Nonnull interferometric testing of spherical gratings under Littrow conditions with opposite diffraction orders

Area of Science:

• Optics and Photonics
• Optical Metrology
• Diffractive Optics

Background:

• Spherical gratings require precise verification of their diffracted wavefronts.
• Direct interferometric testing can be complicated by inherent setup aberrations.

Purpose of the Study:

• To develop a non-null interferometric testing method for spherical gratings.
• To isolate and quantify wavefront errors solely due to manufacturing imperfections.

Main Methods:

• Utilizing Littrow angle autoreflection for non-null interferometric testing.
• Performing dual measurements under opposite diffraction orders to cancel setup aberrations.
• Analyzing geometric aberrations of spherical gratings.

Main Results:

• Simulations show residual errors below 0.004λ RMS for varied line spacing (VLS) gratings.
• Experimental results for a VLS grating yielded a diffracted wavefront error of 0.018λ RMS.
• The proposed method effectively separates manufacturing errors from setup contributions.

Conclusions:

• The developed non-null interferometric method provides accurate wavefront error derivation for spherical gratings.
• This technique is valuable for quality control in the manufacturing of optical components.
• Further analysis of residual misalignment errors is discussed.