Higher-order analysis of four-beam cross grating interferometers

Area of Science:

• Optics and Photonics
• Wave Phenomena

Background:

• Four-beam interference is crucial for applications like optical metrology and data storage.
• Understanding interference pattern formation, especially with partially coherent light, is essential for optimizing device performance.

Purpose of the Study:

• To analyze on- and off-axis four-beam interference patterns using ray tracing.
• To investigate the impact of an accompanying extra term on the interference pattern quality.
• To determine the conditions under which this extra term degrades the desired interference pattern.

Main Methods:

• Ray tracing simulations were employed to analyze the four-beam interference patterns.
• The study focused on the mathematical description of the interference pattern, including an extra term.
• Analysis was performed for various grating spatial frequencies and degrees of light coherence.

Main Results:

• A cross gratinglike interference pattern was identified, accompanied by an extra term of two orthogonal two-beam interference patterns.
• Partially coherent light generally degrades the contrast of the cross gratinglike pattern due to the extra term.
• For high spatial frequency gratings, the extra term's amplitude can dominate, altering the pattern's periodicity.

Conclusions:

• The extra term significantly influences four-beam interference patterns, particularly under partially coherent illumination.
• Careful selection of light sources and grating parameters is necessary to mitigate contrast degradation.
• The findings have implications for the design and performance of optical systems relying on multi-beam interference.