Near-infrared imaging via upconversion in Er3+:CaF2 crystal with dual wavelength excitation.

We propose a system for imaging 1510 nm near-infrared (NIR) wavelength via upconversion (UC) luminescence in an Er3+-doped CaF2 crystal. Er3+ ions are excited from the ground to the excited state levels by an 800-nm pre-excitation wavelength, followed by the promotion of these ions to a higher energy level by the NIR excitation wavelength. Relaxation of these excited ions gives rise to 540 nm UC luminescence in the visible region, enabling the detection of the 1510 nm NIR wavelength. Using this UC scheme, 1510 nm was successfully imaged. Our system enables imaging of NIR wavelengths using low-cost optics and readily available Si-based detectors that are sensitive only to visible wavelengths, opening new possibilities for detection and imaging of NIR wavelengths.

Demonstration of a spherical plasma mirror for the counter-propagating kilojoule-class petawatt LFEX laser system.

A counter-propagating laser-beam platform using a spherical plasma mirror was developed for the kilojoule-class petawatt LFEX laser. The temporal and spatial overlaps of the incoming and redirected beams were measured with an optical interferometer and an x-ray pinhole camera. The plasma mirror performance was evaluated by measuring fast electrons, ions, and neutrons generated in the counter-propagating laser interaction with a Cu-doped deuterated film on both sides. The reflectivity and peak intensity were estimated as ∼50% and ∼5 × 1018 W/cm2, respectively. The platform could enable studies of counter-streaming charged particles in high-energy-density plasmas for fundamental and inertial confinement fusion research.

Refractive index measurements of solid deuterium-tritium.

Physical properties of tritium (T) and deuterium (D) have been of great interest as a fuel for nuclear fusion. However, several kinds of the physical properties in a cryogenic environment have not been reported. Optical properties in liquid and solid phases are indispensable for the quality control of the DT fuel. We study the dependence of the refractive index of solid DT on temperature. A dedicated cryogenic system has been developed and forms a transparent solid DT in a prism cell. Refractive index measurements based on Snell's law were conducted. The refractive indexes of solid DT are from 1.1618 ± 0.0002 to 1.1628 ± 0.0002 in the temperature range of 19.40 K to 17.89 K.

Tunable vacuum ultraviolet cross-luminescence from KMgF under high pressure as potential fast-response scintillator.

We report on the potential of the potassium magnesium fluoride (KMgF) crystal as a fast-response scintillator with tunable cross-luminescence (CL) emission wavelength through high-pressure applications. By performing first-principles density functional theory calculations using the Perdew-Burke-Ernzerhof (PBE) hybrid functional including exact exchange (PBE0) and Green's function and screened Coulomb interaction approximation as implemented in the Vienna Ab initio Simulation Package using plane-wave basis sets within the projector-augmented wave method, we identify the specific valence-to-core band transition that results in the experimentally observed CL emission at 148 nm (8.38 eV) and 170 nm (7.29 eV) wavelengths with intrinsically fast decay times of 290 ps and 210 ps, respectively. Uniform volume compression through hydrostatic high-pressure applications could decrease the energy gap between the valence and core bands, potentially shifting the CL emission wavelength to the ultraviolet (UV) region from 200 nm (6.2 eV) to 300 nm (4.1 eV). The ability to tune and shift the CL emission to UV wavelengths allows for the detection of the CL emission using UV-sensitive photodetectors in ambient atmosphere instead of highly specialized vacuum UV detectors operating in vacuum while maintaining the intrinsically fast CL decay times, thereby opening up new possibilities for KMgF as a fast-response scintillator.

Mid-infrared imaging through up-conversion luminescence in trivalent lanthanide ion-doped self-organizing optical fiber array crystal.

We propose a scheme for imaging mid-infrared (MIR) wavelengths via pre-excitation-assisted up-conversion luminescence in lanthanide ion (Ln3+)-doped Self-organizing Optical FIber Array (SOFIA) crystal. First, near-infrared pre-excitation wavelength excites an electron from the ground state to an excited state of Ln3+. Next, the MIR wavelength to be imaged promotes this excited electron to a higher-lying energy state. Finally, relaxation of the electron from the higher-lying energy state to the ground state emits the up-conversion luminescence in the visible region, completing the MIR-to-visible wavelength conversion. An analysis of the 4f to 4f intra-configurational energy level transitions in Ln3+, together with an appropriate selection of the pre-excitation wavelength and the visible luminescence constrained within the 500-700 nm wavelength range, reveals that trivalent erbium (Er3+), thulium (Tm3+), holmium (Ho3+), and neodymium (Nd3+) can be used to image MIR wavelengths. Our proposed scheme, called MIR imAging through up-Conversion LuminEscence in a SOFIA crystal, will enable the imaging of MIR wavelengths using low-cost optics and readily available silicon-based detectors in the visible spectral region and will open up new possibilities for MIR wavelength detection and imaging.

Effect of Substrate and Thickness on the Photoconductivity of Nanoparticle Titanium Dioxide Thin Film Vacuum Ultraviolet Photoconductive Detector.

Vacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO2) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO2, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO2 film deposited on SiO2 substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO2 detector is about 5.8 µs and is comparable to the 5.4 µs response time of a diamond UV sensor. The development of the TiO2 nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.

Petapascal Pressure Driven by Fast Isochoric Heating with a Multipicosecond Intense Laser Pulse.

Fast isochoric laser heating is a scheme to heat matter with a relativistic intensity (>10^{18} W/cm^{2}) laser pulse for producing an ultrahigh-energy-density (UHED) state. We have demonstrated an efficient fast isochoric heating of a compressed dense plasma core with a multipicosecond kilojoule-class petawatt laser and an assistance of externally applied kilotesla magnetic fields for guiding fast electrons to the dense plasma. A UHED state of 2.2 PPa is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation confirmed that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states.

Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core. Here, we demonstrate a factor-of-two enhancement of laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a magnetic field of hundreds of Tesla that is applied to the transport region from the REB generation zone to the core which results in guiding the REB along the magnetic field lines to the core. This scheme may provide more efficient energy coupling compared to the conventional ICF scheme.

Heating efficiency evaluation with mimicking plasma conditions of integrated fast-ignition experiment.

A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.

Note: Light output enhanced fast response and low afterglow 6Li glass scintillator as potential down-scattered neutron diagnostics for inertial confinement fusion.

The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the world's largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Mégajoule.

Pr3+-doped fluoro-oxide lithium glass as scintillator for nuclear fusion diagnostics.

Experimental results are presented on the neutron scintillating properties of a custom-designed Pr3+ (praseodymium)-doped lithium (Li) glass. Luminescence was observed at 278 nm wavelength, originating from the 5d-4f transition. Time-resolved measurements yielded about 20 ns decay times for ultraviolet and x-ray excitation while much faster decay times of about 6 ns were observed for alpha particle and neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University reveal that it can clearly discriminate fusion neutrons from the much stronger x-rays signals. This material can promise improved accuracy in future scattered neutron diagnostics.