Masaomi Takasaka

Beam-shaping technique for improving the beam quality of a high-power laser-diode stack.

We report a beam-shaping technique that reconfigures the beams to improve the beam quality and enhance the power density for a ten-array high-power laser-diode stack by using two optical rectangular cubes and two stripe-mirror plates. The reshaped beam has threefold improvement in beam quality, and its power density is effectively enhanced. On the basis of this technique, we focus the beam of the high-power laser-diode stack to effectively end pump a high-power fiber laser.

Enhancement of emitting power density with a beam-shaping technique for a high-power laser-diode array stack

We present a beam-shaping technique to enhance emitting power density for a high-power laser-diode array stack. By use of a stripe mirror and a high-reflection mirror, the laser source height of 42 mm is folded to 21 mm and the emitting power density is increased to 365 W/cm 2 from a raw emitting power density of 194 W/cm 2 . Moreover, the beam parameter product (BPP) that is used to evaluate the beam quality is effectively improved to 168-mm mrad from a raw BPP of 336-mm mrad in the fast axis for the collimated high-power laser-diode array stack.

Beam-Shaping Technique for End-Pumping Yb-Doped Fiber Laser with Two Laser-Diode Arrays

We describe a beam-shaping technique for two air-cooled high-power laser-diode arrays for pumping an Yb-doped double-clad fiber laser. In this technique, two right-angle prisms are employed to reshape the pumping beam. As a result, the beams of two air-cooled high-power laser-diode arrays were effectively coupled to the Yb-doped double-clad fiber, and a single-mode output beam of 23.3 W in the 1,080-nm region was obtained.

Beam Combining for Three High-Power Laser-Diode Stacks with a Stripe Mirror Technique

We describe a beam-combining technique for three high-power laser-diode stacks to effectively increase the power density. Employing this beam-combining technique using two slit-stripe mirrors, the power density increased to 722 W/cm2 from a raw power density of 291 W/cm2 by combining the beams of three high-power laser-diode stacks. We also achieved a focused power density of 250 kW/cm2 by focusing the combined beam of the three high-power laser-diode stacks with a lens of 40-mm focal length.

Simultaneously Suppressing Bandwidth and Divergence for a High-Power Laser-Diode Array with an External-Cavity Technique

We report an external-cavity technique to simultaneously suppress the bandwidth and the divergence for a high-power laser-diode array, which features a stripe mirror and a volume Bragg grating. Using this technique, we have effectively suppressed the bandwidth from 1.81 to 0.91 nm and the divergence (1/e2) from 7.5° to 2.3° with an output peak power of 9.3 W.

Ultra-compact imaging plate scanner module using a MEMS mirror and specially designed MPPC

Computed radiography (CR), which is one of the most useful methods for dental imaging and nondestructive testing, uses a phosphor imaging plate (IP) because it is flexible, reusable, and inexpensive. Conventional IP scanners utilize a galvanometer or a polygon mirror as a scanning device and a photomultiplier as an optical sensor. Microelectromechanical systems (MEMS) technology currently provides silicon-based devices and has the potential to replace such discrete devices and sensors. Using these devices, we constructed an ultra-compact IP scanner. Our extremely compact plate scanner utilizes a module that is composed of a one-dimensional MEMS mirror and a long multi-pixel photon counter (MPPC) that is combined with a specially designed wavelength filter and a rod lens. The MEMS mirror, which is a non-resonant electromagnetic type, is 2.6 mm in diameter with a recommended optical scanning angle up to ±15°. The CR’s wide dynamic range is maintained using a newly developed MPPC. The MPPC is a sort of silicon photomultiplier and is a high-sensitivity photon-counting device. To achieve such a wide dynamic range, we developed a long MPPC that has over 10,000 pixels. For size reduction and high optical efficiency, we set the MPPC close to an IP across the rod lens. To prevent the MPPC from detecting excitation light, which is much more intense than photo-stimulated light, we produced a sharp-cut wavelength filter that has a wide angle (±60°) of tolerance. We evaluated our constructed scanner module through gray chart and resolution chart images.

Compact, Rigid, and High-Power Ultrafast Laser System Applying a Glass-Block Cavity

We developed a compact Yb:YAG ceramic regenerative amplification system. A rectangular glass block is used to elongate the cavity. A pulse to be amplified is propagated in a long distance in the glass block by being reflected repetitively at the end faces of the glass under a condition of total internal reflection. Furthermore, we produced transmission gratings with a diffraction efficiency of more than 95%. The floor area of the entire amplification system is reduced to less than 2,000 cm2. In 20-kHz operation, the system generates 1.0-ps compressed pulses of 4.5-W average power, i.e., 0.225-mJ energy.