Institute for Laser Technology

Zero-dimensional (0D) metal halide scintillators have attracted considerable attention owing to their exceptional emissive properties derived from strongly localized self-trapped excitons.In this paper, we report the development of a novel thermal neutron scintillator-Na2-xLixHfI6 (0 x 2)-achieved by strategically substituting lithium for the Na of the 0D Na2HfI6 host.The Na2HfI6 host material has a 0D structure with an [HfI6] 2-octahedral unit, exhibiting broad red-to-near-infrared (NIR) emission with a large Stokes shift, driven by strong electron-phonon coupling (S = 56.7)and high exciton binding energy (Eb = 200 meV).Density functional theory calculations revealed that the A site cations (Na + and Li + ) did not contribute to the valence or conduction band edges.This indicated that the fundamental electronic structure was preserved upon Li substitution; consequently, the Li-alloyed Na2-xLixHfI6 also exhibited the characteristic broad red-to-NIR emission.Remarkably, the Na1.5Li0.5HfI6crystal demonstrated a light yield of 37,000 ph./nth under thermal neutron irradiation, approximately six times higher than that of the standard 6 Li glass scintillator (GS20).With the fast decay time (650 ns) as red/NIR emission, high light output, and red/NIR emission wavelength, Na2-xLixHfI6 offers a robust and high-performance alternative material to conventional scintillators.

Nanostructured targets showed improved interaction with ultra-intense laser pulses in comparison to planar ones, both in simulations and in experiments. By increasing the surface area, the absorption and conversion efficiency of the laser energy to the accelerated particle energy are enhanced due to volumetric heating, leading to advanced proton acceleration, x-ray emission, ultra-high energy density matter creation, and terabar pressure generation. This work is focused on exploring the limits of the electrodeposition methods for the fabrication of nanostructured targets suitable for ultra-intense laser experiments at focused intensities as high as 1023W/cm2. The geometrical characteristics of the nanostructures are expanded to meet a wide range of experimental requirements: diameter, length, distance between structures, and substrate thickness. Nickel nanotubes and nanowires on few hundreds nanometer thick substrates were fabricated using porous alumina as template, obtained by aluminium anodization in various electrolyte solutions. The resulting structures revealed diameters and spacing of several hundreds of nanometers, with length varying between 1–10 micrometers, covering homogeneous areas of several square centimetres. The influence of temperature on the current density, with two electrolyte mixtures containing oxalic, citric, phosphoric acids used for anodization, is also reported. In the initial testing using high-power lasers, we found an increase in proton energy by 1.5 times and flux at high-energy tail of the spectrum higher by an order of magnitude, from the nanostructured targets.

The structure and physical properties of materials, such as elementary exciton processes, are closely interrelated. Doping copper ions in colloidal semiconductor quantum dots (QDs) has been shown to suppress hot electron relaxation. However, the relationship between the local environment of the heterometal ions in the host crystal and the physical properties has been insufficiently explored. In this study, CdSe and InP QDs were synthesized in the presence of heterometal ions. Copper ions were doped into CdSe QDs and segregated into InP QDs, as confirmed by X-ray absorption fine structure measurements, leading to hot electron relaxation being suppressed only in the CdSe QDs. On the basis of these findings, we developed a design strategy and successfully suppressed hot electron relaxation in InP QDs by introducing chromium ions. Understanding the local structure of dopants in QDs is essential for elucidating their physical properties and enabling the rational design of dopants to achieve novel functionalities.

Organic ligand-protected gold clusters (AuCs) consist of a metal core surrounded by organic ligands and exhibit unique properties that depend on their chemical compositions. The physical properties of AuCs, important for applications in photoenergy conversion, are strongly influenced by organic ligands because of their high surface-to-volume atomic ratio compared with gold nanoparticles. However, the influence of ligands on ultrafast carrier dynamics remains unclear. In this study, we synthesized triphenylphosphine (TPP)-derivatized Au11 clusters with different substituent groups and analyzed their excited-state dynamics using femtosecond transient absorption spectroscopy and large-scale hybrid density functional theory calculations without simplifying the AuC structures. Although the Au11 core structure remained nearly identical, the excited-state dynamics varied. The excited-state lifetime of TPP-H/Au11 was longer than that of TPP-F/Au11, attributed to the reduced orbital overlap between the highest occupied and lowest unoccupied molecular orbitals. The trifluoromethyl group exhibits a stronger electron-withdrawing effect than the fluorine group. Because the groups on the ligands influence the gold core through a resonance effect rather than inductive effects, the S1 state lifetime of TPP-CF3/Au11 was longer than that of TPP-F/Au11. This study clarifies how the presence of different groups modulates the photophysical properties of AuCs and provides insights into the design of gold-cluster-based materials for photoenergy conversion applications.

In this study, we conducted a basic study on the visualization of ammonia gas using a flash lidar, which uses the resonance Raman effect, for the purpose of visualizing gas leak locations and analyzing gas flow. We have previously developed a remote ammonia leak detection technology (resonance Raman LIDAR) using the resonance Raman effect. In general, the Raman effect has significant advantages such as the ability to identify various substances that cannot be detected by other optical methods and to perform spectroscopic measurements of multiple substances. On the other hand, the Raman effect is extremely weak compared to other light-matter interactions, so the resonance Raman effect, which can significantly enhance the weak Raman effect, is effective for remote detection of trace components. The resonance Raman effect is a phenomenon in which Raman scattered light corresponding to a conjugate vibration mode is greatly enhanced when the target substance is excited by light with a wavelength corresponding to the electronic absorption band of the target substance. In actual measurements, the pattern of the ultraviolet-visible absorption spectrum indicating the electronic transition energy of the target substance serves as an indicator of the applicability of the resonance Raman effect, and the fifth harmonic of the Nd:YAG laser (wavelength 213nm) matches the electronic absorption band of ammonia. Resonance Raman LIDAR can measure gas concentrations and their distance remotely, but to obtain two- or three-dimensional images of the gas concentration distribution, it is necessary to scan the optical axis of the laser and observation optical system. If flash lidar, a technology that expands a laser beam and emits it into the observation space like a camera flash and uses a camera as a detector to instantly visualize the gas concentration distribution as a two-dimensional image, could be applied to ammonia gas leak detection, its usefulness as a safety technology would be enhanced. In this study, a pulsed laser with a wavelength of 213nm was used as the excitation light source and successfully visualized ammonia gas by observing the 4318cm^-1 spectra among the multiple resonance Raman spectra of ammonia.

In relativistic plasma expansion, a relative motion of plasma components causes absorption of spectral lines to be Doppler-shifted with respect to the emission line centers. The shift of spectral line can be of an order or exceeding the natural linewidth, leading to a significant reduction in self-absorption and optical thickness of the plasma. In this paper we experimentally examine the effect of femtosecond relativistic laser plasma expanding from both sides of the solid foil target. In an experiment, a hot plasma x-ray source in a 1–2 μm thin 4-chlorostyrene foil was created by high-contrast ∼ 1 × 1021 W/cm2 pulses delivered by the J-KAREN-P facility. In addition, the rear side of the target was heated by 1/100 of the main pulse power with a controlled few-nanosecond time delay. It is demonstrated that the high velocity of the downstream and upstream (from the rear side) plasma expansion essentially induces plasma transparency for K-shell emission from He-like chlorine ions dominating the ion charge distribution.

ABSTRACTInduced Compton scattering (CS) is a quantum nonlinear interaction between an intense electromagnetic field and a rarefied plasma. Although the induced CS is expected to occur in radiation fields with high brightness temperatures such as pulsars in nature, the principle of induced CS has not been proven experimentally. Therefore, we conducted a proof‐of‐principle experiment of induced CS using an ultra‐intense laser. We measured the scattered spectra due to the interaction between the ultra‐intense laser and plasma. The observed spectrum shows a nonlinear redshift, which can be explained by induced CS. We also performed particle‐in‐cell simulations, in which induced CS is not included, and found that the experimental results are not explained by classical plasma physics.