Intensity adaptive optics

Abstract

Adaptive optics (AO) is a powerful tool employed across various research fields, from aerospace to microscopy. Traditionally, AO has focused on correcting optical phase aberrations, with recent advances extending to polarisation compensation. However, intensity errors are also prevalent in optical systems, yet effective correction methods are still in their infancy. Here, we introduce a novel AO approach, termed intensity adaptive optics (I-AO), which employs a dual-feedback loop mechanism to first address non-uniform intensity distribution and subsequently compensate for energy loss at the pupil plane. We demonstrate that I-AO can operate in both sensor-based and sensorless formats and validate its feasibility by quantitatively analysing the focus quality of an aberrated system. This technique expands the AO toolkit, paving the way for next-generation AO technology.

Fig. 1. The concept of I-AO.

a An optical system affected by spatial intensity error sources, with a distorted focal spot. In this work, spatially varying intensity losses are introduced through three sources: (1) a spatial light modulator (SLM) sandwiched by two crossed polarisers for precise control of intensity distribution, generating arbitrary intensity errors; (2) a thin biomedical sample (fibrotic tissue); and (3) a material sample (birefringent crystals). b Integration of an I-AO corrector restores intensity uniformity, addressing spatially varying loss to achieve an ideal focus. The I-AO corrector employs an SLM sandwiched by two crossed polarisers for pixelated intensity correction at the pupil plane, with an additional deformable mirror (DM) to compensate for phase errors. c Conceptual schematic of sensor-based I-AO with dual-loop feedback correction (SB1 and SB2), where an intensity sensor measures the intensity errors directly from the pupil plane. d Conceptual schematic of sensorless I-AO with dual-loop feedback correction (SL1 and SL2), where the intensity error is estimated using images obtained from the focal plane. The experimental setup is shown in Supplementary Note 1, and details of the dual-loop mechanism can be found in Supplementary Note 2

Fig. 2. Sensor-based I-AO for intensity error correction.

a Demonstration of the necessity of I-AO for intensity error correction by comparison with the results of traditional phase AO correction. The pupil intensity, DM phase profile, and normalised focus profiles are shown under three conditions: I-AO off with introduced intensity error, phase AO on, and I-AO off without introduced intensity error. b Cross-sectional intensity profiles of the focus from (a), with the ideal Airy disk indicated by a dashed line. c Sensor-based I-AO correction using a dual feedback loop (SB1 and SB2 in Fig. 1c). The pupil intensity, DM phase profile, and normalised focus profiles are shown for each step of the correction process. d Cross-sectional intensity profiles of the focus from (c), compared with the ideal Airy disk. Note that in (c), the final step (I-AO SB2) increases the light source intensity, leading to a higher final intensity compared to earlier steps and scaling other curves after the normalisation in (d). White scale bars in (a) and (c) represent 30 μm for all normalised focus profiles

Fig. 3. Sensorless I-AO for intensity error correction.

a Sensorless I-AO correction procedure. The pupil intensity profiles, DM phase profiles, and normalised focal spots are shown under five steps: I-AO off, phase AO on, I-AO SL1, phase AO SL1, and I-AO SL2. b Cross-sectional intensity profiles of the focal spot for each step in (a), compared with the ideal Airy disk (dashed line). The scale bar in (a) represents 30 μm for all normalised focus images