PURPOSE: To facilitate control with high accuracy by changing the polarization characteristics of incident luminous fluxes on a synthesizing means, thereby controlling quantity of light.
CONSTITUTION: The luminous fluxes LA 1 and LA 2 split by a polarized beam splitter 20 is entered in the same polarization component to a halfwave plate 22. The luminous flux LA 1 enters a polarized beam splitter 32 via a halfwave plate 28 and a mirror 30 and the luminous flux LA 2 enters the polarized beam splitter 20 as it is after transmission through a halfwave plate 22. The incident two luminous fluxes LA 1 and LA 2 are respectively split in the polarized beam splitter 20 which then synthesizes these fluxes to an output luminous flux LB and emits the same as the luminous flux for detection to be detected by a detector 36. The quantity of light of the output luminous flux LB is calculated in a control device 40. The calculated quantity of the output luminous flux LB is stored in a memory device 44 for the integrated quantity of light which controls the driving of the halfwave plate 22 according to the integrated quantity of light. Laser oscillation is stopped at the point of the time when the integrated quantity of light attains the prescribed quantity of light. The adjustment is thereby facilitated and the control of the quantity of light with high accuracy is enabled.
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