Because the working media of laser is gas, and the pressure difference between the inner apparatus and environment of laser is large, so the window of output laser beam must be sealed.

由于其激光工作介质是气体，而且激光腔内的压力与外界环境压强相差很大，激光束的输出窗口必须密封。

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Signal recording method, phase difference detecting circuit, and information apparatus.

信号记录方法，相位差检测电路，及信息装置。

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Jianzui apparatus can also use percussion sheet surface, if the difference between larger business, the internal cavity.

还可以用尖嘴器具敲击板材表面，如果生意差异较大，就说明内部有空洞。

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