Adaptive Optics for Microscopy

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.

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.

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.

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