Ultrashort and intense tunable Mid-IR source promise new insights into the investigation of electron dynamics in quantum materials. Recently, we have developed an OPA providing intense optical excitation in near- and mid-infrared region (1.7 to 8 µm), and it is now used as a pump for time- and angle-resolved photoemission (TR-ARPES). We will discuss preliminary TR-ARPES results on Bi2Te3 to demonstrate the exquisite peformances of our novel TR-ARPES endstation.
Upon photo-excitation of a molecule it will break apart. We can see fragments following direct, conventional dissociation paths, as well as fragments deviating from this minimum energy path. The latter are called roaming fragments and explore the potential energy landscape in a statistical manner. Dissociating and roaming fragments are directly captured using Coulomb Explosion Imaging (CEI) and individual pathways are distinguished based on state-of-the-art theory analysis.
Ultrashort high-energy visible pulses have enabled unprecedented opportunities in temporally resolving ultrafast dynamics in physics, chemistry, and biology. Until now, high-energy sub-10 fs visible pulses have been mostly obtained through complex non-collinear optical parametric amplification setups, followed by some pulse post-compression technique. Here, we present an alternative approach, which relies on considering the typically-undesired multimode nature of large-core hollow-core capillary fibers (HCFs) as an essential asset. In our experiments, 1 mJ 175-fs-long pulses centered at 1035 nm, emitted by an Yb:KGW (Pharos – Light Conversion) laser, were coupled into a 3-m-long HCF (few-cycle Inc.) filled with Argon gas. At a selected pressure of 2.9 bar, a fast energy transfer from the laser broadened via self-phase modulation towards the arising visible light was observed starting at around 0.8 mJ laser pulse energy. At the maximum pulse energy of 0.94 mJ, a continuous spectrum of visible light between 800 nm and 400 nm was measured, with an overall energy of approximately 30 µJ. To understand this process, we implemented 3D carrier-resolved pulse propagation simulations based on the guided mode theory. The simulations predict the direct formation of a pulse of about 5 fs right at the exit of the fiber, considering the visible spectrum in the range 525 - 750 nm. We found that the presence of higher-order modes is crucial to generate such visible pulses and that the Kerr effect is the dominant nonlinearity enabling the modal energy transfer. Experimentally, we characterized the visible pulses by means of a transient-grating frequency-resolved optical gating setup (TG-FROG). At 0.94 mJ and 2.9 bar, a visible pulse duration of 4.6 fs was measured. We also implemented a cross-correlation TG-XFROG, using the separately-compressed laser light and the visible pulses, which demonstrates the possibility of directly implementing high-energy NIR-pump VIS-probe measurements on a sub-10-fs scale.
Streak cameras are popularly used to passively record dynamic events for numerous studies. However, in conventional operation, they are restricted to one-dimensional field of view (FOV) imaging. To overcome this limitation, the multipleshot and the single-shot two-dimensional (2D) steak imaging approaches have been developed. For the former, the (x,y,t) datacube is acquired by combining the conventional manipulation of streak cameras with a scanning operation. For the latter, the (x,y,t) information is obtained by combining streak imaging with other imaging strategies, such as compressed sensing (CS). Despite contributing to many new studies, the multiple-shot methods require a large number of measurements to synthesize the datacube, and the single-shot approaches reduce the spatiotemporal resolutions or the FOV. Here, we overcome these problems by developing streak-camera-based compressed ultrafast tomographic imaging (CUTI), which is a new work mode universally adaptable to most streak cameras. Grafting the principle of computed tomography to the spatiotemporal domain, CUTI uses temporal shearing and spatiotemporal integration to equivalently perform passive projections of a transient event. By leveraging multiple sweep ranges readily available in a standard streak camera and a new CS-based reconstruction algorithm, the datacube of the transient event can be accurately recovered using a few streak images. Compared to the scanning-based multiple-shot 2D streak imaging approaches, CUTI largely reduces the data acquisition time. Compared to the single-shot methods, CUTI eliminates the trade-off between the spatial resolution or the FOV and temporal resolution.
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