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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.

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.

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.

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.

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.

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).

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.

We constructed an experimental system to observe nonlinear effects in the Compton scattering. The electron beam is supplied by an electron gun and a photon beam comes from a Table-top Ten-Tera-watt Ten-Hz Tunable Ti:sapphire laser system, named T6-laser, of Institute of Laser Engineering, Osaka University. As a test experiment, we measured the Compton scattering in a linear regime and had a reasonable agreement with simulation.

The dependencies of dissociation yield and isotope selectivity on FEL frequency for boron trichloride were measured. The measurements have been performed by using metallic cell (38 cm3) filled with a mixture of BCl3 (2 Torr) and H2S (10 Torr). The maximum dissociation yield was obtained at a laser frequency shifted by 10 cm−1 toward the red side from the vibrational resonance of BCl3. The maximum selectivity was ∼1.5, which increased gradually with decreasing the laser frequency toward the red side from the resonance.

C 60 vapor was irradiated with an intense femtosecond laser pulse (1.0×10 16 W/cm 2 in 100 fs at a wavelength of 790 nm). Multiply charged ions, assignable up to C 60 4+ , were observed in the time-of-flight spectra, while C 60 q + ( q ≤2) with many fragments were detected by a nanosecond laser pulse (1.2×10 13 W/cm 2 in 9 ns at 532 nm). The formation of the multiply charged ions will be explained in terms of barrier suppression ionization (BSI) for the case of femtosecond excitation.

F 2 laser (158 nm) photolysis of gas mixtures of CO 2 and hydrofluorocarbons (HFCs) gives the corresponding alcohols and ketones. The initial step of photolysis is a bond breaking reaction to give CO and an electronicaly excited oxygen atom O( 1 D). The excited atom is partially inserted into the HFC CH bonds and is partially quenched to the triplet atom O( 3 P). The dependence of the yields of the alcohols on the gas pressure and the size of the HFC can be explained in terms of the formation of hot alcohols and collisional relaxation. The insertion rate constant of O( 1 D) has been estimated to be (1.5±0.3) × 10 −11 cm 3 molecule −1 s −1 for CF 3 CF 2 CH 3 based on the quantum yield of CF 3 CF 2 CH 2 OH production.

Gaseous CO2 was photoreduced on irradiation with a VUV F2 laser (158 nm). The final products were formaldehyde, methane etc. for the case of a mixture with hydrogen, and alcohol for systems of hydrofluorocarbons.

To study the possibility of triggering lightning with a laser plasma, laboratory laser-induced discharge experiments have been carried out and the following results were obtained. Both long straight and zigzag laser induced discharges between rod-rod electrodes were realized and the effective guiding effect of laser channels for electrical discharges was confirmed. With plane-plane electrode configuration, the investigation concerning the necessary condition for initiating and guiding a streamer reveals that the necessary electric field for initiating a streamer with a laser plasma depends closely on the absorbed energy used to produce laser plasma channels, the minimum electric field is about 200 kV/m, and that the necessary electric field for guiding a streamer by a laser plasma is lower than that for initiating a streamer and the minimum electric field is about 170 kV/m. We propose to use the local electric field near the top of a grounded tower as the necessary field for a laser-produced channel to trigger an upward leader and have proved that this is feasible.

Two-photon absorption has been found to induce the photoreduction of Eu 3+ to Eu 2+ in methanol solution of EuCl 3 . The excitation spectra clearly indicate that the photoreduction occurs via a 4f′ ←4f transition. The second photon is presumed to be absorbed in a transition band of an intermediate level to a charge-transfer level. The reduction efficiency was about 3 × 10 −5 for the excitation at 464.7 nm under 460 mJ/cm 2 .

Tunable UV-VUV light of high power will be available from free electron lasers in the near future. Investigation of wavelength-dependent chemistry and multiphoton chemistry is important for FEL applications. Wavelength-dependent and/or two-photon chemistry has been induced by several wavelengths from excimer lasers. Some examples are described. Photodissociation rates and yields of olefins and alkylbenzenes in the gas phase can be controlled by excitation wavelengths. Photoreduction of lanthanide ions in solution is briefly reviewed.

Quantum yields of hydrated electrons of Cl−, Br−, I−, SO2−4, SCN− and OH− in aqueous solution have been determined by means of 193 nm laser flash photolysis. Shorter wavelength excitation showed higher quantum yields for I− and SCN− ions in three wavelengths of 193, 222 and 248 nm. The highest yield was 0.73 for SO2−4 at 193 nm and the lowest one was 0.015 for SCN− at 248 nm.

An on-line real-time detection method for Cl− in aqueous solution was developed in which the concentration of Cl− was determined by measuring the absorbances of Cl−, e− andCl−2 which were formed by ArF laser irradiation. A linear relationship between absorbance and concentration was confirmed. The calibration graphs were linear for about two orders of magnitude above the detection limit. A detection limit of 1 X 10−5 M was achieved.

Calculated cross sections for resonant charge transfer between atoms and their positive ions are presented in tables and graphs for all nontransition elements in the range of low and intermediate collision velocities (≲1 a.u.). Experimental data obtained since the 1930s are compiled. The cross sections have been calculated by the impact-parameter and close-coupling methods. To solve the one-electron, time-dependent, spinless electronic wave function in a two-atom system, the wave function was expanded in terms of a set of traveling atomic wave functions centered about either nucleus. As the eigenfunction of each atom, Hartree-Fock-Slater wave functions were used. The calculated results are in fairly good agreement with the compiled experimental results for the thoroughly studied elements and thus provide a useful interpolation/extrapolation of the experimental data.

We have observed population trapping in a three-level lambda atomic system under pulsed laser excitation and in the presence of ionization loss from the common upper level. The measured spectrum showed a good agreement with the numerical results. From the view point of obtaining as many ions as possible from both lower levels, the numerically calculated results are discussed including the effects of hyperfine structures in the atomic transition.

Photoreduction yields of Eu3+ to Eu2+ in aqueous and alcoholic solutions were determined. The highest quantum yields were found to be 0.97 ± 0.16 for EuCl3 in methanol under 308 nm excitation and 0.94 ± 0.17 in 2-propanol under 248 nm excitation. The lowest quantum yield was 0.12 ± 0.02 for Eu(ClO4)3 in aqueous solution under 193 nm excitation. The high photoreduction yields for EuCl3 indicate that Cl' reacts efficiently with neighbouring alcohols. The yield was found to depend on the excitation wavelength for EuCl3 in methanol solution.

The photo-reflectance and laser-ablation properties ofa part of an organic solar cell, a perylene derivative and the phthalocyanine (denoted as PV/H 2 Pc) were investigated. The reflectance ofa PV/H 2 Pc bilayerwas higher than the single layer samples of H 2 Pc and PV. Considering the photovoltaic effect in the corresponding solar cell and chemically doped perylene, the present reflection was characterized to be the photo-generated carrier in the PV layer. The present property can be classified into organic reflectance-tunable material, and is useful as a coating material to realize uniform laser ablation. A remarkable difference was observed in laser ablation ofpolystyrene film, in comparison with that of the PV/H 2 Pc bilayer, when 1060 nm laser incident took place on the coating material. Without the coating the laser pulse formed a spiky structure as a trace ofself-focusing, while for the coated film the ablation trace was from the upstream on the axis without a spiky structure. These phenomena are advantageous for the targets of direct-driven inertial fusion energy.

A method of calibrating neutron detectors used in fusion research for their response to 2.45 MeV neutrons is presented. The method is based on the assumption that the ratio of neutrons to protons born by thermonuclear fusion reactions in deuterium fuel is unity, and on the use of CR39 plastic to measure the proton energy and fluence.

Production of the 26 min isomer of 235U has been observed in a laser produced uranium plasma by detecting internal conversion electrons from 235Um. It can be attributed to nuclear excitation by electron transition (NEET).