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A new concept for improving the laser intensity distribution on an inertial confinement fusion target using a phase-controlled multi lens array has been proposed. Circular and hexagonal element lens apertures have been examined, and the circular aperture which eliminated azimuthally asymmetric intensity distribution was chosen. The diffraction fringe of the elementary lens was mitigated in a one-dimensional lens array using edge-shaped plates of a super-Gaussian phase profile. Uniform beam profiles were obtained using a one-dimensional array with 7 spherical lenses and a two-dimensional array with 37 lenses. An approximately flat-top intensity distribution was realized with the lens array with 37 lenses.

We describe the physical mechanisms of the recombination-pumped laser action of the carbon vi Balmer-α line (18.2 nm), which is expected to have a gain duration of as long as 10 nsec in the cylindrical-wall-confinement plasmas produced by a CO_2 laser. We present the modeling of the laser action with the combination of the one-dimensional hydrodynamic code and the multilevel atomic rate equation code. The gain coefficient derived from the calculated dynamics of the level populations is somewhat smaller than the experimental data. Additional expansion cooling may account for the discrepancy. The higher gain coefficient of the order of 5 cm^−1 is expected when we irradiate a high-Z doped cylinder-type target.

Potassium titanyl phosphate (KTP) crystals were grown from the K6P4013(K6) flux using a temperature falling method. Real-time mesurement of the weight of the crystal during the growth was carried out with an electronic load cell in order to estimate the bulk growth rate. It was found that the growth rate of the crystal became too fast and liquid that inclusions were formed during a certain growth term in the growth period by excessively high supersaturation when the temperature falling rate was constant. In order to avoid this process, by changing the temperature cooling rate, a KTP crystal, 32 x 42 x 87 mm (ax bx c) without liquid inclusion was successfully obtained. The refractive indices, which were measured by means of laser interferometry, were found to be varying along the growth direction. Variation of the refractive indices was approximately 1.6 x 10-4for nzand 7.1 x 10-6for nxy, giving rise to a change of the phase matching direction of up to 0.38°.

A three dimensional simulation software system developed to estimate a free electron laser (FEL) gain has been applied to FEL using a standard plane polarized wiggler and an alternately shifted magnet wiggler. It is seen for the latter wiggler that a large filling factor could be selected and each maximum gain corresponding to each orbit of electron beam concentrates at a certain frequency region of FEL radiation. It is, therefore, implied that a proper shift between the adjacent magnets in the wiggler produces the improvement of the FEL gain.

A new plastic microlens array, consisting of 900 lenslets, has been developed for the Shack Hartmann wave-front sensor. The individual lens is 300 μm × 300 μm and has a focal length of 10 mm, which provides the same focal size, 60 μm in diameter, with a constant peak intensity. One can improve the wave-front measurement accuracy by reducing the spot centroiding error by averaging a few frame memories of an image processor. A deformable mirror for testing the wave-front sensor gives an appropriate defocus and astigmatism, and the laser wave front is measured with a Shack Hartmann wave-front sensor. The measurement accuracy and reproducibility of our wave-front sensor are better than λ./20 and λ/50 (λ = 632.8 nm), respectively, in rms.

The propagation characteristics of frequency-swept laser pulse in near-resonant medium were studied by the numerical calculation and the experiment. The characteristics of the frequency-swept laser pulse has been largely modified in comparison with the frequency-fixed laser pulse. These modifications were demonstrated also experimentally for Sm vapor. The results agreed well with the numerically calculated.

A hybrid planar wiggler with a period of 20 mm has been studied as the simplest one which gives the strong field including some higher harmonic components by selecting proper sizes of the ferromagnetic and the permanent magnet. Small gap length of the wiggler and small width of permendur satisfy these conditions to a certain degree. Gain analysis of FEL suggests that for high wiggler field of K>1 ∼ 1.6, higher harmonic gains are improved primarily due to its strong field, and for low wiggler field of K< 1 ∼ 1.6, they are mainly due to the modification of the wiggler field distribution.

A novel polarimeter for measuring the two-dimensional (2D) thermal- and mechanical-stress-induced birefringence in solid-state laser materials such as Nd:YAG is proposed. Using this device, we could sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with sign when δ < π/4. The 2D thermal- and mechanical-stress-induced birefringence in a laser-diode-pumped Nd:YAG rod was successfully measured with the proposed polarimeter. We also found an active quarter-wave Nd:YAG phase retarder.

Efficient lasing of Nd:Ca (Nb, Ga)_2–x Ga_3–garnet (CNGG) disordered crystal pumped by a laser diode was demonstrated. In the end-pumped cw lasing experiment with a single-stripe diode, a slope efficiency of 24.2% and a maximum optical conversion efficiency of 19.3% were obtained. It was shown that the dependence of cw output power on the pump wavelength is insensitive compared with Nd:YAG because of the broad pump absorption bandwidth of Nd:CNGG. From the diode-bar-pumped experiment, it was confirmed that Nd:CNGG is a promising material for diode-bar pumping to obtain high average power with good beam quality, because of its advantages of a broader pump absorption band compared with that of Nd:YAG and the higher thermal conductivity compared with Nd-doped glasses.

A newly designed jet-type, water-cooled heat sink (the funryu heat sink, meaning fountain flow in Japanese) yielded 255-W cw laser output at 808 nm from a 1-cm bar made from InGaAsP/InGaP quantum-well active layers with a 67% fill factor [70 quantum-well laser diode (LD) array along the 1-cm bar]. A funryu heat sink measuring 1.1 mm in thickness gave the LD 0.25 °C/W thermal resistance, one of the lowest values achieved with a 1-cm LD bar. Over a short period of operation, the device reached a maximum cw power of 255 W.?To the best of our knowledge, this is the highest power ever achieved in 808-nm LD operation. In the future, the funryu heat sink may be capable of 80-W cw operation over an extended lifetime of several thousand hours.

We measured the two-dimensional birefringence compensation in laser-diode (LD) pumped Nd:glass (HAP4) laser rods with a high-sensitivity polarimeter. The compensation was performed by inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods with conductive cooling. A considerable reduction of birefringence loss from 9.8% to less than 0.9% after compensation was observed.

A wide range of tunability (1030-1100 nm) was demonstrated with an Yb:YAG laser crystal. The measured bandwidth of ???70 nm corresponds to the Fourier-limited pulse width of ?t?17 fs. This result indicates a new potential of the Yb:YAG as a direct laser-diode (LD)-pumped femtosecond laser amplifier.

To improve the harmonic gain of Free Electron Laser (FEL), we have developed a wiggler having a harmonic wiggler field. We call such a wiggler the "modified wiggler". The modified wiggler consists of a conventional planar wiggler and high-permeability shims. Owing to the simplicity of design, we can develop wigglers having various types of modified fields, easily and economically. We show the design basis for the modified wiggler. Then, we develop a modified wiggler for 5th-harmonic generation.

An experiment on electron beam energy recovery systems has been performed using a laser-heated electron gun and a multistage electron collector. Modeling of the laser heating indicates that the cathode temperature is proportional to the one-fourth power of laser power. The energy recovery efficiency of 99.8% of the designed collector is calculated using a computer code with a beam current of about 10 mA and -75 keV. In the first phase of the recovery experiment, potentials of the collector electrodes are provided through a voltage divider of several hundred megaohms. In order to overcome the drawback of voltage-divider resistance, two high-voltage power supplies are provided in the second phase of the experiment, and charge and energy recovery efficiencies are measured.

We report the generation of long-life plasmas confined by the heavy shell surrounding a plasma produced by lasers. We also demonstrate the neutron production from shell-confined carbon-deuterium plasmas using a GEKKO XII glass laser system at 1.05 µm and 0.53 µm wavelengths. A maximum neutron yield of more than 108per shot without an implosion was obtained. Analyzing these results with the hydrodynamic simulation code, we propose the required conditions for demonstrating magnetic thermal insulation observed by the neutron measurement.

We have developed a conceptual designing technique of a laser diode pumped solid state laser system having high peak power, high efficiency, good beam quality, and high repetition rate. Using this technique, we evaluated the feasibility of the systems with several solid state laser materials for the laser fusion reactor driver with 10 MJ blue output, 10% overall efficiency, and 10 Hz repetition rate. The systems with such as HAP4 glass, Nd:SiO2glass, Nd:Y:CaF2crystal, and Tm, Ho:YAG crystal are shown to be attractive candidates for the reactor driver while the systems with such as LHG8 glass, Nd:YAG crystal, and Tm:YAG crystal will not be selected as the candidates. For an economical laser fusion reactor driver, the solid state laser materials are required to have the following properties; \hbar?/??10 J/cm2(\hbar?: the laser photon energy, ?: the stimulated emission cross section), a thermal shock parameter of ?3 W/cm, a nonlinear index of refraction smaller than ?3×10-13esu, and a fluorescence lifetime of ?4 ms.

Arbitrary temporal waveform control can be achieved by means of amplifier gain control with a chirped laser pulse. In order to simulate precise waveforms of laser pulses, we developed a multilevel simulation code with transitions between each manifold. Using the developed code, we examined the generation of required temporal waveforms for laser fusion experiment. The maximum amount of chirping decreased considerably at low input intensity and large amplifier gain. In the case of the calculation for a specialized laser system (Gekko XII), a tailored pulse shape can be generated with less than 4 nm chirp, using the current modulation technique. Comparing the amplified pulses with chirping to those without chirping, peak intensity and energy up to peak were 2.34 and 1.41 times higher, while total energy was 0.528 times lower. It was indicated that frequency chirping is one of the most promising methods for generating the tailored pulses for future laser fusion experiments.

A single-mode laser beam has a partially incoherent nature. By expressing such a single-mode beam as an array of square-root damping waves, we have derived a factor that describes the influence of the incoherence of a single-mode pump on second-harmonic generation. This factor is analytically formulated as a function of the ratio of crystal length to laser coherence length. When this ratio is smaller than 1.1, the value of the factor is above unity with a maximum of 1.253, indicating that a single-mode pump leads to enhanced second-harmonic intensity.

The effect of an overcoat layer on highly reflective coatings used for high-average-power lasers is presented. For high-average-power lasers, it is important to diffuse temperature localized due to such factors as impurity absorption in the coating. It was predicted from the calculation of thermal diffusion that the temperature rise was considerably relaxed in the radial direction by use of an overcoat layer which had high thermal conductivity. The damage threshold at a pulse repetition rate of 30 Hz was increased to about 20 J/cm2from about 12 J/cm2by adding an Al2O3overcoat layer to a highly reflective coating.

An imaging X-ray microscope using a laser plasma X-ray source, an objective zone plate and an ellipsoidal condenser mirror with multilayer coating is described. The 3.37 nm line emission from a carbon plasma is filtered and focused by the ellipsoidal condenser mirror and used as a light source. A magnified image (magnification: ×287) of a gold zone plate was obtained by a back-illuminated charge coupled device (CCD) whose pixel size is 22 µm×22 µm. The 0.4-µm-period pattern (outermost zones: 0.27 µm line and 0.13 µm space) is clearly resolved.

A quarter-wave retardation was obtained by mechanically induced stress in a Nd:YAG laser rod and a laser gain of 1.15 at 1064 nm was obtained by pumping with a quasi-CW 300 W laser-diode array at 808 nm. The laser rod was held in a brass heatsink in which the mechanical stress was induced horizontally by means of screws. The effective quarter-wave area was measured to be 1 mm (vertical)×2 mm (horizontal) in the center of the 4 mm-diameter Nd:YAG rod by means of a newly constructed polarimeter.

The deuterium-tritium (D-T) thermonuclear reaction region of a laser-driven large-high-aspect-ratio target, which contains D-T mixture gas, has been diagnosed with an ?-particle imaging technique using a pinhole camera. The residual pusher region at the maximum compression has also been observed as an image of scattered ?-particles. Comparison between the ?-particle image and a two-dimensional hydrodynamic simulation shows that laser energy balance significantly influences the implosion uniformity.

Dipole matrix elements were measured for two transitions of the gadolinium atom by detecting the laser-induced fluorescence as a function of laser intensity using Rabi flopping. Those values are 2.7×10-19and 3.0×10-19esu ·cm for 9D2-9F2(0-17381 cm-1) and 9D5-9D4(999-17931 cm-1), respectively. Optical Bloch equations for two-level atoms were calculated for each pair of magnetic sublevels, where the effects of inhomogeneous broadening and laser intensity fluctuation were included. Experimental results were well described by this model. This method is very useful for determining a dipole matrix element which is one of the basic parameters for laser isotope separation.

We report the high-sensitivity measurements of two-dimensional (2D) thermal birefringence distribution in a laser-diode (LD) pumped Nd:glass (HAP4) laser under lasing (at 1054 nm) and under no lasing conditions. The thermal birefringence was reduced under the lasing condition owing to the depletion of stored energy by stimulated emission. By inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods, almost perfect birefringence compensation was achieved. The power loss due to thermal birefringence was evaluated quantitatively using the Jones matrix method. A considerable reduction of power loss, from over 12% before compensation to less than 0.4% after compensation, was observed. The output performance of this laser was in fairly good agreement with the estimation after taking into account the power loss due to thermal birefringence.

The temperature dependence of the emission cross-section of Yb (5 ×1020atoms/cm3)-doped fluorophosphate glass has been investigated in the temperature range from 77 K to 380 K. The emission cross-section has been evaluated from the measured fluorescence spectra and the lifetime, using the Füchtbauer-Ladenburg formula. A large change in the emission cross-section from about 0.6×10-20cm2at 380 K to 1.1×10-20cm2at 77 K was obtained by decreasing the temperature. The effect of reabsorption is found to be significant even at temperatures as low as 160 K which leads to underestimation of the emission cross-section values.

Type I and Type II second-harmonic generations (SHG) with a randomly phased multimode pump have been theoretically analyzed by considering phase mismatch and fundamental bandwidth effect. The equations obtained in the paper are formulated in a very concise and analytic form, which can be used to evalute both conversion efficiency and spectrum. We found that the previously recognized multimode enhancement effect does not exist in Type II SHG. The issue of harmonic instability due to multimode pumping has been also discussed.

Hot electron energy distribution in one-dimensional Cannonball target irradiated by a 10.6 µm laser pulse was investigated by using a multilayered foil technique. The experimental results suggested that the energy distribution of hot electrons in the Cannonball target was quite different from that in the simple planar target. We found that the high energy tail was truncated due to the effects of the presence of front disk in the Cannonball assembly. It is expected that Cannonball targets can quite effectively suppress the hot electron preheating at 10.6 µm laser wavelength.

A new concept of ion beam target is proposed. Ion beam energy was injected inside a solid gold shell. Energy of the radiation converted from the beam was confined and transported inside. This effect was called the Mahobin effect. If the Mahobin target is compared with a direct driven target, several advantages such as power amplification, brightness reduction and higher gain can be expected. Total implosion effciency was estimated to be more than 10%.

A Parameter survey for an inductive storage pulse compression system in a vacuum is presented. The plasma erosion switch was considered a fast opening switch. The optimum power amplification and efficiency were obtained with respect to opening start time, input pulse width and load impedance. A switch with faster opening speed was desired for the high preformance of the pulse compression system. An analysis of the plasma erosion switch showed that switch plasma which has a low density, small area and a high injection velocity is required for the pulse compression system.

A multilayer thin-film polarizer with high damage resistance has been developed by adopting a new coating design that minimizes the induced electric field intensity within the multilayer coating. The damage threshold was ?11 J/cm2for the p-polarized incident beam from the coating side and ?17 J/cm2for the s-polarized backward-reflected beam from the substrate side for a 1.053 µm laser with a pulse width of 1 ns.

A focused proton beam of up to 2×1010W/cm2was obtained using a pinch-reflex ion diode connected to a Reiden IV generator. Experiments on beam target interaction have been carried out using thin foil targets. In this power range the interaction was explained classically. The experimental dependence of ablation pressure on proton beam intensity was obtained as Pa=3×10-3I0.7bar (Iin W/cm2).

The propagation of intense ion beams through a laser-initiated plasma channel is reported. The ion beams were generated using a pinch-reflex ion diode on a Reiden IV generator and were transported over 40 cm in the plasma channel. The beam orbits, estimated from the pattern on the detector-film with energy resolution, were in good agreement with theory.

A method is presented for generating a high magnetic field using a CO2laser pulse. The magnetic field, current and voltage in a one-turn coil were measured as functions of the gap width, where the high voltage was induced by laser irradiation at a fixed intensity of 1.3 × 1014W/cm2. These results could be explained on the basis of lateral transport by hot-electron E× Bmotion and an expansion of the critical density plasma in the gap. The maximum magnetic fields are determined and limited by the filling time of the gap with a critical-density plasma. In order to obtain higher magnetic fields, we tested a cylinder-type one-turn coil attached to the optimized gap. The highest magnetic field observed was 400 T.

The characteristics of pulse propagation through the CO2laser system LEKKO II are analysed numerically using a MELCOM COSMO 700 II digital computer. The amplifiers are treated with a Frantz and Nodvik type rate equation model, and the SF6saturable absorbers are treated with a phenomenological model based on the measurement of energy transmission. The computed results are compared with the observed data on the pulse energy, the rise time of the pulse and the pulse duration (FWHM). It is found that the pulse peak is delayed when the incident pulse energy is relatively small because of the nonlinear absorption chracteristics of SF6; but proceeds effectively when the incident pulse energy is relatively large because of the nonlinear amplification characteristics of CO2lasers.

We have grown Cr3+-doped huntite-borate crystals Cr3+:YAB and Cr3+:YGAB by the top-seeded solution growth (TSSG) method. These crystals have a broad fluorescence ranging from the red to near-IR spectral region, and their lifetimes were measured as 170 µs and 87 µs, respectively. The emission cross sections are estimated to be 0.8 ×10-20and 1.6 ×10-20cm2, respectively. The vibronic levels of their ground state were estimated to be ?1400 cm-1, so they can provide a four-level system. The optical gain of Cr3+:YAB crystal was measured in the range from 744 nm to 852.5 nm. The maximum single-pass gain was 1.9 at 830 nm. Second harmonic generation in the UV region (375 nm) was obtained by a Cr3+:YAB crystal with 1.5 times higher conversion efficiency compared with LBO crystal. Consequently Cr3+:YAB crystal and Cr3+:YGAB crystal have potential as new self-frequency doubling laser materials with tunability.

Simultaneous resonating of the second-harmonic wave with oscillation of its fundamental wave in the same cavity, by scanning the cavity length, was reported. Dual resonance has been achieved by using an Nd:YVO4microchip laser with the etalon effect of the cavity elements, rather than dispersive phase shift. An enhancement of ?89 times the harmonic intensity internal to the cavity was obtained. It is possible to realize intracavity fourth-harmonic generation with this method.

Nonlinear optical (NLO) properties of CsLiB6O10(CLBO) have been investigated. Frequency quadrupling of the 1.064 µ m Nd:YAG laser output for type-I phase matching was observed by using CLBO. The walk-off angle and the effective NLO coefficient deff were estimated to be 1.83° and 1.01 pm/V for fourth harmonics generation of Nd:YAG laser output, respectively. Phase matching for sum frequency generation of 4? (fourth harmonics of Nd:YAG laser)+? (fundamental of Nd:YAG laser), resulting in fifth harmonics of Nd:YAG laser output, has been observed.

In the atomic laser isotope separation process, the laser beams propagate through the atomic vapor over a long distance. It has been shown that the laser-atom interactions significantly modify the laser pulse shape and propagation velocity, resulting in degradation of the isotope separation efficiency. These propagation effects have been analyzed quantitatively, and a simple scaling formula has been derived to estimate the necessary laser energy for such optically thick atomic vapor. The optimum conditions of incident laser pulse have also been discussed.

Hot electron energy distributions in spherical Cannonball targets at 10.6 µm laser wavelensth were measured using the multi-layered target technique and the Monte Carlo electron transport code. In the inner pellet irradiation type of target, a high energy component of the hot electron energy distribution is strongly reduced from Maxwellian, leading to lower preheating.

This paper describes measurements of the ablation pressure for 10.6 µm and 1.05 µm laser irradiation using thin-foil acceleration observed by X-ray backlighting and X-ray streak shadow graphs of the implosion of a spherical target. At an absorbed laser intensity of 1014W/cm2, the ablation pressure was more than 10 Mbar for laser wavelengths of 10.6 µm and 1.05 µm. The results are compared with theories based on the self-regulated flow model and the flux-limited thermal conduction model.

The beam overlap in a multi-plasma channel was studied. A triple wire-exploding channel was formed as a simulational model of an overlap channel system. Post-transported beam particles in the channel overlap region were observed by a pinhole shadow box as a function of the particle energy. Beam expansion and beam deflection in the overlap region could be suppressed when channels and return paths were alternately arranged.

The experimental performance of a diverged electron beam ion diode, high brightness and high efficiency light ion diode for inertial confinement fusion, is presented. Diode brightness of 1.4 TW/cm2rad2and ion efficiency up to 20% was obtained in 5 ? diode operation. Experimental results were scaled to low impedance operation with further high brightness and high efficiency ion diode.

Dependence of intense ion beam divergence on local electron density in diode, difference of the divergence between protons and carbon ions and time varying self-focusing effect were investigated. Experiments were preformed on a Reiden IV generator, loading pinched e-beam ion diode or pinch reflex ion diode. The higher electron current density caused larger beam divergence. According to measured number ratios of carbon to proton, the carbon ions might have smaller divergence than protons. Heavier ions as carbon ions might be suitable for a tighter focus.

The ablation pressure and the mass ablation rate for a 10 µm CO2laser were measured using two methods: a ballistic target pendulum and shifted X-ray emission images which are equivalent to X-ray back-lighting. The measured ablation pressure was 10 Mbar and the mass ablation rate was 106g/cm2·sec at the absorbed laser intensity of 5×1013W/cm2. Comparing the ablation mass rate measured by the pendulum with that derived from the penetration depth of the hot electrons using K?line emission, we could identify the hot electron driven ablation as the dominant process.

A high velocity jet was formed by the Munroe-Neumann effect on a hemi-spherical target irradiated by a relativistic electron beam. The jet velocity and velocity multiplication were measured using N2laser shadowgraphies and a charge collector array. A jet efficiency of about 50% was measured by a calory meter. These values agreed with theoretical predictions. Experimental results indicated that a reduction of the velocity requirement for pellet ignition may be possible.