Improving throughput of two-beam interference lithography using narrow-bandwidth nanosecond pulsed laser

Holographic gratings play a key role in enhancing optical efficiency in AR and VR systems. Slanted gratings further improve performance by optimizing light propagation. We are developing an interference lithography system with two rotating optical arms for adjusting the slant angle of the grating. This system is capable of fabricating high-quality periodic structures. However, conventional systems using continuous-wave (CW) light sources suffer from low throughput due to prolonged exposure times, particularly at 355nm, where CW lasers have low output power. To address this issue, we used a nanosecond pulsed laser to improve throughput. However, its broad spectral width shortened the coherence length, which negatively impacted exposure quality. In this study, we introduced a solid etalon to narrow the spectral width of a 355nm pulsed laser and extend its coherence length. Using a Mach-Zehnder interferometer, we measured the coherence length increase from 1.35mm to 3.05mm with the etalon. SEM observations of the exposed areas confirmed that using the etalon doubled the fringe formation area diameter. These results demonstrate that the etalon effectively enhances coherence length, leading to better exposure quality. Future work will focus on integrating light sources with narrower spectral widths and higher power to develop next-generation exposure systems compatible with both 266nm and 355nm wavelengths.