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A CO 2 laser can be used to melt ice. Here we use a CO 2 laser at 10.6 μm, a wavelength at which ice strongly absorbs, to drill (via melting) through ice. The resulting drilling speed is measured at several irradiation intensities, ice-snow densities, and beam angles relative to the horizontal axis. The speed increases nearly in proportion to the laser intensity. For an intensity of about 50 W/cm 2 , for instance, the melting speed is 4 mm/s for snow of density 153 kg/m 3 and 0.8 mm/s for solid ice. Results also show that for downward beam angles, melt-water accumulates in the hole, reducing the drilling speed. Nevertheless, we also consider other laser mediums and argue that an optical-fiber-coupled laser drilling system could be used for drilling on glaciers and ice sheets.

The M1 strengths (or level density of 1+ states) are of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino-process. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized gamma-ray beam at the polar angle of θ=90° should be followed by a simple function, a + b cos(2φ), where φ, is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region except for light nuclei as deuteron. We have measured neutron angular distributions with (polarized gamma, n) reactions on Au, Nal, and Cu. We have verified the Agodi's prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study M1 strengths in giant resonance regions.

The concentration of furfural in transformer oils is a well known indicator for decomposition of insulating paper. Using laser Raman spectroscopy, we performed detection experiments of furfural dissolved in insulating oils without complex and time consuming preprocessing procedures. Furfural was characterized by Raman signal at ~1707 cm-1, where no spectral interferences caused by oil-derived Raman signals occur. The results show that laser Raman spectroscopy is a useful alternative method for transformer health diagnosis.

Extreme ultraviolet (EUV), 13.5 nm, lithography techniques have attracted a great deal of attention because of the mass production of 50 nm critical dimensions as the future generation lithography. One of key issues to be clarified for the development of a 13.5 nm EUV light source is to improve the conversion efficiency (CE). In this paper, hollow multilayer nanofibers were fabricated through the combination of a layer-by-layer (LBL) technique with the electrospinning technique. The obtained hollow fibers were employed as EUV targets. In order to improve the CE, the irradiated laser energy was increased from 1010 to 1011 W/cm2 and the CE was correspondingly increased from 0.43 to 0.83%.

In this paper, we investigated the mechanism of crystallization induced by femtosecond laser irradiation for an amorphous Si (a-Si) thin layer on a crystalline Si (c-Si) substrate. The fundamental, SHG, THG wavelength of a Ti:Sapphire laser was used for the crystallization process. To investigate the processed areas we performed Laser Scanning Microscopy (LSM), Transmission Electron Microscopy (TEM) and Imaging Pump-Probe measurements. Except for 267 nm femtosecond laser irradiation, the crystallization occurred well. The threshold fluences for the crystallization using 800 nm and 400 nm femtosecond laser irradiations were 100 mJ/cm2 and 30 mJ/cm2, respectively. TEM observation revealed that the crystallization occurred by epitaxial growth from the boundary surface between the a-Si layer and c-Si substrate. The melting depths estimated by Imaging Pump-Probe measurements became shallower when the shorter wavelength was used.

Remarkable improvements in the lifetime of the Nd upper level and in the effective stimulated emission cross-section of Nd/Cr:YAG ceramics have been theoretically and experimentally studied. Until recently, it had been thought that the long energy transition time from Cr ions to Nd ions of Nd/Cr:YAG adversely affects laser action, degrading optical–optical conversion efficiency under CW and flash lamp pumping. However, current research showed that high-efficiency energy transition has a positive effect on laser action. The effective lifetime is increased from 0.23 to 1.1 ms and the emission cross-section is effectively increased to three times for that of the conventional Nd:YAG. A small signal gain is significantly improved, and the saturation power density is reduced to 1/10 that of the Nd:YAG for the same pumping power density. A CW laser light generated in a laser diode (LD)-pumped 1064 nm Nd:YAG laser oscillator was amplified, and the measured output power was saturated. The output laser power calculated using theoretical saturation power density was consistent with the experimental results.

Recent progress in high power lasers enables us to access a regime of high-energy-density and/or ultra-strong fields that was not accessible before, opening up a fundamentally new physical domain which includes laboratory astrophysics and laser nuclear physics. In this article, new applications of high-energy and ultra-intense laser will be reviewed.

A high average-power solid-state laser system for attaining the current goal of 20 J output energy at 10 Hz with a pulse width of 10 ns has been designed to demonstrate scalability to 100 J output energy. We proposed ring and cascade layouts that were useful for a four-pass zig-zag slab laser amplification system with effective extraction of output energy from a laser medium of an amplifier module. The reduction of thermal effects and the suppression in thermal fracture were evaluated by the measurements of temperature distributions of the laser slab. We analyzed the parasitic oscillation of the slab laser and found the threshold values of the parasitic oscillation. We designed a dual module system in consideration of these results, and examined the extraction energy from the system that incorporated an assembly of serrated apertures to suppress the laser-induced damage of optical components and the laser slab.

We have demonstrated an efficient high energy 2 μm laser generation with a 36 mm long large aperture 5 mol% MgO-doped periodically poled LiNbO3 (PPMgLN) nonlinear optical crystal. A high power Q-switched Nd:YAG laser (1.064 μm) was used to pump the quasi-phase matched (QPM) optical parametric oscillator (OPO). A total output energy of 186 mJ with 58% slope efficiency was obtained in two separate beams at 2 μm.

The laser damage on a total internal reflection (TIR) surface as well as on entrance and exit faces was evaluated to design a zig-zag slab laser. Incorporating a phase shift by the Goos–Hanchen effect on a TIR surface of a laser slab in contact with water, formulas for a laser-induced damage threshold (LIDT) were modified. We determined a method for the designing the geometry of a zig-zag slab laser based on LIDT. A thin film for anti-reflection (AR) with a high LIDT must be formed on the entrance and exit faces of a laser slab glass. A sol–gel thin film was adopted for the AR coating of a high-power laser due to its high LIDT. We devised an effective dip-coating method to form a sol–gel thin film uniformly on a small area. The LIDT of the sol–gel thin film was measured and evaluated with a single mode Q-switch Nd:YAG laser by a one-on-one measurement technique.

The laser-driven punched-out scheme, which has been proposed for supplying minimum-mass tin fuels at a high repetition rate, was investigated for use in an extreme ultraviolet (EUV) light source. The density profile of punched-out tin fuel is a critical parameter for validating applicability of this scheme. An EUV backlight technique was developed to measure the density profile and fine structure. Experimental results reveal that a punched-out target does not remain its initial thin shape, but expands into a rarefied gas and liquid and small particles under the present target and laser conditions.

Extreme ultraviolet (EUV) radiation from laser-produced plasma has been studied for mass-production of the next generation semiconductor devices with EUV lithography. A full set of experimental databases are provided for a wide range of parameters of lasers and targets. These data are utilized directly as a technical guide-line for EUV source system design in the industry as well as used to benchmark the radiation hydrodynamic code, including equation-of-state solvers and advanced atomic kinetic models, dedicated for EUV plasma predictions. Present status of the LPP EUV source studies is presented.

200 kW laser diode pumping module aimed for IFE driver was developed. The pumping optics for the uniform irradiation was applied to this module. As a result, 80% filling factor for the pumping distribution was achieved. The maximum peak power of 226 kW was obtained at the 150 μs pump duration. The E-O conversion efficiency over 50% was achieved.

In this paper, we describe the development of a high-average-power solid-state laser system and the derivation of equations for the amplification of a laser beam. This laser system is capable of generating an output energy of 10 J per pulse at a wavelength of 1,053 nm in a 10 Hz operation for scientific and industrial applications. The main amplifier of our system is a laser-diode-pumped solid-state amplifier. A water-cooled Nd:glass slab is pumped with two 803 nm AlGaAs laser-diode modules. The laser beam propagates through zig-zag optical paths four times and is amplified. To estimate laser output energy, we have derived and evaluated equations for the amplification of the laser beam, and designed and constructed a laser system based on the calculated results. Experimental results reveal an output energy of 10.6 J at 1 Hz, which closely fits the results calculated using the derived equations.

The Ml strength (or level density of 1+ states) is of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino- process. We have proposed a method using (γ, n) reactions with linear polarized laser Compton scattering γ-rays to measure Ml strength. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized γ-ray beam at the polar angle of 8=90° can be described by a simple function, a + b cos(θ2), where θ is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region. We have measured neutron angular distributions with (polarized gamma, n) reactions on Au, NaI, and Cu. We have verified the Agodi's prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study Ml strength in giant resonance regions.

We developed a Yb:YAG Zig-Zag Active-Mirror laser amplifier with jet impingement cooling system for high average power laser systems. The output power of laser was beyond 1kW which was stable nearly 30 minutes.

We observed the lasing of highly sensitized Nd/Cr:YAG ceramic disks that use artificial solar radiation pumping. The disk material can be used for high power multi-stage amplifiers pumped by lamplight or sunlight because of its scalability and ability to handle high power densities. A maximum output power of 86 mW was experimentally obtained, and this value correlated well with the calculated results. A small signal gain of 1.9 was obtained, and the estimated stored energy was 0.6 J/cm 3 , which is three or four times higher than that from a Nd:YAG medium.

Isotopic selectivity and ionization efficiency are discussed in the isotope separation processes of Gd based on polarization selection rules and based on isotope shift. Enrichment of 157Gd to 90% was experimentally demonstrated using both methods together. The features of the absorption spectra of Gd in yellow-red and blue regions were summarized. Absorption spectra that are suitable for separation process using isotope shift were examined and an obtainable selectivity and efficiency are quantitatively calculated.

The diode-pumped slab laser for inertial fusion energy driver has been demonstrated, which produces the 1053-nm output energy of 10 J at 10 Hz. The glass slab laser amplifier has been pumped by quasi-CW 290-kW AlGaAs laser-diode arrays at 803 nm. The optical system can compensate for thermal effects by use of zigzag optical propagation, image-relayed telescope, and 45° Faraday rotator. The output energy of 10.6 J at 1 Hz with the optical-to-optical conversion efficiency of 19.9% has been successfully obtained. Also, the 10-Hz operation has been performed with an output energy of 5.1 J. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 27–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20288

Coulomb explosion of hexa-fluorobenzene in an intense laser field (1.0 × 10 16 W cm −2 ) was investigated using time-of-flight (TOF) mass spectrometry. The fluorine ions were mainly ejected parallel to the laser polarization, whereas the carbon ions were broadly distributed. The angular distribution features were totally different from those of benzene. Molecular dynamics simulations indicated that the substitution of fluorine atoms and/or ions caused ultrafast deformation of the carbon framework during the explosion. The effect of molecular alignment induced by the intense laser field is discussed.

Low-density porous tin dioxide (∼0.5 g/cm3) was prepared from a SnCl4/ethanol/H2O mixture and polystyrene (PS) template. Such a low density made the as-synthesized tin dioxide act as a promising target material for laser-induced extreme ultraviolet (EUV) emission. The resulting structure of the as-synthesized tin dioxide (SnO2) was a cellular foam, which was composed of large cells (ca. 103 nm, large macropores) interconnected by windows (ca. 102 nm, small macropores). Scanning electron microscope images showed that SnO2 particles of ∼10 nm constituted the cell wall. The space among particles formed mesopores, which were about 7 nm estimated by nitrogen adsorption−desorption isotherm measurements. Therefore, the as-prepared SnO2 showed a hierarchical porous system from macropores to mesopores. The window size on a submicrometer scale was tunable in the range of ∼480−200 nm by changing the molar ratio of ethanol to SnCl4 in tin source solution from 2:1 to 10:1. By consideration that the windows originated ...

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh–Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti–Goncharov procedure with a one-dimensional...

The present report describes ultralow density (2~10 mg/cm3) hydrocarbon plastic (CH2) foams with a controllable micro- or nano-meter-sized lamella structure. These foams are prepared from a poly(4-...

We detected parent and fragment ions from 14 chlorinated and a few fluorinated compounds as well as dibenzo-p-dioxin (dioxin) in intense laser fields. The irradiation pulse had an intensity from 1 × 1013 to 1 × 1015 W cm-2, with a 130-fs pulse duration at a central wavelength of 800 nm. Irradiation at this intensity led to a singly ionized species and a small amount of atomic ions, indicating the onset of Coulomb explosions. We have previously reported finding a key factor in determining the parent and/or fragment ion formations of organic hydrocarbons with an intense femtosecond laser pulse [Harada, H.; et al. Chem. Phys. Lett. 2001, 342, 563−570]. This key factor is a requirement for parent ion predominance if the excitation laser wavelength and the absorption spectra of the target cation are in nonresonance, and vice versa. Use of this factor has been found to be effective for molecules other than hexachlorobutadiene. The threshold intensities Isat at the infinity ionization rate were determined and ar...

A uniform laser ablation was observed in a polystyrene film coated with a photovoltaic perylene/phthalocyanine bilayer when an incident took place at an intensity range of 10 9 –10 10 W/cm 2 ( λ =1064 nm, 1.1 ns FWHM). Without the bilayer coating, the laser pulse formed spiky structures in the polystyrene film as self-focusing traces of the laser pulse, while for the coated film, the uniform surface ablation trace without the spiky interior structures was observed. In the case of incident of 532 nm where the coating material exhibits no reflection, such difference depending the coating was not observed. These phenomena were coupled with the reflection and conduction properties via its photovoltaic effect, and agreed with the required ablation to achieve high-density compression of the fuel capsule for inertial fusion energy (IFE).

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of ultrasonic vibration on the specimen surface. From the comparison of the broadband ultrasonic waveforms among five stages of fatigue damage, the attenuation coefficient of the longitudinal wave by the intrinsic material attenuation increased progressively with increasing the number of fatigue cycle. Ultrasonic attenuation at 2.5, 5.0, 7.5 and 10.0MHz were also calculated by Fourier transformation in order to compare the decay of the longitudinal wave among these frequency components. From the results, ultrasonic attenuation increased as the number of fatigue cycle increased, in both broadband and narrow...

Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. 10BCl3 was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO2 laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation.

Cylindrical internal defects in carbon steel specimens were detected noncontactly and nondestructively from the measurements of ultrasonic diffraction signals using the laser ultrasonic technique. Laser beams used for both ultrasonic generation and detection have a 0.7-mm diameter. Spatial profiles of the diffracted ultrasonic amplitude were measured for the internal defects of 0.5 to 5.0 mm in diameter, which were in good agreement with the profiles calculated by using Cornu's spiral. This method can be useful for the noncontact detection of internal defects in metal, and is considered to be applicable to the noncontact sizing of the internal defects such as those in power plant components.

Energetic protons generated in a thin plastic foil under the irradiation of ultra-intense femtosecond lasers have been experimentally and computationally investigated. More energetic protons were emitted forward in the direction of laser propagation than backward. The maximum energy of protons has been scaled via laser intensity I as 1 0.7, up to 2 MeV at 1018 W/cm2. The laser intensity scaling law for the maximum proton energy was reproduced by 2D-PIC simulation.

Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid state. A new laser technology ‘ultra-intense’ laser is now opening a new ground of the laser fusion research, which is called as fast ignition. During the last several years, we have extensively studied elementary physics relevant to the fast ignitor. Based on these results, we have succeeded enforced heating of imploded plasmas with a 100 TW laser as the first demonstration of this new approach. The experimental result implies the future possibility of breakeven and ignition with significantly small laser energies. This new approach provides a route toefficientfusionenergy production.

Two pairs of organic molecules (2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene; 1,4-cyclohexadiene, 1,3-cyclohexadiene) were irradiated with a high-intensity 120-fs laser pulse in the intensity region of 10 14 W cm −2 . One molecule in each pair had no allowed electronic transition in the cation at the excitation wavelength of 800 nm, resulting in parent ion dominance. In contrast, the counter molecule, which had a similar structure but with absorption in the cation at the excitation wavelength, showed heavy fragmentation with a negligibly small signal of the parent ion. The previously reported observations are explainable on the basis of the proposed mechanism for fragmentation in femtosecond ionization.

A simple model for calculating the photoionization rate in AVLIS system is proposed. It was found that, forthe different incident laser conditions, the dependence of photoionization rate of target atom on the propagation distance estimated by the model represents well the simulation result. It has been confirmed that thismodel is useful for analyzing the performances of AVLIS plant without simulation.