On-sky multiwavelength phasing of segmented telescopes with the Zernike phase contrast sensor

Area of Science:

• Optical astronomy
• Telescope engineering
• Adaptive optics

Background:

• Extremely large telescopes (ELTs) utilize segmented primary mirrors with hundreds of segments.
• Precise cophasing of these segments is critical for achieving high wavefront quality and optimal observational performance.

Purpose of the Study:

• To develop and demonstrate a multiwavelength scheme for enhancing the capture range of phasing sensors.
• To enable phasing of telescope segments with large initial dephasing errors (micrometers).

Main Methods:

• Implementation of a multiwavelength scheme for the Zernike phase contrast sensor.
• On-sky demonstration at the Very Large Telescope (VLT).
• Testing the sensor's ability to correct piston errors up to ±4.0 μm.

Main Results:

• The multiwavelength scheme successfully extended the phasing capture range from ±λ/2 to several micrometers.
• Demonstrated successful phasing of mirror segments with piston errors up to ±4.0 μm.
• Validated the effectiveness of the Zernike phase contrast sensor with the new scheme.

Conclusions:

• The developed multiwavelength scheme is effective for phasing large segmented mirrors in ELTs.
• This approach is essential for maintaining high phasing accuracy during observations.
• A robust phasing strategy for future ELTs has been established.