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All-optical switching of 75 fs pulses centered at 1560 nm, driven by 270 fs, 1030 nm pulses in a dual-core optical fiber exhibiting high index contrast is presented. The fiber is made of a thermally matched pair of lead silicate and borosilicate glasses used as core and cladding material, respectively. The novel switching approach is based on nonlinear balancing of dual-core asymmetry, by control pulse intensity induced group velocity reduction of the fast fiber channel. Due to the fiber core made of soft glass with high nonlinearity high switching contrast exceeding 20 dB is reached by using control pulses of only few nanojoule energy. The optimum fiber length is 14 mm, which closely match the calculated coupling length at the signal wavelength. The results express significant progress in comparison to similar studies based on self-switching of solitonic pulses in dual-core fibers and represent high application potential.

We introduce a new approach to reduce uncorrelated background signals from fluorescence imaging data, using real-time subtraction of background light. This approach takes advantage of the short fluorescence lifetime of most popular fluorescent activity reporters, and the low duty-cycle of ultrafast lasers. By synchronizing excitation and recording, laser-induced multiphoton fluorescence can be discriminated from background light levels with each laser pulse. We demonstrate the ability of our method to – in real-time – remove image artifacts that in a conventional imaging setup lead to clipping of the signal. In other words, our method enables imaging under conditions that in a conventional setup would yield corrupted data from which no accurate information can be extracted. This is advantageous in experimental setups requiring additional light sources for applications such as optogenetic stimulation.

Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here, we experimentally demonstrate that two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm allows one to generate ultrashort sub-cycle THz pulses with sub-milijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm−1. Our numerical simulations predict that the observed THz yield can be significantly upscaled by further optimizing the experimental setup. Finally, in order to demonstrate the strength of our THz source, we show that the generated THz pulses are powerful enough to induce nonlinear cross-phase modulation in electro-optic crystals. Our work paves the way toward free space extreme nonlinear THz optics using affordable table-top laser systems., Powerful terahertz pulses are generated during the nonlinear propagation of ultrashort laser pulses in gases. Here, the authors demonstrate efficient sub-cycle THz pulse generation by using two-color midinfrared femtosecond laser filaments in ambient air.

The interaction of laser pulses with condensed matter forms the basis of light-wave-driven electronics potentially enabling tera- and petahertz switching rate applications. Carrier control using near- and midinfrared pulses is appealing for integration into existing platforms. Toward this end, a fundamental understanding of the complexity of phenomena concerning sub-band-gap driven semiconductors such as high harmonic generation, carrier excitation due to multiphoton absorption, and interband tunneling as well as carrier-carrier interactions due to strong acceleration in infrared transients is important. Here, stimulated emission from polycrystalline ZnO thin films for pump wavelengths between 1.2 \ensuremath{\mu}m (1 eV) and 10 \ensuremath{\mu}m (0.12 eV) is observed. Contrary to the expected higher intensity threshold for longer wavelengths, the lowest threshold pump intensity for stimulated emission is obtained for the longest pump wavelength corroborating the importance of collisional excitation upon intraband electron acceleration.

Nonlinear self-channeling (filamentation) of intense, ultrashort laser pulses in air has been extensively studied with ultrafast, near-infrared and visible laser sources [1] . Recently these investigations advanced to longer wavelengths, as well as to the regime of few-cycle pulses, where the effects associated with the carrier-envelope phase (CEP) of the laser pulse become important. It has been shown that spectral interference in the white light generated on filamentation of an ultrafast, short-wave infrared laser source carries CEP information [2] . Here, we report using this spectral interference for single-shot characterization of the CEP of an ultrafast, mid-infrared (MIR) laser source at 3.9 µm wavelength.

We demonstrate a time-domain method to quantitatively retrieve the angular dependence of laser-induced electron rescattering from the measured rotational half-revival signals of molecules with a reaction microscope. The method is based on the measured channel-resolved ion yields of single ionization and electron-rescattering-induced double ionization and the in situ measured alignment distribution of molecules. From the measured data for ${\mathrm{CO}}_{2}$, we retrieve the angular dependence of electron rescattering in nonsequential double ionization for both nondissociative and dissociative cases. The results imply that the angular dependence of electron rescattering is affected by the state of the parent ion populated during the first ionization step. The method demonstrated here opens up the possibility to quantitatively retrieve from measured data which molecular orbitals are involved in the interaction of strong laser fields with molecules.

The generation of ultrashort laser pulse bursts has already contributed to many applications such as materials processing [1] , pulsed laser deposition [2] , laser induced breakdown spectroscopy (LIBS) [3] and seeding of free electron lasers [4] . Currently, there is a rising demand on burst sources providing terahertz (THz) intraburst repetition rates or higher corresponding to pulse spacings in the order of a few picoseconds, given by applications such as resonant driving of optical nonlinearities [5] , time-resolved nonlinear spectroscopies [6] , coherent control of quantum systems [7] or as driver for secondary radiation sources, e.g. generation of THz bursts [8] . However, the amplification of bursts to multi-millijoule energies at THz intraburst repetition rates is highly problematic. This is given by the appearance of spectral modes that are mapped into the time-domain, formed by spectral interference of closely spaced pulses which are overlapping when applying Chirped Pulse Amplification (CPA). This leads to insufficient energy extraction in an amplifier and, if pulse spacing is not stabilized on an interferometric scale, to temporally unstable burst generation. Recently, we have successfully demonstrated energy-safe, stabilized CPA of ultrashort pulse bursts with THz intraburst frequencies up to multi-millijoules by applying Vernier-enabled phase-modulation techniques, breaking the mentioned energy-limiting barrier [8] . In this contribution, we demonstrate a new version of our burst-generation technique, which drastically lowers system complexity compared to our previous approach, allowing its application to any master-oscillator regenerative-amplifier combination setup with only minor modifications.

By exploiting stimulated Raman scattering in long nitrogen-filled capillary fibers, we demonstrate continuous tunability of Yb laser systems over the 1.0-1.7 μm range, with conversion efficiency up to 82%, and an up to 10-fold pulse compression.

The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this work we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3&ndash, 4 &micro, m. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.

We describe the results of experiments and simulations performed with the aim of extending photoelectron spectroscopy with intense laser pulses to the case of molecular compounds. Dimer frame photoelectron angular distributions generated by double ionization of ${\mathrm{N}}_{2}\ensuremath{-}{\mathrm{N}}_{2}$ and ${\mathrm{N}}_{2}\ensuremath{-}{\mathrm{O}}_{2}$ van der Waals dimers with ultrashort, intense laser pulses are measured using four-body coincidence imaging with a reaction microscope. To study the influence of the first-generated molecular ion on the ionization behavior of the remaining neutral molecule we employ a two-pulse sequence comprising of a linearly polarized and a delayed elliptically polarized laser pulse that allows distinguishing the two ionization steps. By analysis of the obtained electron momentum distributions we show that scattering of the photoelectron on the neighboring molecular potential leads to a deformation and rotation of the photoelectron angular distribution as compared to that measured for an isolated molecule. Based on this result we demonstrate that the electron momentum space in the dimer case can be separated, allowing us to extract information about the ionization pathway from the photoelectron angular distributions. Our work, when implemented with a variable pulse delay, opens up the possibility of investigating light-induced electronic dynamics in molecular dimers using angularly resolved photoelectron spectroscopy with intense laser pulses.

Ultrashort high-energy pulses at wavelengths longer than 1 µm are now desirable for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality, and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow-core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with a conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between higher-order modes of the HCF, can be readily employed to generate pulses ( ∼ 20 f s ) significantly shorter than the pump ones ( ∼ 200 f s ) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.

We establish a generalized picture of the phase sensitivity of laser-induced directional bond breaking using the H_{2} molecule as the example. We show that the well-known proton ejection anisotropy measured with few-cycle pulses as a function of their carrier-envelope phases arises as an amplitude modulation of an intrinsic anisotropy that is sensitive to the laser phase at the ionization time and determined by the molecule's electronic structure. Our work furthermore reveals a strong electron-proton correlation that may open up a new approach to experimentally accessing the laser-sub-cycle intramolecular electron dynamics also in larger molecules.

All-optical switching of 77 fs pulses centered at 1550 nm, driven by 270 fs, 1030 nm pulses in dual-core optical fibre exhibiting high index contrast is presented. The switching is achieved by nonlinear balancing of dual-core asymmetry. High switching contrast exceeding 20 dB is attained with driving pulses of only few nanojoule energy, which is due to the fibre core made of soft glass possessing high nonlinearity.

We demonstrate an efficient approach for enhancing the spectral broadening of long laser pulses and for efficient frequency redshifting by exploiting the intrinsic temporal properties of molecular alignment inside a gas-filled hollow-core fiber (HCF). We find that laser-induced alignment with durations comparable to the characteristic rotational time scale T R o t A l i g n enhances the efficiency of redshifted spectral broadening compared to noble gases. The applicability of this approach to Yb lasers with (few hundred femtoseconds) long pulse duration is illustrated, for which efficient broadening based on conventional Kerr nonlinearity is challenging to achieve. Furthermore, this approach proposes a practical solution for high energy broadband long-wavelength light sources, and it is attractive for many strong field applications.

Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here we demonstrate both theoretically and experimentally the realization of a novel THz source with high peak power performance based on two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm. Our theory predicts that under this scheme sub-cycle THz pulses with multi-millijoule energies and record conversion efficiencies can be produced. Besides, we elucidate the origin of this high efficiency, which is made up of several factors, including a novel mechanism where the harmonics produced by the mid-infrared pulses strongly contribute to the field symmetry breaking and enhance the THz generation. In our experiments we verify the theoretical predictions by demonstrating ultrashort sub-cycle THz pulses with sub-millijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm-1. Moreover, we show that these intense THz fields can drive nonlinear effects in bulk semiconductors (ZnSe and ZnTe) in free space and at room temperature. Our numerical simulations indicate that the observed THz yield can be significantly upscaled by further optimizing the experimental setup leading to even higher field strengths. Such intense THz pulses enable extreme field science, including into other, relativistic phenomena.

We report on the unambiguous observation of the subcycle ionization bursts in sequential strong-field double ionization of H_{2} and their disentanglement in molecular frame photoelectron angular distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase, in combination with multiparticle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-state-specific Coulomb distortions on emitted electrons in polyatomic molecules.

A conventional hollow core fiber (HCF) scheme is implemented to investigate spectral broadening of Titanium:Sapphire (Ti-Sa) femtosecond laser pulses in saturated hydrocarbon molecules compared to unsaturated ones. While the saturated molecules exhibit a spectral broadening similar to noble gases, for the unsaturated ones with π bonds, broadening towards blue is restrained. Numerical simulations underpin that it is a combination of group velocity dispersion (GVD) and Raman scattering which limits the spectral broadening for the unsaturated molecules. Compression of low energy ∼40fs pulses to ∼8fs using saturated hydrocarbons is demonstrated, suggesting the feasibility of this media for high repetition rate laser pulse compression.

Ultrafast demagnetization, a phenomenon of utmost interest in the context of optical control of magnetically recorded data, has been extensively studied in a variety of different materials. However, only a limited number of studies have investigated the impact of the pump laser wavelength on the process, and only within a narrow spectral range. Performing resonant scattering experiment at the cobalt ${M}_{2,3}$ edges, using extreme ultraviolet radiation photons from a high harmonic source, we studied the ultrafast demagnetization dynamics of Co/Pt multilayers by tuning the pump wavelength to 0.4, 0.8, and 1.8 \ensuremath{\mu}m. We show that the degree of demagnetization at short time scale (100s of fs) is stronger at longer wavelengths. This is explained by the wavelength dependence of both the laser induced heating of the electrons (${T}_{e}\ensuremath{\propto}{\ensuremath{\lambda}}^{2}$) and the spatial distribution of the electromagnetic energy deposited into the multilayer sample.

This works shows a new approach to study the electron recapture process during double and multiple ionization of atoms. This scheme is applicable to non-dissociative processes in molecules, which are not accessible with existing methods based on the measurement of kinetic energy released from fragmentation processes. The experiments show a transition of frustrated double ionization in argon from a non-sequential scenario to a sequential scenario.

We report on the retrieval of the angular dependence of laser-induced electron rescattering in CO2 with a novel method from the measured rotational half revival signals of filed-free aligned molecules using a reaction microscope.

We present strong field autocorrelation measurements of molecular ionization and dissociation with a reaction microscope. Time-frequency analysis of the time-domain signals was performed to obtain electron and nuclear dynamics during molecular ionization and dissociation.

A high harmonics source is used to perform x-ray resonant magnetic scattering on magnetic samples. The dynamics of laser-induced ultrafast demagnetization are probed and longer pump wavelengths are found to increase the initial quenching levels.

We report on the results of a joint experimental and numerical study on the sub-cycle laser field-driven electron dynamics that underlie the population of highly excited electronic states in multiply ionized argon dimers by electron recapture processes. Our experiments using few-cycle laser pulses with a known carrier-envelope phase (CEP) in combination with reaction microscopy reveal a distinct CEP-dependence of the electron emission and recapture process and, furthermore, a small but significant CEP-offset to the scenario in which no excited argon dimers are produced. With the help of classical ensemble trajectory simulations we trace down these different CEP-dependencies to subtle differences in the laser-driven sub-cycle electron trajectory dynamics that involve in both cases the transfer of an electron from one argon ion across the system boundary to the neighboring ion and its transient capture on this ion.

We present experimental studies of long-distance transmission of ultrashort mid-infrared laser pulses through atmospheric air, probing air dispersion in the 3.6–4.2-μm wavelength range. Atmospheric air is still highly transparent to electromagnetic radiation in this spectral region, making it interesting for long-distance signal transmission. However, unlike most of the high-transmission regions in gas media, the group-velocity dispersion, as we show in this work, is anomalous at these wavelengths due to the nearby asymmetric-stretch rovibrational band of atmospheric carbon dioxide. The spectrograms of ultrashort mid-infrared laser pulses transmitted over a distance of 60 m in our experiments provide a map of air dispersion in this wavelength range, revealing clear signatures of anomalous dispersion, with anomalous group delays as long as 1.8 ps detected across the bandwidth covered by 80-fs laser pulses.

Nonlinear (NL) interactions of strong THz electric and magnetic fields with matter are the next frontier in nonlinear optics. NL THz spectroscopy requires ultrashort/broadband THz pulses with high electric field strengths. Here, we report on THz generation from two-color laser filaments, driven by intense midIR pulses centered at $3.9 {\mu } \mathrm {m}$. We demonstrate generation of THz pulses with a spectral bandwidth of $\gt 15$ THz, extraordinary conversion efficiency of 2.34% and remarkably high energy of 0.185 mJ.

A high harmonics source is used to perform x-ray resonant magnetic scattering on a magnetic sample. The dynamics of laser-induced ultrafast demagnetization are probed with respect to the wavelength of the pump beam. Longer pump wavelengths are found to increase the initial quenching levels.

We experimentally investigate laser-induced dissociative recombination of CO$_2$ in linearly polarized strong laser fields with coincidence measurements. Our results show laser-induced dissociation processes originate from an electron recombination process after laser-induced double ionization. After double ionization of CO$_2$, one electron is recaptured by the CO$_2^{2+}$ and localized to O$^+$ or CO$^+$ in the following dissociation process. We found that the probability of electron localization to O$^{+}$ is much higher than that to CO$^+$. Further, our measurements reveal that the recombination probability of the first ionized electron is three times as high as that of the second ionized electron. Our work may trigger further experimental and theoretical studies on involved nuclear and electron dynamics in laser-induced dissociative recombination of molecules and their applications in controlling molecular dissociation with ultrashort laser pulses.

Nonlinear self-channeling (filamentation) of intense, ultrashort laser pulses in air has numerous potential applications ranging from remote sensing in the atmosphere to lightning control [1]. Recent progress in optical parametric chirped-pulse amplification (OPCPA) technology pushes the investigations of filamentation into short-wave infrared [2] and mid-wave infrared [3] regimes. At longer wavelengths, the propagation dynamics is affected by the presence of windows of anomalous dispersion due to the trace constituents of air [4,5]. Multiple odd harmonics of the infrared driver pulse can be easily detected and analyzed.

A generation of optical harmonics by circularly polarized light, which is in general forbidden in an isotropic medium, was recently observed in molecular gases where molecules were aligned and oriented by another linearly polarized laser pulse [1] or by pulses with twisted polarization [2]. In order to generate nth-harmonic with circularly polarized light, a molecule has to "absorb" n photons, having the same handedness, and to emit a single nth harmonic photon while fulfilling the energy and the momentum conservation laws, meaning a necessity to excite the molecule to appropriate rotational state. One can do this by means of intrapulse rotational Raman scattering, which prepares the molecule in the excited state through a subsequent absorption of (n-1) same-handed photons [1]. All previously reported experimental studies on circular harmonic generation in molecular gases were performed with visible/near-IR drivers, in either gas jets or in standing cells and with pre-alignment of molecules by an additional laser pulses. Here we report on the studies of self-action of elliptically polarized mid-IR pulses on the generation of low-order harmonics in filaments ignited in air and in argon, representing a molecular and an atomic gas respectively. The harmonics were driven by 20-mJ, sub-100 fs mid-IR pulses, centred at 3.9 pm wavelength. In the experiments filamentation was assisted by focusing light with a spherical mirror of ROC=-2500 mm into an open-end tube, through which Ar gas was flown at slight overpressure. Polarization of the pulses was controlled by a broadband quarter wave plate (QWP). Spectra of 5th and 7th harmonics were recorded after the filaments with a grating spectrometer (HR4000, OceanOptics). Polarization state of the generated harmonics was analysed with a Glan-Taylor polarizer.

Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling [1]. In this work, we show that mid-IR OPCPA technology could overcome major challenges in enhancing intense broadband THz generation from organic crystals. Strong THz fields are presently under extensive research for its applications in particle accelerations and fundamental understanding of structural dynamics [2]. Currently, the most efficient technique relies on optical rectification (OR) of femtosecond near-IR OPA laser pulses (1.3–1.5 pm) in highly nonlinear organic crystals [3]. However, the technique is still limited to a few mJ of pump energies and organic crystals suffer from a relatively low damage threshold at this pump wavelength. To improve THz generation, it is therefore crucial to use alternative laser pump technologies, such as Cr-Forsterite lasers [4]. However, the associated pump wavelength of 1.25 pm typically leads to an increase in nonlinear absorption, which decreases the crystal damage threshold and lowers the effectively emitted THz spectral contents. Here, we used a high-energy OPCPA system with 3.9 pm central wavelength (20 Hz repetition rate) [1] to generate THz from DSTMS organic crystal (Swiss Terahertz LLC) by OR. The emitted spectrum is broad and extends beyond 5 THz (compared to 2 THz central frequency in the case of Cr-Forsterite pump [4]). In terms of conversion efficiency, we did not observe saturation up to energy fluence of 180–200 mJ/cm2. This is remarkably high as compared to the typical saturation values of sub-10 mJ/cm2 from both Cr-Forsterite and near-IR OPA pump systems [4]. We evaluated the damage threshold of DSTMS at 3.9 pm beyond 250 mJ/cm2, more than an order of magnitude higher than for alternative near-IR pump technologies. These two advantages, due to the small pump photon energies, which are much below the crystal band gap, allow overcoming the major challenge of technology-limited crystal size and address the experimental needs to high spectral contents.

Ultrafast laser sources operating in the mid-infrared spectral region, where many molecules and their functional groups have vibrational and rotational resonances, are very important tools for studying novel regimes of non-linear optics and strong field physics. Next to optical parametric amplifiers (OPAs) based on ZnGeP 2 (ZGP) crystals which, on the one hand, allow generation of energetic ultrashort mid-IR pulses at a mJ energy level, but, on the other, rely on complex and immature holmium pump lasers [1], a difference frequency generation (DFG) in AGS or GaSe crystals starting from a single broadband near-infrared (NIR) pulse [2] or via cascaded two-stage parametric down-conversion [3] is an alternative way to generate mid-IR pulses above 4-μm wavelength. In the later case more conventional Ytterbium, Neodymium or Ti:Saphire lasers are used to pump the frequency conversion stages. The use of a longer-wavelength 1.03 μm Ytterbium laser as compared to Ti:Sapphire pump sources yields an improved phase matching bandwidth, lower group velocity miss-match, as well as a lack of three-photon absorption, which reduces detrimental photo-darkening in AGS.

We experimentally investigate dissociation of ${\mathrm{H}}_{2}^{+}$ in the (near-)zero proton energy region. Based on our experimental results we conclude that the underlying mechanism for the production of protons with such low energy in strong two-color and broadband laser fields is a stimulated Raman-scattering-based zero-photon-dissociation process, ${\mathrm{ZPD}}_{\text{stR}}$, taking place on the electronic ground state. It is furthermore shown that in the (near-)zero energy region the asymmetry in proton ejection induced by asymmetric laser fields is due to the interplay of several processes, rather than only pathway interferences, with vibrational trapping (or bond hardening) taking a key role.

Fiber-optic multioctave supercontinuum generation is a unique resource for ultrafast optical science, enabling ultrabroadband frequency-comb technologies and paving the way for the photonics of subcycle field wave forms. Extension of these methods to the midinfrared spectral range encounters numerous challenges, calling for radically new approaches in fiber optics and short-pulse generation technologies, as well as for closing the gaps in our understanding of optical nonlinearities in the midinfrared range. Here, we confront these challenges by showing that multioctave supercontinua spanning from the ultraviolet to the midinfrared range can be generated by shock-wave-coupled soliton self-compression of ultrashort midinfrared pulses in a gas-filled antiresonance-guiding hollow-core photonic-crystal fiber. Analysis of the fiber output spectra, measured within a broad range of gas pressures and input driver energies, shows that multioctave supercontinuum generation in this setting becomes possible due to soliton self-compression coupled to shock-wave pulse self-steepening, yielding extraordinarily short, sub-half-cycle field transients.

We demonstrate two-dimensional control over the chargelocalization in H2 dissociation using elliptically polarized laser pulses. The influences of the CEP and the laser phase at the instant of ionization are investigated.

In this Letter, we investigate the energy-scaling rules of hollow-core fiber (HCF)-based nonlinear pulse propagation and compression merged with high-energy Yb-laser technology, in a regime where the effects such as plasma disturbance, optical damages, and setup size become important limiting parameters. As a demonstration, 70 mJ 230 fs pulses from a high-energy Yb laser amplifier were compressed down to 40 mJ 25 fs by using a 2.8-m-long stretched HCF with a core diameter of 1 mm, resulting in a record peak power of 1.3 TW. This work presents a critical advance of a high-energy pulse (hundreds of mJ level) nonlinear interactions platform based on high energy sub-ps Yb technology with considerable applications, including driving intense THz, X-ray pulses, Wakefield acceleration, parametric wave mixing and ultraviolet generation, and tunable long-wavelength generation via enhanced Raman scattering.

Physical review / X Expanding access X 9(2), 021029 (2019). doi:10.1103/PhysRevX.9.021029, We report on experimental results in a new regime of relativistic light-matter interaction employing midinfrared (3.9-mu m wavelength) high-intensity femtosecond laser pulses. In the laser-generated plasma, electrons reach relativistic energies already for rather low intensities due to the fortunate lambda(2) scaling of the kinetic energy with the laser wavelength. The lower intensity efficiently suppresses optical field ionization and creation of the preplasma at the rising edge of the laser pulse, enabling an enhanced efficient vacuum heating of the plasma. The lower critical plasma density for long-wavelength radiation can be surmounted by using nanowires instead of flat targets. Numerical simulations, which are in a good agreement with experimental results, suggest that approximate to 80% of the incident laser energy has been absorbed resulting in a long-living, key-temperature, high-charge-state plasma with a density more than 3 orders of magnitude above the critical value. Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate., Published by APS, College Park, Md.

We present high flux table-top 220eV HHG source (>109 photons/s/1% bandwidth) driven directly by a

Burst-mode regenerative amplifiers permit substantial energy and average-power scaling of pump lasers. We demonstrate advantages of parametric burst-to-single-pulse up- and down-conversion in the generation of optical harmonics and in multicolor pumping of long-wave parametric amplifiers.

We experimentally achieve two-dimensional CEP-control of bond breaking in H2 dissociation with elliptically polarized pulses. The lab and molecular frame of reference proton ejection asymmetries are compared.

We report kinematically complete measurements of frustrated double ionization of argon atoms with a reaction microscope. Experimental results show much higher electron trapping probability during the strong-field double ionization than that during the single ionization.

We demonstrate kinematically complete measurements on frustrated double ionization of argon atoms in strong laser fields with a reaction microscope. We found that the electron trapping probability after strong field double ionization is much higher than that after strong field single ionization, especially in case of high laser intensity. The retrieved electron momentum distributions of frustrated double ionization show a clear transition from the nonsequential to the sequential regime, similar to those of strong field double ionization. The dependence of electron momentum width on the laser intensity further indicates that the second released electron has a dominant contribution to frustrated double ionization in the sequential regime.

We present laser-induced condensation as a method for detecting of ultra-low concentrations of volatile organic compounds featuring a detection threshold well below 1 ppb. The method was tested in lab scale experiments and compared with quantitative photo-ionization detection measurements. The method was shown to be sensitive to the laser excitation wavelength between 1.6’2.0 um range.

We report on, to the best of our knowledge, the first results of laser plasma wakefield acceleration driven by ultrashort mid-infrared (IR) laser pulses (λ=3.9 μm, 100 fs, 0.25 TW), which enable near- and above-critical density interactions with moderate-density gas jets. Relativistic electron acceleration up to ∼12 MeV occurs when the jet width exceeds the threshold scale length for relativistic self-focusing. We present scaling trends in the accelerated beam profiles, charge, and spectra, which are supported by particle-in-cell simulations and time-resolved images of the interaction. For similarly scaled conditions, we observe significant increases in the accelerated charge, compared to previous experiments with near-infrared (λ=800 nm) pulses.

We demonstrated high flux table-top 220eV HHG source (>109 photons/s/1% bandwidth) driven directly by a

Modern optical spectroscopy of the atmosphere at high altitudes relies primarily on the powerful and well-established LIDAR technique. A ground-based (or air−/space-borne) laser source is used for standoff linear measurements of the scattering characteristics of molecular, atomic, or particle species in the air in different scattering regimes (Rayleigh, Mie, spontaneous Raman). The incoherent nature of the scattered field measured in the backward direction sets practical limitation on the tracing distance, spatial resolution, and the species-dependent sensitivity threshold. The possibility of standoff initiation of a coherent source of backward-directed radiation in the sky would enable application of different methods of nonlinear optics, such as stimulated Raman scattering, CARS, etc., for the highly sensitive and highly selective spectroscopy of the atmosphere at high altitudes (Hemmer et al. PNAS 108, 3130, 2011; Yuan et al. Laser Phys. Lett. 8, 736, 2011) with (potentially) significantly larger detection range and finer spatial resolution. One of the possibilities to initiate such standoff coherent source of radiation in the atmosphere can be provided by achieving population inversion and laser generation in one of the two main atmospheric constituents, nitrogen (≈78% concentration) and oxygen (≈21% concentration). In principle, both gases allow population inversion and laser generation.

Optical physics and laser technologies are rapidly moving in the direction of exploring the midinfrared spectral range. New methods of mid-IR ultrashort pulse generation allow forming very short flashes of electromagnetic radiation with record high peak power for this range. The first experiments conducted with such systems make possible implementing new regimes of laser–matter interaction and shed light on unusual properties of the nonlinear-optical response of materials in the mid-IR spectral range.

We use orthogonally polarized two-color (OTC) laser pulses to separate quantum paths in the multiphoton ionization of Ar atoms. Our OTC pulses consist of 400 and 800 nm light at a relative intensity ratio of 10∶1. We find a hitherto unobserved interference in the photoelectron momentum distribution, which exhibits a strong dependence on the relative phase of the OTC pulse. Analysis of model calculations reveals that the interference is caused by quantum pathways from nonadjacent quarter cycles.

Pulse burst generation has important applications in material processing [1], seeding of free electron lasers [2] and coherent pulse stacking [3]. In particular, coherent pulse stacking technique allows further scaling of fiber and solid-state amplifiers by splitting the seed pulse into multiple replicas and stacking them into a single dominant pulse after the amplification. For this task, a pulse burst consisting of 4–90 pulses, with fully controllable amplitudes and phases is required. In this contribution we demonstrate pulse burst generation method based on the Vernier effect. The pulse burst with controllable amplitudes and phases is formed using a femtosecond oscillator and regenerative amplifier cavity that have slightly different round trip times. This operation mode can be used for the purposes of coherent pulse stacking, rapid material miroprocessing and rapid scan spectroscopy. Unlike in the case of pulse burst formation from a GHz repetition rate oscillator [4], the pulse burst formation using the Vernier effect allows very high repetition rate (much higher than the driving oscillator frequency) pulse burst formation with controllable amplitudes and phases.

High brightness XUV sources in the 140–170 eV spectral range are of great demand as this spectral range covers important magnetic and molecular materials, such as the N-edge of Gadolinium and Terbium (145 and 155 eV) and L 2 , 3 edge of sulphur [1]. High-order harmonic generation (HHG) allows performing ultrafast dynamics measurements with high temporal resolution in this spectral range because of extremely short, potentially sub-fs, temporal envelopes that are intrinsically synchronized to the near-IR driving laser pulses. We present HHG in the 170 eV range using 8.5 mJ post-compressed 20 fs 1.03 μm pulses from a 14 mJ Yb:CaF 2 laser chirped pulse amplifier operating at 0.5 kHz repetition rate.

On the Earth, oxygen molecules are generated mostly via the photosynthesis by green plants and algae from carbon dioxide and water: nCO 2 + nH 2 O light→ (CH 2 O)n + nO 2 [1]. Although, theoretical studies showed the possibility of O 2 production via CO 2 fragmentation [2] and experimental investigations achieved the detection of C+ (referring the creation of O 2 on the other side) [3], the direct observation of O2 formation did not yet happen to our knowledge. In this submission, we report the direct experimental observation of molecular oxygen formation from carbon dioxide molecule after being doubly ionized by a strong laser pulse.