Phase-locked-loop interferometry applied to aspheric testing with a computer-stored compensator.

Area of Science:

• Optical Engineering
• Metrology
• Interferometry

Background:

• Null testing of aspheres is crucial for precision optics manufacturing.
• Traditional interferometric techniques often require separate phase unwrapping steps, adding complexity.
• Digital phase-locked loop (PLL) offers potential for real-time phase determination.

Purpose of the Study:

• To apply a continuous-phase determination technique using a digital phase-locked loop (PLL) for the null testing of aspheres.
• To investigate a method that integrates phase unwrapping and detection within the PLL.
• To utilize a computer-generated holographic compensator for efficient aspheric surface testing.

Main Methods:

• A digital phase-locked loop (PLL) was employed for continuous-phase determination of interferograms.
• A computer-generated holographic compensator was used as the reference signal.
• The PLL simultaneously performed phase detection and unwrapping, eliminating a separate unwrapping step.
• The method was applied to null testing of aspheric surfaces.

Main Results:

• The proposed PLL scheme successfully achieved simultaneous phase unwrapping and detection.
• Wave-front differences of approximately 1 lambda were readily handled by the technique.
• The use of a computer-stored holographic compensator streamlined the interferometric process.
• The technique demonstrated its efficacy in the null testing of aspheres.

Conclusions:

• The digital PLL technique provides an efficient and integrated approach for asphere null testing.
• Simultaneous phase determination and unwrapping simplify the interferometric measurement process.
• Computer-generated holographic compensators are effective tools for advanced optical testing.