Let’s dive into a pretty exciting leap in single-pixel microscopy. This technique has always struggled with optical aberrations from the digital micromirror device (DMD), but now there’s a clever workaround.
Researchers have built a system that drops a multi-actuator adaptive lens (M-AL) right into a Hadamard-based single-pixel microscopy (HSPM) setup. The result? Sharper, higher-contrast images, nearly at the diffraction limit, and you don’t have to give up speed or crank up the complexity.
From Single-Pixel Detection to High-Resolution Imaging
Active single-pixel microscopy (SPM) is catching on fast. Instead of a traditional camera sensor, it uses just one detector.
Here’s how it works: SPM projects structured illumination patterns onto the sample, then reconstructs the image from the measured intensities. Most setups generate these patterns with spatial light modulators (SLMs). DMDs are especially popular for this job because they can flip micro-mirrors on and off in a flash to create detailed spatial patterns.
Why Hadamard-Based SPM Stands Out
Hadamard-based single-pixel microscopy (HSPM) stands out from the crowd. It uses orthogonal Hadamard patterns to probe the sample and grabs direct info about its spatial frequency spectrum.
This method shines in situations where regular cameras just can’t cope. Think:
But when you push HSPM to its highest resolution, the DMD optics start to misbehave.
The Resolution–Aberration Trade-off in DMD-Based Microscopy
HSPM’s spatial resolution hits a wall because of two main things: geometrical demagnification of the DMD pattern and the system’s optical diffraction limit. Usually, people “bin” several DMD micromirrors into one bigger pixel to keep the patterns crisp and avoid blur.
Binning keeps images clean, but it throws away detail. So, you miss out on the technique’s full resolving power.
When You Minimize Binning, DMD Aberrations Take Over
If you want to get as close as possible to the diffraction limit, you have to cut back on binning and project smaller patterns. That’s when a new headache appears: aberrations from the DMD, especially astigmatism.
These aberrations warp the illuminating light’s wavefront and lead to:
Unless you fix these issues, all that fine patterning doesn’t pay off.
Adaptive Optics with a Multi-Actuator Adaptive Lens (M-AL)
To tackle DMD aberrations, the team brought in a multi-actuator adaptive lens (M-AL) at the system’s pupil plane. This lens can actively reshape the wavefront and fix distortions as they happen.
The M-AL works by adjusting Zernike polynomial coefficients. That’s just a fancy way of saying it can correct for a bunch of common optical problems—defocus, astigmatism, coma, and other annoyances.
Why a Transmissive Adaptive Lens Is a “Plug-and-Play” Solution
The M-AL has some perks over other high-resolution-endoscopic-imaging/”>adaptive optics like deformable mirrors or phase-only SLMs:
You can think of the M-AL as a plug-and-play adaptive optics module for HSPM. It goes right after the root cause of high-res image problems.
Sharper, Higher-Contrast Images Near the Diffraction Limit
When the M-AL corrects DMD-induced aberrations, the difference in image quality is obvious. Even with patterns sized right up to the diffraction limit, the fixed system delivers:
All this comes without having to go back to coarse binning, so you keep all that delicious spatial resolution that HSPM promises.
Wavefront Sensor-Less (WSL) Correction Using the Hadamard Spectrum
Adding a separate wavefront sensor? That’d make things messier and pricier. Instead, the authors came up with a wavefront sensor-less (WSL) correction trick that uses the directly measured Hadamard spectrum.
Since HSPM already measures frequency-domain data, you can use changes in the spectrum to tweak the M-AL settings. This feedback loop lets you automatically fix:
No extra wavefront-sensing hardware needed. That keeps the whole setup compact and efficient.
Implications for the Future of Single-Pixel Microscopy
This work shows a practical way to combine adaptive optics with Hadamard-based single-pixel microscopy. It’s a real step forward for building high-resolution and versatile SPM platforms.
Key outcomes include:
Single-pixel methods are moving into biomedical imaging, low-light sensing, and even tricky scattering media. Adaptive strategies like these seem pretty crucial. By mixing DMD-based patterning, M-AL correction, and wavefront sensor-less tweaks, researchers now have a more practical way to build single-pixel microscopy systems that are precise, flexible, and ready for more real-world challenges.
Here is the source article for this story: Hadamard based single-pixel microscopy using sensor-less adaptive optics supported by multi-actuator adaptive lens