| 摘要 |
PURPOSE:To prevent a transmitting laser beam from being displaced greatly due to a refraction which follows its passing, by placing relatively the first and the second photodetecting sensors on the opposite side against the reference axis so that the photodetecting surfaces are turned in the opposite direction to each other. CONSTITUTION:The first and the second half mirrors 10, 11 are placed in a placed state that each surface direction of said mirrors is roughly orthogonal to each other, that is to say, they are inclined to the opposite side to each other in the reference axis P direction. Accordingly, the parallel displacement direction of a laser beam, which follows passing of the first half mirror 10, and the parallel displacement direction of the laser beam, which follows passing the second half mirror 11 become the opposite direction to each other. In this way, the displacements which follow passing each half mirror 10, 11 are offset each other, and with respect to a laser beam L which has been projected in the scheduled propulsive direction, a large displacement of a transmitting laser beam L3 of after the first and the second half mirrors 10, 11 have passed can be dissolved effectively. |
