Wavefront correction in two-photon microscopy with a multi-actuator adaptive lens

The group leaded by P. Artal at Murcia University has recently published an interesting paper related to adaptive optics using an adaptive lens. When working in a real scenario, imperfections in the optical elements you use or just the objects you want to image introduce optical aberrations in the pictures you obtain. Usually these aberrations reduce the quality of your images just a bit (introducing a bit of defocus or some astigmatism), but in the worst case scenario it may result in completely useless results.

In order to overcome this problem, usually liquid crystal spatial light modulators or deformable mirrors are used in optical systems to introduce phase corrections to the light going through the system, countering the phase of these aberrations and thus restoring the image quality. However, these systems present several problems. Even though both spatial light modulators and deformable mirrors can correct the problems I mentioned earlier, they work in a reflection configuration. This introduces additional complexity to the optical systems. Also, liquid crystal spatial light modulators are sensitive to polarization, usually have low reflectance values, and tend to be slow.

As a way to tackle those obstacles, the authors have used an adaptive lens in a two-photon microscope to perform the adaptive optics procedure. Adaptive lenses are being used more and more recently to perform aberration correction. In contrast to both spatial light modulators and deformable mirrors, they work in transmission and present very low losses. Moreover, they can introduce low and mid-order aberrations at refresh rates of almost 1 kHz. The working principle can be seen in this figure:

Adaptive_lens
Schematics of the working principle of an adaptive lens. The lens is formed by two thin glass layers, and a liquid in between. Each actuator is triggered by an electrical signal, which deforms the glass windows, generating different shapes and changing the phase of the wavefront passing through the lens. Figure extracted from Stefano Bonora et. al., “Wavefront correction and high-resolution in vivo OCT imaging with an objective integrated multi-actuator adaptive lens,” Opt. Express 23, 21931-21941 (2015)

In the paper, they show how this device can obtain results comparable to the traditional spatial light modulator approach, with the benefits mentioned before, in a multi-photon microscope.

Wavefront correction in two-photon microscopy with a multi-actuator adaptive lens

by Juan M. Bueno et al., at Optics Express

Abstract:

A multi-actuator adaptive lens (AL) was incorporated into a multi-photon (MP) microscope to improve the quality of images of thick samples. Through a hill-climbing procedure the AL corrected for the specimen-induced aberrations enhancing MP images. The final images hardly differed when two different metrics were used, although the sets of Zernike coefficients were not identical. The optimized MP images acquired with the AL were also compared with those obtained with a liquid-crystal-on-silicon spatial light modulator. Results have shown that both devices lead to similar images, which corroborates the usefulness of this AL for MP imaging.

results_bueno.png
Experimental results showing the improvement on the image obtained with the adaptive lens system. Figure 3 from the paper: Juan M. Bueno, et. al, “Wavefront correction in two-photon microscopy with a multi-actuator adaptive lens,” Opt. Express 26, 14278-14287 (2018)

 

Weekly recap (29/04/2018)

This week we have a lot of interesting stuff:

Observing the cell in its native state: Imaging subcellular dynamics in multicellular organisms

Adaptive Optics + Light Sheet Microscopy to see living cells inside the body of a Zebra fish (the favorite fish of biologists!). Really impressive images overcoming scattering caused by tissue. You can read more about the paper on Nature and/or Howard Hughes Medical Institute.

 


The Feynmann Lectures on Physics online

I just read on OpenCulture that The Feynmann Lectures on Physics have been made available online. Until now, only the first part was published, but now you can also find volumes 2 and 3. Time to reread the classics…


Imaging Without Lenses

An interesting text appeared this week in American Scientist covering some aspects of the coming symbiosis between optics, computation and electronics. We are already able to overcome optical resolution, obtain phase information, or even imaging without using traditional optical elements, such as lenses. What’s coming next?


All-Optical Machine Learning Using Diffractive Deep Neural Networks

A very nice paper appeared on arXiv this week.

Xing Lin, Yair Rivenson, Nezih T. Yardimci, Muhammed Veli, Mona Jarrahi, Aydogan Ozcan

We introduce an all-optical Diffractive Deep Neural Network (D2NN) architecture that can learn to implement various functions after deep learning-based design of passive diffractive layers that work collectively. We experimentally demonstrated the success of this framework by creating 3D-printed D2NNs that learned to implement handwritten digit classification and the function of an imaging lens at terahertz spectrum. With the existing plethora of 3D-printing and other lithographic fabrication methods as well as spatial-light-modulators, this all-optical deep learning framework can perform, at the speed of light, various complex functions that computer-based neural networks can implement, and will find applications in all-optical image analysis, feature detection and object classification, also enabling new camera designs and optical components that can learn to perform unique tasks using D2NNs.

Imagine if Fourier Transforms were discovered before lenses, and then some day someone comes up with just a piece of glass and says “this can make the computations of FT at the speed of light”. Very cool read.


OPEN SPIN MICROSCOPY

I just stumbled upon this project while reading Lab on the Cheap. Seems like a very good resource if you plan to build a light-sheet microscope and do not wanna spend $$$$ on Thorlabs.


Artificial Inteligence kits from Google, updated edition

Last year, AIY Projects launched to give makers the power to build AI into their projects with two do-it-yourself kits. We’re seeing continued demand for the kits, especially from the STEM audience where parents and teachers alike have found the products to be great tools for the classroom. The changing nature of work in the future means students may have jobs that haven’t yet been imagined, and we know that computer science skills, like analytical thinking and creative problem solving, will be crucial.

We’re taking the first of many steps to help educators integrate AIY into STEM lesson plans and help prepare students for the challenges of the future by launching a new version of our AIY kits. The Voice Kit lets you build a voice controlled speaker, while the Vision Kit lets you build a camera that learns to recognize people and objects (check it out here). The new kits make getting started a little easier with clearer instructions, a new app and all the parts in one box.

To make setup easier, both kits have been redesigned to work with the new Raspberry Pi Zero WH, which comes included in the box, along with the USB connector cable and pre-provisioned SD card. Now users no longer need to download the software image and can get running faster. The updated AIY Vision Kit v1.1 also includes the Raspberry Pi Camera v2.

Looking forward to see the price tag and the date they become available.

The week in papers (22/04/18)

As a way to keep posts going, I am starting a short recap about interesting papers being published (or being discovered) every now and then. Probably I will write longer posts about some of them in the future.

Let’s get this thing going:

Two papers using ‘centroid estimation‘ to retrieve interesting information:

Extract voice information using high-speed camera

Mariko AkutsuYasuhiro Oikawa, and Yoshio Yamasaki, at The Journal of the Acoustical Society of America