Key Takeaways: Adaptive optics enhance optical system performance by correcting wavefront distortions in real time using deformable mirrors, wavefront detectors, and controllers.  Initially developed for astronomical telescopes to mitigate atmospheric turbulence, it now also improves imaging in biological microscopes and retinal diagnostics.  This technology enables precise corrections, enhancing resolution in complex environments, such as thicker biological samples and dynamic ocular structures.  By actively adapting to aberrations, adaptive optics significantly advances optical applications in science and medicine. Introduction to Adaptive Optics Adaptive optics is a technology designed to improve the resolution of optical systems that may be affected by environmental factors or the state of the observed object. In real-world applications, optical systems often deviate from ideal performance, necessitating correction measures to enhance imaging quality.  A familiar example is the human eye. When vision is impaired due to nearsightedness or farsightedness, corrective lenses, such as glasses, address these aberrations. However, traditional corrective lenses are not adaptable. If a person’s vision deteriorates further, a new pair of glasses is needed. This highlights the need for a deformable correction mechanism that can adjust dynamically to the actual conditions of the imaging system. In adaptive optics, a deformable mirror is incorporated into the optical system. This mirror measures wave aberration in real time to correct distortions, reducing environmental impacts and improving imaging quality. Essentially, adaptive optics actively corrects errors in optical systems, combining scientific principles with engineering applications to play a crucial role in modern optics.  Understanding Wavefront A wavefront refers to the surface formed by points that are in the same phase during light wave propagation. A point source generates a spherical wavefront, while a parallel source generates a plane wavefront. Ideally, the wavefront should be perfectly spherical or planar. However, due to aberrations in optical systems, even a perfect wavefront can deviate and exhibit wavefront error after passing through the system. Wavefront error Device of Adaptive optics Adaptive optics operates through a closed loop of detection, control, and correction, utilizing components such as wavefront sensing detectors, controllers, and correction elements.  Wavefront Sensor: Before adjustments can be made, the wavefront situation must be assessed. A wavefront sensor is a specialized component that measures wavefront distortion in real time, serving as the core component of an adaptive optics device. There are various types of wavefront sensors, each with distinct operation principles. A  common wavefront sensor, for example Hartmann-Shack sensor, consists of a microlens array and an image sensor. The wavefront is divided into small regions by the microlens array, which projects images onto the sensor. If the wavefront is tilted, the image spots shift from their ideal positions. Each microlens acts as a microelement, allowing for the calculation of the average slope of the wavefront in each region. This data is compiled to reconstruct the complete wavefront profile. Hartmann-Shack Wavefront Sensor Wavefront Controller: The wavefront sensor provides the measured wavefront shape information to the wavefront controller. The controller processes the sensor data and determines a compensation strategy using algorithms. Correction Element: After calculating the compensation scheme, the wavefront controller sends signals to the correction element, which compensates for the wavefront errors. Simply put, the correction element generates a reverse wavefront aberration to counter the original aberration, effectively canceling the aberration out. The correction element is deformable; by applying voltage or other means, its surface shape can be altered. This adjustment modifies the optical path difference, producing the required correction. Applications of Adaptive Optics One of the first applications of adaptive optics was in astronomical telescopes. The resolution of these space telescopes often cannot achieve the ideal diffraction limit due to irregular movements in the Earth’s upper atmosphere. Atmospheric turbulence creates wave aberrations that significantly hinder the telescopes’ imaging capabilities of celestial objects.  Wavefront sensors measure these wavefront distortions caused by atmospheric turbulence, while deformable mirrors make real-time corrections to improve image quality. Consequently, adaptive optics has become an essential technology in modern astronomical observation, with nearly all large telescopes now incorporating adaptive optics systems. High Resolution Biological Microscopes Biological microscopes are precision optical instruments used to observe transparent or translucent objects, such as biological slices and living tissues. For example, when imaging a biological sample with an infinity-corrected microscopy objective lens, the light emitted by the sample forms a spherical wave. This light wave is collected by the objective lens, converted into a plane wave, and then focused by the tube lens before being captured by the sensor. However, the complex internal structure of biological samples, particularly in thicker specimens, often leads to optical aberrations. Combined with optical system errors, these aberrations significantly affect imaging quality. To achieve high resolution imaging, correcting these errors is essential. Adaptive optics techniques have been introduced into various microscopy imaging systems to correct aberrations and enhance image resolution. A beamsplitter and a deformable mirror are integrated into the optical path. The beamsplitter separates a light beam for wavefront analysis, and this information is fed back to the deformable mirror to make necessary corrections. Adaptive optics can also predict and correct wave aberrations using adaptive correction elements based on wavefront detection. Biological Microscope Retinal Imaging Another significant application of adaptive optics is retinal imaging. Ophthalmoscopes are used to examine the retina for fundus lesions. While traditional ophthalmoscopes can detect and diagnose retinal issues, they struggle to observe fine retinal structures due to limited resolution and inherent eye aberrations. Although compensating lenses can reduce primary aberrations, their effectiveness is limited. Adaptive optics technology allows for real-time correction of dynamic eye aberrations, overcoming the limitations of traditional ophthalmoscopes and enabling high-resolution retinal imaging. Retinal Imaging Comprehensive understanding of Adaptive Optics In conclusion, adaptive optics represents a transformative leap in optical technology, addressing and correcting aberrations in real time to enhance imaging quality across diverse applications. From revolutionizing astronomical observations by compensating for atmospheric turbulence to enabling high-resolution biological microscopy and retinal imaging, adaptive optics bridges the gap between theoretical precision and practical performance. Its ability to dynamically adjust optical systems ensures superior resolution and clarity, making it indispensable in both

Key Takeaways Ritchey Chrétien telescopes (RC telescopes) eliminate spherical aberration, coma, and astigmatism, ensuring sharp, distortion-free imaging. Their wide, flat field of view makes them ideal for galaxy mapping, supernova detection, and dark matter studies. Compact, lightweight designs reduce launch costs, while thermal stability ensures reliable performance in extreme conditions. RC systems support advanced instruments for multi-purpose missions. Iconic examples like Hubble and JWST showcase their impact.   The importance of RC telescope in Space Optics In the realm of space exploration, precision is everything. The Ritchey-Chrétien (RC) telescope has become a cornerstone for astronomical instruments, offering exceptional performance through its advanced optical design. Here’s why the RC telescope is pivotal in space optics and what sets it apart. Astrophotography and space-based observations demand unparalleled clarity. The RC telescope excels in eliminating optical aberrations: 1. Aberration Correction Spherical Aberration: RC telescopes are designed to eliminate spherical aberration through the use of hyperbolic primary mirrors and secondary mirrors. This ensures that light from celestial objects converges at a single focal point, enhancing image sharpness. Coma Correction: Unlike simpler telescope designs, such as Newtonian or Cassegrain telescope systems, the RC configuration corrects for coma, which causes off-axis stars to appear distorted or elongated. This is crucial for capturing accurate and uniform data over a wide field of view. Astigmatism Reduction: RC telescopes are designed to minimize astigmatism, further improving the focus and clarity of images across the entire field. This image shows the Ritchey Chrétien telescope with two pieces of flat field lens Example of an F=8.3 Cassegrain telescope, where on-axis performance achieves the diffraction limit, but off-axis aberrations, especially coma, are visible 2. Wide Field of View RC telescopes provide a wide, flat field of view, a critical feature for missions requiring detailed surveys of vast regions of the sky. Applications include: Galaxy Mapping: Capturing high-resolution images of galaxies across the universe. Supernova Detection: Observing transient celestial events. Dark Matter Exploration: Studying cosmic structures influenced by dark matter. 3. Compact and Lightweight Design Space missions are constrained by size and weight due to launch vehicle limitations. The RC design offers a shorter optical tube length compared to other high-performance optical systems, reducing the telescope’s overall size and weight while maintaining high resolution and performance. 4. Thermal Stability in Space Environments Operating under extreme and variable temperatures, space-based telescopes require robust designs. The RC telescope remains thermally stable, minimizing alignment shifts and reducing reliance on complex active adjustment systems. This stability ensures reliable, long-term performance. 5. High Reflectivity and Efficiency RC telescopes use advanced reflective coatings, such as aluminum or enhanced silver, to maximize light collection. This efficiency is crucial for studying: Exoplanets: Observing faint planetary systems around distant stars. Distant Galaxies: Investigating the universe’s most remote structures. Cosmic Background Radiation: Analyzing the remnants of the Big Bang. 6. Seamless Instrument Integration Flexibility is key for multi-purpose missions. The RC telescope’s design allows for easy attachment of advanced instruments such as spectrographs, cameras, and coronagraphs, enabling a wide range of observational techniques. 7. Space Applications RC telescopes play an indispensable role in various astronomical missions: Deep Space Exploration: Imaging distant galaxies and nebulae with unmatched resolution. Exoplanet Research: Supporting precise measurements for photometry and spectroscopy. Astrophysical Phenomena: Studying black holes, gravitational waves, and cosmic microwave background radiation. Deep Space Exploration 8. Iconic Examples of RC Telescopes Hubble Space Telescope: An RC design that has provided some of the most iconic images of the universe with minimal optical distortions. James Webb Space Telescope (JWST): Employing principles of the RC system with deployable optics, it observes infrared wavelengths, pushing the boundaries of what’s possible in space observation. A Telescope Designed for Space’s Challenges The Ritchey Chrétien telescope’s ability to deliver aberration-free, high resolution imaging in a compact and thermally stable form makes it essential for space missions. Whether mapping the cosmos, detecting exoplanets, or exploring astrophysical phenomena, the RC telescope continues to be a driving force in advancing our understanding of the universe. At Avantier, our exceptional engineering knowledge and decades of experience enable us to produce high precision optics, such as SiC mirrors and off-axis parabolic mirrors, for space optics. We provide customized solutions tailored to the unique demands of space-based applications. With top-notch techniques in designing and manufacturing optical lens assemblies, we are committed to supporting groundbreaking advancements in space exploration. Related Content

Key Takeaways Optics for UAVs must be lightweight, durable, and capable of performing in tough environmental conditions.  Key requirements include balancing size, weight, and power (SWaP), achieving high-resolution imagery from long distances, and enduring temperature and pressure changes.  Thermalized designs help compensate for material expansion, while ruggedized systems withstand vibrations, shocks, and flying particles. UAV optics are critical for various applications, such as vegetation analysis, search and rescue, and industrial inspections, utilizing multispectral, thermal, and machine vision systems for diverse imaging needs. Optics for UAVs must be lightweight and durable, yet offer superior performance even in adverse environmental conditions. These optical assemblies are in many ways the heart of any UAV system, and an unmanned aerial vehicle is only as robust as its machine vision system. Here we’ll look at some of the unique challenges that optics for UAVs must surmount— and the wide range of special imaging capabilities they can bring to an unmanned aerial vehicle. Requirements of Optics for UAVs When designing an optical system for a UAV, an optical designer will need to balance a number of important requirements. Size, weight, and power consumption— sometimes abbreviated as SWaP— are often thought as the big three. Especially when working with small UAVs, every gram directly decreases flight endurance. Weight and size considerations makes continuous zoom a good option, for instance, instead of packing a different lens for every field of view. But there’s more. Optical systems for drones and UAVs must be capable of capturing quality imagery, even from significant distances and under adverse environmental conditions.  Long focal lengths and a good field of view can aid imaging assemblies to produce high resolution images, and special coatings can reduce reflection under strong sunlight.  However UAV optics must also be ruggedized for mechanical shock, vibrations, extreme temperature differences, and pressure changes.  Here we’ll look at the ruggedization requirements for UAV optics. Temperature Changes The refractive index of many substrates depends on temperature, but that’s not the chief worry when it comes to temperature changes and UAV optics. The coefficient of thermal expansion (CTE) of each part must be carefully considered. Glass, metal, and other substrates expand and contract at different rates, and the size of a particular component will be different at different temperatures. Optics for UAVs must be built for the temperature changes they will encounter in the atmosphere. When different materials are used in an assembly, temperature changes can cause lenses to shift, become misaligned, or even crack. A system that will undergo temperature changes must be carefully designed to minimize these issues, compensating for changing sizes when heated or cooled. We call these designs athermalized designs.  Pressure Changes Pressure is another significant issue when it comes to optical systems meant to be used in drones and other aerial vehicles. An assembly designed to have inner and outer chambers at equilibrium when used at ground level will no longer be at equilibrium when outdoor pressure changes. Careful modeling at different pressure values enables optical engineers to design a system that functions well at the low pressures encountered at high altitudes as well as at high-pressure locations.  Mechanical Durability An optical system designed for use within a UAV doesn’t only need to be able to withstand pressure and temperature changes; it also has to be protected against flying particles and ruggedized to withstand vibrations, the shock of quick acceleration changes, and any collusions.  These factors are important to consider when choosing substrates, but it is also important to ensure the final design is as simple and robust as possible, with connections between components reinforced where appropriate.  Optics for UAVs should be designed with carefully sealed components to keep moisture and dust outside. Precise orbital detection of mid-sized debris can also be achieved using carefully designed orbital laser ranging and LIDAR techniques. Often passive optical means and solar illumination are used to first recognize a piece of space debris, which is then illuminated with an intense ns-pulsed TOF laser. The receiver telescope is equipped with single photon detectors, capable of detecting  backscattered photons. This detection method has been used to detect objects of as little as 10 cm in diameter, and typical ranging accuracy is about 3 m rms. Applications of Optics for UAVS The optics you choose for your UAV will depend primarily on your imaging applications and the purpose of the UAV operations. Measurement and control of height above the ground can be accomplished by either active or passive sensing, using machine vision systems that guide the vehicle autonomously at a desired altitude.  For vegetation analysis, high spectral resolution spectrometry, multispectral cameras, or NIR cameras can all provide different imaging capabilities. In search and rescue operations a mixture of RGB and thermal imaging—either short wavelength infrared (SWIR), medium wavelength MWIR, or long wavelength infrared are often used in concert to obtain fail-safe operations under poor environmental conditions. Industrial inspection also often relies on thermal imaging payloads. Optics for UAVs at Avantier At Avantier, we produce custom high-performance optics for UAVs, providing customers in a wide range of fields with the quality optical assemblies they need. Whether you are in industry, surveillance, agriculture or defense, we can work with you to design and produce the optics you need. Contact us today to set up an initial consultation.  References Johnston, C. (2012). Technical challenges for small UAV payloads. Electronic Military and Defense. https://smithmillermoore.com/Pdfs/technicalarticles/7-11_HT_EM&D_TechChallenges_forSmallUAV_Payloads.pdf Srinivasan, M. V., Thurrowgood, S., & Soccol, D. (2006, November). An optical system for guidance of terrain following in UAVs. In 2006 IEEE International conference on video and signal based surveillance (pp. 51-51). IEEE. https://ieeexplore.ieee.org/abstract/document/4020710/ Von Bueren, S. K., Burkart, A., Hueni, A., Rascher, U., Tuohy, M. P., & Yule, I. J. (2015). Deploying four optical UAV-based sensors over grassland: challenges and limitations. Biogeosciences, 12(1), 163-175. https://doi.org/10.5194/bg-12-163-2015 Related content

Key Takeaways VR optics utilize head-mounted displays (HMDs) to immerse users in virtual environments by projecting virtual scenes through an optical system, reducing eye strain.  Key performance indicators include field of view (FOV) for immersion, EyeBox for comfortable eye movement, distortion control for image accuracy, and dispersion reduction to prevent color fringing.  Optical solutions vary by design: aspherical lenses reduce spherical aberrations, Fresnel lenses are lightweight but can distort images, and Pancake lenses are compact and high-quality but more expensive. An Introduction To VR Optics A head-mounted display (HMD)—commonly referred to as a headset—projects signals from the display screen to the eyes through an optical system, creating a visual experience distinct from reality. Virtual Reality (VR) technology has rapidly advanced, immersing users in entirely virtual environments that feel like another world. At the core of VR display technology lies optical imaging, which projects virtual scenes to users’ eyes, enabling realistic visual experiences. Without an optical system, displays placed too close to the eyes would require constant diopter adjustments, leading to eye strain or damage. Moreover, if the display is closer than the eye’s focal adjustment range, imaging becomes impossible. VR optical systems address this by converting the near-eye display’s point light signals into approximately parallel light rays, minimizing diopter adjustment strain and creating a comfortable, immersive experience.   Early VR optical systems used single lenses, borrowing principles from simple eyepieces like magnifying glasses. However, modern VR systems must balance imaging quality, device size, and weight, leading to the development of specialized optical solutions. Indicators of VR optics Field of view Field of view (FOV) is a critical metric that directly impacts user immersion. FOV refers to the maximum visible area users can see when wearing a headset, defined as the angle between the edges of the field of view. If expressed in the form of an angle, the size of the field of view is the size of the angle between the field of view at the edge of the object and the eye, that is, the maximum visible range, which is called the field of view angle. The field of view angle is an important parameter to judge immersion, which defines the visible area that VR users can see when wearing a headset. A wider field of view allows for a more immersive experience, allowing users to truly be in a virtual environment. In VR optics, 90° FOV is considered to be the pass line for VR immersion experience, 120° FOV is generally considered to be the standard for achieving partial immersive experience, and 180° FOV is the standard for VR to achieve full immersion. Currently, most VR devices offer FOVs between 90° and 120°. EyeBox The EyeBox defines the range within which a user’s eyes can move while still perceiving the image clearly. For a comfortable experience, the EyeBox must accommodate eye movement and variations in user eye spacing. The entry pupil diameter of the human eye is approximately 4 mm, making this the minimum size for the EyeBox. When using VR devices, users usually move their eyes. And each person’s eye distance is different, and the condition of wearing the device is also different when using it. So the EyeBox should be as big as possible. Expanding the EyeBox improves comfort but complicates VR optical design and may impact other performance metrics.   Distortion VR optics transmits the virtual picture to the human eye through the optical system, and the human eye as the entrance pupil is outside the optical system, the system is asymmetric, and due to the large field of view requirements, the optical system often has more obvious distortion. Distortion occurs when the optical system transmits images with geometric inaccuracies, such as “pincushion distortion (pillow distortion),” where images stretch at the edges. Distortion is intrinsic to VR optical systems due to their asymmetrical design and large FOV requirements. Pre-processing images into a “barrel” shape compensates for distortion but reduces resolution. Improved optical designs can alleviate processing demands and enhance quality.  Illustration of Pincushion and Barrel Distortion in VR Optics Dispersion Dispersion is a situation that most VR devices encounter when they are used, manifesting as color fringing, where different wavelengths of light (colors) diverge at the image’s edges. This is because the VR device transmits the signal to the human eye through refraction and transmission, so with the increase of the field of view, the vertical color difference will be more obvious. Off-axis light beam of different wavelengths is focused through the lens after the height of the plane is different, that is, the magnification of each wavelength after imaging is different, so the vertical axis color difference is also called the power color difference. The focal points of multiple wavelengths are sequenced in the direction of the height of the image plane, and the final visible edge of the image plane produces a rainbow band. Lens combinations with differing Abbe coefficients correct chromatic aberrations but increase cost and weight. Image pre-processing is another method to counteract dispersion. Other key indicators in VR optics include resolution, pupil spacing, entry pupil distance, volume, and weight, all of which influence the overall design and usability of the optical system. Optical solutions for VR devices Aspherical lens In theory, near-eye displays can be achieved using a single spherical lens. However, spherical lenses suffer from significant spherical aberration, resulting in poor imaging performance. Additionally, spherical lenses exhibit large field curvature, leading to poor image quality at the edges of the field of view. Spherical lenses also have fewer adjustable parameters, limiting their ability to address these issues effectively. The surface of an aspherical lens is irregular, with curvature that changes depending on the lens’s height. By adjusting aspherical parameters, spherical aberration can be eliminated, and field curvature minimized. This is particularly effective when both lens surfaces are aspherical, offering significantly better imaging quality compared to spherical lenses. Processing aspherical lenses is more complex than spherical lenses. While traditional precision polishing technology offers higher accuracy, it is time-consuming, expensive,

Key Takeaways Adaptive optics for microscopy improves image quality by correcting refractive aberrations in specimens, especially in deep tissue imaging.  Techniques involve sensors, deformable mirrors (DMs), and spatial light modulators (SLMs) to dynamically counteract distortions. DMs, ideal for broadband light, adjust with electrostatic or piezoelectric forces, while SLMs suit laser-based, wavelength-specific applications. Adaptive optics setups vary by microscope type, as aberration correction needs differ. Customized AO solutions allow users to optimize high resolution imaging for complex optical applications. There’s a promising new way to improve image quality and correct for the inevitable aberrations in high resolution microscopy.  Adaptive optics for microscopy. Choosing high quality optics enables you to improve your image quality and produce high resolution microscope images. But even if you’re working with optical components that are ideal and perfect in every sense, there are some aberrations that won’t go away. These are the aberrations caused by the spatial variations in the refractive index of the specimens being studied. The deeper the tissue being imaged, the worse the problem gets.  Adaptive optics involves a range of techniques that enable you to correct for these aberrations before the image is produced, making high-resolution and even super-resolution imaging possible in tissue as deep as tens or hundreds of micrometers. Here we’ll look at just how adaptive optics work to make high quality microscopy possible even with deep tissue imaging. Understanding Adaptive Optics for Microscopy How can you correct for aberrations caused by inhomogeneous samples and specimens with complex optical structures? The trick is to use optics that can transform themselves based on their environment, adapting on-the-go when faced with specific aberrations.   Dynamic aberration correction involves an optical system that includes a special sensor that measures aberration at different parts of the sample. This might, for instance, be a wavefront sensor. A sequence of measurements is used to optimize the aberration correction, and deformable mirrors (DMs) or liquid spatial light modulators  (SLMs) respond in real-time. These dynamic optics provide conjugate aberrations— equal but opposite—- to cancel out the problematic aberrations at each point on the sample. caption: This series of images demonstrates how adaptive optics for microscopy work to cancel out the aberrations caused by the nonuniform optical profile of the specimen. Choosing the Right Adaptive Optics for Microscopy Adaptive optics can work well in many types of high-resolution microscopes, from fluorescence  and multi-photon fluorescence microscopes to laser scanning microscopes and parallelism scanning systems. But it’s important to realize there’s no one plug-and-play adaptive optical solution that works in any microscope you might want to use. The adaptive system will need to be customized based on both the physical configuration of the microscope and the image formation process that is used.  Suppose you use a conventional wide field fluorescence microscope. In this microscope, the illumination path is used simply to illumine the sample in a uniform way, and aberrations are only a problem when it comes to the imaging path.  In a confocal microscope, however, aberration is problematic in both the illumination and imaging paths, and adaptive optics need to be set up to compensate in both areas.  But those are not the only two possibilities. In a two-photon excitation fluorescence microscope, the resolution is dependent on the illumination path, and it is here you might need adaptive optics: aberrations in the imaging path will have no effect on the final results. When using adaptive optics for microscopy with a confocal microscope, attention must be paid to both illumination and imaging paths. Comparing Adaptive Optic Elements When it comes to the actual optical elements within your AO microscopy system, you have two major options: liquid crystal spatial light modulators or deformable mirrors.  A deformable mirror is a dynamic optic manufactured with a reflective surface. The shape of this surface may be continuous or segmented, but either way is designed in such a way that it can be ‘deformed’ or changed by the application of tens to hundreds of actuators, which are acted upon by either electrostatic, electromagnetic, or piezoelectric forces. Deformable mirrors are polarization independent and typically provide high reflectance over a broadband. DMs are generally the best choice for fluorescence light and other weak emissions, or when multiple wavelengths of light must be corrected simultaneously. A spatial light modulator is wavelength dependent and can only be used with parallel light. There are different types of SLMs, but liquid crystal on silicon (LCOS), used in reflection mode,  is one frequently used option. Most SLMs have lower optical efficiency than DMs, but they are a good choice for many laser applications. There’s also a third possibility, which is not yet widely used in microscopes but may gain importance in the future: transmissive adaptive elements. A transmissive adaptive element is formed of transparent, fluid-filled chambers. The shape of these chambers can be dynamically altered to create the desired aberration. References Booth, M. Adaptive optical microscopy: the ongoing quest for a perfect image. Light: Science and Applications 3, e165 (2014). https://doi.org/10.1038/lsa.2014.46 Marx, V. Microscopy: hello, adaptive optics. Nature Methods 14, 1133–1136 (2017). https://doi.org/10.1038/nmeth.4508 Jingyu Wang, Yongdeng Zhang. 2021: Adaptive optics in super-resolution microscopy. Biophysics Reports, 7(4): 267-279. DOI: 10.52601/bpr.2021.210015 Booth, M. J. (2019). A basic introduction to adaptive optics for microscopy (1.0). Zenodo. https://doi.org/10.5281/zenodo.3471043 Related Content