Here, we report the recent progress on the front end developed for the 100 PW-class laser facility. Using 3 stages of optical parametric chirped-pulse amplification (OPCPA) based on lithium triborate (LBO) crystals, we realized a 5.26 J/0.1 Hz amplified output with a bandwidth over 200 nm near the center wavelength of 925 nm. After the compressor, we obtained a pulse duration of 13.4 fs. As the compression efficiency reached 67%, this OPCPA front end could potentially support a peak power of 263 TW at a repetition rate of 0.1 Hz. To the best of our knowledge, among all the 100 TW-level OPCPA systems, it shows the widest spectral width, the shortest pulse duration, and it is also the first OPCPA system working at a repetition-rate mode.

13.4 fs, 0.1 Hz OPCPA Front End for the 100 PW-Class Laser Facility

Spatiotemporal optical vortex (STOV) is a unique optical vortex with phase singularity in the space-time domain and the photons in a STOV can carry transverse orbital angular momentum (OAM). The STOV shows many fantastic properties which are worth exploring. Here, we theoretically and experimentally study the diffraction property of STOV, which is a fundamental wave phenomenon. The diffraction behaviors of STOVs are obviously affected by the transverse OAM. The diffraction patterns of STOV pulses diffracted by a grating show multi-lobe structure with each gap corresponding to 1 topological charge. The diffraction properties of lights with transverse OAM are demonstrated clearly and help us understanding the physical properties of STOV, which will be of special applications, such as the realization of fast detection of STOVs with different topological charges, which may pay the way for STOV based optical communication. Photons carrying orbital angular momentum (OAM) is an intrinsic property of optical vortex beams. The orientations of the OAM can be parallel or orthogonal to the propagation direction of the light beam, which are classified as longitudinal and transverse OAM, respectively. Conventional spatial optical vortex beam with phase singularity in the spatial plane possesses longitudinal OAM had been demonstrated [1]. Optical vortex beams have wide applications, such as optical tweezer and microparticle manipulation[2, 3], stimulated emission depletion (STED) microscopy[4], optical communication [5]. Spatiotemporal optical vortex (STOV) is a novel optical vortex with phase singularity in the space-time domain and the photons in a STOV can own transverse orbital angular momentum (OAM) [6-8]. Recently, STOVs were observed in experiments [9] and can be generated by using 4 f pulse shaper system [10, 11]. Furthermore, significant properties of STOV are analyzed, such as the conservation of transverse OAM in nonlinear optical process, second harmonic generation [12, 13], the propagation and generation properties of STOV [10, 14, 15], angular momenta and spin-orbit interaction of STOV [16] and transverse shifts and time delays occurred when STOV reflected and refracted at a planar interface [17]. Moreover, technologies for the measurement of STOV have also been presented, such as transient-grating single-shot supercontinuum spectral interferometry (TG-SSSI) [18] and interference methods [11]. The STOV beam opens a new area of vortex beam and may has special applications. Understanding the physical properties of STOV is not only important in theoretical areas, but also meaningful for the practical application of STOV. Diffraction is a fundamental phenomenon of light wave, which is well known for a conventional polychrome light beam. However, the diffraction property of STOV light has not been reported, to our knowledge. As it is well known that, for a conventional light beam without spatiotemporal coupling, the spectra are diffracted into one continuous line. However, for a STOV light beam with phase singularity in the space-time domain, energy is coupled between

Diffraction properties of lights with transverse orbital angular momentum

The petawatt (PW) laser has experienced a rapid development in the past two decades, and tens of giant facilities have been constructed worldwide. After realizing 10–100 PW, it seems to be close to some sort of engineering limit but its focused peak intensity still is much lower than the Schwinger limit, and therefore some technology improvements or innovations become indispensable for further increasing the peak power as well as the focused peak intensity. By quick reviewing the development of the PW laser in history, it is shown that reducing the pulse duration to near a single optical cycle is a feasible (easy and cheap) choice for this purpose. Here, technologies for the optical‐cycle pulse generation, ultrabroadband amplification, and capability boosting that aim to provide possible approaches for optical‐cycle PW lasers are briefly reviewed and discussed. Meanwhile, key bottlenecks that challenge the current as well as the future short‐pulse PW lasers and their possible solutions are summarized and discussed. This technology review aims to provide a possible roadmap for the next‐stage development of the short‐pulse PW laser.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/lpor.202100705

Further Development of the Short‐Pulse Petawatt Laser: Trends, Technologies, and Bottlenecks

The petawatt (PW) laser facility of the Berkeley Lab Laser Accelerator (BELLA) Center has recently commissioned its second laser pulse transport line. This new beamline can be operated in parallel with the first beamline and enables strong-field quantum electrodynamics (SF-QED) experiments at BELLA. In this paper, we present an overview of the upgraded BELLA PW facility with a SF-QED experimental layout in which intense laser pulses collide with GeV-class laser-wakefield-accelerated electron beams. We present simulation results showing that experiments will allow the study of laser-particle interactions from the classical to the SF-QED regime with a nonlinear quantum parameter of up to $$\chi \sim $$ 2. In addition, we show that experiments will enable the study and production of GeV-class, mrad-divergence positron beams via the Breit–Wheeler process. 

/pdf/strong-field-qed-experiments-using-the-bella-pw-laser-dual-3b5wdiqj.pdf

Strong-field QED experiments using the BELLA PW laser dual beamlines

Manganese dioxide (MnO 2 ) is a widely used and well-studied 3-dimensional (3D) transition metal oxide, which has advantages in ultrafast optics due to large specific surface area, narrow bandgap, multiple pores, superior electron transfer capability, and a wide range of light absorption. However, few studies have considered its excellent performance in ultrafast photonics. γ-MnO 2 photonics devices were fabricated based on a special dual-core, pair-hole fiber (DCPHF) carrier and applied in ultrafast optics fields for the first time. The results show that the soliton molecule with tunable temporal separation (1.84 to 2.7 ps) and 600-MHz harmonic solitons are achieved in the experiment. The result proves that this kind of photonics device has good applications in ultrafast lasers, high-performance sensors, fiber optical communications, etc., which can help expand the prospect of combining 3D materials with novel fiber for ultrafast optics device technology. 

https://spj.science.org/doi/pdf/10.34133/ultrafastscience.0006?download=true

High-performance γ-MnO
 2
 dual-Core pair-hole fiber for ultrafast photonics

Surface plasmonics with its unique confinement of light1,2 is expected to be a cornerstone for future compact radiation sources and integrated photonics devices. The energy transfer between light and matter is a defining aspect that underlies recent studies on optical surface-wave-mediated spontaneous emissions3–5. However, coherent stimulated emission of free electrons, which is essential for free-electron light sources, and its dynamical amplification process remain to be disclosed in a clear, unambiguous and calibrated manner. Here we present the coherent amplification of terahertz surface plasmon polaritons via free-electron-stimulated emission: a femtosecond optical pulse creates an in-phase free-electron pulse with an initial terahertz surface wave, and their ensuing interactions intensify the terahertz surface wave coherently. The underlying dynamics of the amplification, including a twofold redshift in the radiation frequency over a one-millimetre interaction length, are resolved as electromagnetic-field-profile evolutions using an optical pump–probe method. By extending the approach to a properly phase-matched electron bunch, our theoretical analysis predicts a super-radiant surface-wave growth, which lays the ground for a stimulated surface-wave light source and may facilitate capable means for matter manipulation, especially in the terahertz band. Stimulated emission by free electrons is used to amplify terahertz surface plasmon polaritons in a manner resembles that of light amplification in a high-gain free-electron laser. 

/pdf/coherent-surface-plasmon-polariton-amplification-via-free-2hc718uq.pdf

Coherent surface plasmon polariton amplification via free-electron pumping

The aberration-free characteristic endows the double-grating Offner stretcher with the advantages of good beam quality and perfect-dispersion-match with conjugated Treacy compressor, and therefore makes it an ideal pulse stretcher for optical parametric chirped pulse amplification (OPCPA) systems featuring with low material dispersion. We numerically and experimentally demonstrate the feasibility of dispersion control in OPCPA systems by the use of double-grating Offner stretcher. The numerical results indicate that near Fourier-transform-limited (FTL) pulses can be realized in the double-grating Offner stretcher based petawatt (PW) level broadband OPCPA systems. Moreover, in a proof-of-principle experiment, amplified pulses with ∼210 nm spectral bandwidth and ∼3 ns chirped pulse duration are also compressed to near FTL pulse duration of 15.4 fs just by cooperating a double-grating Offner stretcher with a Treacy compressor. To our knowledge, it is the first time to realize near FTL compression of laser pulses with such a broadband spectrum and such a large chirped pulse duration simultaneously, while without using any extra dispersion compensation methods. 

Use of double-grating Offner stretcher for dispersion control in petawatt level optical parametric chirped pulse amplification systems

Abstract Fine structured targets are promising in enhancing laser-driven proton acceleration for various applications. Here, we apply 3D-printed microwire-array (MWA) structure to boost the energy conversion efficiency from laser to proton beam. Under irradiation of high contrast femtosecond laser pulse, the MWA target generates over 1.2 × 10 12 protons (&gt;1 MeV) with cut-off energies extending to 25 MeV, corresponding to top-end of 8.7% energy conversion efficiency. When comparing to flat foils the efficiency is enhanced by three times, while the cut-off energy is increased by 32%. We find the dependence of proton energy/conversion-efficiency on the spacing of the MWA. The experimental trend is well reproduced by hydrodynamic and Particle-In-Cell simulations, which reveal the modulation of pre-plasma profile induced by laser diffraction within the fine structures. Our work validates the use of 3D-printed micro-structures to produce high efficiency laser-driven particle sources and pointed out the effect in optimizing the experimental conditions. 

https://www.nature.com/articles/s42005-022-00900-8.pdf

Ruxin Li

Papers

13.4 fs, 0.1 Hz OPCPA Front End for the 100 PW-Class Laser Facility

Coherent surface plasmon polariton amplification via free-electron pumping

Use of double-grating Offner stretcher for dispersion control in petawatt level optical parametric chirped pulse amplification systems

Further Development of the Short‐Pulse Petawatt Laser: Trends, Technologies, and Bottlenecks

High efficiency laser-driven proton sources using 3D-printed micro-structure