Enhanced measurement of deep-ultraviolet optical systems using a point diffraction heterodyne interferometer

Area of Science:

• Optical Engineering
• Metrology
• Deep Ultraviolet (DUV) Optics

Background:

• Interferometers are crucial for optical aberration testing.
• Point diffraction interferometers (PDIs) offer high accuracy using diffraction.
• DUV optical systems necessitate specialized interferometers due to unique challenges.

Purpose of the Study:

• To develop and demonstrate a DUV heterodyne point diffraction interferometer (DH/PDI).
• To achieve precise wavefront measurement in the DUV region.
• To address photodamage issues inherent in DUV PDI.

Main Methods:

• Implementation of a DH/PDI system for DUV wavefront analysis.
• Utilizing two-layer point diffraction modules to mitigate DUV laser photodamage.
• Employing acousto-optic modulators (AOMs) for heterodyne detection and frequency difference generation.
• Adjusting AOM power for high-contrast interferograms with varying mirror reflectivity.

Main Results:

• Successful demonstration of a DH/PDI for precise DUV wavefront measurement.
• Mitigation of extreme photodamage through a two-layer diffraction module design.
• High-speed, anti-interference heterodyne detection achieved via AOMs.
• Obtained high-contrast interferograms for diverse mirror reflectivities.

Conclusions:

• The DH/PDI system shows significant promise for DUV optical system analysis.
• The developed interferometer effectively addresses key challenges in DUV metrology.
• This technology enables enhanced resolution and accuracy in DUV optical manufacturing and testing.