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1. In situ measurement of the isoplanatic patch for imaging through intact bone

   https://doi.org/10.1002/jbio.202000160  

   Forouhesh Tehrani, Kayvan; Koukourakis, Nektarios; Czarske, Jürgen; Mortensen, Luke J. (October 2020, Journal of Biophotonics)

   Abstract Wavefront‐shaping (WS) enables imaging through scattering tissues like bone, which is important for neuroscience and bone‐regeneration research. WS corrects for the optical aberrations at a given depth and field‐of‐view (FOV) within the sample; the extent of the validity of which is limited to a region known as the isoplanatic patch (IP). Knowing this parameter helps to estimate the number of corrections needed for WS imaging over a given FOV. In this paper, we first present direct transmissive measurement of murine skull IP using digital optical phase conjugation based focusing. Second, we extend our previously reported phase accumulation ray tracing (PART) method to provide in‐situin‐silicoestimation of IP, called correlative PART (cPART). Our results show an IP range of 1 to 3 μm for mice within an age range of 8 to 14 days old and 1.00 ± 0.25 μm in a 12‐week old adult skull. Consistency between the two measurement approaches indicates that cPART can be used to approximate the IP before a WS experiment, which can be used to calculate the number of corrections required within a given field of view. 

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2. Birefringent coating to remove polarization dependent phase shift

   Miller S.; Jiang L.; Pau, S. (May 2022, Optics express)

   Polarization aberrations are found in most optical components due to a materials differing response to s- and p-polarizations. This differing response can manifest either as diattenuation, retardance, or both. Correction of polarization aberrations, such as these, are critical in many applications such as interferometry, polarimetry, display, and high contrast imaging, including astronomy. In this work, compensators based on liquid crystal polymer and anti-reflection thin-films are presented to correct polarization aberrations in both transmission and reflection configurations. Our method is versatile, allowing for good correction in transmission and reflection due to optical components possessing differing diattenuation and retardance dispersions. Through simulation and experimental validation we show two designs, one correcting the polarization aberrations of a dichroic spectral filter over a 170nm wavelength band, and the other correcting the polarization aberration of an aluminum-coated mirror over a 400nm wavelength band and a 55-degree cone of angles. The measured performance of the polarization aberration compensators shows good agreement with theory. 

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3. Birefringent coating to remove polarization aberrations

   https://doi.org/10.1364/OE.458859  

   Miller, Sawyer; Jiang, Linan; Pau, Stanley (May 2022, Optics Express)

   Polarization aberrations are found in most optical components due to a materials-differing response tos- andp-polarizations. This differing response can manifest either as diattenuation, retardance, or both. Correction of polarization aberrations, such as these, are critical in many applications such as interferometry, polarimetry, display, and high contrast imaging, including astronomy. In this work, compensators based on liquid crystal polymer and anti-reflection thin-films are presented to correct polarization aberrations in both transmission and reflection configurations. Our method is versatile, allowing for good correction in transmission and reflection due to optical components possessing differing diattenuation and retardance dispersions. Through simulation and experimental validation we show two designs, one correcting the polarization aberrations of a dichroic spectral filter over a 170nm wavelength band, and the other correcting the polarization aberration of an aluminum-coated mirror over a 400nm wavelength band and a 55-degree cone of angles. The measured performance of the polarization aberration compensators shows good agreement with theory. 

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4. Synthetic spatial aperture holographic third harmonic generation microscopy

   https://doi.org/10.1364/OPTICA.521088  

   Farah, Yusef; Murray, Gabe; Field, Jeff; Varughese, Maxine; Wang, Lang; Pinaud, Olivier; Bartels, Randy (May 2024, Optica)

   Third harmonic generation (THG) provides a valuable, label-free approach to imaging biological systems. To date, THG microscopy has been performed using point-scanning methods that rely on intensity measurements lacking phase information of the complex field. We report the first demonstration, to the best of our knowledge, of THG holographic microscopy and the reconstruction of the complex THG signal field with spatial synthetic aperture imaging. Phase distortions arising from measurement-to-measurement fluctuations and imaging components cause optical aberrations in the reconstructed THG field. We have developed an aberration-correction algorithm that estimates and corrects these phase distortions to reconstruct the spatial synthetic aperture THG field without optical aberrations. 

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5. Closed-loop wavefront sensing and correction in the mouse brain with computed optical coherence microscopy

   https://doi.org/10.1364/BOE.427979  

   Liu, Siyang; Xia, Fei; Yang, Xusan; Wu, Meiqi; Bizimana, Laurie_A; Xu, Chris; Adie, Steven_G (July 2021, Biomedical Optics Express)

   Optical coherence microscopy (OCM) uses interferometric detection to capture the complex optical field with high sensitivity, which enables computational wavefront retrieval using back-scattered light from the sample. Compared to a conventional wavefront sensor, aberration sensing with OCM via computational adaptive optics (CAO) leverages coherence and confocal gating to obtain signals from the focus with less cross-talk from other depths or transverse locations within the field-of-view. Here, we present an investigation of the performance of CAO-based aberration sensing in simulation, bead phantoms, andex vivomouse brain tissue. We demonstrate that, due to the influence of the double-pass confocal OCM imaging geometry on the shape of computed pupil functions, computational sensing of high-order aberrations can suffer from signal attenuation in certain spatial-frequency bands and shape similarity with lower order counterparts. However, by sensing and correcting only low-order aberrations (astigmatism, coma, and trefoil), we still successfully corrected tissue-induced aberrations, leading to 3× increase in OCM signal intensity at a depth of ∼0.9 mm in a freshly dissectedex vivomouse brain. 

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