| 摘要 |
The frequency conversion element for producing light of higher harmonic wave from the fundamental wave laser oscillator is provided with strain gauges 4, 4 or piezoelectric elements 4', 4' or thermo-couples 6, 6, output signals whereof are led to a signal processor and to a comparator, thereby to issue a control signal to decrease power of the input laser light, to prevent thermal breakdown of the frequency conversion element.
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