Here, we introduce some novel light-source technologies for next-generation laser processing. Compact and simple lasers including a laser diode and a fiber laser with high brightness are in demand for many applications.

View full abstract

We describe recent progress of high-beam-quality high-power, namely high-brightness, photonic crystal lasers. To realize such lasers, we develop unique double-lattice photonic crystal resonators, which are used for generating stable fundamental-mode oscillation while suppressing unwanted higher-order-mode oscillations, even in large areas (>500 μm). We successfully fabricate this unique structure by employing air-hole retained crystal regrowth using metalorganic vapor phase epitaxy. A high output power of 10 W with a high beam quality M2～2 is achieved with a large lasing area of 500 μm-diameter under pulse operation. The brightness is found to be ～300 MWcm-2sr-1 which is the highest brightness of semiconductor lasers ever reported. In addition, continuous wave operation with an output power of ～7 W is also successfully achieved from a single-chip.

View full abstract

AlGaN deep-ultraviolet (DUV) laser diodes (LDs) have the potential to be used as compact, highly efficient, high-power light sources. The applications for DUV-LDs include sterilization and fine machining of metals or other advanced materials, utilizing the advantage of the very high absorption coefficient of UV light in these materials. In this work, we fabricated AlGaN DUV LD structures based on growth techniques used for fabricating highly efficient AlGaN light-emitting diodes (LEDs). We fabricated laser mirror facets using a laser stealth-dicing (SD) process. With current injection of 0.1 KA/ cm2 and under continuous wave (CW) operation, spontaneous emission at a wavelength of 277 nm from the DUV LD structure with a relatively high external quantum efficiency (EQE) of over 4% was observed. We also observed stimulated emission by optical pumping from the AlGaN DUV quantum wells with low threshold exciting power density of 68 kW/cm2 at room temperature.

View full abstract

We achieved 129 W continuous-wave operation of a single-chip InGaN laser in the 400-nm wavelength range. Novel wall-plug-efficiency approximation clarifies the relations between the thermal saturation power and laser parameters, which enable high-power device designs. With the direct diode laser scheme, this short-wavelength light source shows more efficient copper processing than that operating in the 900-nm range.

View full abstract

We overview progress in quantum dot (QD) lasers, emphasizing the advantage of the QD lasers for application to laser processing technology. Recent advances in our development of the QD lasers toward high quantum efficiency and high out power at the NEDO project are also discussed.

View full abstract

We are developing a compact, high-efficiency continuous-wave UV (CW-UV) laser system whose concept is that the CW-UV laser source is only generated by a second harmonic generation (SHG) technique with a visible fiber laser excited by blue laser diodes (primary visible fiber laser) as a fundamental laser beam. We used a Pr-doped double-clad structured single-mode waterproof fluoroaluminate glass fiber as the laser medium of the primary visible fiber laser. Such a CW-UV laser source is expected to have higher conversion efficiency than previous CW-UV laser systems because they use a third harmonic generation (THG) or fourth harmonic generation (FHG) technique with a doubleconversion process. We are aiming to develop 2-W CW-UV laser systems at 260 and 320 nm in this project.

View full abstract

Micro-MOPA, which is a master oscillator power amplifier system with a microchip-based sub-ns laser and a beam cleaning gain aperture, can generate extremely high brightness of 18 PW/sr･cm2 with 200- mJ pulses1). However, the current repetition rate of the Nd:YAG-rod amplifier in our Micro-MOPA was limited to 10 Hz due to its thermal problems under high power operation. In this work, we achieved 100- Hz operation in a PW/sr･cm2-class Micro-MOPA by optimizing the optics from the evaluation of the thermal lens effect in a highly excited Nd:YAG-rod of Micro-MOPA.

View full abstract