Keisuke Furuta

28% electrical-efficiency operation of a diode-side-pumped Nd:YAG rod laser.

We propose a highly efficient quasi-cw Nd:YAG rod laser with a novel side-pumping design that uses microlens-free diode stacks. We demonstrate 320-W output power with 28% electrical-to-optical efficiency, which is, to our knowledge, the highest efficiency reported for diode-pumped solid-state lasers.

Diode-pumped 1 kW Q-switched Nd:YAG rod laser with high peak power and high beam quality

We have demonstrated high-peak-power generation at 1 kW average power by applying an acousto-optic Q switch to a quasi-cw diode-pumped Nd:YAG master oscillator power amplifier. We achieved a maximum peak power of 2.3 MW by driving the Q switch in burst mode. The average repetition rate was 6 kHz. The corresponding beam quality was M2 = 9.

1-kW high-quality beam generation from a diode-side-pumped Nd:YAG rod laser

We demonstrated a power scaling of Nd: YAG rod laser by cascaded-coupling of two identical bifocusing compensation resonators. The maximum output power of 1030 W was achieved with the beam quality of M2 = 9. The corresponding electrical-to-optical efficiency was 23 %.

Efficient high-beam-quality operation by use of a diode-stacks-side-pumped quasi-cw Nd:YAG laser

Laser power over 500W was obtained with the beam quality factor M2=4 and high electrical-to-optical efficiency over 20% by using two diode-stacks-side-pumped modules. The electrical-to-optical efficiency of 28% was achieved with single module operation.

Highly efficient high-brightness diode stacks side-pumped Nd:YAG rod laser

We have proposed a highly efficient and high-brightness quasi-cw Nd:YAG rod laser with a novel-side-pumping design using micro-lens free diode-stacks. We demonstrated 320-W output power with 28-% electrical-to-optical efficiency, which is, to our knowledge, the highest efficiency reported for diode-pumped solid-state lasers. We also achieved the beam quality of M2 =4 with the output power of 500 W by introducing a bifocusing compensation resonator. The corresponding electrical-to-optical efficiency was 20 %.

High-power high-brightness diode-pumped solid state laser for precise laser processing

We have proposed a highly efficient and high-brightness quasi-cw Nd:YAG rod laser with a novel-side-pumping design using micro-lens free diode-stacks. We achieved 320W output power with 28-% electrical-to-optical efficiency, which is, to our knowledge, the highest efficiency reported for diode- pumped solid-state lasers. We generated the high quality beam of M2equals4 with the output power of 500W while maintaining the electrical-to-optical efficiency of 20%. We also demonstrated through-hole formation of 1mm thick copper plate using the high brightness laser beam and successfully obtained round holes with the diameter of less than 40 micrometers .

Novel circular-beam equalizing techniques that use graded-index fiber optics for a high-power laser diode.

We demonstrate a novel method of equalizing a laser diode (LD) beam into a circular beam. This method uses the twist effect of graded index (GI) fiber optics. An asymmetric LD beam with beam qualities of M2 = 500 in the slow axis and M2 = 4 in the fast axis is converted successfully into a symmetric circular beam with a beam quality of M2 = 175. The circular-output beam with 92% coupling efficiency from the fiber input to the fiber output is obtained with a 5-m-long GI1200 (1200 means a core diameter of 1200 microm) fiber for a 2-W LD array. We extend the experiments to a higher-power source with higher asymmetric beam qualities of M2 = 3000 and M2 = 4. By slightly bending the GI10000 (10000 means a core diameter of 10,000 microm) fiber, we have succeeded in generating a symmetric beam with a improved beam quality of M2 = 2000. The average beam quality is preserved when the asymmetric ratio is not high, and the beam quality degradation ratio is investigated up to asymmetric ratios of 750.

Highly efficient and high-quality beam generation of a diode-stacks-pumped Nd:YAG rod laser

Summary form only given. Because of long lifetime of diode bars, good quality of laser beams, and high efficiency of overall systems, high-power diode-pumped solid-state lasers could promise practical industrial tools for a variety of cutting, drilling and welding applications. Over the past several years, cost reduction and power scaling of diode bars accelerated the replacement conventional lamp pumped systems with diode-pumped solid-state lasers. Recent progress in diode-stack technology offers significant, power enhancement of diode-pumped solid-state lasers. However, both beam quality and electrical efficiency of high-power diode-pumped systems are several times lower than those of industrial CO/sub 2/ lasers resulting in specific applications. In this paper, we describe a highly efficient Nd:YAG rod laser with a novel-side-pumping design using microlens free diode-stacks. We also report high-brightness operation by introducing bifocusing compensation resonator.

Novel circular-beam equalizing techniques using graded-index (GI) fiber optics for high-power laser diode

We demonstrate a novel method of equalizing laser diode beam into circular beam. The method uses the twist effect of graded index(GI) fiber optics. An asymmetric laser diode beam with the beam qualities of M2=500 in the slow axis and M2=4 in the fist axis is successfully converted into a symmetric circular beam with the beam quality of M2=175. The circular output beam with 92% coupling efficiency is obtained by using a 5m long GI1200 fiber for 2W laser diode array. We have Ibund that the required minimum length of G11200 fiber is 550mm for circular beam equalizing. We extend the experiments to higher power source with higher asymmetric beam qualities of M2=3000/M2=4. By using a large core diameter ofGI10000 fiber, the higher asymmetric beam is not converted into a perct symmetric beam. We consider that the length is too short Ibr this large core fiber. Since the GI1200 fiber required 550mm, the GI10000 fiber should require at least 4583mm, however, the fiber length is limited to 500mm because ofthe production matter. By slightly bending the fiber, however, we have succeeded in generating symmetric beam with improved beam quality of M2=2000. The average beam quality is preserved when the asymmetric ratio is not high and the beam quality degradation ratio is investigated up to asymmetric ratios of 750.

Highly efficient quasi-cw Nd:YAG laser side-pumped in a diffusive cavity by P-polarized stacked diode beams

We have demonstrated a highly efficient quasi-cw Nd:YAG laser with a novel side-pumping configuration using micro-lens free stacked-diode-bars. In this configuration, the fast-axis of the diode bars is arranged in parallel to the rod axis which means highly efficient P-polarization pumping of the Nd:YAG rod. The pumping beams are coupled into a cylindrical diffusive reflector by using wedge lenses (1-dimensional lens duct). The pump radiation in the slow axis direction is focused by the cylindrical surface of the wedge lens, and the radiation in the fast axis direction is transferred by the total internal reflection. Six micro-lens free diode bars are arranged around the Nd:YAG rod. The transfer efficiency of the wedge lens was 89%. Laser power of 270 W was obtained at the beam quality of 20 mm mrad at the electric efficiency of 18.4%. The experimental results are well explained by calculations and we consider further enhancement of the efficiency is possible by optimizing the diffusive cavity design.