The focusing characteristics of ring mode CO₂laser beam have been analyzed by using the diffraction theory. Then the influence of the focusing performance, the beam power and welding speed on the penetration depth have been investigated with the 5 kW CO₂laser.
It has been demonstrated experimentally that the welding performance depend on both the magnetification factor and F number especially under the high speed conditions.
The bead-transition phenomena according to changing the focusing position can be evaluated by the parameter (Wd-f) /F (Wd is work distance and f is focal length).

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To make a planar small cone-trapezoid form and ellipse form lenses by optical damage, MMA (Methyl Meth-Acrylate) plate is processed by the irradiation of pulse YAG laser. Those lenses are obtained by setting MMA plate at In-focus position and making ellipse form field-pattern of YAG laser. The refractive-index distribution of cone-trapezoid form lens shows gauss shape. The maximum refractive-index difference of this lens is 4.8×10^-4 and the lens diameter is 1.6mm. The maximum refractive-index difference of ellipse form lens is 0.2-7.6×10^-4 and the ratio of the diameter of major axis to that of minor axis is 2.1-1.2.

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Random-modulation cw (RM-CW) lidar has characteristics that make it possible to use a small-power cw laser as the light source. Development of laser diodes (LD) has been very rapid recently. The laser diode is compact in size and can be driven with little energy compared with traditional lasers, so that it is the most promising candidate for use in a portable, compact and practical lidar system. In this paper, a prototype portable RM-CW lidar system with an LD light source is reported. This is the first report of a practical LD system, to the authors' knowledge. Measurements of the spatial aerosol profile up to several hundred meters, as well as cloud ceiling-height up to several kilometers, were detected, at night time with this system and are shown in this paper.

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