Passively Q-switched microchip (MC) laser with a compact cavity configuration, allowing a sub-nanosecond pulse generation, is an attractive source for the industrial applications including laser processing. Polarization control in such a laser system can be achieved by arranging a polarization-selective element inside of the cavity, e.g. thin film polarizer, resulting in the linearly-polarized output. However, the arrangement impacts on the cavity-length, which leading to expanded the pulse width of the laser output. In this work, we have successfully demonstrated a compact, sub-nanosecond green pulse laser, based on second harmonic generation (SHG) of the MC laser, in which the polarization-selective photonic crystal grating mirror was employed as an output coupler. This system enables to freely select the polarization direction of the linearly-polarized output by just azimuthally rotating the output coupler and thus can accomplish the second harmonic process via a nonlinear crystal without a half-wave plate. The MC laser, pumped by a fiber-coupled 808 nm quasi-continuous wave laser diode, was comprised of 4 mm long Nd3+:YAG crystal with high reflectivity at 1064 nm, Cr4+:YAG crystal as a saturable absorber, and the photonic crystal grating mirror with 50 % reflectivity for 1064 nm. The resulting millijoule-level, sub-nanosecond laser pulse with 45o polarization direction to the crystal axis of a KTiOPO4 (KTP) crystal (Type-II, 9 mm long) for the SHG was frequencyconverted to 532 nm laser output. The total length of this laser system (including the MC laser and the KTP crystal) was also around 35 mm.
We developed an orange fiber laser as the light source for an ophthalmic photocoagulator with superior beam quality and focusing ability. An optical system was also fabricated to verify the spot size of the newly developed laser. It is a simple optical system without the zoom lenses of a conventional delivery system. The laser focal spot has a diameter of 6.8 μm as measured by the knife-edge method. We verified that the laser spot could be reduced to less than that of conventional systems by removing optical system aberrations using wavefront analysis and knife-edge method. However, the effect of laser irradiation cannot be verified with a conventional observation system of photocoagulator. Therefore, we fabricated a laser irradiation device to examine micro spots by modifying an optical microscope. We used our unique pseudo-biological tissue to verify the effect of high-brightness laser irradiation on a human eye. The pseudobiological tissue is comprised of albumin and human gelatin. The laser irradiation caused coagulation and heat
denaturation to the pseudo-biological tissue. We evaluated the relationship of the irradiated area with the power intensity
and irradiation time. As a result, the coagulation spot size was only slightly dependent on power intensity and irradiation
time while the heat denaturation size was strongly dependent on them, especially on irradiation time. The effects of highbrightness
laser irradiation will be thermally analyzed in a future paper.
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