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Imaging multiple Rydberg wave packets from shaper-generated two-color femtosecond pump-probe sequences
摘要： We combine a bichromatic white light polarization pulse shaping scheme with angle- and energy-resolved photoelectron spectroscopy to image the dynamics of atomic Rydberg wave packets. Background-free detection of the Rydberg dynamics is performed using shaper-generated bichromatic linearly and circularly polarized femtosecond pump-probe pulse sequences. Photoelectron momentum distributions from linearly polarized bichromatic fields feature pronounced time-, energy-, and angle-dependent dynamics, which result from the interference of s-, d-, and g-type photoelectron wave packets from the ionization of the Rydberg np and nf series. Detailed analysis of the highly differential data allows us to extract the dynamics of both Rydberg wave packets separately. The results are experimentally verified by additional pump-probe studies with bichromatic circularly polarized pulse sequences, which exclusively map the dynamics of the Rydberg nf series via g-type photoelectron wave packets.
关键词： Rydberg wave packets,pump-probe spectroscopy,photoelectron imaging,femtosecond lasers,polarization pulse shaping
更新于2025-09-23 15:23:52
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Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber
摘要： We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 μm2 to 900 μm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 μm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 μm and 2 μm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.
关键词： ultrafast processes in fiber,large-mode-area fiber,high peak power femtosecond pulses,pulse shaping,tapered fiber,pulse compression
更新于2025-09-23 15:22:29
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A Generalized Spectral Shaping Method for OFDM Signals
摘要： Orthogonal frequency division multiplexing (OFDM) signals with rectangularly windowed pulses exhibit low spectral confinement. Two approaches usually referred to as pulse-shaping and active interference cancellation (AIC) are classically employed to reduce the out-of-band emission (OOBE) without affecting the receiver. This paper proposes a spectral shaping method that generalizes and unifies these two strategies. To this end, the OFDM carriers are shaped with novel pulses, referred to as generalized pulses, that consist of the ones used in conventional OFDM systems plus a series of cancellation terms aimed at reducing the OOBE of the former. Hence, each generalized pulse embeds all the terms required to reduce its spectrum in the desired bands. This leads to a data-independent optimization problem that notably simplifies the implementation complexity and allows the analytical calculation of the resulting power spectral density (PSD), which in most methods found in the literature can only be estimated by means of simulations. As an example of its performance, the proposed technique allows complying with the stringent PSD mask imposed by the EN 50561-1 with a data carrier loss lower than 4%. By contrasts, 28% of the data carriers have to be nulled when pulse-shaping is employed in this scenario.
关键词： out-of-band emission,pulse-shaping,sidelobes suppression,OFDM,cancellation carriers
更新于2025-09-23 15:22:29
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Dephasingless Laser Wakefield Acceleration
摘要： Laser wakefield accelerators (LWFAs) produce extremely high gradients enabling compact accelerators and radiation sources but face design limitations, such as dephasing, occurring when trapped electrons outrun the accelerating phase of the wakefield. Here we combine spherical aberration with a novel cylindrically symmetric echelon optic to spatiotemporally structure an ultrashort, high-intensity laser pulse that can overcome dephasing by propagating at any velocity over any distance. The ponderomotive force of the spatiotemporally shaped pulse can drive a wakefield with a phase velocity equal to the speed of light in vacuum, preventing trapped electrons from outrunning the wake. Simulations in the linear regime and scaling laws in the bubble regime illustrate that this dephasingless LWFA can accelerate electrons to high energies in much shorter distances than a traditional LWFA—a single 4.5 m stage can accelerate electrons to TeV energies without the need for guiding structures.
关键词： ponderomotive force,phase velocity,Laser wakefield accelerators,spatiotemporal pulse shaping,dephasing
更新于2025-09-23 15:21:01
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Optical Waveform Tailoring in Passive and Laser Cavity Fibre Systems
摘要： The interplay among the effects of dispersion, nonlinearity and gain/loss in optical fibres is a powerful tool to generate a broad range of pulse shapes with tuneable properties. Here we propose a method to optimise the systems parameters for a given pulse target. By reducing the system complexity and applying machine-learning strategies, we show that it is possible to efficiently identify the sets of parameters of interest. Two configurations are numerically investigated: pulse shaping in a passive normally dispersive fibre and pulse generation in a dual-pump nonlinear-amplifying-loop-mirror mode-locked fibre laser.
关键词： pulse shaping,optical processing,nonlinear fibre optics,fibre lasers
更新于2025-09-23 15:21:01
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Generation of J-shaped pulses in ultra-long Ytterbium doped mode locked fiber laser
摘要： We report, for the first time, generation of J-shaped pulses in figure-eight type ultra-long, all-normal dispersion Ytterbium-doped fiber laser mode locked by the combined effect of nonlinear polarization evolution and nonlinear optical loop mirror. Cavity birefringence based spectral filtering introduced by polarization controllers is used for the formation of J-shaped as well as step-like and flat-top pulses. The shape and duration of generated pulse is found to depend on applied birefringence as well as pump power. J-shaped pulses of 180 ns duration and 332 nJ pulse energy at 201.45 kHz fundamental repetition rate are generated at 200 mW pump power. Experimentally, a strong correlation between spectral and temporal profile of the generated pulse shapes is established where it has been shown that asymmetric spectral filtering is responsible for generation of J-shaped and step-like pulses. Numerically, the spectral transmission of figure-eight type resonator under different cavity birefringence and intra-cavity power is investigated which qualitatively supports the experimental results.
关键词： mode locked lasers,Ytterbium doped fiber lasers,dissipative soliton resonance,pulse shaping
更新于2025-09-23 15:21:01
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Customizing supercontinuum generation via on-chip adaptive temporal pulse-splitting
摘要： Modern optical systems increasingly rely on complex physical processes that require accessible control to meet target performance characteristics. In particular, advanced light sources, sought for, for example, imaging and metrology, are based on nonlinear optical dynamics whose output properties must often finely match application requirements. However, in these systems, the availability of control parameters (e.g., the optical field shape, as well as propagation medium properties) and the means to adjust them in a versatile manner are usually limited. Moreover, numerically finding the optimal parameter set for such complex dynamics is typically computationally intractable. Here, we use an actively controlled photonic chip to prepare and manipulate patterns of femtosecond optical pulses that give access to an enhanced parameter space in the framework of supercontinuum generation. Taking advantage of machine learning concepts, we exploit this tunable access and experimentally demonstrate the customization of nonlinear interactions for tailoring supercontinuum properties.
关键词： machine learning,optical pulse shaping,supercontinuum generation,photonic chip,nonlinear optics
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Precursor reaction method with high Ga Cu(In,Ga)(S,Se) <sub/>2</sub> to achieve increased open-circuit voltage
摘要： Direct detection transceivers offer advantages, including low cost and complexity, in short- and medium-haul links. We carried out studies seeking to identify the signal formats which offer the highest information spectral densities and maximum transmission distances for direct detection links. The performance of two spectrally efficient optical signal formats, single-sideband (SSB) Nyquist pulse-shaped subcarrier modulation (SCM) and SSB orthogonal frequency-division multiplexing (OFDM), are compared by means of simulations. The comparison is performed for a range of wavelength-division multiplexing (WDM) net information spectral densities up to 2.0 b/s/Hz by varying the signal bandwidth, modulation cardinality, and WDM channel spacing. The signal formats’ tolerance to signal–signal beating interference, resulting from square-law detection, is investigated, and the Nyquist-SCM format is found to suffer lower penalties from this nonlinearity at high information spectral densities. In 7 × 28 Gb/s WDM transmission at 2.0 b/s/Hz (with electronic pre-distortion and EDFA-only amplification), Nyquist-SCM signals can be transmitted over distances of up to 720 km of standard SMF in comparison to a maximum of 320 km with the OFDM signal format.
关键词： Digital signal processing,direct detection,wavelength division multiplexing,subcarrier modulation,electronic pre-distortion,optical communication,Nyquist pulse shaping,signal–signal beating interference,orthogonal frequency division multiplexing
更新于2025-09-23 15:19:57
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Tilted Snowplow Ponderomotive Electron Acceleration With Spatio-Temporally Shaped Ultrafast Laser Pulses
摘要： We propose a novel scheme for using the ponderomotive force of a tilted ultrafast laser pulse to accelerate electrons in free space. The tilt of the intensity envelope results from the angular dispersion of the pulse’s spectrum and slows down the interaction of the pulse with free electrons. The slower effective pulse velocity allows time for the electrons to accelerate from rest while remaining on the wave. We present both non-relativistic and relativistic analytic single-particle models in the adiabatic ponderomotive approximation, describing the process for an ideal infinite tilted pulse as well as a finite width beam. The analysis predicts the threshold intensity as a function of the pulse front tilt angle and shows that in the ideal case the output energy of the electrons is four times that of the ponderomotive potential at the capture threshold. Full-field simulations using the 2D OSIRIS 4.0 particle-in-cell code confirm the basic scheme. This tilted pulse acceleration scheme shows promise as a lab-scale method of accelerating electrons to the MeV level with good energy and angular resolution, to be used for ultrafast electron diffraction or injection into a second stage accelerator.
关键词： ponderomotive force,spatio-temporal pulse shaping,ultrafast lasers,laser electron accelerators,relativistic kinematics
更新于2025-09-23 15:19:57
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Experimental Investigation of Power-Scaled Dissipative Soliton Generation
摘要： We conduct a power scaling study for the femtosecond dissipative soliton generation with a 10-μm core diameter, ?ber-based, compact-sized, and low-cost all-normal-dispersion laser con?guration. Laser performance, in terms of spectra distribution, temporal characteristic, average power, and stability in 8 h, for different ?ltering bandwidths has been investigated. The obtainable highest output power and shortest pulse duration are 4.5 W and 85 fs, respectively. To our best knowledge, this is the shortest pulse duration among the reported all-?ber pumped Watt-level mode-locked ?ber lasers.
关键词： mode-locking,pulse-shaping,dissipative soliton,laser performance,power-scaling
更新于2025-09-23 15:19:57