Fig. 1. Schematic of solar telescope and ESAOT wavefront correction. (a) Traditional solar telescope and solar adaptive optical system. (b) ESAOT architecture. (c) Wavefront correction principle in a ESAOT. PM: primary mirror; DSM: deformable secondary mirror; FM: fold mirror; TTM: tip-tilt mirror; DBS: dichroic beam-splitter; M1, M2, M3: collimator and off-axis parabolic mirrors for beam shrinking.

Fig. 2. Wavefront detection process of conventional cross-correlation HS WFS. NCC: normalized cross-correlation; Recon.: reconstruction.

Fig. 3. Measurement principle of the HS f-WFS for detecting global tip-tilt and higher-order aberrations using time-sequenced sub-images.

Fig. 4. Design optimization of the 61-DSM and the HS f-WFS configuration. (a) Preliminary actuator distribution of the 61-DSM. (b) Optimized actuator arrangement of the 61-DSM. (c) Zernike mode compensation performance (the first 25 orders) for both actuator configurations. (d) Control matrix condition number versus HS f-WFS spatial sampling resolution. (e) Co-registered HS f-WFS lenslet array and DSM actuator positions. Annotation: annular region bounded by white circles denotes the clear aperture.

Fig. 5. Schematic diagram of the numerical simulation workflow (CCC: cross-correlation coefficient).

Fig. 6. Numerical validation process and outcomes. (a) Representative random phase screen generated under Kolmogorov turbulence conditions. (b) First 65 Zernike mode coefficients corresponding to the phase screen in (a). (c) Temporal evolution of wavefront aberration RMS values before and after 61-DSM correction. (d) Structural similarity index (SSIM) progression for degraded and corrected images, reflecting quality improvement through adaptive optics compensation.

Fig. 7. Laboratory validation of ESAOT using the 61-actuator DSM. (a) Screened PZT actuators. (b) Optical polishing of the 61-DSM. (c) Delivered 61-DSM. (d) Surface profile of the 61-DSM after self-correction (RMS=12.5 nm). (e) Schematic of laboratory validation system. (f) Image before wavefront correction. (g) Image after wavefront correction, showing a 15-fold increase in peak intensity. (h) Dynamic wavefront aberration correction results: the purple region represents the RMS curve with the DSM OFF (average RMS≈0.91λ), and the green region represents the RMS curve with the DSM ON (average RMS≈0.07λ).

Fig. 8. Prototype of the 600 mm ESAOT and its first-light on-sky observation results. (a) Light-weighted primary mirror (PM) during polishing. (b) DSM integrated with the hexapod structure. (c) Completed fold mirror (FM). (d) Operational 600 mm ESAOT, with the 2.4 m Lijiang telescope visible approximately 300 m away. First-light images of the 600 mm ESAOT capturing the solar photosphere. (e) Uncorrected image. (f) Image after wavefront correction. (g) Image after wavefront correction and reconstruction. (h) Time-varying RMS of high-order wavefront aberrations before (average RMS≈0.71λ) and (average RMS≈0.17λ) DSM correction.