Amplitude

We demonstrate that chirped pulse up-conversion (CPU), a method routinely used with systems based on 1-kHz Titanium:Sapphire lasers, can be extended to a repetition rate of 100 kHz with an Ytterbium diode-pumped femtosecond amplifier. Individual mid-infrared spectra can thus be measured directly in the near infrared using a fast CMOS linescan camera. After an appropriate Fourier processing, a spectral resolution of 1.1 cm⁻¹ is reported, currently limited by our spectrometer. Additionally, we demonstrate the application of CPU to a pump-probe measurement of the vibrational relaxation in carboxy-hemoglobin, and we show that the combination of fast scanning and fast acquisition enables a straightforward removal of pump scattering interference.

Intrapulse Difference Frequency Generation (iDFG) is an interesting technique for generating femtosecond pulses in the Mid-Infrared (MIR) range with unique properties such as robust Carrier-Envelope Phase (CEP) stability. However, its efficiency is low compared to other techniques. In this paper, we describe an iDFG system operating within the 4–10 \(\upmu\)m range that features an original architecture to enhance efficiency. First, we introduce an interesting technique on the generation process. This approach involves polarization and spectral phase shaping techniques on the driving pulse to maximize the number of photons enrolled in the process. Second, we demonstrate that the polarization shaping allows further enhancement of efficiency by recycling the iDFG signal to pump a subsequent optical parametric amplification (OPA) stage. These two concepts and the associated parameters optimization are described into details, and supported by experimental results. Combined with a high-power Yb-fiber-based pump laser, these techniques allow to achieve record efficiencies, and generate \(\upmu\)J-level, few-cycle, tunable, CEP-stable pulses in the MIR at repetition rates above 100 kHz.

We demonstrate nonlinear temporal compression of a vortex beam by propagation in a gas-filled capillary. Starting from an ytterbium-based laser delivering 700 μJ 640 fs pulses at a 100 kHz repetition rate, the vortex beam is generated using a spiral phase plate and coupled to a capillary where it excites a set of four modes that have an overlap integral of 97% with a Laguerre–Gauss LG10 mode. Nonlinear propagation of this hybrid, orbital angular momentum (OAM)-carrying mode results in temporal compression down to 74 fs at the output. Beam and pulse characterizations are carried out to determine the spatial profile and temporal duration of compressed pulses. This result in multimode nonlinear optics paves the way towards the generation of OAM-carrying few-cycle pulses, isolated attosecond XUV pulses, and tunable UV pulses through resonant dispersive wave emission.

Performance of the novel high repetition rate HF-PW laser system of ELI ALPS is presented in its first operation phase at 400 TW and 700 TW levels. Long-term operation was tested at 2.5 and 10 Hz repetition rates, where an exceptional 0.66% and 1.08% shot-to-shot energy stability was demonstrated, respectively. Thorough spatio-spectral and temporal measurements confirmed high quality output pulses with a Strehl ratio of >0.9 after compression at both repetition rates. Amplified pulses with an unprecedentedly high 240 W average power were reached for the first time from a PW-class amplifier chain by using novel pseudo-active mirror disk amplification-based pump lasers.

Micromachining of various materials with femtosecond lasers operating in the GHz-burst regime has recently attracted great attention. In this contribution, we show our latest results on top-down percussion drilling in different dielectrics in this new operating regime. The dependence on the burst parameters such as burst repetition rate, number of pulses per burst, and burst energy are discussed. Moreover, we will focus on the influence of the burst shape on the drilling process. The quality of the drilled holes and their reachable dimensions are presented.

Free-space optics allows for design freedom and control, but miniaturization and manufacturability are limited. Here, we present a method for manufacturing complex miniaturized free-space optical systems that combines contactless femtosecond laser-activated alignment with femtosecond laser 3D manufacturing of a substrate incorporating optomechanical elements. Specifically, we demonstrate a palm-sized, all-glass GHz femtosecond laser cavity, whose alignment and lasing operation are permanently tuned in a contactless manner via laser–matter interaction using another femtosecond laser. The manufactured Yb:KYW oscillator shows self-starting mode-locking with a diffraction-limited beam and outputs a stable train of solitons with 182 fs pulse width at 1.0925 GHz repetition rate, for 725 mW incident pump power.

Femtosecond laser sources with high repetition rate in the ultraviolet (UV) and vacuum UV (VUV) are fundamental tools enabling tabletop time-resolved and angle-resolved photoemission spectroscopy in solids. We describe a VUV source at 114 nm (10.8 eV) based on an industrial grade ytterbium-doped ultrafast laser, a nonlinear pulse width selection stage, and two cascaded frequency tripling stages, first in crystals, second in xenon. The role of ionization in gas-based perturbative third harmonic generation phase-matching is analyzed using a simple theory, numerical simulations, and experimental data. The source features high photon flux, high repetition rate, and adjustable time resolutions. Thereby, in combination with a state-of-the-art angle-resolved photoemission spectroscopy (ARPES) apparatus it enables the study of the electronic dynamics of the whole Brillouin zone in a large number of materials.

Coherent time-domain spectroscopy (TDS) using terahertz radiation is valuable for fundamental science, security, and medical applications. This study investigates the performance of air-biased coherent detection terahertz spectroscopy (ABCD-THz) when an extended plasma filament is created in the air over long distances. We report on the latest results obtained within the follow-up of the ALTESSE project (Bergé L. et al ., EPL , 126 (2019) 24001) whose objective is to measure a set of spectral signatures characterizing suspicious materials over meter-long distances. As one of the most critical steps towards routinely applying this technique, we verified the feasibility of a remote THz time-domain spectroscopy by loosely focusing two-color ultrashort laser pulses at more than 3 meters from the laser source. The absorption spectra of amino acids and explosives analyzed in such a filamentation geometry are compared with those obtained using a standard ABCD scheme where the plasma is generated at much shorter distances of .

We study a second harmonic generation interaction geometry in the case where both group velocity mismatch and walk-off have significant impacts. This results in a frequency-converted beam exhibiting a pulse front tilt. Using the global response function of the crystal, we provide an analytical model that allows to predict the spatiotemporal structure of the second harmonic wave packet and verify its validity using numerical simulations and a simple experiment. Distinctive features of this geometry are the suppression of back-conversion and the ability to conserve the fundamental bandwidth in space and time domains. Subsequent compensation of the pulse front tilt should allow efficient generation of ultrashort pulses in the deep ultraviolet.

We characterize the intensity noise of two mid-infrared (MIR) ultrafast tunable (3.5-11 μm) sources based on difference frequency generation (DFG). While both sources are pumped by a high repetition rate Yb-doped amplifier delivering 200 μJ 300 fs at a central wavelength of 1030 nm, the first is based on intrapulse DFG (intraDFG), and the second on DFG at the output of an optical parametric amplifier (OPA). The noise properties are assessed through measurement of the relative intensity noise (RIN) power spectral density and pulse-to-pulse stability. The noise transfer mechanisms from the pump to the MIR beam is empirically demonstrated. As an example, improving the pump laser noise performance allows reduction of the integrated RIN (IRIN) of one of the MIR source from 2.7% RMS down to 0.4% RMS. The intensity noise is also measured at various stages and in several wavelength ranges in both laser system architectures, allowing us to identify the physical origin of their variation. This study presents numerical values for the pulse to pulse stability, and analyze the frequency content of the RINs of particular importance for the design of low-noise high repetition rate tunable MIR sources and future high performance time-resolved molecular spectroscopy experiments.

Bursts of GHz repetition rate pulses can significantly increase the ablation efficiency of femtosecond laser material processing.. Ablation by GHz repetition rate bursts of femtosecond pulses is a multi-step process, consisting of a first thermal incubation phase, followed by a highly efficient ablation phase. GHz ablation therefore combines thermal and non-thermal ablation mechanisms. With an optimal choice of the burst duration, the ablation efficiency can be highly enhanced. Long bursts, comprising tens to hundreds of pulses, are required to take full advantage of the increase in ablation efficiency.

We report novel results on top-down percussion drilling in different glasses with femtosecond laser GHz-bursts. Thanks to this particular regime of light-matter interaction, combining non-linear absorption and thermal cumulative effects, we obtained crack-free holes of aspect ratios exceeding 30 in sodalime and 70 in fused silica. The results are discussed in terms of inner wall morphology, aspect ratio and drilling speed.

We demonstrate an ultrafast mid-infrared source architecture that implements both intrapulse difference frequency generation (iDFG) and further optical parametric amplification (OPA), in an all-inline configuration. The source is driven by a nonlinearly compressed high-energy Yb-doped-fiber amplifier delivering 7.4 fs pulses at a central wavelength of 1030 nm, at a repetition rate of 250 kHz. It delivers 1 µJ, 73 fs pulses at a central wavelength of 8 µm, tunable over more than one octave. By enrolling all the pump photons in the iDFG process and recycling the long wavelength pump photons amplified in the iDFG in the subsequent OPA, we obtain an unprecedented overall optical efficiency of 2%. These performances, combining high energy and repetition rate in a very simple all-inline setup, make this technique ideally suited for a growing number of applications, such as high harmonic generation in solids or two-dimensional infrared spectroscopy experiments.

We report on an analysis of the nonlinear absorption in lithium triborate (LBO) used for second and third harmonic generation of ultrashort laser pulses at average powers in the order of kW and with sub-picosecond pulse duration. Thermographic imaging of the LBO crystals together with a simple analytical model revealed the presence of nonlinear absorption in both harmonic generation processes. Subsequent processing with a numerical model considering the nonlinear mixing, the absorption, and the heat conduction was used to estimate the absorption coefficients. Average powers exceeding 100 W in the ultraviolet and 400 W in the visible spectral range were obtained while maintaining a good beam quality by avoiding excessive nonlinear absorption.

We present a technique to optimize the intrapulse difference frequency generation efficiency for mid-infrared generation. The approach employs a multi-order wave plate that is designed to selectively rotate the polarization state of the incoming spectral components on the relevant orthogonal axes for subsequent nonlinear interaction. We demonstrate a significant increase of the mid-infrared average power generated, of a factor ≥2.5 compared with the conventional scheme, owing to an optimally distributed number of photons enrolled in the difference frequency generation process.

Results of the 2018 commissioning and experimental campaigns of the new High Power Laser Facility on the Energy-dispersive X-ray Absorption Spectroscopy (ED-XAS) beamline ID24 at the ESRF are presented. The front-end of the future laser, delivering 15 J in 10 ns, was interfaced to the beamline. Laser-driven dynamic compression experiments were performed on iron oxides, iron alloys and bismuth probed by online time-resolved XAS.