Pump Pulse Shape Research Articles

Orchestrating time and color: a programmable source of high-dimensional entanglement

High-dimensional encodings based on temporal modes (TMs) of photonic quantum states provide the foundations for a highly versatile and efficient quantum information science (QIS) framework. Here, we demonstrate a crucial building block for any QIS applications based on TMs: a programmable source of maximally entangled high-dimensional TM states. Our source is based on a parametric downconversion process driven by a spectrally shaped pump pulse, which facilitates the generation of maximally entangled TM states with a well-defined dimensionality that can be chosen programmatically. We characterize the effective dimensionality of the generated states via measurements of second-order correlation functions and joint spectral intensities, demonstrating the generation of bi-photon TM states with a controlled dimensionality in up to 20 dimensions.

Carrier dynamic and carrier Temperature in Quantum Well

Carrier temperature in quantum well (QW)semiconductor optical amplifier (SOA) has been studied,depending density matrix theory (DMT) and carrier dynamicin quantum well. The effect of volume carrier density, dopingon effect, pulse shape, nonradiative relaxation, and nonlineargain coefficients on the carrier temperature and carrierheating has been investigated. The theoretical results showthat; the time recovery increases straightforward withnonradiative recombination, where the relaxation time ofnonradiative recombination reduces the rate of carrieroccupation in quantum states. Also, the carrier temperatureincreases with carrier density, free carrier absorption, carrierheating lifetime and reduces with pulse shape of pump pulses

Optimal control for suppressing wave-packet spreading with strong nonresonant laser pulses

We use nonlinear optimal control simulation to systematically examine how to suppress wave-packet spreading with strong nonresonant near-infrared (NIR) laser pulses through a case study of a vibrational wave packet in the $B$ state of ${\mathrm{I}}_{2}$. As the degree of spreading of the vibrational wave packet is controllable by adjusting the pump pulse shape, the vibrational wave packet may be regarded as a prototype system to study spreading suppression by using nonresonant laser pulses. We quantitatively define spreading suppression in terms of the probability of finding the wave packet in the analytically defined, initially excited state at every vibrational period. From optimal control simulation and simulation by using model Gaussian pulse trains that mimic optimal pulses, we conclude that a simple periodic NIR pulse train without highly tuned temporal widths, amplitudes, or irradiation timings can almost perfectly stop the wave-packet spreading over a long control period, provided that the degree of spreading is not too large.

Design of the front-end system for a subexawatt laser of the XCELS facility

A concept of the front-end system of the XCELS (eXawatt Center for Extreme Light Studies) facility is presented. Its design is aimed at achieving high stability of laser radiation parameters and possibility of their control in a wide range. Optically synchronised chirped signal (wavelength 910 nm, bandwidth more than 100 nm, and duration ∼3 ns) and pump (wavelength 1054 nm, bandwidth ∼1 nm, and duration ∼4 ns) pulses for XCELS parametric amplifiers will be implemented at the output of the front-end system. Chirped femtosecond pulses with energies above 100 mJ [no more than 15 fs long after compression, with carrier-envelope phase (CEP) stabilisation] will have a repetition rate up to 100 Hz, which will allow one to implement active energy stabilisation and to minimise the angular jitter of the emitted beam at the XCELS output. The application of picosecond pumping in the parametric amplifier of the front-end system should provide a high contrast of femtosecond pulses. The pump pulse will be linearly frequency-modulated; this approach will not affect the parametric amplification efficiency but make it possible to use spectral methods to control the pump pulse shape in order to form a pulse of specified shape at the output of power amplifiers, even under conditions of their strong saturation.

Efficient, watt-level, tunable 1.7 µm fiber Raman laser in H2-filled hollow-core fibers

We report here an efficient watt-level tunable 1.7 µm fiber gas Raman laser. Pumped by a homemade pulsed fiber amplifier around 1.5 µm wavelength, a tunable laser ranging from 1687 to 1723 nm is demonstrated in a hydrogen-filled hollow-core photonic crystal fiber (HC-PCF). A maximum average power of ∼ 0.8 W (pulse energy of ∼ 1.6 µ J ) is achieved on a 20-m-long HC-PCF filled with 16 bar of hydrogen gas, corresponding to a maximum Raman power conversion efficiency of 60%. A steady-state model of the rotational stimulated Raman scattering in hydrogen-filled HC-PCF, considering the pump pulse shape, is also established. The predicted output power and pulse shapes of the pump and Stokes waves are in good agreement with the experimental results. Our system offers an elegant solution for realizing efficient, tunable, and high-power fiber lasers operating at 1.7 µm wavelength range.

High-Efficiency Optical Parametric Oscillator Based on Stimulated Brillouin Scattering Pulse Shaping

We present an optical parametric oscillator (OPO) that uses a pump pulse shape tailored by stimulated Brillouin scattering. The theoretical analysis is carried out for comparison between Gaussian pump and the step function pulse pump. The steep leading edge of the pulse helps minimize the buildup time of the OPO when applied to step function pulse. The study then focuses on obtaining step function pulse through stimulated Brillouin scattering pulse compression. With this control of the pump pulse's temporal shape, the experimental OPO energy conversion efficiency is 34.3%. Compared with an OPO pumped by a Gaussian-shaped pulse, the oscillation threshold is reduced and the energy conversion efficiency is improved by around 10%.

UWB DEER and RIDME distance measurements in Cu(II)-Cu(II) spin pairs.

Distance determination by Electron Paramagnetic Resonance (EPR) based on measurements of the dipolar coupling are technically challenging for electron spin systems with broad spectra due to comparatively narrow microwave pulse excitation bandwidths. With Na4[{CuII(PyMTA)}-(stiff spacer)-{CuII(PyMTA)}] as a model compound, we compared DEER and RIDME measurements and investigated the use of frequency-swept pulses. We found very large improvements in sensitivity when substituting the monochromatic pump pulse by a frequency-swept one in DEER experiments with monochromatic observer pulses. This effect was especially strong in X band, where nearly the whole spectrum can be included in the experiment. The RIDME experiment is characterised by a trade-off in signal intensity and modulation depth. Optimal parameters are further influenced by varying steepness of the background decay. A simple 2-point optimization experiment was found to serve as good estimate to identify the mixing time of highest sensitivity. Using frequency-swept pulses in the observer sequences resulted in lower SNR in both the RIDME and the DEER experiment. Orientation selectivity was found to vary in both experiments with the detection position as well as with the settings of the pump pulse in DEER. In RIDME, orientation selection by relaxation anisotropy of the inverted spin appeared to be negligible as form factors remain relatively constant with varying mixing time. This reduces the overall observed orientation selection to the one given by the detection position. Field-averaged data from RIDME and DEER with a shaped pump pulse resulted in the same dipolar spectrum. We found that both methods have their advantages and disadvantages for given instrumental limitations and sample properties. Thus the choice of method depends on the situation at hand and we discuss which parameters should be considered for optimization.

RDEER: A Modified DEER Sequence for Distance Measurements Using Shaped Pulses

The DEER (double electron-electron resonance, also called PELDOR) experiment, which probes the dipolar interaction between two spins and thus reveals distance information, is an important tool for structural studies. In recent years, shaped pump pulses have become a valuable addition to the DEER experiment. Shaped pulses offer an increased excitation bandwidth and the possibility to precisely adjust pulse parameters, which is beneficial especially for demanding biological samples. We have noticed that on our home built W-band spectrometer, the dead-time free 4-pulse DEER sequence with chirped pump pulses suffers from distortions at the end of the DEER trace. Although minor, these are crucial for Gd(III)-Gd(III) DEER where the modulation depth is on the order of a few percent. Here we present a modified DEER sequence—referred to as reversed DEER (rDEER)—that circumvents the coherence pathway which gives rise to the distortion. We compare the rDEER (with two chirped pump pulses) performance values to regular 4-pulse DEER with one monochromatic as well as two chirped pulses and investigate the source of the distortion. We demonstrate the applicability and effectivity of rDEER on three systems, ubiquitin labeled with Gd(III)-DOTA-maleimide (DOTA, 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid) or with Gd(III)-DO3A (DO3A, 1,4,7,10-Tetraazacyclododecane-1,4,7-triyl) triacetic acid) and the multidrug transporter MdfA, labeled with a Gd(III)-C2 tag, and report an increase in the signal-to-noise ratio in the range of 3 to 7 when comparing the rDEER with two chirped pump pulses to standard 4-pulse DEER.

Improved signal fidelity in 4-pulse DEER with Gaussian pulses

The introduction of arbitrary waveform generator (AWG) technology and the availability of high power microwave amplifiers mark a “new era” in pulse EPR due to significant sensitivity improvements and the possibility to perform novel types of experiments. We present an optimized 4-pulse DEER setup that uses Gaussian observer pulses (GaussDEER) in connection with a Gaussian/shaped pump pulse. Gaussian pulses allow to experimentally remove the “2+1” pulse train ESE signal which is intrinsically present in any DEER experiment performed with rectangular pulses. Further signal improvements are obtained with shaped pump pulses, which can significantly increase the modulation depth of the DEER experiment due to their tailored excitation bandwidth. Although sequences like CP (Carr-Purcell) DEER offer advantages such as a prolongation of the dipolar evolution time, they suffer from post-processing of the time-domain data to remove artifacts. Therefore, it is worth having a 4-pulse DEER experiment free of residual “2+1” signal since this is still the main dipolar spectroscopic technique used in structural biology. In this work we focus on nitroxides, which are the spin probes primarily used in site-directed spin labeling studies of biomolecules, however, the advantages introduced by Gaussian pulses can be extended to any spin type.

Tailoring nonlinear processes for quantum optics with pulsed temporal-mode encodings

The time-frequency degree of freedom is a powerful resource for implementing high-dimensional quantum information processing. In particular, field-orthogonal pulsed temporal modes offer a flexible framework compatible with both long-distance fibre networks and integrated waveguide devices. In order for this architecture to be fully utilised, techniques to reliably generate diverse quantum states of light and accurately measure complex temporal waveforms must be developed. To this end, nonlinear processes mediated by spectrally shaped pump pulses in group-velocity engineered waveguides and crystals provide a capable toolbox. In this review, we examine how tailoring the phasematching conditions of parametric downconversion and sum-frequency generation allows for highly pure single-photon generation, flexible temporal-mode entanglement, and accurate measurement of time-frequency photon states. We provide an overview of experimental progress towards these goals, and summarise challenges that remain in the field.

Pulse-shape dependence of stimulated Brillouin scattering pulse compression to sub-phonon lifetime.

A new approach to sub-phonon lifetime pulse compression by stimulated Brillouin scattering (SBS) is presented. Triangular and step pulse pumps are both used as a pump source in a single-cell SBS compression setup. Compared with a Gaussian pump (shortest compressed pulse is the phonon lifetime with the highest energy conversion, approximately 60% under the same conditions), the compression ratio is significantly improved in the case of triangular and step pulse pumps, and there is some improvement in the energy conversion when a step pulse pump is used. A pulse as short as a quarter of a phonon lifetime is produced by a triangular pulse pump, with an energy conversion above 30%. The pump pulse shape is identified as the key parameter in achieving sub-phonon lifetime pulse compression. By using a step pulse shape, a 4.5 ns pump pulses with a 60mJ at 1064-nm are compressed down to 292 ps (below semi-phonon-lifetime) in 3M Fluorinert Electronic Liquid FC-770 with an energy conversion above 65%. This work presents a route to reliable generation of sub-semi-phonon-lifetime pulses by SBS compression.

Heralded generation of high-purity ultrashort single photons in programmable temporal shapes.

We experimentally demonstrate a source of nearly pure single photons in arbitrary temporal shapes heralded from a parametric down-conversion (PDC) source at telecom wavelengths. The technology is enabled by the tailored dispersion of in-house fabricated waveguides with shaped pump pulses to directly generate the PDC photons in on-demand temporal shapes. We generate PDC photons in Hermite-Gauss and frequency-binned modes and confirm a minimum purity of 0.81, even for complex temporal shapes.

Amplification assisted difference frequency generation for efficient mid-infrared conversion based on monolithic tandem lithium niobate superlattice

We report the investigation on the performance of an amplification assisted difference frequency generation (AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the reduction in conversion efficiency resulting from wider acceptance bandwidths for the input lasers. We believe that such systems combining the merits of high stability inherited from cavity-free configuration and high efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community, especially when the pulse shaping technique is incorporated.

Optimal pump pulse shapes for optical parametric oscillators

In this paper we theoretically investigate the most efficient pump temporal shape for pulsed operation of optical parametric oscillators (OPOs). The theoretical analysis consists of solving the optimal control problem using the rate equation formalism. The OPO optimal buildup behavior is derived for any OPO configuration, and we show that the optimal pump pulse shape is a double rectangle. The first rectangle is optimized for the buildup process, while the second one is optimized for the steady state, and both depend differently on the OPO mirror reflectivities as well as the available pump energy and maximum peak power. This double rectangle is quantitatively described and is consistent with previous results reported in the literature. Also, numerical simulations are used to validate our analytical model on a doubly resonant OPO and show consistent results. The numerical simulations also show that an optimal top-hat temporal profile could provide performances very close to the ones achieved with the optimal double rectangle.

Theoretical Analysis of Spectral Correlations Between Photon Pairs Generated in Nanoscale Silicon Waveguides**Supported by the State Key Program for Basic Research of China under Grant No. 2012CB921802, the National Natural Science Foundation of China under Grant Nos. 91321312, 91121001, 11321063, 11174121, and 61475099, and the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and

Spontaneous four wave mixing in nonlinear waveguide is one of the excellent technique for generating photon pairs in well-defined guided modes. Here we present a comprehensive study of the frequency characteristic of correlated photon pairs generated in telecom C-band from a dispersion-engineered silicon wire waveguide. We have demonstrated that the waveguide configuration, shape of pump pulse, two-photon absorption as well as linear losses have significant influences on the biphoton spectral characteristics and the amount of frequency entanglement generated. The superior performance as well as the structural compactness and CMOS compatibility makes the silicon wire waveguide an ideal integrated platform for the implementation of on-chip quantum technologies.

Compact tunable dual-wavelength mid-infrared optical parametric oscillator pumped by high power gain-switched fiber laser

We report, to the best of our knowledge, the first demonstration of a gain-switched fiber laser pumped tunable dual-wavelength optical parametric oscillator (OPO) operating around 3–5 µm. A homemade APMgLN crystal was used as the nonlinear material. A ‘figure-of-h’ shaped pump pulse was employed to improve the nonlinear conversion efficiency of the OPO. A maximum total idler output power of 4.82 W was obtained under pump power of 44.6 W with corresponding pump-to-idler conversion efficiency of 10.5%. The idler wavelengths were measured to be 3.34 and 3.65 μm at a temperature of 40 °C, which can be successfully tuned with a rate of about 2 nm °C−1 by adjusting the working temperature of the APMgLN crystal from 20 °C to 80 °C.

Design of pump pulses for InGaAs quantum well semiconductor disk lasers

It has been demonstrated experimentally that pulsed pumping can significantly improve thermal management, thus upgrade the output power of an optically pumped semiconductor disk laser (SDL). The transient heat conduction equation is solved by the use of the finite element method, and the maximum temperature rise of the active region in an InGaAs quantum well SDL under pulsed pumping is focused. Based on the numerical results, the influences of width, repetition rate, and shape of pump pulses on the maximum temperature rise are discussed, the optimized design of width, repetition rate, and shape of pump pulses are concluded, and the theoretical results are in good agreement with the reported experiments.

Vibrational ladder climbing in carboxy-hemoglobin: effects of the protein environment.

We present simulations on vibrational ladder climbing in carboxy-hemoglobin. Motivated by recent experiments, we study the influence of different realistic pump probe parameters. To allow for a direct comparison with experimental results, transient absorption spectra obtained by a weak probe pulse following the strong, shaped pump pulse are calculated. The influence of the protein fluctuations is taken into account using a recently developed microscopic model. This model consists of a quantum Hamiltonian describing the CO vibration in carboxy-hemoglobin, together with a fluctuating potential, which is obtained by electronic structure calculation based on a large number of protein configurations. Using realistic pulse parameters, vibrational excitations to very high-lying states are possible, in qualitative agreement with experimental observations.

Variable square pulse vs conventional PFN pumping of Er:YAG laser

The influence of the flashlamp pump current pulse shape on Er:YAG laser efficiency and laser rod thermal focusing was studied theoretically and experimentally. Two pulse shapes, PFN (Pulse Forming Network) and VSP (Variable Square Pulse), were considered. Theoretical modeling and experimental measurements show that the pump pulse shape itself does not have a significant influence on the Er:YAG laser efficiency or thermal focusing. Instead, the major parameter influencing Er:YAG laser efficiency and thermal focusing was found to be the overall pulse duration. For PFN pulses, rise and fall times directly define the overall pulse duration, and therefore do have influence on thermal focusing. By contrast, VSP pulse duration is defined by the externally controlled on-time of the switching transistor. For square shaped pulses, short rise and fall times do not have a direct beneficial influence on thermal lensing.

Compound FDTD method for silicon photonics

Attempt to manufacture photonics devices on silicon requires theoretical and numerical prediction. This essay presents Compound FDTD (C-FDTD) method for comprehensive simulation of silicon photonics devices. Although this method is comprehensive, it maintains conventional Yee algorithm. The method involves variation of refractive index due to nonlinear effects. With the help of this simulator, refractive index change due to free-carriers created through two photon absorption and Kerr effect in silicon waveguide is considered. Results indicate how to choose pump pulse shape to optimum operation of active photonics devices. Also conductivity variation of Si waveguide due to change in free-carrier density is studied. By considering variations in conductivity profile, we are able to design better schemes for sweep free carriers away with reverse bias or nonlinear photovoltaic effect for fast devices and Raman amplifiers.