In this work, a pronounced ultrashort pulse contrast enhancement was realized via the utilization of the nonlinear Transient Grating technique with a fiber-chirped pulse amplifier system in the 1μm regime. A YVO4 crystal with significantly enhanced nonlinearity relative to glasses yielded a distinct advantage in pulse cleaning by inducing Transient Grating with intensities that are nearly order of magnitude lower compared to, e.g., fused silica. In addition, the clean beam was inherently separated from the generating beams, eliminating the necessity for supplementary filtration, potentially compromising the final contrast. Up to 40 dB contrast enhancement was observed with ∼1μJ of energy. The absolute measured peak-to-noise contrast was 80 dB, albeit full verification might be masked by the noise floor limit. Setup modifications for higher pulse energies and corresponding higher efficiencies are underway, with the aim of evaluating their suitability for large laser systems.

The generation and control of large amplitude plasma gratings and other plasma structures is of paramount importance for the realization of plasma photonics. Autoresonant excitation of such structures by means of chirped amplitude-modulated lasers has been recently discussed and analyzed theoretically. Here we discuss the parameter space for the realization of such a scheme and describe the laser system that was built towards this goal. We also expand our earlier theoretical study to account for the more realistic case of a moderately focused laser beam, instead of the simplified plane wave approximation.

The problem of tunneling ionization and the associated questions of how long it takes for an electron to tunnel through the barrier, and what the tunneling rate has fascinated scientists for almost a century. In strong field physics, tunnel ionization plays an important role, and accurate knowledge of the time-dependent tunnel rate is of paramount importance. The Keldysh theory and other more advanced related theories are often used, but their accuracy is still controversial. In previous work, we suggested using a curved waveguide as a quantum simulator to simulate the tunnel ionization process. Here we implemented for the first time such a curved waveguide and observed the simulated tunneling ionization process. We compare our results with the theory.

We demonstrate temporal shape improvement of a short laser pulse using chirped aperiodic nonlinear frequency converter within an optical parametric amplifier. The aperiodic converter generated walk-off free high spatial quality pulse with ∼40% efficiency second harmonic while preserving the pump bandwidth. A <300 fs idler pulse was generated, with ∼10 nm central wavelength tunability around 1053 nm by pump generation and phase matching control. A pronounced contrast pedestal suppression of up to 40 dB was observed within a few picoseconds range around the peak. Such pedestal suppression has good scalability potential to high energies.

We present an all-passive efficient KGW Raman laser with an external-cavity configuration in the 2 µm spectral regime. The Raman laser was pumped by a passively Q-switched Tm:YAP laser emitting at 1935 nm. Due to the bi-axial properties of the KGW crystal, the laser exhibits stimulated Raman emission at two separate spectral lines: 2272 nm and 2343 nm. The output energies achieved at these two lines are 340 µJ/pulse and 450 µJ/pulse, accordingly. The seed to Raman laser conversion efficiencies achieved of 19.2% and 23.5%, respectively, are comparable to actively Q-switched laser arrangements. To the best of our knowledge, this is the first time an efficient Raman laser in the 2 µm regime is demonstrated in a completely passive configuration.

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having &\#x201C;drifted away&\#x201D; from the original parent ion.

As one of the most important physical processes of strong-field laser-matter interaction, laser-driven electron-ion recollision is the fundamental process. As we have known, the well-known three-step model of HHG predicts that the cutoff law obeys Ecutoffþinspace}=þinspace}Ipþinspace}+þinspace}3.17Up, implying that the maximum kinetic energy of returning electron can be greatly extended by increasing the driving wavelength. With the long wavelength mid-infrared laser pulse, it is easy for the ponderomotive energy of the returning electron to be very large to excite the deep inner-shell electron, which may be used to investigate the ultrafast inner-shell electron dynamics.

We study the formation of large-amplitude standing ion acoustic waves (SIAWs) by nonlinear phase-locking (autoresonance) with a weak, chirped frequency standing ponderomotive drive. These waves comprise a nonlinear two-phase solution, with each phase locked to one of the two traveling waves comprising the drive. The autoresonance in the system is guaranteed provided that the driving amplitude exceeds a threshold. The phenomenon is illustrated via water bag simulations within a nonlinear ion fluid model and analyzed using Whitham's averaged variational principle. The local ion and electron densities in the autoresonant SIAWs may significantly exceed the initial unperturbed plasma density and are only limited by kinetic wave-breaking.

Appeared also in SciLight

Our Cr:ZnSe laser amplifier, seeded by parametric difference mixing, produces 72fs long pulses at the central wavelength of  2.37&\#x00B5;m. The stability of the carrier-to-envelope phase of the amplified seed pulses, attained at the stage of their parametric generation, is preserved through 6 orders of magnitude of laser amplification.

This paper presents a KGW Raman laser with an external-cavity configuration at the 2 &\#x00B5;m region. The Raman laser is pumped by an actively Q-switched Tm:YLF laser, especially designed for this purpose emitting at 1880 nm. Due to the KGW bi-axial properties, the Raman laser is able to lase separately at two different output lines, 2197 nm and 2263 nm. The output energies and pulse durations that were achieved for these two lines are 0.15 mJ/pulse at 21 ns and 0.4 mJ/pulse at 5.4 ns, respectively. To the best of our knowledge, this is the first time that the KGW crystal, which is well known for its wide use in shorter wavelengths, is demonstrated in a Raman laser in the 2 &\#x00B5;m region. According to the achieved results and due to the KGW properties, it appears to be a suitable crystal for energy scaling and efficient Raman conversion in this spectral range. An estimation of the Raman gain coefficient for this wavelength is provided as well.

With conventional poling techniques of pyroelectric crystals, the thickness of the periodically poled crystals is typically limited to 0.5&\#x2013;1&\#x00A0;mm. Such a small aperture of the crystal limits the amount of energy/power that this device may deliver. Here we discuss diffusion bonding as an alternative method to achieve a wider periodically poled crystal, with virtually unlimited width. It is shown that the amplified signal preserved a good beam profile despite a possible phase shift between the stitched crystals. This technique may be extended to larger aperture optical parametric amplifiers and allows for high energy output from periodically poled crystals.

The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids.

A pulsed high energy and narrow bandwidth tunable Tm:YLF laser at the milli-Joule level is demonstrated. The spectral bandwidth was narrowed down to 0.15 nm FWHM, while 33 nm of tunability range between 1873 nm and 1906 nm was achieved using a pair of YAG Etalons. The laser was actively Q-switched using an acousto-optic modulator and mJ level pulse energy was measured along the whole tuning range at a repetition rate of 1 kHz. Up to 1.97 mJ of energy per pulse was achieved at a pulse duration of 37 ns at a wavelength of 1879 nm, corresponding to a peak-power of 53.2 kW and at a slope efficiency of 36 &\#x00025;. The combination of both high energy pulsed lasing and spectral tunability, while maintaining narrow bandwidth across the whole tunability range, enhances the laser abilities, which could enable new applications in the sensing, medical and material processing fields.

Quantum dot (QD) solids and arrays hold a great potential for novel applications which are aimed at exploiting quantum properties in room-temperature devices. Careful tailoring of the QD energy levels and coupling between dots could lead to efficient energy-harvesting devices. Here, we used a self-assembly method to create a disordered layered structure of QDs, coupled by covalently bonded organic molecules. Energy transfer rates from small (donor) to large (acceptor) QDs are measured. Best tailoring of the QDs energy levels and the length of the linking molecules results in an energy transfer rate as high as 30 ps–1. Such rates approach energy transfer rates of the highly efficient photosynthesis complexes and are compatible with a coherent mechanism of energy transfer. These results may pave way for new controllable building blocks for future technologies.

Nonlinear light&\#x2013;matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigated at free-electron laser (FEL) facilities. Yet, electron dynamics are often too fast to be captured with the femtosecond resolution of state-of-the-art FELs. Attosecond pulses from laser-driven XUV-sources offer the necessary temporal resolution. However, intense attosecond pulses supporting nonlinear processes have only been available for photon energy below 50&\#x00A0;eV, precluding XUV-pump/XUV-probe investigation of typical inner-shell processes. Here, we surpass this limitation by demonstrating two-photon absorption from inner electronic shells of xenon at photon energies around 93&\#x00A0;eV and 115&\#x00A0;eV. This advance opens the door for attosecond real-time observation of nonlinear electron dynamics deep inside atoms.

A hybrid laser scheme for the generation and amplification of mid-IR ultrashort pulses, with a carrier to envelope stable phase, is presented. Seed mid-IR pulses with picojoule energies are obtained via intrapulse difference frequency generation from an 8 fs Ti:sapphire oscillator. The energy of these seed pulses is then amplified in a multipass Cr:ZnSe laser amplifier to more than a nanojoule/pulse level. The duration of the amplified impulses is measured to be 87 fs, and the width of their spectrum supports their compression to ~50 fs.

Understanding the interaction of atoms and molecules with an intense laser radiation field is key for many applications such as high harmonic generation and attosecond physics. Because of the non-perturbative nature of strong field physics, some simplifications and approximation methods are often used to shed light on these processes. One of the most fruitful approaches to gain an insight into the physics of such interactions is the three-step-model, in which, the electron first tunnels out through the barrier and then propagates classically in the continuum. Despite the great success of this and other more sophisticated models there are still many ambiguities and open questions, e.g. how long it takes for the electron to tunnel through the barrier. Most of them stem from the difficulties in understanding electron trajectories in the classically ‘forbidden’ zone under the barrier. In this theoretical paper we show that strong field physics and the propagation of electromagnetic waves in a curved waveguide are governed by the same Schrödinger equation. We propose to fabricate a curved optical waveguide, and use this isomorphism to mimic strong field physics. Such a simulating system will allow us to directly probe the wave-function at any point, including the ‘tunneling’ zone.

The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.