Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics

Area of Science:

• Astronomy and Astrophysics
• Optical Engineering
• Exoplanet Detection

Background:

• Direct exoplanet detection and imaging necessitate advanced high-contrast adaptive optics (AO) systems.
• Accurate correction and calibration of quasi-static aberrations are critical for AO system performance.
• The pupil-modulated point-diffraction interferometer (m-PDI) was previously introduced as a solution for aberration calibration.

Purpose of the Study:

• To experimentally validate the concept and performance of the pupil-modulated point-diffraction interferometer (m-PDI).
• To assess the accuracy, dynamic range, precision, and completeness of the m-PDI system.
• To evaluate m-PDI performance under both monochromatic and polychromatic light conditions.

Main Methods:

• Characterized instrument accuracy and dynamic range by measuring the spatial transfer function across all spatial frequencies and amplitudes.
• Closed an adaptive optics (AO) control loop using visible monochromatic light to calibrate systematic bias, testing precision and completeness.
• Ran the AO control loop with polychromatic light (77 nm FWHM around R-band) to assess performance under broadband conditions.

Main Results:

• Achieved a residual error of 7.7 nm root mean square (rms) in a central pupil region (72% of total radius) during monochromatic testing.
• Demonstrated high precision and completeness in aberration calibration using the AO control loop.
• Observed no performance degradation with polychromatic light, maintaining a final Strehl ratio greater than 0.7.

Conclusions:

• The pupil-modulated point-diffraction interferometer (m-PDI) is a validated and effective tool for calibrating aberrations in high-contrast AO systems.
• m-PDI demonstrates robust performance across a range of spatial frequencies, amplitudes, and light conditions (monochromatic and polychromatic).
• The system's ability to achieve high Strehl ratios makes it suitable for exoplanet detection and imaging applications.