[Smith, Hirose, Saito]

The optic that was identified as a BS in the previous experiment (klog:37052) was replaced with a mirror. In addition, while attempting to correct beam clipping on the edge of a mirror, it was found that the beam was not passing through the center of the 150 mm focal-length lens. Since the beam was laterally displaced, an attempt was made to move the lens sideways. However, due to the mounting configuration, the lens could not be translated laterally. Modifying the mount to allow lateral adjustment would likely cause interference with a nearby mirror and shift the lens from its original position. Therefore, it will be necessary to move the mirror instead. Furthermore, because two lenses were removed during the alignment procedure, mode matching must be redone. In addition, the short distance between the 150 mm focal-length lens and the nearby mirror, as well as the difficulty of adjusting the mirror near the lens, have led us to consider redesigning the optical layout.
 

• First, the optic at Spot 1 in the photograph, which had been identified as a BS in the previous experiment (klog:37052), was replaced with a mirror. (Please note that although a mount labeled "NON POL 50:50" was used, the optic itself is a mirror (HYD-10).) The alignment of the main laser was then readjusted, and the alignment of the sub-laser was performed using two irises.
   
• However, when the sub-laser power was measured at Spot 2 in the photograph, it was found to be approximately 830 mW. Therefore, Spot 3 was inspected, and it was discovered that the beam was clipping on the edge of a mirror. The alignment was then adjusted so that the main laser beam was centered on the mirror. However, under these conditions, when the beam was adjusted to pass through the center of the 200 mm focal-length lens, it clipped on the side edge of the mirror at Spot 4. To correct this, the alignment was adjusted using mirrors located upstream of the two lenses so that the beam would pass through the centers of both the lenses and the mirrors. However, this was not successful. It was suspected that the presence of the lenses was making the alignment process difficult, so the two lenses were temporarily removed. With the lenses removed, the beam was aligned to pass through the centers of the mirrors, and the 150 mm focal-length lens was then reinstalled. However, the beam became laterally displaced. An attempt was made to adjust the lateral position of the lens, but this was not possible because of the way the lens was mounted. Furthermore, modifying the mount to allow lateral adjustment appeared impractical because the lens was located very close to a mirror, making it difficult to reinstall the lens in its original position.
   
• Therefore, it will be necessary to move the mirror located before the lens. In addition, because the two lenses were removed, mode matching must be performed again. Considering this, together with the short distance between the 150 mm focal-length lens and the nearby mirror and the difficulty of adjusting the mirror in that region, we are considering redesigning the optical layout.