Shigeaki Uchida

High-efficiency and economical solar-energy-pumped laser with Fresnel lens and chromium codoped laser medium

The authors achieved 11%–14% slope efficiency of solar-pumped laser by Cr-codoped Nd:yttrium aluminum garnet ceramic and Fresnel lens focusing from natural sunlight. The laser output of 24.4W was achieved with 1.3m2 Fresnel lens. The maximum output for unit area of sunlight was 18.7W∕m2, which is 2.8 times larger than previous results with mirror collector. The utilization of Cr3+ ion enabled efficient absorption and energy transfer to Nd3+ ion of solar spectrum. The fluorescence yield at 1064nm for various pumping wavelengths was measured both for Crcodoped and nondoped laser media, and 1.8 times enhancement of laser output from sunlight is predicted.

Characterization of extreme ultraviolet emission from laser-produced spherical tin plasma generated with multiple laser beams

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.

Demonstrated fossil-fuel-free energy cycle using magnesium and laser

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.

Solar-pumped 80 W laser irradiated by a Fresnel lens

A solar-pumped 100 W class laser that features high efficiency and low cost owing to the use of a Fresnel lens and a chromium codoped neodymium YAG ceramic laser medium was developed. A laser output of about 80 W was achieved with combination of a 4 m(2) Fresnel lens and a pumping cavity as a secondary power concentrator. This output corresponds to 4.3% of conversion efficiency from solar power into laser, and the maximum output from a unit area of Fresnel lens was 20 W/m(2), which is 2.8 times larger than previous results with mirror-type concentrator.

100 W-class solar pumped laser for sustainable magnesium-hydrogen energy cycle

A solar pumped laser system with 7%–9% slope efficiencies has been developed. A Fresnel lens (2×2 m, f=2000 mm) is mounted on a two-axis sun tracker platform and focuses solar radiation toward laser cavity, which embraces Cr:Nd:yttrium aluminum garnet ceramic rod. The maximum emitted laser power is 80 W corresponding to maximum total area performance of 20 W/m2 for the Fresnel lens area. This solar laser system would be used as a section of power plant in a magnesium energy cycle as a cost-efficient solar energy converter. Using direct solar radiation into laser, 4.3% net conversion efficiency has been achieved.

Noncatalytic dissociation of MgO by laser pulses towards sustainable energy cycle

We succeeded in dissociating MgO using laser pulses without a reducing agent. The energy efficiency from laser to magnesium reaction energy exceeded 42.5%. Although 1kW CO2 cw laser and Nd-YAG pulse laser are used in this experiment, the laser can be pumped by natural resources such as solar light or wind power. Thus natural resources are stored in the form of magnesium, which can be used through the reaction with water whenever we need the energy, and thus a renewable energy system will be established. This paper reports the preliminary experiments of MgO reduction toward a sustainable energy cycle.

Laser-induced magnesium production from magnesium oxide using reducing agents

Experiments for laser induced production of magnesium (Mg) from magnesium oxide (MgO) using reducing agents (R) were conducted. In these experiments, continuous wave CO2 focused laser is focused on a mixture of magnesium oxide and reducing agent. High power density of focused laser leads to high temperature and the reduction reaction resulting in Mg production. The resultant vapor is collected on a copper plate and analyzed in terms of magnesium deposition efficiency. Deposition efficiencies with various reducing agents such as Zr, C, and Si have been measured to be 60, 9.2, and 12.1 mg/kJ respectively. An excess addition of reducing agent over their corresponding reaction stoichiometric amounts is found to be optimum condition for the most of performed laser induced reactions. In addition, utilizing solar-pumped laser in Mg production with reducing agent will reduce CO2 emission and produce magnesium with high-energy efficiency and large throughput.

Properties of EUV and particle generations from laser-irradiated solid- and low-density tin targets

Properties of laser-produced tin (Sn) plasmas were experimentally investigated for application to the Extreme Ultra-Violet (EUV) lithography. Optical thickness of the Sn plasmas affects strongly to EUV energy, efficiency, and spectrum. Opacity structure of uniform Sn plasma was measured with a temporally resolved EUV spectrograph coupled with EUV backlighting technique. Dependence of the EUV conversion efficiency and spectra on Sn target thickness were studied, and the experimental results indicate that control of optical thickness of the Sn plasma is essential to obtain high EUV conversion efficiency and narrow spectrum. The optical thickness is able to be controlled by changing initial density of targets: EUV emission from low-density targets has narrow spectrum peaked at 13.5 nm. The narrowing is attributed to reduction of satellite emission and opacity broadening in the plasma. Furthermore, ion debris emitted from the Sn plasma were measured using a charge collector and a Thomson parabola ion analyzer. Measured ablation thickness of the Sn target is between 30 and 50 nm for the laser intensity of 1.0 x 1011 W/cm2 (1.064 μm of wavelength and 10 ns of pulse duration), and the required minimum thickness for sufficient EUV emission is found to be about 30 nm under the same condition. Thus almost all debris emitted from the 30 nm-thick mass-limited Sn targets are ions, which can be screened out by an electro-magnetic shield. It is found that not only the EUV generation but also ion debris are affected by the Sn target thickness.

Laser-induced Mg production from magnesium oxide using Si-based agents and Si-based agents recycling

We succeeded in laser-induced magnesium (Mg) production from magnesium oxide (MgO) using Si-based agents, silicon (Si) and silicon monoxide (SiO). In these experiments, a cw CO2 laser irradiated a mixture of Mg and Si-based agents. Both experimental studies and theoretical analysis help not only understand the function of reducing agents but also optimize Mg extraction in laser-induced Mg production. The optimal energy efficiencies 12.1 mg/kJ and 4.5 mg/kJ of Mg production were achieved using Si and SiO, respectively. Besides, the possibility of recycling Si and SiO was preliminarily investigated without reducing agents but only with laser-irradiation. As for the Si-based agents recycling, we succeed in removing 36 mol % of oxygen fraction from SiO2, obtaining 0.7 mg/kJ of Si production efficiency as well as 15.6 mg/kJ of SiO one at the same time. In addition, the laser irradiation to MgO-SiO mixture produced 24 mg/kJ of Si with more than 99% purity.

Evaluation of tracking ability of a phase conjugate mirror using a CCD array and spatial light modulator for optical energy transmission

We investigate the tracking ability of an optical phase conjugator using a commercial CCD array and a projector LCD panel. This system allows one to use two separate laser oscillators for capturing interference patterns and generating phase conjugate light. Since a long coherence length is not required for the latter part, amplification of the phase conjugate light can be easily attained by using a laser oscillator for high-power applications such as machining. The wavelengths of the two laser oscillators can be independently chosen. For our experimental configuration an amplification factor of 7.8×10(4) is theoretically possible. Also, a formula for the maximum tracking range is derived. The proposed system is particularly suitable for power transmission by light.