The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BEAT is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches.

The measurement and control of light field oscillations enable the study of ultrafast phenomena on sub-cycle time scales. Electro-optic sampling (EOS) is a powerful field characterization approach, in terms of both sensitivity and dynamic range, but it has not reached beyond infrared frequencies. Here, we show the synthesis of a sub-cycle infrared-visible pulse and subsequent complete electric field characterization using EOS. The sampled bandwidth spans from 700 nm to 2700 nm (428 to 110 THz). Tailored electric-field waveforms are generated with a two-channel field synthesizer in the infrared-visible range, with a full-width at half-maximum duration as short as 3.8 fs at a central wavelength of 1.7 µm (176 THz). EOS detection of the complete bandwidth of these waveforms extends it into the visible spectral range. To demonstrate the power of our approach, we use the sub-cycle transients to inject carriers in a thin quartz sample for nonlinear photoconductive field sampling with sub-femtosecond resolution.

Dynamics of CCl4+ prepared by 800 nm strong-field ionization, as studied with X-ray transient absorption spectroscopy (XTAS) and quantum chemical calculations.

Understanding the relaxation pathways of photoexcited molecules is essential to gain atomistic level insight into photochemistry. Herein, we performed a time-resolved study of ultrafast molecular symmetry breaking via geometric relaxation (Jahn-Teller distortion) on the methane cation. Attosecond transient absorption spectroscopy with soft X-rays at the carbon K-edge revealed that the distortion occurred within 10 ± 2 femtoseconds after few-femtosecond strong-field ionization of methane. The distortion activated coherent oscillations in the asymmetric scissoring vibrational mode of the symmetry broken cation, which were detected in the X-ray signal. These oscillations were damped within 58 ± 13 femtoseconds, as vibrational coherence was lost with the energy redistributing into lower-frequency vibrational modes. This study completely reconstructs the molecular relaxation dynamics of this prototypical example and opens new avenues for exploring complex systems.

Today’s high-power laser systems are capable of reaching photon intensities up to 10 22 W cm −2 , generating plasmas when interacting with material. The high intensity and ultrashort laser pulse duration (fs) make direct observation of plasma dynamics a challenging task. In the field of laser-plasma physics and especially for the acceleration of ions, the spatio-temporal intensity distribution is one of the most critical aspects. We describe a novel method based on a single-shot (i.e. single laser pulse) chirped probing scheme, taking nine sequential frames at frame rates up to THz. This technique, to which we refer as temporally resolved intensity contouring (TRIC) enables single-shot measurement of laser-plasma dynamics. Using TRIC, we demonstrate the reconstruction of the complete spatio-temporal intensity distribution of a high-power laser pulse in the focal plane at full pulse energy with sub-picosecond resolution.

Figure 4. a) EOS (in red) and b) LPS (in blue) spectral response functions calculated with different GDD values applied to the VIS-UV pulse. c) EOS response calculated for a compressed VIS-UV pulse and different crystal thicknesses.

Simple and compact laser systems facilitate the stable and reproducible generation of high-power few-cycle laser pulses. We demonstrate the amplification of 15 fs pulses at 2.1 µm, employing a hybrid phase-matching scheme for optical parametric chirped pulse amplification. A combination of two BBO crystals with type-I and type-II phase-matching placed in close vicinity is utilized as a single amplification stage. This allows for a greatly simplified layout, achieving high conversion efficiency while avoiding the backconversion regime and the associated spatiotemporal distortions. The resulting system yields mJ-level pulses with integrated electro-optic sampling to directly measure the output waveform and study ultrafast light-matter interaction.

Access to the complete spatiotemporal response of matter due to structured light requires field sampling techniques with sub-wavelength resolution in time and space. We demonstrate spatially resolved electro-optic sampling of near-infrared waveforms, providing a versatile platform for the direct measurement of electric field dynamics produced by photonic devices and sub-wavelength structures both in the far and near fields. This approach offers high-resolution, time- or frequency-resolved imaging by encoding a broadband signal into a narrowband blueshifted image, lifting the resolution limits imposed by both chromatic aberration and diffraction. Specifically, measuring the field of a near-infrared laser with a broadband sampling laser, we achieve 1.2 µm resolution in space and 2.2 fs resolution in time. This provides an essential diagnostic for complete spatiotemporal control of light with metasurface components, demonstrated via a metalens as well as a meta-axicon that forms broadband, ultrashort, truncated Bessel beams in the near infrared. Finally, we demonstrate the electric field dynamics of locally enhanced hot spots with sub-wavelength dimensions, recording the full temporal evolution of the electric field at each point in the image simultaneously. The imaging modality opens a path toward hyperspectral microscopy with simultaneous sub-wavelength resolution and wide-field imaging capability.