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The authors propose an energy cycle based on a renewable fuel. Magnesium is chosen as an energy carrier and is combusted with water to retrieve energy using many power devices. MgO, the combustion residue, is reduced back to Mg by laser radiation generated from solar and other renewable energy sources. They have achieved an energy recovery efficiency of 42.5% for converting MgO to magnesium, using a laser. Combined with a demonstrated 38% efficiency for converting an artificial sunlight source (metal halide lamp) into laser output energy indicates that the proposed energy cycle is already in a feasible range for practical use.

Spherical solid tin targets were illuminated uniformly with twelve beams from the Gekko XII laser system to create spherical plasmas, and the extreme ultraviolet (EUV) emission spectra from the plasmas were measured. The highest conversion efficiency of 3% to 13.5nm EUV light in 2% bandwidth was attained for an irradiance of around 5×1010W∕cm2. The experimental results were reproduced fairly well using a theoretical model taking the power balance in the plasma into consideration.

The dynamic behavior of a blowoff plasma of a thin‐layered target was observed optically by shadowgraphy. The results are explained by means of ablative and explosive models. Experimental evidence of highly efficient beam coupling which includes hydrodynamic driving of the plasma is presented.

Thermonuclear burn time and burn duration in ablatively driven high‐aspect‐ratio targets have been measured. While the observed burn times were in agreement with results of a one‐dimensional hydrodynamic simulation, the observed burn durations were excessively long.

Energy flow to a target rear surface due to hot electrons was experimentally studied by irradiating a 10‐μm wavelength laser. Lateral heat conduction produced a plasma of low and uniform temperature, whose size was nearly one order larger than that of a laser focal spot for plane targets. Experimental results were simulated by using a one‐dimensional hydrodynamic simulation code to investigate the effects of hot electron diffusion.

Lateral transport of hot electrons on a spherical target irradiated with two beams of CO2 laser (4.8×1014 W/cm2) is studied by spatially resolved Kα x‐ray measurements. The hot‐electron energy and spatial distribution in the target are found to depend on the method of irradiation: tight and overlapped focusing conditions.

In ambient atmosphere, a protuberant shock wave driven by laser‐produced fast ions was observed by time‐resolved photographs with 5‐μm and 30‐psec resolutions. This protuberant shock wave appeared only when the incident laser intensity exceeded 5×1013 W/cm2. At this intensity, the fast ions were observed using the charge collectors.

Emission from the rear side of 263‐nm laser irradiated thin foil targets shows the temporal profile of rear surface heating by several processes with different energy transport mechanisms. Formation and decay of shock waves are observed by varying target thickness. Propagation of a thermal conduction wave is clearly separated from the shock propagation.

We propose a 1‐cm‐long cylinder‐type target as the gain medium of a recombination‐pumped extreme‐ultraviolet (XUV) laser. The gain medium plasma was pumped by a long‐pulse CO2 laser (400 J energy in 50 ns pulse duration). At the C VI 3d–2p transition (18.2 nm) we obtained the gain‐length product up to 2.4, which was estimated from the line intensity ratio of the axial to transverse directions. The electron temperature of 54 eV and density of 1.2×1019 cm−3 near the cylinder wall measured using soft‐x‐ray spectroscopy satisfied the condition for the generation of the population inversion between n=3 and 2 levels of the C VI ions.

A new method which suppresses target preheating by hot electrons is proposed. The suppression was verified by means of particle measurements on the rear side of a foil irradiated by a CO2 laser with a thick plate placed in front of the irradiated foil to absorb the energetic electrons which preferentially expand from the critical surface. The results can be explained by the generation of the electrostatic field between the foil and the plate.

A shock wave in fusion fuel filled in a glass microballoon target was directly observed. The shock speed and the width of the shock front were 5×107 cm/s and a few μm, respectively, which are in good agreement with the shock‐tube theory.

Mechanically hard and broadband gradient refractive index antireflection coating was developed. It has a high damage threshold of ≳6 J/cm2 at 355 nm and 12–13 J/cm2 in the visible to near‐infrared region. It will be applicable to high power pulsed lasers as well as to industrial uses.

Strong anisotropy on angular distribution of alpha particles in D‐T reaction was observed in locally irradiated exploding pusher mode compression. This indicates asymmetric generation of an electric field localized around the laser irradiated spots whose scale length and shape were estimated to be about 300 μm and radially extended from the irradiated spots.

An energy distribution of transmitted electrons through thin‐foil targets irradiated by a tightly pinched relativistic electron beam has been measured by a multichannel electrostatic particle energy analyzer. The experimental result indicates the existence of an anomalous energy dissipation of beam electron in low‐z target.

X‐ray conversion efficiency in a 0.53‐μm laser‐produced copper plasma is studied in the 1.5–5.0 keV range as a function of laser pulse duration (τL) with a laser intensity of 1×1014 W/cm2. The efficiency increases as τ1.3L at pulse lengths of less than 400 ps. For a 200‐ps pulse duration, an enhancement of the conversion efficiency is observed with the use of a prepulse. The efficiency is found to be proportional to the scale length of a preformed plasma. Enhancement of a factor 3 is observed for the shots with a prepulse.

The first demonstration of a fuel density‐radius product measurement using secondary nuclear fusion reactions is presented. This technique involves using neutrons and protons generated by DT {T(d,n)α} and D3He {3He(d,p)α} fusion reactions, respectively, in a pure deuterium fuel.

Driving pressure uniformity on the pusher surface has been significantly improved using a thick low density foam coated pellet with 120‐ps laser pulse irradiation. The pusher surface is geometrically kept at 100 μm from the laser absorption region. The hydrodynamic converging mechanism in the foam medium may be responsible for the observed smoothing.

Measurements of foil acceleration by streaked x‐ray shadowgraphy are compared with optical shadowgraphy and the ablation pressure measured by layer burnthrough. The latter two show a factor 3–4 discrepancy with the x‐ray shadowgraphy.

We obtained damage‐resistant crystals of potassium dihydrogen phosphate (KDP) by reducing organic impurities in the growth solution. To prevent organic impurity exuded from the wall of the growth vessel, Pyrex glass was used. The residual organic impurities, which mainly derived from KDP raw powder, were reduced by photochemical dissociation using a combination of ultraviolet light and an oxidant (hydrogen peroxide). The resultant total organic carbon of the solution was less than 0.1 ppm. The damage threshold of the crystals grown from this solution was always high (20–22 J/cm2), which is about three times higher than that of crystals grown by conventional methods.

A laser plasma isolator was developed to attenuate a retropulse in a high‐power CO2 laser system. An attenuation ratio of 1/20 of a main laser beam (∼1‐J 3‐nsec pulse‐width FWHM) was obtained by blowing off a carbon plasma induced by a plasma production laser beam (∼0.5‐J 3‐nsec pulse‐width FWHM) onto the waist of the main laser beam.