A versatile high-average-power ultrafast infrared driver tailored for high-harmonic generation and vibrational spectroscopy.

We report on an ultrafast infrared optical parametric chirped-pulse amplifier (OPCPA), pumped by a 200-W thin-disk Yb-based regenerative amplifier at a repetition rate of 100 kHz. The OPCPA is tunable in the spectral range 1.4-3.9 [Formula: see text]m, generating up to 23 W of < 100-fs signal and 13 W of < 200-fs idler pulses for infrared spectroscopy, with additional spectral filtering capabilities for Raman spectroscopy. The OPCPA can also yield 19 W of 49-fs 1.75-[Formula: see text]m signal or 5 W of 62-fs 2.8-[Formula: see text]m idler pulses with active carrier-to-envelope-phase (CEP) stabilisation for high-harmonic generation (HHG). We illustrate the versatility of the laser design, catering to various experimental requirements for probing ultrafast science.

Highly stable, 15 W, few-cycle, 65 mrad CEP-noise mid-IR OPCPA for statistical physics.

We demonstrate a 100 kHz optical parametric chirped-pulse amplifier delivering under 4-cycle (38 fs) pulses at ~3.2 µm with an average power of 15.2 W with a pulse-to-pulse energy stability <0.7% rms and a single-shot CEP noise of 65 mrad RMS over 8h. This source is continuously monitored, by using a fast 100 kHz data acquisition device, and presents an extreme stability, in the short and long terms.

Author Correction: Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers.

Structural isomers, molecules having the same chemical formula but with atoms bonded in different order, are hard to identify using conventional spectroscopy and mass spectrometry. They exhibit virtually indistinguishable mass spectra when ionized by electrons. Laser mass spectrometry based on photoionization of the isomers has emerged as a promising alternative but requires shaped ultrafast laser pulses. Here we use transform limited femtosecond pulses to distinguish the isomers using two methods. First, we probe doubly charged parent ions with circularly polarized light. We show that the yield of doubly charged ortho-xylene decreases while para-xylene increases over a range of laser intensities when the laser polarization is changed from linear to circular. Second, we probe high harmonic generation from randomly oriented isomer molecules subjected to an intense laser field. We show that the yield of high-order harmonics varies with the positioning of the methyl group in xylene isomers (ortho-, para- and meta-) and is due to differences in the strength of tunnel ionization and the overlap between the angular peaks of ionization and photo-recombination.

4-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad carrier-envelope phase noise.

We demonstrate an optical parametric chirped-pulse amplifier delivering 4-cycles (38-fs) pulses centered around 3.1 µm at 100-kHz repetition rate with an average power of 4 W and an undersampled single-shot carrier-envelope phase noise of 81 mrad recorded over 25 min. The amplifier is pumped by a ~1.1 ps, Yb-YAG, thin-disk regenerative amplifier and seeded with a supercontinuum generated in bulk YAG from the same pump pulses. Carrier-envelope phase stability is passively achieved through difference-frequency generation between pump and seed pulses. An additional active stabilization at 10 kHz combining 2f-to-f interferometry and a LiNbO3 acousto-optic programmable dispersive filter achieves a record low phase noise.

Mid-infrared nonlinear absorption in As2S3 chalcogenide glass.

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.

Multioctave infrared supercontinuum generation in large-core As2S3 fibers.

We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 µm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 µm, a mid-infrared background loss of 0.2 dB/m, and a maximum loss of only 0.55 dB/m at the S-H absorption peak around 4.05 µm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 µm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.

Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation.

The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations.

Frequency domain optical parametric amplification.

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.

Mid-infrared supercontinuum generation in fluoroindate fiber.

We report the generation of mid-infrared supercontinua in a step-index fluoroindate-based fiber. The large core of the fluoroindate fiber allows the guiding of multiwatt laser power over a broad spectral range. These fibers exhibit zero dispersion at 1.83 µm, minimal loss of 0.1 dB/m at 3.2 µm up to only 0.8 dB/m at 5 µm. These specifications enable mid-infrared supercontinuum generation and propagation with low loss. By using mid-infrared ultrashort laser pulses from an optical parametric amplifier, we demonstrate generation of a 20 dB spectral flatness supercontinua from 2.7 to 4.7 µm in the fluoroindate fiber, which is twice the spectral broadening compared to a ZBLAN fiber under similar conditions.

Time-resolved photoelectron spectroscopy of the CH(3)I B(1)E 6s [2] state.

The predissociation dynamics of the vibrationless level of the 6s (B (2)E) Rydberg state of CH(3)I was studied by femtosecond-resolved velocity map imaging of photoelectrons. By monitoring the decay of the CH(3)I(+) produced by photoionizing the B state, the predissociation lifetime was measured to be 1310 ± 70 fs. Photoelectron spectra were recorded as a function of the excitation scheme (one or two photons to the B state), and as a function of the ionizing wavelength. All of these photoelectron spectra show a simple time dependence that is consistent with the decay time of the CH(3)I(+) ion signal. The photoelectron angular distributions for the ionization of the B state depend on the excitation scheme and the ionizing wavelength, and show a strong dependence on the vibrational modes excited in the resulting CH(3)I(+). At long delays, the photoelectron spectra are characterized by photoionization of the I((2)P(1/2)) fragment formed by predissociation of the B state.