbitrary pulse shapes and exponentially distributed intensities. Specifically, analytic results concerning transitions between different correlation regimes and the long-time asymptotic probability distribution functions are shown to be controlled by the shape of the pulses and dissipative parameter as time progresses. This program is motivated by the study of stochastic partial differential equations perturbed by space Poisson disorder and becomes the main focus of applications of the present exact functional approach.

Fast pulse shaping for a novel gated electron mirror.

We present the design and prototype of a switchable electron mirror, along with a technique for driving it with an arbitrary pulse shape. We employ a general technique for electronic pulse-shaping, where high fidelity of the pulse shape is required, but the characteristics of the system, which are possibly nonlinear, are not known. This driving technique uses an arbitrary waveform generator to pre-compensate the pulse, with a simple iterative algorithm used to generate the input waveform. This is a broadly applicable, general method for arbitrary pulse shaping. Driving our switchable electron mirror with a flat-top pulse, we demonstrate an improvement in rms error of roughly two orders of magnitude compared to an uncompensated waveform. Our results demonstrate the feasibility of high fidelity waveform reproduction in the presence of nonidealities, with immediate applications in the realization of novel electron optical components.

Efficient numerical method for predicting nonlinear optical spectroscopies of open systems.

Nonlinear optical spectroscopies are powerful tools for probing quantum dynamics in molecular and nanoscale systems. While intuition about ultrafast spectroscopies is often built by considering impulsive optical pulses, actual experiments have finite-duration pulses, which can be important for interpreting and predicting experimental results. We present a new freely available open source method for spectroscopic modeling, called Ultrafast Ultrafast (UF2) spectroscopy, which enables computationally efficient and convenient prediction of nonlinear spectra, such as treatment of arbitrary finite duration pulse shapes. UF2 is a Fourier-based method that requires diagonalization of the Liouvillian propagator of the system density matrix. We also present a Runge-Kutta-Euler (RKE) direct propagation method. We include open system dynamics in the secular Redfield, full Redfield, and Lindblad formalisms with Markovian baths. For non-Markovian systems, the degrees of freedom corresponding to memory effects are brought into the system and treated nonperturbatively. We analyze the computational complexity of the algorithms and demonstrate numerically that, including the cost of diagonalizing the propagator, UF2 is 20-200 times faster than the direct propagation method for secular Redfield models with arbitrary Hilbert space dimension; it is similarly faster for full Redfield models at least up to system dimensions where the propagator requires more than 20 GB to store; and for Lindblad models, it is faster up to Hilbert space dimension near 100 with speedups for small systems by factors of over 500. UF2 and RKE are part of a larger open source Ultrafast Software Suite, which includes tools for automatic generation and calculation of Feynman diagrams.

Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

Summary Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins.

Comparative Modeling of Biphasic Defibrillation Pulses: Quasi-sinusoidal and Trapezoidal with Sloping Rise and Fall

A model of a defibrillator power module generating pulses of arbitrary shape with load impedance of 25-250 Ω was used to obtain the characteristics of biphasic pulses: quasi-sinusoidal pulses (Gurvich–Venin pulses) and trapezoidal pulses with sloping rise and fall. At high load impedances (100-250 Ω), production of trapezoidal pulses, as compared with quasi-sinusoidal, produced larger mean first-phase currents (by 11-20%) and greater pulse energy (by 25-35%).

P206 A magnetic neurostimulator with arbitrary pulse shape

P206 A magnetic neurostimulator with arbitrary pulse shape

Rear-surface integral method for calculating thermal diffusivity: Finite pulse time correction and two-layer samples

We study methods for calculating the thermal diffusivity of solids from laser flash experiments. This experiment involves subjecting the front surface of a small sample of the material to a heat pulse and recording the resulting temperature rise on the opposite (rear) surface. Recently, a method was developed for calculating the thermal diffusivity from the rear-surface temperature rise, which was shown to produce improved estimates compared with the commonly used half-time approach. This so-called rear-surface integral method produced a formula for calculating the thermal diffusivity of homogeneous samples under the assumption that the heat pulse is instantaneously absorbed uniformly into a thin layer at the front surface. In this paper, we show how the rear-surface integral method can be applied to a more physically realistic heat flow model involving the actual heat pulse shape from the laser flash experiment. New thermal diffusivity formulas are derived for handling arbitrary pulse shapes for either a homogeneous sample or a heterogeneous sample comprising two layers of different materials. Presented numerical experiments confirm the accuracy of the new formulas and demonstrate how they can be applied to the kinds of experimental data arising from the laser flash experiment.

Photonic implementation of a highly reconfigurable wideband RF spectral shaper

In emerging Radio Frequency (RF) systems, the capability to dynamically process a wide range of frequency bands is highly desired due to the multi-frequency operation in multi-function RF systems and the large signal bandwidth usage associated with data-intensive applications. As the operation bandwidth increases, the frequency response uniformity of both RF components and microwave transmission medium degrades, that leads to the need of broadband RF spectrum equalization to support wideband high-quality services. Therefore, a wideband and reconfigurable RF spectral shaper is highly desired for dynamically manipulating the RF spectrum from low- to high-frequency band. Unfortunately, it is very challenging for conventional RF electronics to achieve dynamic spectral control over a wide operation bandwidth. In this paper, we take advantages of photonics and demonstrate a highly-reconfigurable RF spectral shaper that can manipulate an RF spectrum of tens of GHz wide. The proposed scheme is based on a microwave photonic filter architecture with multiple tunable, reconfigurable and switchable passbands. By manipulating the shape, bandwidth, and frequency of the passbands, highly reconfigurable wideband frequency responses for spectral equalization are experimentally achieved, covering the entire 0 to 10 GHz frequency range with adjustable attenuation up to 40 dB. Various RF equalization functions including tunable positive/negative slope, non/inverted parabolic, and multi-point spectral control with tunable floor are experimentally demonstrated using the proposed system. Several of the demonstrated RF functions have also been applied to arbitrary pulse shaping. The RF spectral shaper can be tuned to adapt to different scenarios dynamically, which could benefit a variety of applications including RF signal processing systems and communication networks.

Towards a 10-fs hyperspectral spectroscopy source with arbitrary pulse shaping based on adiabatic frequency conversion

We introduce a 10-fs hyperspectral source architecture for facilitating nonlinear spectroscopy with multi-color sequences of arbitrarily shaped 10-fs UV/Vis, near-IR, and mid-IR pulses. Design principles and initial experimental results are provided.

Review of the ELI-NP-GBS low level rf and synchronization systems

The Gamma Beam System (GBS) of ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module, for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described.

Accuracy of Distance Determination by Range–Intensity Correlation Methods for Nonrectangular Illuminating Pulse Shape

We have analyzed the accuracy of distance determination by range–intensity correlation methods in the case of an arbitrary pulse shape. We show that the absolute error is proportional to the pulse duration τL. For a trapezoidal pulse shape, which is a reasonable approximation of the real pulse shape, we obtain an analytical estimate of the extremal error and the distance at which is it realized. The maximum error in the distance obtained in calculations with trapezoidal pulses corresponds to an extremely asymmetric pulse and is a little over 10% of the spatial pulse length τLc, where c is the speed of light. Symmetric pulses give an error due to nonrectangularity of the pulse that is smaller by a factor of ~2. Since a trapezoidal shape can qualitatively reproduce the shape of practically any real pulse, probably the trapezoidal pulse model gives an estimate of the highest possible error.

Amplification of Dynamic Nuclear Polarization at 200 GHz by Arbitrary Pulse Shaping of the Electron Spin Saturation Profile.

Dynamic nuclear polarization (DNP) takes center stage in nuclear magnetic resonance (NMR) as a tool to amplify its signal by orders of magnitude through the transfer of polarization from electron to nuclear spins. In contrast to modern NMR and electron paramagnetic resonance (EPR) that extensively rely on pulses for spin manipulation in the time domain, the current mainstream DNP technology exclusively relies on monochromatic continuous wave (CW) irradiation. This study introduces arbitrary phase shaped pulses that constitute a train of coherent chirp pulses in the time domain at 200 GHz (7 T) to dramatically enhance the saturation bandwidth and DNP performance compared to CW DNP, yielding up to 500-fold in NMR signal enhancements. The observed improvement is attributed to the recruitment of additional electron spins contributing to DNP via the cross-effect mechanism, as experimentally confirmed by two-frequency pump-probe electron-electron double resonance (ELDOR).