Multicolor and multi-spot observations of Starlink's Visorsat

This study provides the results of simultaneous multicolor observations for the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite, STARLINK-1113 in the $U$, $B$, $V$, $g'$, $r$, $i$, $R_{\rm C}$, $I_{\rm C}$, $z$, $J$, $H$, and $K_s$ bands to quantitatively investigate the extent to which Visorsat reduces its reflected light. Our results are as follows: (1) in most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on Visorsat, therefore, contributes to the reduction of the reflected sunlight; (2) the magnitude at 550 km altitude (normalized magnitude) of both satellites often reaches the naked-eye limiting magnitude ($<$ 6.0); (3) from a blackbody radiation model of the reflected flux, the peak of the reflected components of both satellites is around the $z$ band; and (4) the albedo of the near infrared range is larger than that of the optical range. Under the assumption that Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering factor, $C_{\rm f}$, of the sunshade on Visorsat, using the blackbody radiation model: the covering factor ranges from $0.18 \leq C_{\rm f} \leq 0.92$. From the multivariable analysis of the solar phase angle (Sun-target-observer), the normalized magnitude, and the covering factor, the phase angle versus covering factor distribution presents a moderate anti-correlation between them, suggesting that the magnitudes of Visorsat depend not only on the phase angle but also on the orientation of the sunshade along our line of sight. However, the impact on astronomical observations from Visorsat-designed satellites remains serious. Thus, new countermeasures are necessary for the Starlink satellites to further reduce reflected sunlight.Comment: 31 pages, 9 figures, published in PAS

Hot electron and ion spectra on blow-off plasma free target in GXII-LFEX direct fast ignition experiment

Polystyrene deuteride shell targets with two holes were imploded by the Gekko XII laser and additionally heated by the LFEX laser in a direct fast ignition experiment. In general, when an ultra-intense laser is injected into a blow-off plasma created by the imploding laser, electrons are generated far from the target core and the energies of electrons increase because the electron acceleration distance has been extended. The blow-off plasma moves not only to the vertical direction but to the lateral direction against the target surface. In a shell target with holes, a lower effective electron temperature can be realized by reducing the inflow of the implosion plasma onto the LFEX path, and high coupling efficiency can be expected. The energies of hot electrons and ions absorbed into the target core were calculated from the energy spectra using three electron energy spectrometers and a neutron time-of-flight measurement system, Mandala. The ions have a large contribution of 74% (electron heating of 4.9 J and ion heating of 14.1 J) to target heating in direct fast ignition

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.Kojima S., Abe Y., Miura E., et al. Demonstration of a spherical plasma mirror for the counter-propagating kilojoule-class petawatt LFEX laser system. Optics Express 30, 43491 (2022); https://doi.org/10.1364/oe.475945

Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)

Fast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. \u27Direct heating\u27 means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed \u27axial\u27 and \u27transverse modes\u27, respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8%< η <2.1% at low power (low LFEX energy) and 0.4%< η <2.5% at high power (high LFEX energy). For the transverse mode, 2.6%< η <7% at low power and 1.5%< η <7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η <12%, which appeared near to the η for the transverse mode, except that the error bar is very large

Amorphous nanostructuralization in HOPG by 10(14) W cm(-2) laser

This reports provide an amorphous nanostructuralization technique on the surface modification in Highly Oriented Pyrolytic Graphite (HOPG) by using a femtosecond laser. We showed, for the first time, that the surface of HOPG is changed to the amorphous nanostructuralization graphite by using a femtosecond laser-driven compression technique. Our results also suggest that the HOPG surface is changed until the deeper area from the surface by the laser-driven shock wave. A single shot of a femtosecond laser beam (1.27,similar to,1.33x10(14) W cm(-2) in intensity, with 2mm-diameter, and 110 fs in pulse width) is irradiated under the vacuum ambience onto a 2mm-thick of HOPG. The calculated impact pressures on a sample was 8.3 similar to 8.7 GPa. Crystal structure in the HOPG were analyzed using a Raman spectroscopy and an X-ray diffraction, those analyzing depth from the surface were 50 nm and 350pm, respectively

Hot Electron and Ion Spectra in Axial and Transverse Laser Irradiation in the GXII-LFEX Direct Fast Ignition Experiment

An electron spectrometer was used to measure the electron and ion spectra in two different irradiations of implosion laser to the deuterated spherical shell targets at the direct fast ignition experiments on the Gekko-LFEX facility. In the transverse irradiation against the LFEX laser axis, the low effective hot electron temperature (Teff) and huge neutron yield (Ny) could be obtained although high Teff and low Ny could be observed in the axial irradiation. In the transverse irradiation, the efficient core heating could be obtained because the laser-plasma interaction position is close to the core and the diffusive/ion drag heating may be effective