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We report experiments on the direct observation of O2 formation from CO2 in strong laser fields. Our simulations and pump-probe measurements suggest that CO2 undergos bending motion during strong-field ionization which supports the O2 formation.

We report on the parametric generation of 100 fs sub-6-cycle 40 μJ pulses with the center wavelength at 5.2 μm using a 1 ps 2.1 μm pump laser and a dispersion management scheme based on bulk material. Our optically synchronized amplifier chain consists of a Ho:YAG chirped-pulse amplifier and white-light-seeded optical parametric amplifiers providing simultaneous passive carrier-envelope phase locking of three ultrashort longwave pulses at the pump, signal, and idler wavelengths corresponding, respectively, to 2.1, 3.5, and 5.2 μm. We also demonstrate bandwidth enhancement and efficient control over nonlinear spectral phase in the regime of cascaded χsup2/supnonlinearity in ZnGePsub2/sub.

Recent breakthroughs in ultrafast photonics in the mid-IR help understand complex interactions of high-intensity mid-IR field waveforms with matter, offer new approaches for x-ray generation, enable mid-IR laser filamentation in the atmosphere, facilitate lasing in filaments, give rise to unique regimes of laser-matter interactions, and reveal unexpected properties of materials in the mid-IR range.

Laser filamentation is understood to be self-channeling of intense ultrashort laser pulses achieved when the self-focusing because of the Kerr nonlinearity is balanced by ionization-induced defocusing. Here, we show that, right behind the ionized region of a laser filament, ultrashort laser pulses can couple into a much longer light channel, where a stable self-guiding spatial mode is sustained by the saturable self-focusing nonlinearity. In the limiting regime of negligibly low ionization, this post-filamentation beam dynamics converges to a large-scale beam self-trapping scenario known since the pioneering work on saturable self-focusing nonlinearities.

The removal of electrons from polyatomic molecules by ionization with intense, ultrashort laser pulses may trigger complex restructuring and fragmentation dynamics. Depending on the valence-shell from which the electrons are removed the molecular ion might be put into a certain dissociative or binding state by the ionization process. With control over the ionization process it might thus be possible to gain control over the subsequent restructuring and fragmentation process on a purely electronic level. Here we introduce two conceptually similar schemes that allow controlling the outcome of molecular restructuring and fragmentation processes in polyatomic molecules on sub-femtosecond time-scales. The first one involves recollision double ionization in few-cycle laser fields with a known carrier-envelope phase (CEP). We demonstrate experimentally CEP-control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene). As the recollision energy for a given intensity sensitively depends on the CEP, tuning of the CEP allows controlling the removal of inner-valence electrons and the controlled population of dissociative excited states. The second control scheme uses the strong preponderance of ionization from specific molecular orbitals to the alignment of the molecular axis with respect to the laser polarization direction for determining which valence level the electrons are removed from. We demonstrate experimental control over different two-body fragmentation and dissociation pathways from the cation and the dication of the acetylene molecule using the field-free alignment angle as a control knob. Finally, we turn from the demonstration of control schemes working at sub-femtosecond time-scales, for which the nuclear dynamics following the ionization are not essential, to the investigation of the coupled nuclear-electronic dynamics that in general take place for longer pulse durations. We explore experimentally the mechanism behind the surprisingly high charge states recently observed in the ionization of hydrocarbon molecules that have been explained by a multi-bond version of the well known enhanced-ionization (EI) mechanism taking place in parallel at many C–H bonds. Our experimental results are in agreement with the proposed multi-bond version of EI.

Quasifree field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecond-duration extreme ultaviolet emission in the process of high-harmonic generation. The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer and the efficient return of the launched electron trajectories. It has been predicted that these limits can be significantly exceeded by an appropriately ramped-up cycle shape [L. E. Chipperfield et al., Phys. Rev. Lett. 102, 063003 (2009)]. Here, we present an experimental realization of similar cycle-shaped waveforms and demonstrate control of the high-harmonic generation process on the single-atom quantum level via attosecond steering of the electron trajectories. With our improved optical cycles, we boost the field ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, 2 orders of magnitude enhancement of the generated extreme ultraviolet flux together with an increased spectral extension. This application, which is only one example of what can be achieved with cycle-shaped high-field light waves, has significant implications for attosecond spectroscopy and molecular self-probing.

Over the past decade intense laser fields with a single-cycle duration and even shorter, subcycle multicolour field transients have been generated and applied to drive attosecond phenomena in strong-field physics. Because of their extensive bandwidth, single-cycle fields cannot be emitted or amplified by laser sources directly and, as a rule, are produced by external pulse compression—a combination of nonlinear optical spectral broadening followed up by dispersion compensation. Here we demonstrate a simple robust driver for high-field applications based on this Kagome fibre approach that ensures pulse self-compression down to the ultimate single-cycle limit and provides phase-controlled pulses with up to a 100 μJ energy level, depending on the filling gas, pressure and the waveguide length., Single-cycle and sub-cycle field transients are typically generated by external pulse compression where a combination of nonlinear broadening followed up by dispersion compensation is used. Here, Balciunas et al. use self-compression in a Kagome fibre to generate phase-controlled single-cycle pulses.

Double ionization of neon with orthogonally polarized two-color (OTC) laser fields is investigated using coincidence momentum imaging. We show that the two-electron emission dynamics in nonsequential double ionization can be controlled by tuning the subcycle shape of the electric field of the OTC pulses. We demonstrate experimentally switching from correlated to anticorrelated two-electron emission, and control over the directionality of the two-electron emission. Simulations based on a semiclassical trajectory model qualitatively explain the experimental results by a subcycle dependence of the electron recollision time on the OTC field shape. © 2014 American Physical Society.

We investigate the possibility of using molecular alignment for controlling the relative probability of individual reaction pathways in polyatomic molecules initiated by electronic processes on the few-femtosecond time scale. Using acetylene as an example, it is shown that aligning the molecular axis with respect to the polarization direction of the ionizing laser pulse does not only allow us to enhance or suppress the overall fragmentation yield of a certain fragmentation channel but, more importantly, to determine the relative probability of individual reaction pathways starting from the same parent molecular ion. We show that the achieved control over dissociation or isomerization pathways along specific nuclear degrees of freedom is based on a controlled population of associated excited dissociative electronic states in the molecular ion due to relatively enhanced ionization contributions from inner valence orbitals.

The two-dimensional sub-cycle-time to electron momentum mapping provided by orthogonal two-color laser fields is applied to photoelectron spectroscopy. Using neon as the example we gain experimental access to the dynamics of emitted electron wave packets in electron momenta spectra measured by coincidence momentum imaging. We demonstrate the opportunities provided by this time-to-momentum mapping by investigating the influence of the parent ion on the emitted electrons on laser-sub-cycle times. It is found that depending on their sub-cycle birth time the trajectories of photoelectrons are affected differently by the ion's Coulomb field.

We experimentally investigate the ionization mechanism behind the formation of remarkably high charge states observed in the laser-pulse-induced fragmentation of different hydrocarbon molecules by Roither et al. [Phys. Rev. Lett. 106, 163001 (2011)], who suggested enhanced ionization occurring at multiple C-H bonds as the underlying ionization mechanism. Using multiparticle coincidence momentum imaging we measure the yield of multiply charged fragmenting ethylene and acetylene molecules at several intensities and pulse durations ranging from the few-cycle regime to 25 fs. We observe, at constant intensity, a strong increase of the proton energy with increasing laser pulse duration. It is shown that this is caused by a strong increase in the yield of highly charged parent molecular ions with pulse duration. Based on experimental evidence we explain this increase by the necessary population of precursor states in the parent ion that feature fast C-H stretch dynamics to the critical internuclear distance, where efficient ionization via enhanced ionization takes place. For increasing pulse duration these precursor ionic states are more efficiently populated, which leads in turn to a higher enhanced-ionization probability for longer pulses. Our work provides experimental evidence for the existence of a multiple-bond version of enhanced ionization in polyatomic molecules.

Filamentation of femtosecond pulses in transparent solids with anomalous group-velocity dispersion is investigated for a broad range of the peak powers. Solitonic self-compression of multi-millijoule mid-IR pulses is achieved using a 1.5-mm-thick CaF2 plate.

A novel frequency synthesis scheme and feed-forward approach is applied directly for stabilization of a sub-MHz frequency comb from a Yb:KGW CPA laser not only reduces the phase noise but also greatly simplifies the stabilization setup.

Strong narrow-band coherent emission lines of the \(\mathrm{B}^{2} \varSigma_{\mathrm{u}} ^{+} \mbox{--} \mathrm{X}^{2} \varSigma_{\mathrm{g}} ^{+}\) transition of \(\mathrm{N}_{2} ^{+}\) in air and the A2 Π u–X2 Π g transition of \(\mathrm{CO}_{2} ^{+}\) in CO2 gas are observed from filaments generated by intense infrared femtosecond laser pulses (1150–2000 nm

We experimentally demonstrated control of chemical bond break of ethylene in intense laser fields with employing both electronic dynamics and nuclear vibrational dynamics.

Powerful 90 fs pulses at a midinfrared wavelength of l=3.9mm drive a femtosecond hard x-ray source (Cu Ka: hbaro=8.05 keV). Up to 10^8 X-ray photons/pulse are generated which is twice as many as with 800 nm drivers of a 100 times higher peak intensity.

110-mJ sub 200-fs pulses are generated at the repetition rate of 50 Hz in a cryogenically cooled multipass Yb:CaF2 amplifier. The amplifier output is scalable in both energy and repetition rate.

Advanced Solid State Lasers (ASSL) © OSA 2014 Fig. 1: Rayleigh range for Optical pumping with low brightness (left) and High brightness (right) Abstract: The exceptional brightness of an Yb fiber pump laser allows to measure unexpectedly high gain in Yb amplifiers, achieve pure Kerr-lens mode-locking and demonstrate the shortest fs pulse ever generated with an Yb oscillator.

We demonstrate a simple solution to a seemingly deadlocked problem of efficient nonlinear pulse compression designed to act on the whole beam, yield the ultimate single-cycle duration, and sustain pulse energy on the 100 µJ level which, given the single-cycle duration of the produced waveform, is immediately suited for a variety of challenges in high-field applications, including high-order harmonic generation.

We demonstrate sub-cycle gigawatt peak power pulses self-compressed by optical shock waves in a simple manner based on gas-filled kagome hollow-core photonic crystal fiber.

Stimulated Raman scattering combined with ASE lasing from nitrogen molecules in a femtosecond filament is shown to provide a highly directional chemical-bond-sensitive coherent readout in the direction opposite to that of the driver laser beams.

Four-wave-mixing-based amplification in a gas-filled hollow fiber operated in the regime of a narrow, intensity-controlled time gate delivers tunable compressed mid-IR pulses with energies >10 μJ suggesting a promising source for applications in time-resolved IR spectroscopy.

Self-compressed single-cycle 1.7-µm with energies up to 100 µJ from a Kagome gas-filled waveguide are coupled into a high-harmonic-generation cell to efficiently produce coherent XUV below 60 eV in a uniquely simple setup.

We report on a diode-pumped cryogenically cooled bulk Yb:CaF2 12-pass amplifier delivering 110-mJ, 1030-nm pulses at a 50-Hz repetition rate. The pulses have a spectral bandwidth of 13 nm and are compressed to 225 fs pulse duration in a double reflection grating based compressor having a transmission efficiency of >90%. The measured output beam quality is M2

We report a 5-fold acceleration of the backward intermolecular electron transfer between a rhodamine 800 dye molecule and N,N-dimethylaniline (DMA). This effect results from the controlled variation of the solvent dynamical properties in binary mixtures of DMA and acetonitrile. The observed acceleration reflects the competition between solvent-controlled and nonadiabatic electron transfer in the limit of barrierless reaction. A linear dependence of the electron-transfer time on the longitudinal relaxation time, as predicted by the outer sphere electron-transfer model by Rips and Jortner [Rips, I.; Jortner, J. J. Chem. Phys. 1987, 87, 2090.], is clearly observed.

We propose a new criterion for the assessment of ultrashort pulse reconstruction quality. Our idea is based on the use of a two-dimensional Wigner representation of the electric field. This allows introducing a single measure to represent the quality of both phase and amplitude retrieval. The new criterion is employed to examine two contemporary pulse characterization techniques: FROG (Frequency Resolved Optical Gating) and SPIDER (Spectral Interferometry for Direct Electric-field Reconstruction). For SPIDER, the influence of reference pulse stretching on the quality of phase extraction is investigated.Next, we ascertain the limitations in the use of a Fabri-Perrot etalon in the SPIDER apparatus for producing delayed pulse replicas. For the FROG technique we examine the impact of the doubling crystal orientation on the quality of the amplitude-phase retrieval of sub-5-fs pulses. The introduced criterion is also applied to study the respective sensitivity of FROG and SPIDER to the limited phase-matching bandwidth of the non-linear medium and detector noise.

Employing photon echo techniques, we investigate the early relaxation dynamics of the equilibrated hydrated electron within the first 200 fs upon photoexcitation. The use of 5-fs laser pulses provided unprecedented temporal resolution of our measurements. We show that even for extremely short pulse durations the signals obtained in photon echo spectroscopy, can be described in the conventional way, provided care is taken of the spectral filtering effect and experimental beam arrangement. We next conclude that the absorption spectrum of the hydrated electrons is primarily homogeneously broadened. The comparison of two pulse photon echo experiments on pure water and on hydrated electrons allows us to measure the pure dephasing time of ∼1.6 fs. The line shape of the absorption spectrum is described excellently by an extended Lorentzian contour with a spectral width fully determined by the pure dephasing time. From the polarization-dependent transient grating experiments we establish that the polarization ani...

Hydrated-electron dynamics is examined by frequency-resolved pump-probe experiments using pulses of 13 fs centered at 780 nm. A recurrence at ~40 fs signifies a strong coupling of the electronic transition to underdamped solvent motions. Wave packet dynamics launched by the pump pulse produces an ultrafast red-shift of the electronic transition by approximately 6500 cm-1. Gross features of the pump-probe experiments are analyzed using a two-level system.

Photon echo and resonant transient grating experiments on the equilibrated aqueous electron are reported, using 15 fs excitation pulses. Both experiments exhibit clear signatures of wave packet dynamics, attributed to an underdamped solvent motion of about $850\mathrm{cm}{}^{\ensuremath{-}1}$. Experiments in ${D}_{2}\mathrm{O}$ expose the librational nature of this mode. The overall agreement between experiment and quantum-molecular dynamics simulations is good, except for the initial oscillatory dynamics, which have not been predicted.

We report the observation of forward-propagating UV stimulated emission in atmospheric nitrogen pumped, at a standoff distance of 2.6 m, by an energetic laser pulse at a wavelength of 1053 nm and with the duration in the picosecond range. The generated optical gain at 337 nm is seeded by third harmonic of the pump beam. This demonstration is an important step towards the development of techniques for standoff optical sensing in the atmosphere.

Summary form only given. Yb-doped femtosecond fiber chirped pulse amplifiers (FCPAs) are extremely attractive to replace their solid-state counterparts in when it comes to robustness and ease of operation. However, in most Yb-doped FCPAs delivering high-energy output pulses the advantages of robustness and ease of operation are forfeited since free-space optical components are used to stretch and compress the pulses. The main bottleneck to obtain fiber based stretching and compression is to match the dispersion of the stretcher and compressor. Recent advances have yielded good results with fiber-based stretchers and free space compressors [1-3]. However, the free space compressors require rather large distances between the compressor elements, which reduces the robustness of the system. On the other hand, while anomalous dispersion solid-core fibers have been available, e.g. photonic crystal fibers [4] or higher-order mode fibers [5], such fibers are not suitable as compressor fibers for pulse energies exceeding several nJ, because of the high nonlinearities experienced in the solid core. The use of a hollow-core (HC) photonic bandgap fiber (PBF) can alleviate this problem, an approach that was demonstrated in Er-doped fiber lasers [6]. Short lengths of HC PBF have been used to compress pulses from Yb-fiber oscillators [7], but not yet in Yb-FCPA. Here, we present a μJ-level femtosecond Yb-FCPA that uses a dispersion-matched dispersion compensating fiber (DCF) stretcher [8] and a HC PBF compressor.The Yb-fiber laser system consists of an all normal dispersion Yb-fiber oscillator operating at 40 MHz repetition rate, two PM single mode fiber (SMF) preamplifiers and a PM large mode area (LMA) fiber amplifier. The pulses from the oscillator are stretched in a hybrid fiber-pulse stretcher that consists of 8 m of ClearLite 980 fiber followed by 5 m of DCF. After amplification, the pulses are compressed in 25 m of HC PBF. The measured group delay dispersion of the compressor at 1060 nm is about -2 ps2 resulting in a stretched pulse duration of ~30 ps. Because the effective area of the DCF is rather small (~6.7 μm2), the seed energy was limited to 0.2 nJ and the pulses were pre-stretched in the ClearLite 980 fiber in order to minimize the nonlinearities in the DCF stretcher. After the first amplification stage a fiber pigtailed acousto-optic modulator (AOM) was used to reduce the repetition rate to 2 MHz. In preliminary test experiments, we used a large mode area (LMA) power amplifier as a final amplification stage. The LMA has a core diameter of 30 μm, corresponding to a mode field area of ~625 μm2. Free space coupling and mode conversion was used to couple the amplified pulses into the HC PBF. The output pulses from the compressor were characterized by second harmonic frequency resolved optical gating (SH FROG). The shortest compressed pulse duration was achieved by optimizing the fiber length of the pre-stretcher. Figure 1 shows the retrieved pulse with a duration of 220 fs and its spectral phase for a pulse energy of 250 nJ. At the moment experiments using a power amplification stage utilizing a single mode fiber with 10 μm core diameter are underway. This will allow us to directly couple (by fusion-splicing) the light from the power amplifier to the HC PBF. The results from these experiments will be presented at the conference. We thank K. Jespersen and L. Gruner-Nielsen from OFS Denmark for their support, providing the fiber stretcher and measuring the stretcher and compressor dispersion.

Summary form only given. The gain bandwidth of Ho-doped crystals is sufficiently broad to support femtosecond operation, which would allow pumping of ultrashort-pulse mid-IR optical parametric amplifiers (OPAs) [1,2] and, upon reaching adequate peak powers, eye-safe filamentation in the >2-μm transparency window of the atmosphere. In this contribution, we report on, to our knowledge, the first demonstration of a femtosecond cw-pumped Ho:YAG chirped pulse amplifier (CPA) system operating at room temperature and producing broadband pulses supporting ~440 fs pulse durations at the energy level of up to 3 mJ at a 5-kHz repetition rate. The CPA system consists of a seed source, stretcher, Ho:YAG regenerative amplifier (RA) and compressor. The RA is based on an AR coated Ho:YAG rod end-pumped by 70-W Tm fiber laser (IPG Photonics). Due to the unavailability of Faraday rotators capable to withstand high peak intensities, we have designed a ring-shaped RA cavity, in which the injection and output beam ports are separated and the amplification of the injected beam is unidirectional. Because of the ring-cavity design, the Pockels cell (RTP) is operated in the λ/2 regime.The RA is seeded with 2.1-μm pulses generated in a white-light-seeded two-stage OPA based on type I BBO and type II KTA crystals. In early experiments the OPA was pumped by a commercial 0.4-mJ Yb:KGW DPSSL system. More recently, we have demonstrated that the 10-μJ, 190-fs pulses from our monolithic Yb fiber amplifier [3] are sufficient to generate the 0.7-μJ, 260-fs pulses at 2.1 μm in the OPA. The output of the OPA is directed to the positive dispersion Offner stretcher. When seeded with an unshaped spectrum at low pump powers, the RA generates narrowband, 2.4-nm FWHM, pulses centered at around 2090 nm. For higher pump powers, a weaker second band appears which is centered at the 2097 nm gain peak of Ho:YAG (Fig.1a). In order to compensate for gain narrowing in the RA cavity, we have installed a simple mechanical amplitude shaper in the Fourier plane of the stretcher. The shaping, although at a cost of 85% of the seed pulse energy, results in a substantially broadened, > 12 nm FWHM, amplified spectrum. The amplified pulses are recompressed with a grating compressor based on a 600 l/mm grating pair. The pulse duration inferred from frequency-resolved optical gating (FROG) is 530 fs (Fig. 1b), whereas the calculated spectrum-limited pulse duration is ~440 fs. The output of the RA exhibits a rather good spatial profile (inset in Fig.1d) with the beam quality factor M2=1.3. In the ring cavity, picosecond pulses propagate only in one direction, while the Q-switched radiation develops in both directions, which allows monitoring of the Q-switched background in the direction opposite to the seed propagation and, consequently, evaluating the contrast of the amplified picosecond pulses (Fig. 1c). Measurements reveal that for achieving high contrast a strong seed is essential. Measurements using the full available pump power, presented in Fig. 1d, have proven the scalability of the RA toward a multi-mJ operation. The saturation of the output energy seen in Fig. 1d is due to worsened pump beam quality at high pump powers.

Ytterbium doped fiber chirped pulse amplifiers (FCPAs) are attractive sources to replace their solid-state counterparts in applications like micromachining, for example for manufacturing photonic devices in bulk glass substrates. For such applications, a pulse duration of several tens of fs is often considered to be optimal so that one can write features with a sub-wavelength precision. However, the shortest attainable pulse duration from μJ -level Yb-doped FCPAs is limited to ~160 fs because of gain narrowing in such systems. Therefore, spectral broadening of the output of the Yb-doped FCPA is needed to allow recompression to several tens of fs. Many methods to obtain spectral broadening are rather lossy (e.g. white light generation in a bulk substrate followed by spatial filtering) or produce pulses that are difficult to compress (e.g. spectral broadening in highly nonlinear or photonic crystal fibers). In a bid to obtain well-compressible pulses with a high energy-efficiency, we couple the compressed output pulses from our monolithic Yb-doped FCPA into a 20 cm long piece of polarization maintaining (PM) large mode area (LMA) fiber.

Here we demonstrate a direct method to stabilize the CEP of an Yb:KGW MOP A laser system, resulting in sub-100 mrad stability. To the best of our knowledge, this value surpasses most previously measured CEP jitter for Ti:sapphire CPA systems as well as any previous attempt to stabilize Yb-based oscillator and amplifier systems. This is a crucial step in widening the utility of amplifier femtosecond Yb sources, which are easily scalable in average power and pulse energy but could not be meaningfully employed in attosecond optics until now, given the difficulty of their CEP control.

We present first results of simultaneous attosecond streaking measurements of shake-up electrons and Auger electrons emitted from xenon. We extract relative photo-emission delays for electrons emitted from the 4d, 5s and 5p subshell, as well as for the 5p −2 5d correlation satellite (shake-up electrons).

We observed the filamentation of mid-infrared ultrashort laser pulses (3.9 μm, 80 fs) in molecular gases. It efficiently generates a broadband supercontinuum over two octaves in the 2.5–6 μm spectral range, with a red-shift up to 500 nm due to the Raman effect, which dominates over the blue shift induced by self-steepening and the gas ionization. As a result, the conversion efficiency into the Stokes region (4.3–6 μm) 65% is demonstrated.

We present a mode-locked Yb-fiber oscillator with higher-order-mode fiber operating in the normal-dispersion regime, delivering 7.2 nJ pulses compressible down to 62 fs. Theoretical predictions reveal an operation regime with highest pulse fidelity.

Angstrom and attosecond control of free electron wave packets is one of the pinnacles of attosecond science. Orthogonally polarized two-color (OTC) laser fields allow to control the motion of field-ionizing electronic wave packets both in time and space[1]. In OTC pulses time and space are connected and thus an attosecond time scale is established in the polarization plane for both the emitted and the re-colliding wave packets[2,3]. © 2013 IEEE., 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, 12 May 2013 through 16 May 2013, Munich

We describe several implementations of multi-color shaping of the optical cycles of intense laser pulses, which allow direct control of strong-field dynamics and have important implications for many of their applications. After reviewing a purely optical detection method for attosecond tunneling ionization bursts in gases and transparent solids, we experimentally demonstrate the steering of the induced tunneling electron current via the optical cycle shape of the driving laser pulses. We describe two examples: the control of the electron emission direction in above-threshold ionization, and a new scheme for the efficient generation of tunable THz radiation. Finally, we also describe an application of shaped optical cycles to the generation of ultrafast XUV pulses and present first results on steering of the returning electron trajectories in HHG.

We review the status in the development of intense mid-IR ultrashort pulse sources and highlight several applications in extreme non-linear optics. Scalability of average power, pulse energy, duration and wavelength will be addressed. Article not available.

We present experimental and numerical investigation of a new filamentation regime of mid-infrared femtosecond pulses in solids. Efficient emission of dispersive waves without fundamental spectrum broadening and continuum generation is observed in this regime.

Filamentation-assisted pulse compression in the gas phase is shown to enable the generation of subterawatt few-cycle pulses in the mid-infrared (mid-IR). With both spatial modulation instabilities and excessive plasma scattering of the mid-IR beam prevented through a careful choice of gas pressure and input peak power, providing a single-filament regime of pulse propagation, peak powers as high as 0.3 TW are achieved in a truly single-mode, almost diffraction-limited 35 fs output at a central wavelength of 4 μm. Applications in molecular spectroscopy, semiconductor electronics, high-field physics, standoff detection, and innovative x-ray sources are envisaged.

We present a concept of a white-light-seeded-cascaded mid-infrared (mid-IR) optical parametric amplifier (OPA) based on potassium titanyl arsenate and zinc germanium phosphate nonlinear optical crystals and producing 100-μJ level pulses centered at 5300 nm, with the spectrum supporting four-optical-cycle pulse duration. The OPA is pumped by 2090-nm master oscillator/power amplifier based on a Tm,Ho-fiber laser seeder and a Ho:YAG regenerative amplifier delivering 3.8-mJ sub-ps pulses at a repetition rate of 1 kHz. We validate that output parameters of the OPA are scalable by means of increasing the pulse energy, decreasing the pulse duration and redshifting the central wavelength.

We report an experimental proof and full characterization of laser generation in molecular nitrogen in an argon-nitrogen gas mixture remotely excited at a distance above 2 m in a femtosecond laser filament. Filamentation experiments performed with near-infrared, 1-\ensuremath{\mu}m-wavelength and midinfrared, 4-\ensuremath{\mu}m-wavelength short-pulse laser sources show that mid-IR laser pulses enable radical enhancement of filamentation-assisted lasing by N${}_{2}$ molecules. Energies as high as 3.5 \ensuremath{\mu}J are achieved for the 337- and 357-nm laser pulses generated through the second-positive-band transitions of N${}_{2}$, corresponding to a 0.5$%$ total conversion efficiency from midinfrared laser energy to the energy of UV lasing.

Using a 3.9µm driving laser focused into a high-pressure gas-filled waveguide, we generate bright, phase matched, fully spatially coherent high harmonic beams in the keV region for the first time.

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wavepackets, whose recollision energy in few-cycle ionizing laser pulses strongly depends on the optical waveform. Our work demonstrates an efficient and selective way of pre-determining fragmentation and isomerization reactions in polyatomic molecules on sub-femtosecond time-scales.

We demonstrate shaping of high-energy broadband Yb amplifier pulses for the generation of a (sub)picosecond top-hat temporal pulse profile that significantly improves pumping efficiency of an optical parametric amplifier (OPA). Phase-only modulation is applied by an acousto-optic programmable dispersion filter. This simple scheme is scalable to a high average power due to a relatively broad bandwidth of the Yb:CaF(2) gain medium used in the amplifier that supports a sub-150-fs transform-limited pulse duration. Additionally we show that OPA seeding with supercontinuum remains possible because top-hat-shaped pulses passed through a glass block recompress to ≈200 fs with minimum satellite production.