A device with a solid funnel shape is designed for diode-pumped slab amplifier of kW-class cw laser. The solid funnel guides the diode beam in fast axis and expands the pump beam in slow axis. The beam guiding and shaping by the funnel enhance uniformity of absorbed diode beam distribution in the slab Nd:YAG amplifier. The effect of slole angle of the funnel on transmission efficiency is also presented.
We evaluated characteristics of various shapes of reflector to get uniform and efficient pumping of Nd:YAG rod
even with single-side pumping geometry using commercial software ZEMAX and LASCAD. The combined application
of the software enabled us to evaluate numerically the laser performance and absorbed pump diode profile. We tried
various shape of reflector such as semi-circular, square, elliptical reflectors, and cusp-shape, to get uniform pumping. In
the calculation, water flows inside the cooling tube which surrounds the Nd:YAG rod. For further improvement a planarconcave
window was placed in front of the diode to enlarge pump beam divergence angle. Through several trial and
error, we found optimal pumping chamber configuration for single-side pumping, which gives reasonably uniform and
efficient pumping of Nd:YAG rod. The output power and pulsewidth of Q-switched laser output were optimized by
varying the laser cavity length and the output coupler reflectivity.
Among various trials on improving energy conversion efficiency of silicone based photo-voltaic cell, laser doping
casts promising future. Several research groups are suggesting their own methods for laser doping. Usually, doping laser
is injected inside of narrow phosphoric acid jet. The injected beam propagates through the jet and it grooves surface of
silicone cell. The laser energy also heats the silicone surface and phosphorous is penetrated through the surface. In this
work, we separate the grooving laser and heating laser. The silicone surface was grooved by a pulsed fiber laser. The
spot size of the laser was 50 μm. For surface measurement, grooved with of 200 μm was needed. To have the groove
width, we scanned the laser several times. SEM image of the grooved surface showed ripple of the surface. The
phosphoric acid was sprayed on the grooved surface. A fiber coupled cw diode laser heated the sprayed Si surface. After
heating, the Si was washed thoroughly by deionized water. The depth profile of penetrated phosphorous was examined
by using SIMS. The profile indicated that phosphorous was penetrated about 50 nm. Four point measurement of surface
resistance also indicated successful laser doping.
Temporal jittering has been problem in industrial application of passively Q-switched laser. To address
this, we tried two methods. The first is preventing pump laser absorption in the Cr:YAG, which is used for
saturable absorber. The saturation of the Cr:YAG should be affected by intracavity photons generated by
stimulated emission in Nd:YVO4 crystal for reliable Q-switching operation. To prevent pump absorption, we
applied 808 nm mirror coating on the Cr:YAG crystal. This coating also enhanced efficiency of pump laser
utilization because the reflected beam was reabsorbed in the Nd:YVO4 crystal. As the second method, we
applied pulsed current to the laser diode. The Q-switched laser is generated only after the pulse diode laser beam
was absorbed in the Nd:YVO4 crystal. The pulsewidth of current pulse was carefully adjusted for Q-switched
output pulse per each pump pulse. Air circulation is reduced by contacting crystals together and applying output
coupler coating on the Cr:YAG crystal surface.
Thin organic film is coated on the laser absorbing layer. The organic material coated heat absorbing layer is closely
contacted with the substrate. When the laser is incident on the heat absorbing layer, the absorbing layer is expanded and
the organic film is transferred to the substrate. When the laser has Gaussian spatial profile, the profile of printed organic
material becomes non-uniform. We tried several laser beam profile shaping methods to get a clean and sharp printing.
The dependences of eliminated organic material profile from donor plate on the laser power, beam shaping method, and
the layer thickness are also investigated.
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