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We present post-compression of 22-mJ 90-fs pulses at 3.9 µm via spectralbroadening in a noble-gas-filled 1 mm core diameter 3 meter long capillary with over 60% throughput and recompressed in a bulk BaF2 plate down to 33 fs.

A novel broadband 6-um parametric amplifier driven by a fs 2.1-um Ho:YAG chirped-pulse amplifier is demonstrated. It offers an all-in-one solution for seeding, pumping, and CEP-stabilization of few-cycle pulses in ZnGeP2 and similar mid-IR crystals.

Using a double-pulse scheme we visualize and control molecular dynamics taking place on intermediately populated states during different sequential double ionization pathways of CO2. Exchanging the pulse-sequence can almost completely switch the pathway.

We report on the design and performance of a cryogenic cw-pumped Yb:CaF2 CPA producing 30-mJ, 200-fs pulses. Operation in the repetition frequency range of 0.5—10 kHz is demonstrated, sustaining >15 W average power.

Intense pulses at low terahertz (THz) frequencies of 0.1–2 THz are an enabling tool for constructing compact particle accelerators and for strong-field control of matter. Optical rectification in lithium niobate provided sub-mJ THz pulse energies, but it is challenging to increase it further. Semiconductor sources suffered from low efficiency. Here, a semiconductor (ZnTe) THz source is demonstrated, collinearly pumped at an infrared wavelength beyond the three-photon absorption edge and utilizing a contact grating for tilting the pump-pulse front. Suppression of free-carrier absorption at THz frequencies in this way resulted in 0.3% THz generation efficiency, two orders of magnitude higher than reported previously from ZnTe. Scaling the THz energy to the mJ level is possible simply by increasing the pumped area. This unique THz source with excellent focusability, pumped by novel, efficient infrared sources, opens up new perspectives for THz high-field applications.

We demonstrate control over the localization of high-lying Rydberg wave packets in argon atoms with phase-locked orthogonally polarized two-color laser fields. With a reaction microscope, we measure ionization signals of high-lying Rydberg states induced by a weak dc field and blackbody radiation as a function of the relative phase between the two-color fields. We find that the dc-field-ionization yield of high-lying Rydberg argon atoms oscillates with the relative two-color phase with a period of $2\ensuremath{\pi}$ while the photoionization signal by blackbody radiation shows a period of $\ensuremath{\pi}$. Accompanying simulations show that these observations are a clear signature of the asymmetric localization of electrons recaptured into very elongated (low angular momentum) high-lying Rydberg states after conclusion of the laser pulse. Our findings thus open an effective pathway to control the localization of high-lying Rydberg wave packets.

We report self-action of 0.5-TW peak-power few-cycle 4-um pulses in air and bulk dielectrics that is strikingly different compared to the case of near-IR drivers. An example of scalable nonlinear self-compression of 20-mJ is highlighted.

We report a novel source for mid-IR nonlinear spectroscopy in the molecular fingerprint spectral range based on a white-light-seeded ZnGeP2 OPA tunable in the 3-4.2 µm (signal) and 4.2-7 µm (idler) range and pumped by a 1-ps 2090-nm Ho:YAG laser.

We report on 3.2 μm pulse post-compression via spectral broadening in hollow core capillary filled with noble gas. The mid-IR input pulses are generated in a femtosecond OPA based on KTA crystals, which delivers 6 mJ, 80 fs, 3.2 μm CEP-stable idler pulses. Pulses were spectrally broadened in a 3 meter long differentially pumped hollow-core capillary with ∼50% transmission and a statically filled 50 cm capillary. The spectrally broadened pulses were compressed in a CaF2 bulk material down to 31 fs and pulse bandwidth supporting Fourier-limited pulse duration below 15 fs were obtained, which corresponds to sub-two cycle pulse at this wavelength.

We demonstrate the detection of high-lying Rydberg states produced in strong laser fields with coincidence spectroscopy. Electron emission after the interaction of strong laser pulses with atoms and molecules is measured together with the parent ions in coincidence measurements. These electrons originate from high-lying Rydberg states with quantum numbers from $n\ensuremath{\sim}20$ up to $n\ensuremath{\lesssim}120$ formed by frustrated field ionization. Ionization rates are retrieved from the measured ionization signal of these Rydberg states. Simulations show that both tunneling ionization by a weak dc field and photoionization by blackbody radiation contribute to delayed electron emission on the nano- to microsecond scale. Furthermore, the dependence of the Rydberg-state production on the ellipticity of the driving laser field indicates that such high-lying Rydberg states are populated through electron recapture. The present experiment provides detailed quantitative information on Rydberg production in strong-field interaction.

The effect of intensity, duration, and polarization of ultrashort laser pulses (795 nm, 40-100 fs, and 0.15-1.5 × 10(15) W/cm(2)) on the hydrogen migration in methanol is systematically investigated using Coulomb explosion coincidence momentum imaging. The ratio of the ion yield obtained for the migration pathway CH(3)OH(2+) → CH(2)(+) + OH(2)(+) with respect to the sum of the yields obtained for the migration pathway and for the nonmigration pathway CH(3)OH(2+) → CH(3)(+) + OH(+) exhibits a small (10-20%) but clear dependence on laser pulse properties, that is, the ratio decreases as the laser peak intensity increases but increases when the pulse duration increases as well as when the laser polarization is changed from linear to circular.

We discuss nonlinearity management versus energy scalability and compressibility in a three-stage monolithic 100-kHz repetition rate Yb-fiber amplifier designed as a driver source for the generation and tunable parametric amplification of a carrier-envelope phase stable white-light supercontinuum.

The cascaded Auger decay following ionization or excitation with 94 eV soft-X-ray pulses from the 3d subshell in krypton has been energy-and-time-resolved for the first time. The decay time of the 4s −14p −2 nl → 4p −3 + e and/or 4s −14p −1 nl → 4p −2 + e transition is measured to be 74 ± 20 fs. Furthermore, our data shows that the electrons with a kinetic energy around 25 eV (generally assigned as 3d −1 np → 4s −2 n′p + e) emitted after core excitation are emitted in a second decay step suggesting an alternative assignment of the form 4s −2 np 4p −2 + e.

One of the most advanced frontiers of ultrafast optics is the control of carrier-envelope phase (CEP) ϕ of light pulses, which enables the generation of optical waveforms with reproducible electric field profile. Such control is important for pulses with few-optical-cycle duration, for which a CEP variation produces a strong change in the waveform, so that strongly nonlinear optical phenomena, such as multiphoton absorption, above-threshold ionization and high-harmonic generation become CEP-dependent. In particular, CEP control is the prerequisite for the production of isolated attosecond pulses. Standard laser systems generate pulses that are CEP unstable; the CEP can be stabilized using either active or passive methods. Passive, all-optical schemes rely on difference-frequency generation (DFG) between two pulses sharing the same CEP: in this process the phases of the two pulses add up with opposite signs, leading to cancellation of the shot-to-shot CEP fluctuations. This paper presents an overview of passive CEP stabilization schemes, starting from the basic concepts and progressing to the details of the practical implementations of the idea. The passive approach allows the generation of CEP-controlled few-optical-cycle pulses covering a very broad range of parameters in terms of carrier frequency (from visible to mid-IR), energy (up to several mJs) and repetition rate (up to hundreds of kHz)

Water is the major natural resource that enables life on our planet. Rapid detection of water pollution that occurs due to both human activity and natural cataclysms is imperative for environmental protection. Analytical chemistry–based techniques are generally not suitable for rapid monitoring because they involve collection of water samples and analysis in a laboratory. Laser‐based approaches such as laser‐induced breakdown spectroscopy (LIBS) may offer a powerful alternative, yet conventional LIBS relies on the use of tightly focused laser beams, requiring a stable air–water interface in a controlled environment. Reported here is a proof‐of‐principle, quantitative, simultaneous measurement of several representative heavy‐metal contaminants in water, at ppm‐level concentrations, using ultraintense femtosecond laser pulses propagating in air in the filamentation regime. This approach is straightforwardly extendable to kilometer‐scale standoff distances, under adverse atmospheric conditions and is insensitive to the movements of the water surface due to the topography and water waves.

We demonstrate the generation of 10-mJ 1.5-μm few-cycle pulses from a 4-stage OPCPA system. The system is based on a fusion of femtosecond DPSS Yb technology and a picosecond Nd:YAG pump laser. In a first preliminary filamentation experiment in argon at 5 atm, we observe significant spectral broadening of the recompressed multi-mJ 1.5-μm pulses. The filamentation output spectrum supports the generation of 8 fs pulses equivalent to sub-to-cycle pulses at 1.5 μm. We foresee that our terawatt-peak-power sub-to-cycle pulse source will open the door to exciting new experiments in attosecond high-field science in the near future.

Coherent radiation in the ultraviolent (UV) range has high potential applicability to the diagnosis of the formation processes of soot in combustion because of the high scattering efficiency in the UV wavelength region, even though the UV light is lost largely by the absorption within the combustion flames. We show that the third harmonic (TH) of a Ti:sapphire 800 nm femtosecond laser is generated in a laser-induced filament in a combustion flame and that the conversion efficiency of the TH varies sensitively by the ellipticity of the driver laser pulse but does not vary so much by the choice of alkanol species introduced as fuel for the combustion flames. We also find that the TH recorded from the side direction of the filament is the Rayleigh scattering of the TH by soot nanoparticles within the flame and that the intensity of the TH varies depending on the fuel species as well as on the position of the laser filament within the flame. Our results show that a remote and in situ measurement of distributions of soot nanoparticles in a combustion flame can be achieved by Rayleigh scattering spectroscopy of the TH generated by a femtosecond-laser-induced filament in the combustion flame.

We identify a physical scenario whereby soliton transients generated in freely propagating laser beams within the regions of anomalous dispersion in air can be compressed as a part of their free-beam spatiotemporal evolution to yield few-cycle mid- and long-wavelength-infrared field waveforms, whose peak power is substantially higher than the peak power of the input pulses. We show that this free-beam soliton self-compression scenario does not require ionization or laser-induced filamentation, enabling high-throughput self-compression of mid- and long-wavelength-infrared laser pulses within a broad range of peak powers from tens of gigawatts up to the terawatt level. We also demonstrate that this method of pulse compression can be extended to long-range propagation, providing self-compression of high-peak-power laser pulses in atmospheric air within propagation ranges as long as hundreds of meters, suggesting new ways towards longer-range standoff detection and remote sensing.

We discuss a four-stage optical parametric chirped-pulse amplifier that delivers carrier-envelope phase-stable ~1.5 μm pulses with energies up to 12.5 mJ before recompression. The system (previously reported in Opt. Lett. 34, 2498 (2009)) is based on a fusion of femtosecond diode-pumped solid-state Yb technology and a picosecond 100-mJ Nd:YAG pump amplifier. Pulses with 62 nm bandwidth are recompressed to a 74.4 fs duration, which is close to the transform limit. Here, to show the way towards a TW-peak-power single-cycle IR source, we perform detailed investigations of single-filament IR supercontinuum generation via femtosecond filamentation in noble gases. Depending on the experimental conditions, two filamentation regimes can be achieved: (i) in the filamentation regime without plasma-induced pulse self-compression, we generate 4-mJ 600-nm-wide IR supercontinua of high spatial quality supporting 8-fs pulse durations, which corresponds to less than two optical cycles at 1.5 μm; (ii) in the self-compression regime, we demonstrate self-compression of 2.2 mJ pulses down to 19.8 fs duration in a single filament in argon with a 1.5 mJ output energy and 66% energy throughput. By adapting the experimental conditions, further energy upscaling of the self-compressed pulses seems feasible. Keywords: optical parametric amplification, filamentation, pulse self-compression, intense few-cycle infrared pulses

Two-body dissociation processes of H2C@CH–CH@CH 2þ 2 induced by an intense laser field were investi

Photonic-crystal fibers (PCFs) with a specifically designed dispersion profile and nonlinearity are shown to enable an accurate broadband compensation of the stretcher-compressor dispersion in fiber laser sources of high-peak-power ultrashort light pulses. We demonstrate that the nonlinear phase shift in such systems can partially compensate for the fourth-order dispersion, allowing the stretcher—compression group delay to be compensated up to the fourth-order dispersion terms by using a sequence of only two fibers—a standard optical fiber and a PCF.

We experimentally and theoretically investigated the deprotonation process on nanosecond to microsecond timescale in ethylene and acetylene molecules, following their double ionization by a strong femtosecond laser field. In our experiments we utilized coincidence detection with the reaction microscope technique, and found that both the lifetime of the long-lived ethylene dication leading to the delayed deprotonation and the relative channel strength of the delayed deprotonation compared to the prompt one have no evident dependence on the laser pulse duration and the laser peak intensity. Quantum chemical simulations suggest that such delayed fragmentation originates from the tunneling of near-dissociation-threshold vibrational states through a dissociation barrier on a dication electronic state along C--H stretching. Such vibrational states can be populated through strong field double ionization induced vibrational excitation on an electronically excited state in the case of ethylene, and through intersystem crossing from electronically excited states to the electronic ground state in the case of acetylene.

A high-energy supercontinuum spanning 4.7 octaves, from 250 to 6500 nm, is generated using a 0.3-TW, 3.9-μm output of a mid-infrared optical parametric chirped-pulse amplifier as a driver inducing a laser filament in the air. The high-frequency wing of the supercontinuum spectrum is enhanced by odd-order optical harmonics of the mid-infrared driver. Optical harmonics up to the 15th order are observed in supercontinuum spectra as overlapping, yet well-resolved peaks broadened, as verified by numerical modeling, due to spatially nonuniform ionization-induced blue shift.

We report on the design and performance of a Yb:CaF 2 booster with a pass-by-pass compensated spatial gain narrowing. A 5-concave-mirror design affords a flexible number of passes as well as 4f image relay and progressive beam magnification onto the laser crystal.

Nonlinear self-compression of 1.7-µm pulses in a gas-filled Kagome fiber down to a single cycle duration and pulse energies up to 100 µJ provides a uniquely simple driver source for high-harmonic generation and above-threshold ionization experiments.

We experimentally and theoretically show that by controlling the dynamics of removing three electrons from ethylene with ultrashort intense laser pulses allows for the determination of the relative probabilities for fragmentation into two respectively three molecular moieties.

We experimentally and theoretically demonstrate channel-selective control over strong-field induced fragmentation of a polyatomic molecule, acetylene, using impulsive laser alignment as the control mechanism.

Midinfrared powerful 90 fs pulses at a wavelength of λ=3.9μm drive a femtosecond hard x-ray source (Cu~Kα: \hbar ω =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.

We discuss prospects of the generation of high power mid-IR pulses by analyzing soliton self-compression of multi-mJ 4-μm pulses and the development of few-optical-cycle 6-μm optical parametric amplifier. Scalability of pump lasers is addressed.

Using orthogonally polarized two-color laser fields on neon and coincidence momentum imaging we gain access to the Coulomb influence in single ionization on sub-cycle times, and demonstrate a strong electron-electron anti-correlation in double ionization.

we present the results of experimental and theoretical investigations for remote initiation of lasing in nitrogen and air by femtosecond filaments generated by laser pulses with different wavelengths, polarization and applying adaptive control methods

Virtually lossless self-compression of 10-mJ 3.9-um sub-100 fs pulses in bulk YAG resulting in 9-mJ 33-fs pulses is reported. Generated peak power exceeds 250 GW which is suitable for filamentation in ambient air.

We developed a multicolour, high-peak-power mid-IR parametric amplifier with the base period corresponding to 3.1 µm and a combined pulse energy >15 mJ, which is aimed at a “perfect wave” driver for high harmonic generation.

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 perform a proof-of-principle demonstration of chemically specific standoff gas sensing, in which a coherent stimulated Raman signal is detected in the direction anticollinear to a two-color laser excitation beam traversing the target volume. The proposed geometry is intrinsically free space as it does not involve back-scattering (reflection) of the signal or excitation beams at or behind the target. A beam carrying an intense mid-IR femtosecond (fs) pulse and a parametrically generated picosecond (ps) UV Stokes pulse is fired in the forward direction. A fs filament, produced by the intense mid-IR pulse, emits a backward-propagating narrowband ps laser pulse at the 337 and 357 nm transitions of excited molecular nitrogen, thus supplying a counter-propagating Raman pump pulse. The scheme is linearly sensitive to species concentration and provides both transverse and longitudinal spatial resolution.

The use of temporally shaped pump pulses for optical parametric chirped-pulse amplification can increase the efficiency and suppress possible spectral distortions in this process. With this goal in mind a novel method for shaping narrowband picosecond pulses has been developed. The method is based on the pulse stacking principle, where replicas of the incoming pulse are created in a specially designed four-beam interferometer. The replicas are recombined with appropriate relative delays. The interferometer design allows for a unique flexibility in varying the pulse shape, since all relevant degrees of freedom, such as relative intensities and delays between the pulse replicas are independently adjustable. Here we describe the design of our device in detail and report on the experimental demonstration of its pulse-shaping capabilities.

We demonstrate direct simultaneous seeding of a few-cycle optical parametric chirped pulse amplifier (OPCPA) in the 700-1000-nm spectral range, and of a Nd:YLF amplifier emitting 30-ps pulses at 1053 nm by use of a chirped-mirror 6-fs Ti:sapphire oscillator. This approach of employing a single master oscillator to drive two power amplifiers simplifies the pump laser design and is applied to eliminate the timing jitter between the seed and the pump pulses in the OPCPA chain. We show that 10 mJ fundamental picosecond pump pulses with the intensity contrast in excess of 10/sup 4/ relative to the nanosecond Q-switched background can be achieved with the seed intensity available in the edge of the oscillator spectrum around 1053 nm. Cross-correlation measurements between the picosecond pump and femtosecond oscillator pulses reveal no traceable timing jitter between the OPCPA pump and seed pulses. The estimated long-term jitter of 0.3 ps is attributed to the thermal expansion of the cavity of the Nd:YLF regenerative amplifier.

Seit einigen Jahren sind Ultrakurzpulslaser vom Entwicklungsstadium zu nutzlichen Instrumenten herangereift, die in der Hochfeldphysik und der Metrologie Anwendung finden. Heute decken Ultrakurzpulslaser das gesamte Spektrum ab zwischen Pulsenergien im sub-μJ-Bereich bei Repetitionsraten von einigen MHz und hochenergetischen Pulsen mit Spitzenleistungen im Terawattbereich bei Wiederholraten von einigen kHz.

Raman soliton phenomena in photonic crystal fibers are shown to allow efficient tunable frequency shifting of sub-10-fs laser pulses. Soliton self-frequency shift in a photonic-crystal fiber with a core diameter less than 2 μm is used to transform the spectrum of a 6-fs 2-nJ Ti: sapphire-laser pulse, dominated by a 670-nm peak, into a spectrum featuring a well-resolved intense spectral component centered at 1064 nm, which is ideally suited as a seed for Nd: YAG- and ytterbium-based laser devices.

Attosecond science can take enormous advantage of intense laser pulses consisting of two optical cycles or less (few-cycle pulses). The temporal variation of the field, which directly governs strong-field interactions, therefore depends on whether the maximum of the pulse amplitude coincides with that of the wave cycle or not, i.e. on the phase of the field with respect to the pulse envelope. It is demonstrated that the direction of electron emission from photoionized atoms can be controlled by varying the phase of the field, providing a tool for its accurate determination. Different phase-dependent effects in strong-field photoionization and their suitability for phase measurement are discussed as well as the limitations of the f-to-2f scheme.

The temporal variation of the electromagnetic field of a few-cycle laser pulse depends on whether the maximum of the pulse amplitude coincides with that of the wave cycle or not, i.e., it depends on the phase of the field with respect to the pulse envelope. Fixation of this ‘carrier-envelope’ phase has only very recently become possible for amplified laser pulses. This paved the way for a completely new class of experiments and for coherent control down to the attosecond time scale because it is the field and not the pulse envelope which governs laser-matter interactions. However, this novel technique still affords much potential for optimization. In this paper we demonstrate a novel stabilization scheme for the carrier-envelope phase that not only guarantees a stable phase for arbitrarily long measurements, but also makes it possible to restore any given phase for an application after a pause of any kind. This is achieved by combining a stereo-ATI phase meter with a feedback loop to correct phase drifts inside and outside the laser system.

A detailed frequency-resolved pump-probe study of hydrated electron dynamics, performed with 5-fs pulses, is presented. We show that the experimental data can be successfully described with a model in which the excited state lifetime is similar to50 fs in regular water and similar to70 A in heavy water. The deuteration effect on the lifetime strongly suggests that OH-vibrational modes in the first solvation shell act as accepting modes for energy relaxation. (C) 2004 Elsevier B.V. All rights reserved.

Intense ultrashort waveforms of light that can be produced with an exactly predetermined electromagnetic field are essential in a number of applications of extreme nonlinear optics, most prominently in laser-driven sources of high-energy attosecond radiation. Field reproducibility in each laser shot requires stabilization of the carrier-envelope phase. The authors analyze different schemes of phase-stable pulse amplification and identify constraints limiting the precision with which the phase can be maintained. Next, they describe a phase-stabilized laser system based on a 20-fs multipass Ti:sapphire amplifier supplemented with a fiber compression stage for producing pulses in the few-cycle regime. It is shown that the amplifier introduces only a slow millihertz phase drift and, therefore, can be seeded by a standard phase-stabilized oscillator. This residual phase drift is assigned primarily to the beam pointing instability and can be precompensated in the phase-control loop of the seed oscillator using a feedback signal from a phase detector placed in the amplifier output. The phase stability of the resultant 5-fs 400-/spl mu/J pulses at a 1-kHz repetition rate is subsequently independently verified by higher order harmonic generation, in which different carrier-envelope phase settings are shown, both theoretically and experimentally, to produce distinctly different spectral shapes of the XUV radiation. From a series of such spectral patterns, the authors succeed in calibrating the value of the carrier envelope phase (with a /spl plusmn//spl pi/ ambiguity), which in turn allows them to fully characterize the temporal structure of the electric field of the laser pulses. The estimated precision of the phase control on the XUV target is better than /spl pi//5, which reduces the timing jitter between the driving laser pulse and the XUV bursts to /spl sim/ 250 as and opens the way to generate stable isolated attosecond pulses.

The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10(-15) s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 x 10(-18) s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents--these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.

Transform-limited visible pulses with as short as sub-4 fs duration have been generated for the first time by several improvements made to our previous noncollinear optical parametric amplifier (NOPA). All of the signal–idler group-velocity matching and pump–signal pulse-front matching and angular dispersion matching of the parametric amplification processes and the final fine tuning of dispersion compensation using deformable mirror after a pair of chirped mirrors are essentially important to generate such short pulses. We demonstrated the generation of a continuous, simultaneously phase-matched 250 THz parametrically amplified spectrum. Resulting visible–near-IR signal-wave pulses have been compressed to a 4 fs duration using a micro-machined flexible mirror. Feedback for the iterative computer-controlled dispersion compensation algorithm is based on pulse characterization by a second-harmonic generation frequency-resolved optical gating. Tunable operation with bandwidth-limited sub-10 fs pulses in the visible (550–700 nm) and near infrared (900–1300 nm) was also performed by changing the seed delay with respect to the pump after increasing the seed chirp. The NOPA is one of the most useful light sources for ultrafast spectroscopy at the present stage on an extremely short timescale. Application to the vibrational wavepacket dynamics in terms of dynamic mode coupling is discussed. The future prospect of the NOPA is described at the end.

We present a double-pass non-collinear optical parametric amplifier (NOPA) that delivers 4-fs visible–near-infrared pulses. The paper discusses geometrical and temporal properties of the NOPA configuration, which allow us to broaden the gain band of simultaneous parametric amplification in excess of 250 THz. The key elements of the bandwidth enhancement include (i) the use of a broadband second-harmonic pump, (ii) optimization of the incidence angle of all monochromatic spectral components of the pump in order to produce a favorable offset of the corresponding phase-matching curves, and (iii) selection of the chirp rate and time delay between the stretched pump and seed pulses. We next devise a two-stage compressor that incorporates a flexible mirror for adaptive pulse shaping and develop a simple and trustworthy feedback loop based on a one-dimensional spectral measurement. Our rapid numerical algorithm for adaptive control of the flexible membrane is found superior to more complex search routines that are less resistant to the fluctuations of the laser intensity. The automated optimization procedure results in the generation of two-cycle pulses with a carrier wavelength at ∼600 nm. The absence of deep modulation on the parametrically amplified spectrum in combination with the adaptive phase correction lead to a high quality of the temporal profile and allow concentrating 90% of the pulse energy within only a 7.5-fs time window.

We identify and experimentally demonstrate a physical scenario whereby high-peak-power mid-infrared (mid-IR) pulses can be compressed as a part of their free-beam spatiotemporal evolution within the regions of anomalous dispersion in air to yield few-cycle subterawatt field waveforms. Unlike filamentation-assisted pulse compression, the pulse-compression scenario identified in this work does not involve any noticeable ionization of air, enabling a whole-beam self-compression of mid-IR laser pulses without ionization-induced loss. Ultrashort high-peak-power 3.9 μm laser pulses are shown to exhibit such self-compression dynamics when exposed to the dispersion anomaly of air induced by the asymmetric-stretch rovibrational band of carbon dioxide. Even though the group-velocity dispersion cannot be even defined as a single constant for the entire bandwidth of mid-IR laser pulses used in experiments, with all soliton transients shattered by high-order dispersion, 100–200 GW, 100 fs, 3.9 μm laser pulses can be compressed in this regime to 35 fs subterawatt field waveforms.