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Lightwave pulse shaping in the picosecond regime has remained unaddressed because it resides beyond the limits of state-of-the-art techniques, due to either its inherently narrow spectral content or fundamental speed limitations in electronic devices. The so-called picosecond shaping gap hampers progress in all areas correlated with time-modulated light–matter interactions, such as photoelectronics, health and medical technologies, and energy and materials sciences. We report on a novel nonlinear method to simultaneously frequency-convert and adaptably shape the envelope of light wave packets in the picosecond regime by balancing spectral engineering and nonlinear conversion in solid-state nonlinear media, without requiring active devices. We capture computationally the versatility of this methodology across a diverse set of nonlinear conversion chains and initial conditions. We also provide experimental evidence of this framework producing picosecond-shaped, ultranarrowband, near-transform-limited light pulses from broadband, femtosecond input pulses, paving the way toward programmable lightwave shaping at gigahertz-to-terahertz frequencies. 

Abstract The application high intensity ultrafast lasers to compact plasma-based electron accelerators has recently been an extremely active area of research. Here, for the first time, we show experimentally and theoretically that carefully sculpting an intense ultrafast pulse in the spatio-temporal domain allows ponderomotive pressure to be used for direct acceleration of electron bunches from rest to relativistic energies. With subluminal group velocity and above-threshold intensity, a laser pulse can capture and accelerate electrons, pushing on them like a snowplow. Acceleration of electrons from rest requires a substantial reduction of group velocity. In this demonstration experiment, we achieve a group velocity of ∼0.6c in a tilted pulse by focusing the output of a novel asymmetric pulse compressor we developed for the petawatt-class ALEPH system at Colorado State University. This direct laser-electron approach opens a route towards exploiting optical spatio-temporal control techniques to sculpt electron beams with desired properties such as narrow energy and angular distributions. The tilted-pulse snowplow technique can be scaled from small-scale to facility-scale amplifiers to produce short electron bunches in the 10 keV−10 MeV range for applications including ultrafast electron diffraction and efficient injection into laser wakefield accelerators for acceleration beyond the GeV level. 

We present a novel, versatile framework to generate W-level temporally shaped, near transform-limited, UV picosecond pulses via non-colinear sum frequency generation and demonstrate it producing temporally flattop, high-power UV pulses capable of enhancing femtosecond- and attosecond-level electron and Xray free electron lasers brightness. 

While there has been success in Wakefield acceleration of electrons, there are a number of applications that could benefit from acceleration to modest energy (~MeV) by the laser field, for example, ultrafast electron diffraction and injection into higher-energy laser-driven accelerators. Here we outline our scheme for ponderomotive acceleration of electrons (and in principle, positrons) in which we control the group velocity of ultrafast pulses through pulse front tilt. Provided the intensity is above the threshold for capture of electrons, the leading part of the pulse front effectively acts like a moving mirror whose shape is controlled by the spatio-temporal topology of the intensity profile. Our analytic models of the propagation of spatially-chirped beams, simple relativistic single-particle models of the laser-electron interaction and our implementation of these beams in particle-in-cell simulations help to predict the output electron energy and direction. We are preparing experiments on the ALEPH laser system at Colorado State University in which we will use the diagnostic techniques that we have developed to align our scaled-up design of a high-energy pulse compressor that will deliver spatially chirped pulses. 

Vigorous efforts to harness the topological properties of light have enabled a multitude of novel applications. Translating the applications of structured light to higher spatial and temporal resolutions mandates their controlled generation, manipulation, and thorough characterization in the short-wavelength regime. Here, we resort to high-order harmonic generation (HHG) in a noble gas to upconvert near-infrared (IR) vector, vortex, and vector-vortex driving beams that are tailored, respectively, in their spin angular momentum (SAM), orbital angular momentum (OAM), and simultaneously in their SAM and OAM. We show that HHG enables the controlled generation of extreme-ultraviolet (EUV) vector beams exhibiting various spatially dependent polarization distributions, or EUV vortex beams with a highly twisted phase. Moreover, we demonstrate the generation of EUV vector-vortex beams (VVB) bearing combined characteristics of vector and vortex beams. We rely on EUV wavefront sensing to unambiguously affirm the topological charge scaling of the HHG beams with the harmonic order. Interestingly, our work shows that HHG allows for a synchronous controlled manipulation of SAM and OAM. These EUV structured beams bring in the promising scenario of their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source. 

We􀀁explore􀀁an􀀁electron􀀁acceleration􀀁scheme􀀁which􀀁uses􀀁the􀀁ponderomotive􀀁force􀀁of􀀁a􀀁tilted􀀁ultrafast􀀁laser􀀁as􀀁the􀀁drive􀀁mechanism􀀁for􀀁acceleration. The􀀁effect􀀁of􀀁pulse􀀁front􀀁curvature􀀁on􀀁the􀀁acceleration􀀁process􀀁is􀀁also􀀁discussed. 

We present a novel, versatile framework to generate W-level temporally shaped UV picosecond pulses via non-colinear sum frequency generation and demonstrate it producing temporally flattop, high-power UV pulses capable of enhancing femtosecond- and attosecond-level X-ray free electron lasers. 

The study of the physics of naturally occurring electrostatic discharges (ESDs) at early times is challenged by the difficulty in overcoming pre-trigger requirements of laser probes. In this work, ultraviolet (UV) pulses from a diode-pumped solid-state, Q-switched laser system are used to trigger ESDs. We use an open-air spark gap with a gap voltage held near threshold. The laser intensity is in the microjoule range so that seed electrons are produced through the photoelectric effect on the cathode. In contrast to laser-triggered spark gaps, the resulting discharges are anticipated to be very similar to those produced by random seed electrons. The triggering produces ESDs with a yield of >65%. While there is ~10ns jitter, co-recording of the current pulse will allow for time-resolved experimental diagnostics with ns timing resolution. Early results show a relatively short delay between triggering and the arc discharge (~100ns), indicating that collisional UV generation is a more likely source of secondary electrons than ion return current. Our experiment will be compared to our numerical models for plasma temperature and species evolution measurements in ESDs. Future experiments will be completed in a discharge chamber which allows for control of the gas composition and pressure. 

We introduce a self-referenced system that retrieves the full spatio-temporal profile of an ultrashort pulse using a Shack-Hartmann and second harmonic generation FROG. The key feature is the precise co-location of a spectral phase measurement at one spatial position with the spectrally resolved spatial measurements. 

We generalize our method for propagating spatially chirped Gaussian beams to properly calculate the evolution of geometric spectral phase through a lens. By expanding the spectral phase around the local central frequency, we analytically calculate the spatio-temporal field. Applications to intentionally detuned pulse compressors are discussed.