Schematic of alignment module for 4Pi cavity setup. HWP, half-wave plate; QWP, quarter-wave plate; PBS, polarizing beam splitter cube; CCD, charge-coupled device. The red, blue, and green dashed lines indicate s-, p-, and circularly polarized beams, respectively. The split beams propagate following the arrows.|@|~(^,^)~|@|The normalized powers of a beam on the CCD1 camera measured at each rotation angle of (a) HWP2, (b) QWP1, and (c) QWP2, respectively, at 0.5° intervals. The x-axes in the graphs represent the angle of the rotation mount; Therefore, the angle does not correspond to the fast axis of the wave plates. CCD, charge-coupled device; HWP, half-wave plate; QWP, quarter-wave plate.|@|~(^,^)~|@|Normalized power of two beams on the CCD1 camera at each rotation angle of HWP1: (a) over 90° with 0.1° intervals and (b) over 1° with 0.01° intervals. CCD, charge-coupled device; HWP, half-wave plate.|@|~(^,^)~|@|Schematic of a Sagnac interferometer aligned with a half-wave plate (HWP); quarter-wave plate (QWP); polarizing beam splitter cube (PBS); and charge-coupled device (CCD) using the proposed method. The red, blue, green, and yellow dashed lines indicate s-, p-, circularly-, and 45°-polarized beams, respectively.|@|~(^,^)~|@|Interference patterns and corresponding intensity profiles: (a) When all retarders are well-aligned using our method, and when there are misalignments of HWP1’s fast axis (θ_e) with (b) 11° and (c) 22°, respectively. The intensity profiles are acquired by averaging intensities between the yellow dashed lines, which are 40 pixels apart.

Curr. Opt. Photon. 2024;8:421~426 https://doi.org/10.3807/COPP.2024.8.4.421