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A Frequency Resolved Optical Gating instrument accepting s or p polarized input pulses ranging from 205 nm to 2000 nm, durations from 2 cycles to 100 ps, and nano-Joule energies is presented.

The results are based on a commercial Yb:KGW regenerative amplifier (Pharos, Light Conversion) delivering 1 mJ, 170 fs pulses at 1 to 6 kHz. This beam is precisely matched to the fundamental mode of a large core HCF ( few-cycle Inc.) of 1 mm inner diameter, by realizing a focal spot diameter of 660 μm at 1/e 2 of intensity (corresponding approximately to a Rayleigh range of 0.3 m).

Nonlinear parametric processes involving ultrashort pulses are typically carried out in time domain, which mathematically corresponds to a convolution of their frequency spectra. In contrast, this spectral convolution changes into a multiplication operation when performing the nonlinear interaction in frequency domain. Here, we extend the scope of frequency-domain nonlinear optics by demonstrating its ability to perform a temporal convolution. Through this approach, nonlinear optical operations that are inaccessible in time domain can be realised: specific optical information can be coherently advanced by picoseconds within a pulse sequence—a newly generated second harmonic pulse carries the amplitude and phase information of two input pulses. This central pulse is isolated when using an input field consisting of two cross-polarized input pulses in combination with type-II second harmonic generation. The effects of nonlinear temporal convolution can be viewed from the aspect of signal processing and pulse shaping, where the nonlinear interaction in the parametric crystal plays the role of a dynamic linear optical filter—in contrast to conventional static filters—with a shaping mask instantaneously adapting to the laser field.

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

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

We present a novel, to the best of our knowledge, approach for scaling the peak power of mid-infrared laser pulses with few-cycle duration and carrier-to-envelope phase stabilization. Using frequency domain optical parametric amplification (FOPA), selective amplification is performed on two spectral slices of broadband pulses centered at 1.8 µm wavelength. In addition to amplification, the Fourier plane is used for specific pulse shaping to control both the relative polarization and the phase/delay between the two spectral slices of the input pulses. At the output of the FOPA, intrapulse difference frequency generation provides carrier–envelope phase stabilized two-cycle pulses centered at 9.5 µm wavelength with 25.5 µJ pulse energy. The control of the carrier–envelope phase is demonstrated through the dependence of high-harmonic generation in solids. This architecture is perfectly adapted to be scaled in the future to high average and high peak powers using picosecond ytterbium laser technologies.

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

We introduce hydrofluorocarbon molecules as an alternative medium to noble gases with low ionization potential like krypton or xenon to compress ultrashort pulses of relatively low energy in a conventional hollow core fiber with subsequent dispersion compensation. Spectral broadening of pulses from two different laser systems exceeded those achieved with argon and krypton. Initially 40 fs, 800 nm, 120 μJ pulses were compressed to few optical cycles duration. With the same approach a compression factor of more than 10 was demonstrated for an ytterbium-based laser (1030 nm, 170 fs, 200 μJ) leading to 15.6 fs.

We present a straightforward route for extreme pulse compression, which relies on moderately driving self-phase modulation (SPM) over an extended propagation distance. This avoids that other detrimental nonlinear mechanisms take over and deteriorate the SPM process. The long propagation is obtained by means of a hollow-core fiber (HCF), up to 6 m in length. This concept is potentially scalable to TW pulse peak powers at kW average power level. As a proof of concept, we demonstrate 33-fold pulse compression of a 1 mJ, 6 kHz, 170 fs Yb laser down to 5.1 fs (1.5 cycles at 1030 nm), by employing a single HCF and subsequent chirped mirrors with an overall transmission of 70%.

Owing to the increasing significance of high harmonic generation (HHG) as a tabletop coherent x-ray source and the coming of age of intense infrared (IR) lasers, the development of high brightness soft x-ray beamlines is gaining a lot of attention. We discuss the self-guided propagation of high energy IR pulses around 1.8 mu m centre wavelength being loosely focused into a long, high-pressure gas cell. A bright x-ray beam with photon energies extending up to the oxygen K-edge at 543 eV is achieved with a flux of 2.9 x 10(3) photons/shot/1% bandwidth around the carbon K-edge (280 eV). We provide experimental and numerical evidence of an ionization steady state condition in the generation medium causing self-channelling and intensity clamping of the driving field. While the later limits the HHG cut-off energy for a given driving field wavelength, self-channelling increases the HHG flux through a longer, phase-matched, interaction length and provides a well-collimated HHG beam covering more than three octaves from

The powerful technique of optical parametric amplification (OPA) experienced a huge advance with the invention of optical parametric chirped pulse amplification (OPCPA) and later noncollinear OPA. In this paper, we describe a radically different approach of performing parametric interaction in the frequency domain instead of the time domain. The frequency domain is reached via optical Fourier transformation, which provides a separation ansatz. It allows breaking down a big task into smaller ones which ultimately enables simultaneous up-scaling of peak power and bandwidth. The first proof-of-concept experiment yielding 1.4 mJ, two cycle pulses at 1.8-μm wavelength is complemented by a high gain (>2000) setup at 800-nm wavelength with 2.5 kHz repetition rate. A very low amount of parasitic superfluorescence without degradation of the picosecond pulse contrast within the pump pulse duration has been observed upon high gain conditions.

Broadband optical parametric amplification in the IR region has reached a new milestone through the use of a non-collinear Frequency domain Optical Parametric Amplification system. We report a laser source delivering 11.6 fs pulses with 30 mJ of energy at a central wavelength of 1.8 μm at 10 Hz repetition rate corresponding to a peak power of 2.5 TW. The peak power scaling is accompanied by a pulse shortening of about 20% upon amplification due to the spectral reshaping with higher gain in the spectral wings. This source paves the way for high flux soft X-ray pulses and IR-driven laser wakefield acceleration.

Using a non-collinear FOPA, a source delivering 1.8 μm, 30 mJ, 13 fs laser pulses is demonstrated. This is the first step towards 100 mJ for ∼10 TW. This laser opens the way for high brightness soft X-ray attosecond pulses.

FNO enables deep UV pulse shaping through direct phase transfer of conventionally shaped NIR pulses at 830nm to their 4th harmonic. We demonstrate first time pulse characterization with a transient grating FROG at 207nm.

Frequency-domain Nonlinear Optics (FNO) merges the simplicity of linear optics with the power of nonlinear optics. Employing FNO, we demonstrate pulse shaping in the deep UV and amplification of two-cycle infrared pulses to 2.5 TW., Nonlinear Optics, 17-21 July 2017, Waikoloa, Hawaii

A non-collinear Frequency domain Optical Parametric Amplifier is used to produce a 1.8 μm, 30 mJ, 13 fs laser source, leading to 2.5 TW peak power. This laser opens the way for high brightness soft X-ray attosecond pulses., CLEO: QELS_Fundamental Science, May 14-19, 2017, San Jose, California, USA

We present a system for extremely broadband terahertz (THz) generation based on an Ytterbium (Yb) amplified laser emitting 170-fs-long pulses centered at 1030 nm. The pulses are first spectrally broadened in an Ar-filled hollow-core capillary fiber (HCF) and then recompressed down to ∼18 fs with a chirped-mirror pair. Extreme broadband THz pulses of bandwidths up to 60 THz and peak electric field as high as 55 kV/cm are obtained via two-color plasma generation. The combination of high-power Yb laser systems with gas-filled HCF opens the path towards the realization of the next generation high-repetition-rate, extremely broadband, and intense-field THz time-domain spectroscopy systems.

The time-dependent field of an electromagnetic pulse can be measured if there is a fast enough gate. For terahertz radiation, femtosecond photoinjection of free carriers into a semiconductor in the presence of the terahertz radiation can serve as the gate1. For visible or infrared radiation, attosecond photoionization of a gas target in the presence of the optical field is a direct analogue2,3,4,5,6,7,8. Here, we show that nonlinear optical mixing9,10,11,12,13 in a medium in which attosecond pulses are being generated can also be used to measure the time-dependent field of an optical pulse. The gate is the phase accumulated by the recollision electron during the subcycle time interval between ionization and recombination. We show that the instantaneous field of an unknown pulse is imprinted onto the deflection of the attosecond extreme ultraviolet pulse using an all-optical set-up with a bandwidth up to 1 PHz. A new laser-field measurement technique is demonstrated that exploits nonlinear optical mixing in a gas in which attosecond pulses are being generated. The instantaneous field of an unknown pulse is imprinted onto the deflection of an attosecond pulse using an all-optical set-up with a bandwidth of up to 1 PHz.

A novel scheme of flexible hollow-core fiber compression is used to achieve 2-cycles pulses at 1.8µm with 5mJ pulse energy. This source is shown to greatly enhance the efficiency of the high harmonic generation process.

6-mJ passively CEP-stabilized 3.2-μm, 80-fs idler pulses from a 1-μm-pumped femtosecond KTA parametric amplifier are spectrally broadened in a noble-gas-filled capillary and recompressed, with a 50% throughput, in an output CaF2 window down to 31 fs.

Starting from a 100kHz picosecond Yb laser, we derive tunable 10–15fs visible pulses for intrapulse difference frequency generation of potentially CEP stable, few-cycle IR pulses as the seed source for a subsequent FOPA chain.

We report the amplification up to 13 mJ of a broadband 1.8 µm femtosecond pulse in a two crystal Fourier optical parametric amplifier (FOPA) pumped by 80 mJ picosecond TiSa pulses.

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 produce harmonics in the molecule ethylene ( C 2 H 4 ) with two different wavelengths and three pulse durations. Due to the low ionization potential ( I p = 10.5 eV ) of C 2 H 4 , longer wavelengths are needed to extend the maximum photon energy produced. Our results show that regardless of the strong dependence of the efficiency of the harmonic generation process with wavelength, at 1820 nm the cutoff observed is larger than that obtained with 800 nm, 15 fs pulses. We obtain harmonics with energies exceeding 70 eV at 9.0 × 10 13 W / cm 2 with a 73 fs 1820 nm pulse. Under these circumstances, the limiting factor for the further extension of the cutoff seems to be the photoionization cross section of the molecule.

The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to reconstruct momentum-dependent band gaps by exploiting the coherent motion of electron-hole pairs driven by intense midinfrared femtosecond laser pulses. Applying the method to experimental data for a semiconductor ZnO crystal, we identify the split-off valence band as making the greatest contribution to tunneling to the conduction band. Our new band structure measurement technique is intrinsically bulk sensitive, does not require a vacuum, and has high temporal resolution, making it suitable to study reactions at ambient conditions, matter under extreme pressures, and ultrafast transient modifications to band structures.

International audience; By employing pulse compression with a stretched hollow-core fiber, we generated 2-cycle pulses at1.8 $\mu$m (12 fs) carrying 5 mJ of pulse energy at 100 Hz repetition rate. This energy scaling in themid-infrared spectral range was achieved by lowering the intensity in a loose focusing condition,thus suppressing the ionization induced losses. The correspondingly large focus was coupled into ahollow-core fiber of 1 mm inner diameter, operated with a pressure gradient to further reduce detrimentalnonlinear effects. The required amount of self-phase modulation for spectral broadeningwas obtained over 3 m of propagation distance

General restrictions arising from gain-narrowing and phase-matching are circumvented by employing parametric amplification in the frequency rather than the time domain. Frequency-domain OPA has been used for amplifying few-cycle pulses and for high gain amplification.

We investigate the behavior of resonant-induced harmonics from tin using driving lasers with tunable wavelengths. The intensity of the resonant harmonic is suppressed by the tuning laser wavelength around 1.8μm to understand the interaction dynamics of continuum electron with the autoionizing states.

By employing hollow-core fiber compression using a stretched flexible fiber, we achieved 2-cycles pulses centered on 1.8μm with more than 5mJ energy per pulse.

Optics Express, 25 (15), ISSN:1094-4087

We report on a setup for coherent multidimensional spectroscopy based on visible continuum generation obtained by propagating 130 fs

When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Recently, high harmonics have been generated from bulk crystals, but what mechanism dominates the emission remains uncertain. To resolve this issue, we adapt measurement methods from gas-phase research to solid zinc oxide driven by mid-infrared laser fields of 0.25 volts per ångström. We find that when we alter the generation process with a second-harmonic beam, the modified harmonic spectrum bears the signature of a generalized recollision between an electron and its associated hole. In addition, we find that solid-state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology. Future experiments will permit the band structure of a solid to be tomographically reconstructed. © 2015 Macmillan Publishers Limited. All rights reserved.

Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43 mJ two-cycle pulses at 1.8 μm wavelength., Optical parametric amplification is a process that amplifies the power of laser pulses. Here, Schmidt and colleagues demonstrate that performing this amplification in the frequency domain rather than the optical domain could lead to higher power outputs.

800nm, nJ level pulses are amplified 2.000 to 12.000 times in a single 2mm BBO crystal, pumped by picosecond 400nm pulses. Blocking the seed input yielded a 1400 times weaker superfluorescence level.

800nm, nJ level pulses are amplified >2.000 times in a single 2mm BBO crystal, pumped by picosecond 400nm pulses. Experiments evidence that the picosecond pulse contrast within the pump window remains unchanged upon amplification.

800nm, nJ level pulses are amplified >2.000 times in a single 2mm BBO crystal, pumped by picosecond 400nm pulses. Experiments evidence that the picosecond pulse contrast within the pump window remains unchanged upon amplification.

Optical parametric amplification (OPA) in the frequency domain rather than in time domain circumvents phase mismatch and damage threshold limitations. This approach enables amplification of few-cycle pulses, and nJ to microJ in a single stage.

We investigate the nonlinear wave-mixing in gases between intense, short optical pulses and long-wavelength fields (mid infrared and terahertz). We show numerically that the beating between the sum- and difference-frequency generation components can be isolated in the spectrogram of the interaction, and can be used to sample the electric field oscillations of the long-wavelength pulses. This, in turn, could be employed as a possible characterization method that provides information on the real electric field amplitude. Our numerical model is supported by spectrally resolved measurements of the four-wave mixing signals obtained from the interaction of intense, single-cycle terahertz fields (λ > 15 μm) and optical pulses (λ ≃ 800 nm, 50 fs duration) in air.

Low-frequency currents induced by ultrashort laser-driven ionization can emit extremely broadband, single-cycle terahertz pulses. We present a model that predicts a strong wavelength dependence of the THz emission in good agreement with our experimental study. This reveals that the combined effects of plasma currents rising proportionally to the square of the pump wavelength and wavelength-dependent focusing conditions lead to 30 times higher THz emission at 1800 nm compared to an 800 nm wavelength. Unrivaled single-cycle electric field strengths of 4.4 MV/cm are achieved with this compact table-top setup.

High harmonic generation in gas targets leads to the production of attosecond pulses. The process of high harmonic generation requires that the gas be ionized by an intense femtosecond laser field. The highest photon energy produced is related to the laser intensity times the wavelength squared. This cutoff is reached only if good phase matching is achieved. Using a laser with a wavelength of 1800 nm, we estimate the laser intensity in the gas jet by recording the ion yield, and simultaneously record the high harmonic spectrum. We show that the cutoff energy matches the measured intensity, confirming that good phase matching is achieved to 100 eV. We also use the ion collector to characterize the spatial size of the gas jet and to measure the confocal parameter of the laser beam, parameters that are useful for numerical modelling.

We report mid-infrared (MIR) nonlinear absorption in As2S3 glasses which results from two-photon excitation of valence electron to the Urbach extension followed by strong linear absorption of excited states. The measured MIR nonlinear absorption can be 3 to 4 orders of magnitude stronger than the two-photon absorption in the near-infrared for similar laser intensities and does not result from contaminants, but it is intrinsic to As2S3 glasses. As2S3 fibers are widely used to generate supercontinuum by pumping them with high peak power laser pulses. For a 100 kilowatt peak power MIR soliton propagating in single mode As2S3 fiber, the nonlinear absorption can be of similar magnitude than the fiber background loss. Finally, for laser peak power around 1 MW, the MIR nonlinear absorption can be ~2 orders of magnitude larger than the fiber background loss in single mode As2S3 fiber.

© 2016 AIP Publishing LLC. We demonstrate broad bandwidth and intense sub-100 eV high-order harmonics from diatomic carbon molecules driven by long-wavelength laser pulses. Up to now, one limitation of the intense carbon harmonic source driven by a 0.8 μm wavelength Ti:sapphire laser has been the low cutoff around ∼32 eV. In this paper, we show that this harmonic cutoff is extended to ∼70 eV by increasing the driving laser wavelength to 1.71 μm. Surprisingly, the carbon harmonic intensity is found to be high despite the long wavelength driving laser. Experiments show only ∼30% decrease in the harmonic intensity when changing the driving laser wavelength from 0.8 μm to 1.71 μm. Such intense sub-100 eV coherent X-rays would have important applications in various domains of science and technology.

Energetic electrons generation by longitudinal field acceleration from a laser pulse was demonstrated. The longitudinal field was generated by focusing a radially polarised TM01 ultrashort laser pulse (1,8 microns, 550 uJ, 15 fs) with a high numerical aperture parabola. The created longitudinal field was intense enough to ionised and accelerated electrons with a few tens of keV from a low density oxygen gaz. The energy, spectrum, number of charges per shot and divergence of the generated electron bunches have been measured and will be presented. Electron bunch pulse duration, space charge effects and energy tunability will also be discussed.

We report the extension of hollow-core fibre pulse compression to longer wavelengths. High-energy multi-cycle infrared pulses are generated via optical parametric amplification and subsequently broadened in the fibre. 2.5-cycle pulses at the Signal wavelength (1.4 ?m) and 1.6-cycle pulses at the Idler wavelength (1.8 ?m) in the sub-millijoule regime have been generated. New compression schemes can be applied at 1.8 ?m and beyond. In this manner, 1.6-cycle carrier envelope phase stable pulses were generated by linear propagation in the anomalous dispersion regime of bulk glass which surprisingly enables compression below its third-order dispersion limit. Furthermore, a dispersion-free way of controlling the carrier envelope phase is demonstrated. Moreover, we experimentally confirm the increase in high-harmonic cut-off energy with driving laser wavelength and demonstrate the beneficial effect of few-cycle pulses which enable higher saturation intensities on target compared to multi-cycle pulses. It will be an ideal tool for future synthesis of isolated attosecond pulses in the sub-keV regime. With this laser source, we revealed for the first time multi-electron effects in high harmonic generation in xenon.

Interferometric CEP control in a white light seeded optical parametric amplifier is demonstrated by relative phase shifting between white light and pump beam prior to their difference frequency generation, resulting in CEP controlled Idler pulses.

We describe a method for electric-field characterization of few-cycles pulses with wavelengths from mid-infrared to the THz region, based on electric-field induced second harmonic spectrograms. The method is demonstrated with single cycle THz pulses.

We developed a novel scheme for intense terahertz pulse generation by two-color driven ionization of gasses that allows for MV/cm level peak-fields. The nonlinear mixing between such high-field terahertz pulse and an optical pulse results in an electric-field-induced second harmonic generation, both in gasses and in condensed media. We report on our recent investigations on this phenomenon that allows e.g. for the terahertz pulses three-dimensional mapping.

Recent advances in optical parametric amplification (OPA) based few-cycle pulse generation at 1.8 µm wavelength led to the discovery of multi-electron correlation effects in high harmonic generation (HHG), in particular the giant resonance in Xe. The novel scheme for sub-two cycle pulse generation rests upon nonlinear propagation of OPA pulses in a hollow-core fiber and subsequent compression solely by linear propagation through Fused Silica which exhibits anomalous dispersion [1]. The spectral phase introduced by self-phase modulation and self-steepening cancels material dispersion up to third order to provide an ideal laser source for HHG in gases with low ionization potential.

The generation of isolated 80 attosecond laser pulses has almost reached its physical limitation when using established Ti:Sa schemes at 800 nm of the driving field [1]. Further shortening of attosecond pulse duration utilizing high harmonic generation (HHG) can be achieved by using few cycle pulses at longer wavelengths because the HHG cut-off shifts towards higher photon energies proportional to the square of the laser wavelength [2]. In this paper, we present (1) a simple and robust experimental approach to generate carrier envelope phase (CEP) stable quasi single cycle laser pulses at 1.8 µm and (2) HHG from Argon using those pulses.

By using the novel approach for pulse compression that combines spectral broadening in hollow-core fiber (HCF) with linear propagation in fused silica (FS), we generate 1.6 cycle 0.24 mJ laser pulses at 1.8 μm wavelength with a repetition rate of 1 kHz. These pulses are obtained with a white light seeded optical parametric amplifier (OPA) and shown to be passively carrier envelope phase (CEP) stable.