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We demonstrate, using ethylene, that controlling lower-valence ionization and field-driven excitation dynamics with ultrashort, intense laser pulses allows steering fragmentation reactions of polyatomic molecules along a certain pathway towards a specific set of fragment ions.

We present recent achievements of single stage hollow-core fiber compression as HHG driving sources enabling: large compression factors (x22), highest output energies of 10mJ and operation at >100W of average power with generally >70% efficiency.

Photoelectron circular dichroism (PECD) is a process that leads to a forward-backward asymmetry (with respect to the laser propagation direction) in photoelectron distributions created upon interaction of a circularly or elliptically polarized laser with a chiral molecule. The PECD effect has been shown in a broad range of ionization mechanisms from direct photoionization through multi-photon regime, above-threshold ionization to the tunnel ionization [1]. The fact that the effects of chirality can be observed in the tunnel ionization regime opens up the possibility to connect this fundamental effect to strong-field science with prospects for studying and driving sublaser-cycle and attosecond phenomena connected to PECD [2]. However, a thorough understanding of PECD in the tunneling regime is of yet missing. In this study the effect of trajectory related parameters like electron energy or CEP on the PECD is investigated in order to determine the role of the scattering on the chiral potential.

We demonstrate, strong THz emission from two-color mid-infrared (3.9 μm) femtosecond laser filaments. The conversion efficiency approaches the percent level, at least one order of magnitude higher than the previously reported for plasma-based THz sources.

We visualize and control molecular dynamics taking place on intermediately populated states during different sequential double ionization pathways of CO2 using a sequence of two delayed laser pulses which exhibit different peak intensities. Measured yields of CO2 (2+) and of fragment pairs CO(+)/O(+) as a function of delay between the two pulses are weakly modulated by various vibronic dynamics taking place in CO2 (+). By Fourier analysis of the modulations we identify the dynamics and show that they can be assigned to merely two double ionization pathways. We demonstrate that by reversing the sequence of the two pulses it becomes possible to control the pathway which is taken across CO2 (+) towards the final state in CO2 (2+). A comparison between the yields of CO2 (2+) and CO(+)/O(+) reveals that the modulating vibronic dynamics oscillate out-of-phase with each other, thus opening up opportunities for strong-field fragmentation control on extended time scales.

The relative and absolute phases of femtosecond 1.03-µm pump, 1.55-µm signal and 3.09-µm idler pulses are stabilized paving the way for the generation of optimized driver-waveforms for higher-order-harmonic generation and electron impulsive momentum transfer.

We demonstrate a compact 20-Hz-repetition-rate mid-IR OPCPA for application in high-field science which operates at 3900 nm with a FWHM bandwidth of 600 nm delivering 6-mJ pulses compressed to 75±10 fs (< 6 optical cycles).

We report on experimental results in adaptive control over UV fluorescence from a femtosecond filament created in nitrogen. We demonstrate that an optimized sequence of femtosecond pulses can effectively align, selectively ionize and excite molecular nitrogen ions, resulting in stimulated amplification of a filament continuum seeded emission at 391 nm, 358 nm and 428 nm wavelengths.

Ultrafast lasers are of interest for applications in medicine, material processing [1] and as drivers for mid-IR optical parametric frequency converters [2]. Recently a sub-picosecond operation of Ho:YAG chirped pulse amplification (CPA) system was realized by extending the amplified pulse spectrum over two emission peaks centered at 2090 nm and 2096 nm [3], which required strong adaptive spectral shaping of the seed pulse to equalize spectral amplitude gain. In addition, dispersion management of the CPA was complicated due to the resonant spectral phase distortion and could only be accomplished by using an acousto-optic programmable dispersive filter (DAZZLER). The most intense emission line of Ho:YAG is centered at 2090 nm, and, without compensation of gain narrowing, supports amplified bandwidth of >1.5 nm corresponding to

Single 4-mJ supercontinuum filaments supporting 8-fs pulses are generated by focusing ultrashort pulses from a four-stage KTP-OPCPA into a noble-gas cell. The use of a 1.6-µm wavelength permits efficient energy scaling in the single-filament regime.

High-order harmonic generation (HHG) in crystalline bulk semiconductors originates from nonlinear intraband currents and interband transitions of the electrons driven by the strong mid-IR electric field. By reducing the size of a semiconductor crystal to nanoscale and making it smaller than the exciton Bohr radius in all three dimensions, quantum dots (QD) are formed with electronic structure distinctly different from the bulk. Spatial quantization of electron and hole motion leads to discrete energy levels instead of a band structure as in the bulk [1]. Therefore, QDs can be considered as artificial atoms and enable transition from atomic/molecular gases to bulk solids. It was predicted recently that the efficiency of HHG in these quantum confined structures is significantly enhanced in comparison to bulk, which is explained by a reduction of quantum diffusion as a result of the reduced amount of the available states [2]. Here, we report on experimental investigation of HHG by mid-IR femtosecond laser pulses in arrays of CdSe QDs as a function of the laser pulse intensity and polarization.

We demonstrate bright coherent X-ray supercontinua generated through fully phase-matched upconversion of mid-IR laser light into the keV spectral region. The ultrabroad bandwidths can support pulse durations of few attoseconds, scalable to zeptosecond time scales.

Energy scaling of μJ fs pulses from monolithic YDFAs is limited by pulse pedestal formation. We demonstrate a chirped-pulse fiber-amplifier that uses a newly developed dispersion compensating fiber stretcher matching the dispersion of a grating pair.

Energy saturation is achieved by seeding 1-kHz Yb:CaF 2 amplifier by μJ pulses from a monolithic Yb-fiber MOPA leading to 6-mJ output. The saturation is possible at any rep-rate with appropriate seed and optical loss levels.

We realize a multicolor, multi-cycle combination of commonly CEP-locked three waves from a single femtosecond OPA driven by a CEP-stable 7-mJ kHz Yb laser system and report HHG driving with individual and combined colors.

A novel type dual-core fiber (DCF), composed of two in-house synthesized glasses with high index contrast enabling significant anomalous dispersion [1] and cm range coupling length was optimized and studied in the near infrared. Following promising results of numerical simulations [2], we performed an experimental study in the 1500–1900 nm spectral range by using a tunable ultrafast laser source generating 70-fs pulses at a few μJ energy level. Continuous control of attenuation and polarization direction of the input field was ensured under separate excitation of a single fiber core, made of the low index glass with an effective mode area of 1.73 μm2 at 1500 nm. The dual-core cladding is made of high index glass including the 1.4-μm gap between the two cores. The series of camera pictures, imaging the output facet of the dual-core fiber at different input pulse energies, indicated nonlinear switching at distinct excitation conditions. A change in the dominancy of the output core of 32 mm long DCF was registered when 1700 nm, 70 fs pulses with increasing energies in range of 100–300 pJ (measured before in-coupling optics) were launched into the fiber. Output spectra were registered separately for the two cores, when the nonlinear switching was observed according to the camera registrations. The spectra were processed by plotting the curves representing a ratio R(λ) of the spectral intensities of the two cores: R(λ) = S t (λ)/S b (λ) − 1, where S t (λ) represent the spectra registered from the top core (dominant at low pulse energies) and S b (λ) are the spectra originating from the bottom core (Fig. 1a). In Fig. 1b, the excitation energy dependence of R(λ) is depicted, with positive and negative values representing the cases of the dominancy of the top and the bottom cores, respectively. The spectra reflect the similar energy dependence as the series of camera images, shown in the insets of Fig. 1b. In the case of low excitation energy, the spectral intensity ratio curves reveal a dominancy of the top core, while at higher pulse energies a majority of launched pulse energy is located in the bottom core. According to our knowledge, the presented simultaneously recorded spatial and spectral study is the first experimental demonstration of the nonlinear switching of a whole ultrashort pulse in a DCF in a solitonic propagation regime. Furthermore, in contrast to previously reported cases, the switching identified here is accompanied by rather moderate spectral broadening at pulse energies in the sub-nJ range.

We present a mode-locked 24 MHz Yb-doped fiber oscillator with a higher-order mode fiber for dispersion compensation. The oscillator operates in the net normal dispersion regime and generates clean 6 nJ pulses that can be dechirped down to 150 fs.

In this contribution we present the review of recent experimental and numerical investigations in a very new research field of nonlinear optics - interaction of high energy femtosecond mid-infrared laser pulses with matter. Following current developments in the field of optical parametric chirped pulse amplification (OPCPA) we have designed a sub-terawatt OPCPA laser system delivering 10 mJ, 80 fs pulses at the central wavelength of 3.9 μm [1]. Using this unique laser system, a large number of experiments on the interaction of high intensity mid-IR laser pulses with gases and solids were carried out. We show that even in the case of collimated beam propagation of high power mid-IR radiation in air is accompanied by highly nonlinear interaction with the gas which includes not only the lowest for centrosymmetric media third order nonlinearity but also higher fifth and seventh order contributions. Soft focusing of the mid-IR beam in gases leads to the generation of multiple optical harmonics (Fig. 1a) which opens new perspectives for nonlinear molecular spectroscopy. By increasing the gas pressure, filamentation of the mid-IR femtosecond laser pulses was demonstrated and investigated for the first time. In atomic gases like argon, an impressive super-continuum, spanning over three octaves, is generated (Fig. 1b). We show that this continuum builds-up via the efficient generation of low-order harmonics and cascaded four-wave mixing processes [2]. In molecular gases, efficient continuum generation further in the mid-IR spectral range is demonstrated (Fig. 1b), revealing important role of stimulated Raman scattering in filament dynamics.

Demonstration of an acousto-optic filter based infrared spectrometer featuring a 5 cm-1 resolution over more than 2 octaves (1 to 5 mm) is reported. © 2014 OSA.

Recently, selective fragmentation of polyatomic molecules using the carrier-envelope phase (CEP) of few-cycle ionizing laser pulses as the control parameter has been demonstrated. It was shown that the underlying mechanism is selective removal of specific (inner-valence shell) electrons, which puts the molecule into a dedicated dissociative electronic state from which the molecule then fragments along a desired pathway.

This work presents an experimental data obtained using a method from an atomic system, xenon, from which more different electron wavepackets including shake-up electron wavepackets are emitted, and where a spectral overlap of some of these wavepackets can be observed. The spectral overlap of the different emitted electronic wavepackets can eliminate the relative phase ambiguity, and thus allows for a more reliable measurement of the relative emission phase and delay. In the experimental data , the streaking of the 5p, 5s and 4d photoelectrons and the 5p-25d shake-up satellite from xenon is well resolved, and the Auger lines and corresponding sidebands are individually resolved.

Third- and fifth-harmonic generation by 80-fs pulses of 3.9-µm radiation enables efficient multiplex frequency conversion of ultrashort mid-IR pulses, metrology of high-order nonlinear-optical susceptibilities, and remote sensing of the atmosphere.

We present a unified picture of phase matching of high harmonic upconversion spanning the electromagnetic spectrum from the VUV to keV, combining both microscopic and macroscopic physics. We validate this picture with experiment and theory.

The development of intense, short pulse duration IR driver has been one of the most demanding challenges pursued in the field of ultrafast optics over the past decades, driven by a number of applications in strong field physics, such as coherent soft X-ray high-harmonic generation [1], incoherent hard X-ray generation [2], laser-plasma acceleration [3], filamentation for atmospheric remote sensing. Different post-compression approaches have been demonstrated to achieve intense TW peak power pulses. Hollow core fibre (HCF) compression is one of the most successful and straightforward approaches, delivering excellent spatial profile as compared to filamentation [5]. So far, the output pulse energy of HCF compression for state-of-the-art Ti:Sapphire lasers is limited only to few mJ [6] due to the limits in critical peak power. Recently, the compression of laser pulses to the record value of 13mJ has been demonstrated, but with an efficiency below 20% [6]. In this work, we demonstrated a new route for generation and highly efficient compression of TW pulses with multi-tens mJ level. The combination of the start of art, high energy Yb laser with stretched HCF waveguide technology enabled us to achieve the record value of 40mJ, 25fs.

Optical parametric chirped pulse amplification (OPCPA) is rapidly gaining ground as an approach to generate intense few-cycle pulses and reach IR wavelength ranges. However, the high OPA gain has its negative side: for a bell-shaped intensity profile of the pump pulse/beam the unsaturated gain varies exponentially with intensity, resulting in an effective temporal/spatial filter. Here we demonstrate shaping of high-energy broadband Yb amplifier pulses for the generation of a top-hat temporal profile that provides efficient pumping of an optical parametric amplifier. Phase-only modulation is applied by an acousto-optic programmable dispersion filter (AOPDF). Whereas the described technique requires minimal changes of the pump laser source, it brings significant advantages: 1) a substantial increase in the OPA conversion efficiency, 2) avoidance of OPCPA gain roll-off in the pump pulse wings, i.e. the temporal equivalent of spectral gain narrowing, 3) increase of the OPA signal and idler pulse contrast as compared to the standard use of bell-shaped pump pulses whereby the chirped seed pulse is purposely overlapped only with a narrow temporal section of the pump around the pulse peak and the temporal wings of the pump pulse are responsible for raising the ASE (superfluorescence) background outside the temporal overlap with the seed pulse.

We show that the interplay of electron removal and nuclear dynamics on the few femtosecond range, controlled by the duration of few-cycle laser pulses, determines the ratio of C2H43+ fragmentation into two respectively three moieties.

Dependence of ethylene double ionization on laser pulse duration and intensity was studied by Coulomb explosion imaging technique. It was found that multiple molecular orbitals are involved in the strong field double ionization of ethylene.

We study an effect of pulse duration of 2.09-pm laser on the laser de-bonding of gold from silicon wafers. Developed picosecond Ho:YAG laser with a simple dispersion management is found to be optimal for the process.

Recently, we have demonstrated multimillijoule optically synchronized and passively carrier-envelope-phase (CEP) stable optical parametric chirped-pulse amplification (OPCPA) at 1.5 µm [1]. Our four-stage infrared OPCPA system is based on a DPSS Yb-MOPA-driven (Pharos, Light Conversion Ltd.), CEP-stable front-end [2] and two successive power-amplification stages pumped by a 100-mJ 60-ps 20-Hz 1.064-µm Nd:YAG amplifier (Ekspla Ltd.), which is seeded from the Yb master oscillator [1]. In the amplification stages 2–4, we employ (nearly) collinear type-II phase matching in KTP/KTA reaching the pulse energy of ∼12.5 mJ at a 20-Hz repetition rate before a grating compressor.

We experimentally and theoretically demonstrated effective control of molecular ionization and fragmentation in strong laser fields with impulsive alignment of a molecule. Channel selective control over molecular fragmentation reactions can be realized.

Second-order autocorrelation of ultrashort laser pulses by using two-photon-induced photocurrent in semiconductors offers several advantages compared with traditionally employed combination of a second harmonic (SH) crystal and a photomultiplier tube. A low-priced commercially available photodiode [1] allows to overcome principal drawbacks of SH-based autocorrelation: limited phase-matching bandwidth and wavelength-dependent sensitivity of the light detector leading to a spectral filtering effect, pulse broadening due to crystal bulk dispersion, low conversion efficiency which decreases with increase of SH bandwidth, high cost and manufacturing problems associated with thin SH crystals. A significant advantage of incorporating a semiconductor photodiode into autocorrelation measurements is that the desired two-photon response and the transformation of light into electric current are combined into a single solid-state device. It has been shown recently that for the vast majority of practically realisable pulses the complete phase and amplitude information could be rapidly recovered from the autocorrelation trace and the pulse spectrum by means of a two-stage iterative algorithm [2]. In this contribution we demonstrate that due to absence of spectral filtering effect and high dynamic range of quadratic response to the incident intensity in a GaAsP photodiode [1], correct retrieval of temporal profile and phase from autocorrelation and spectrum can be achieved for ultrashort laser pulses with bandwidths as large as 130 nm and pulse energies as low as several pJ.

We demonstrate generation of continuously-tunable, narrowband THz pulses from phase- locked multi-millijoule femtosecond pulse bursts by optical rectification in a tilted-pulse-front setup. Experimental results indicate advances in both, femtosecond pulse burst and high-energy THz source technology.

Laser-induced electron excitation is a general process in strong laser field interactions with atoms and molecules. Previous studies revealed that up to 10% released electrons can be populated into high-lying excited states through electron trapping by the Coulomb potential of their parent ions [1,2]. In case of dissociative double ionization of molecules, one of the two liberated electrons may be trapped and localized to one of the ionic fragments. This process is referred as dissociative frustrated double ionization. So far, researches about dissociative frustrated double ionization mainly focused on homonuclear diatomic molecules, such as H 2 , D 2 and Ar 2 [3–5]. In this work, we investigate electron dynamics in dissociative frustrated double ionization of CO 2 . The non-symmetry two-body dissociation of CO 2 allows us to study not only the electron trapping process itself but also electron localization to different ionic fragments and the importance of such electron dynamics to laser-induced molecular dissociation.

We observed high-lying (n>238) Rydberg states which survived from strong field interaction of atoms and molecules with electron and ion coincidence detection. The high-lying Rydberg states are measured through field ionization with weak DC fields.

We demonstrate self-referenced wavefunction retrieval of a valence electron wavepacket during its creation by strong-field ionization with sub-10-attosecond precision, based on a distinct separation of interferences arising at different time-scales.

We present experimental and numerical investigation of multi-millijoule mid-IR supercontinuum generation by mid-IR femtosecond filaments in molecular gases. Drastic difference in spectra between atomic and molecular gases and crucial role of Raman scattering is demonstrated.

We demonstrate a broadband parametric amplifier at 6 μm driven by a femtosecond 2.1-μm Ho:YAG chirped-pulse amplifier. The scheme offers an all-in-one solution for seeding, pumping and CEP stabilization of few-cycle pulses in ZnGeP2 and similar mid-IR crystals.

Here we present a coherent pulse stacking approach for up-scaling energy of a solid-state femtosecond chirped pulse amplifier. We demonstrate pulse splitting into four replicas, amplification in a specially designed regenerative amplifier cavity, and phase-locked stacking into one dominant pulse. An optimized regenerative amplifier design for non-overlapping pulse train amplification is presented.

Measuring kinetic energy release (KER) of dissociating molecules can be used as a clock to time the ultrafast processes in laser-matter interactions [1]. At the few-cycle limit we use this technique, also known as molecular clock, as a slow time scale. In combination with a faster time scale — electron emission angle [2,3] — we can narrow down the intervals when the first and second ionization steps of a hydrogen molecule happen. We show that by additionally exploiting the dependence of the electron and ion momenta on CEP we can separate, with some restrictions, the first from the second emission step in the measured momentum distributions. This opens up studying the influence of the two-center molecular ion's Coulomb potential on the trajectories of the two emitted electrons separately, as we will show during our presentation.

In this contribution we report on the results of an experimental comparative study of high order harmonic generation (HHG) from strong mid-IR femtosecond laser pulses in two-dimensional (2D) materials consisting of a single layer. Beside their promising application in electronics and photonics, these materials allow to study microscopic light-condensed-matter interaction on the atomic scale. HHG in 2D materials, in comparison to a bulk, have several distinct qualitative features: single atom layer essentially excludes propagation effects and minimizes absorption, whereas weak charge screening results in significantly higher exciton binding energy. Here we report on comparative study of intensity and polarization dependence of HHG in polycrystalline single layers of MoS 2 and WS 2 .

Bright narrowly timed coherent UV emission from molecular Nitrogen cations is explained in terms of transient rotational alignment of the ground and excited electronic states leading to laser gain in absence of population inversion.

Summary form only given. The past three years in a row marked the 50th anniversaries of three significant innovations in optics: the invention of the laser; the discovery of the nonlinear upconversion of laser light in a spectral region where laser light has not been available; and the outlining of phase matching of this upconversion process - a recipe that makes the newly generated laser-like light bright and usable for applications. The same revolution that made it possible to create well directed beams in the visible region of the spectrum is only now happening for X-rays. Large-scale X-ray free electron lasers are promising to capture images of ultrafast dynamics in a single shot. An extreme version of nonlinear optics - high harmonic generation (HHG) - can also generate bright, coherent, beams of X-rays, with very short wavelengths 1.3 keV) that any light source, large or small scale, can generate to date. Such an ultrabroad spectral bandwidth can support X-ray pulses as short as 2.5 attoseconds and is scalable towards zeptosecond pulse durations. These unique, ultrafast, laser-like X-ray beams promise revolutionary new capabilities for understanding and controlling how the nanoworld works on its fundamental time and length scales. This understanding is relevant to the next generation data and energy storage devices, nano-electronics, bioimaging, and future medical diagnostics.

It is generally considered that rigorous measurement of the carrier envelope phase (CEP) requires a fieldsensitive nonlinear process such as optical field ionization by a particular half-cycle of a few-cycle field, which results in well-known spectro-temporal signatures in the cut-off regions of above-threshold ionization (ATI) [1] and higher-order harmonic generation (HHG) [2]. Conversely, methods based on multiple quantum pathway interference (QPI) [3,4] and techniques based on f-to-n·f spectral interferences of harmonic orders [5] are only appropriate for tracking the CEP drift, because they are based on direct or indirect observation of an interference term containing the information on a relative phase shift and do not provide access to the CEP value itself unless the nonlinear phase meter has been previously calibrated by a “time-domain-sensitive” technique. In this contribution we provide simple considerations that the absolute CEP calibration does not actually require access to the temporal envelope because, following from the Fourier phase shift theorem, the very same phase is the common phase offset of all spectral components of the pulse. Therefore, the challenge is to find a way to calibrate this common (spectral) phase via nonlinear spectral interference. This is a seemingly difficult task because for a field described by equation where ‘∼’ denotes the amplitude and phase of the Fourier transformed field, the frequency-independent phase offset ϕ 0 can be chosen arbitrarily, unless it is pegged to the phase delay of an optical fringe in the time domain. Nevertheless, the freedom of choosing ?0 as an arbitrary parameter is constrained if more than one spectral interference term of different nonlinearity orders is detected simultaneously. For example, the interference of 1st, 2nd, and 3rd-order nonlinear polarizations in the region of a mutual spectral overlap will yield three interference cross-terms that will depend on the cosines of two differential phases equation and equation. All these terms will form a peak of constructive interference at equation, which means that the phase offset is now defined. Therefore, unlike in the case of a single-term interference between the nearest harmonic orders, which reveals the common phase drift from one laser shot to another, simultaneous interference of several terms gives access to full phase calibration (within the cyclic ambiguity of 2πn.) We illustrate this multiple-order interference technique experimentally by measuring the interference of low-order optical harmonics of a mid-IR (λ 0 =3.9 µm) few-cycle-pulse generated in an OPCPA system with a free-running CEP phase. Because of the low carrier frequency in the mid-IR, it becomes straightforward to achieve spectral overlap of not just adjacent orders but also more distant harmonics (Fig.1a). As shown in Fig.1b, taken in the single-shot acquisition mode, spectrally broadened 5th, 7th and 9th harmonics can be brought into overlap around 500 nm resulting in a three-way interference that uniquely defines ϕ 0 . Figure 1c shows the distribution of ϕ 0 obtained from 1500 consecutive OPCPA shots.

We present two methods which exploit the two-dimensional spatial character of the emitted radiation. The first one is the production of attosecond pulse trains the use of which is equivalent to that of isolated attosecond pulses, provided polarization selective detection is applied. The second method uses the fact that the harmonics are emitted from a range of angles, which can significantly simplify orbital tomography of molecules and permits single-shot tomographic measurements.

The rapidly rising technology of optical parametric chirped pulse amplification (OPCPA) [1] offers unique advantages, among others, such as high broadband gain, including frequency ranges inaccessible to direct laser amplification, and efficient energy conversion using narrowband picosecond pump pulses. The perennial problems of OPCPA, significantly slowing down its development into a mainstream amplifier technology, are pump-seed pulse synchronization and generation of a frequency-detuned compressible broadband seed pulse for the optical parametric amplifier (OPA). Demonstrated approaches to the synchronization of pump pulse sources include active locking of two master oscillators [2], nonlinear frequency shifting in a photonics crystal fiber (PCF) [3] and simultaneous seeding of the pump pulse laser and the OPA from an ultrabroadband Ti:sapphire oscillator [4]. IR OP(CP)A systems with passive carrier envelope phase (CEP) stabilization were realized using a broadband difference-frequency-generation (DFG) seed produced via spectral broadening of the output of full-fledged Ti:sapphire [5,6] and Yb [7] CPA systems. In this contribution we demonstrate a drastically simplified seeding/synchronization approach based on an environmentally stable µJ-energy 200-fs 100-kHz Yb-doped fiber amplifier (YDFA) that generates a white light continuum in bulk sapphire, pumps a DFG OPA and provides an optical seed compatible with most Nd and Yb ∼1-µm pump pulse amplifiers (Fig. 1).

We demonstrate a compact 20 Hz repetition-rate mid-IR OPCPA system operating at a central wavelength of 3900 nm with the tail-to-tail spectrum extending over 600 nm and delivering 8 mJ pulses that are compressed to 83 fs (

Variation of the sign of dispersion in air in the vicinity of 3.6 pm [1] makes propagation and filamentation of mid-IR pulses extremely sensitive to the chirp, which allows to take control over the temporal pulse splitting, spectral broadening, energy losses and spatial profile. Here we report on filamentation of 30-mJ, 3.9-pm pulses produced by a hybrid OPA/OPCPA system [2]. Filamentation in ambient air is assisted by loose 7-m focusing and controlled by adjusting the chirp of the output of the OPCPA system.

A new, uniquely simple method for complete amplitude-phase characterization of broadband laser pulses is suggested and demonstrated experimentally. The spectral phase is determined from the fundamental and second-harmonic spectrogram of the interference between the test pulse and its chirped replica. The technique allows measuring pulses down to a single cycle in duration.

We demonstrate an interferometrically stable pulse multiplexing-amplification-recombination scheme for direct laser amplification of picosecond pulses. Switching from single pulse amplification to the burst mode increases extraction efficiency, gain in cw-pumped crystals and output energies.