特殊共振器鏡を用いたCO_2レーザー出力の偏光特性

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A CO_2 laser has been utilized in various fields because of its high efficiency and good beam quality. But an excellent optical fiber is not available which imposes restrictions on applications. A hollow metallic waveguide is one of potential alternatives for the transmission line of a CO_2 laser. The optical mode with the lowest loss in the hollow metallic waveguide is a TE_<01> mode. We devised a conical cavity mirror for CO_2 laser to obtain the output laser beam with a TE_<01> like mode. A plane metallic mirror was inserted within the laser cavity to form a folded laser cavity in order to understand the basic mechanism to generate the TE_<01> like mode using the conical cavity mirror. Polarization properties of laser output were investigated for different folding angle to the plane mirror. A slight difference of reflectivity of the plane mirror for an incident ray with P and S polarization was enhanced through the multiple reflection within the laser cavity, because a laser system forms a feedback system to reach a laser oscillation. By using this idea of feedback system, a laser output with a linear large degree of polarization (> 95 percent) was obtained, when a difference of reflection ratio for P and S polarization was only about 0.2 percent. This polarization property cannot be explained using only a difference of reflection ratio for P and S polarized ray. The effect of mode competition considered for longitudinal modes caused by population pulsation in the laser cavity was assumed for transverse modes to explain the property. In the model, the intensity of P polarization is restrained by amplification of the intensity of S polarization. The number of round trip obtained by using the model was about 30 times.

特殊共振器鏡を用いたCO_2レーザー出力の偏光特性

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