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.
Coherent all-solid-state light source of a wavelength below 200nm is attracting a lot of attention for industrial
applications such as semiconductor processing, eye surgery, and micro machining. Multi-stage wavelength conversion
from a high power infrared solid-state laser is a promising solution. We have developed a technology for quasi-phasematching
(QPM) in crystalline quartz that utilizes stress-induced twinning. In the present paper, we report a novel stressmaintaining
module that suppresses back-switching of twinning and enables QPM-SHG in the vacuum ultraviolet (VUV)
region. We demonstrated the fabrication of finest periodic twins with a period of 9.6 μm and performed QPM-SHG
experiment. Vacuum ultraviolet 193.4 nm light of 17 mW was generated from 177 mW fundamental light. To the best of
our knowledge, this is the shortest emission wavelength ever obtained with QPM technology.
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.
For the light source of photocoagulators for ophthalmology, orange laser is more suitable than green laser because of low
scattering loss by the crystalline lens, and low absorption by xanthophylls in the retina. We developed two orange fiber
lasers (580 nm and 590 nm) to investigate the effect depending on the difference in the range of orange.
The 580nm laser is composed of a 1160 nm fiber laser and a Periodically Polled Lithium Niobate (PPLN) crystal for
second harmonic generation. The 1160 nm fiber laser beam is focused into the MgO-doped PPLN crystal whose length is
30 mm with 3-pass configuration. Continuous-wave 1.3 W output power of 580 nm was obtained with 5.8 W input
power of 1160nm for the first time. The conversion efficiency was 22%. The band width of the second harmonic was
0.006 nm (FWHM). The 590 nm laser is almost the same as 580 nm laser source. In this case we used a Raman shift
fiber to generate 1180 nm, and the output power of 590 nm was 1.4 W.
We developed an evaluation model of photocoagulator system using these two laser sources. A 700 mW coagulation
output power was obtained with this orange fiber laser photocoagulator system. This is enough power for the eye
surgery. We have the prospect of the maintenance-free, long-life system that is completely air-cooled. We are planning
to evaluate this photocoagulator system in order to investigate the difference between the two wavelengths at the field
test.
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