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How to select the right deformable mirror for you Part 1: Imaging

Posted by Michael Feinberg on Tue, Jun 15, 2010 @ 02:10 PM

Tags: deformable mirror, adaptive optics, boston micromachines, Boston University, product information, Woofer Tweeter, resolution, response time

deformable mirrorIn this multi-part series, I will be exploring the basic questions that one needs to answer in order to determine which type of deformable mirror is best suited for their application. This list is by no means exhaustive, but if one has an understanding of these topics, the journey to creating spectacular images will be much smoother and equally as rewarding. I am starting with imaging since this is a field that is constantly expanding to new disciplines and often involves researchers who are not familiar with adaptive optics. The next topic will be beam shaping, with further topics to be introduced in the future.
Potential customers come to us at Boston Micromachines to design an adaptive optics system for many different applications: Confocal microscopy, conventional microscopy, astronomy, etc. However, many of them don't know their options when selecting the right mirror. We think we've reduced the questions you need to ask to four simple topics. If each customer reviews this list before giving us a call, finding a mirror best suited for their application will be as exciting as viewing that killer image you're trying to get:

1) Aperture: How big is your image? How big (or small) can you make it?
The size of the wavefront is the first and foremost issue to understand. Some applications have no control over this while others can change the size of their wavefront through the use of some simple focusing optics. Before doing research into your alternatives, you should figure out what your limitations are in relation to this.

2) Resolution: How complex are your aberrations? zernike
Having the right aperture is great, but if your mirror does not have a high enough level of precision, your image improvement will be greatly limited. In the deformable mirror industry, we call this distance between control points, "pitch." In our devices, it is the distance between actuators. In membrane-type mirrors, it will be the distance between electrodes that are underneath but not directly connected to the surface. If your aperture can be manipulated, the precision to which you can control the wavefront will most likely be directly affected by this adjustment. Also, the size of the pitch can affect the price of the mirror. So, understanding what the relationship is between aperture, pitch and price can help you not only find the right mirror, but minimize your costs.

3) Aberration: How big (deep) are your aberrations?DM  Profile
While aperture and resolution cover you in two dimensions, depth is the final critical physical dimension. The size of your aberrations will directly impact the necessary stroke (the distance the surface of the mirror can travel up and down). If you have very small aberrations and require a high level of precision to correct your wavefront, you can focus on MEMS-based solutions, like those provided by Boston Micromachines (available stroke is between 1.5 and 5.5um). However, if you require larger stroke, you may need to focus on more flexible electro-static or piezo-electrically motivated membrane surfaces. Most recently, some have executed what we call a woofer-tweeter approach where a larger mirror corrects for the larger aberrations (the woofer) and a smaller, more precise mirror fine-tunes the image (the tweeter). You can see an article on this in the June 2010 issue of Photonics Spectra: "Dual Deformable Mirror Systems Take the High and Low Roads to Imaging Success." Size of the aberrations is a critical point to understand due the fact that if you don't have enough stroke or high enough level of precision, your image may not improve enough to be impactful.

4) Response: How fast do your aberrations move?
If you're dealing with static medium, then this is not an issue. However, if you are dealing with atmospheric turbulence, as in astronomy, or in vivo conditions in live specimens, then this is a critical parameter. While this is dependent on the structural composition and design of the mirror, it is also dependent on the drive electronics and controller. So, make sure that both your system (PC or other controller) and the electronics associated with the mirror are up to snuff for your application.

Purchasing a deformable mirror should be an exciting endeavor: The images obtained to date have been astounding. I'm sure that with proper preparation and understanding, it can be successful for you as well.

ARVO 2010: Indications of the maturity of adaptive optics and 3 takeaways

Posted by Michael Feinberg on Thu, May 13, 2010 @ 01:13 PM

Tags: deformable mirror, adaptive optics, boston micromachines, Woofer Tweeter, OCT, SLO, ARVO

This year at the Association for Research in Vision and Ophthalmology (ARVO) Annual Meeting, there were some notable differences from past years. There was a shift in focus in the use of adaptive optics from talking about the technology to making discoveries.  Here are the two major indicators:

1)      Adaptive Optics is leaving the Title Page

In past years, there has been amazing research produced from the labs the likes of Roorda, Burns and Williams. But, you'll have to admit that for many of these studies the big "wow" in using adaptive optics for imaging the eye has been the technological innovation and the impressive science and not necessarily the clinical applications.  One indicator of this change is the fact that until this year, most of the papers presented at ARVO which used adaptive optics contained the term "adaptive optics" in the title and not just the abstract.  This year, that number dwindled significantly as the main focus shifted away from coolness factor.  Whether it be new discoveries of cone structure properties with subjects which have genetic mutations or realizations about different types of color blindness, it is now the science and the promise of clinical applications that is center stage and not the technology.

2)      Posters and presentations are showing fewer optical layouts

I spent three days last week at ARVO reaching out to the community and listening in on what is new and interesting. I found it difficult to figure out which mirror was used in any given experiment.  This is simply due to the fact that most of the presentations and posters did not specifically call out what equipment was used in their research.  As much as this made my job a little more difficult, I welcome this progression.  It means that AO is becoming just another piece of equipment rather than a unique addition.

I welcome you to visit the ARVO site and type "adaptive optics" into the keyword finder.  There, you'll discover all of the interesting research that is going on in the industry related to our mirrors.  The main takeaways that I had from the show:

  • Precision+stroke = success

The removal of higher-order aberrations is most often paramount in obtaining high-quality images. However, while low-order aberrations can be removed with fixed optics, increased stroke is key to convenience and in some cases, performance. To that end, more and more woofer-tweeter systems (using two deformable mirrors: one long-stroke, low precision and the other short-stroke, high precision) are being used to obtain great images.  Check out the upcoming June issue of Photonics Spectra for a byline article on the topic.

  • Two-photon: The next frontier in vision science?

While there were very few groups using this two-photon fluorescent microscopy, this is a discipline that I found very interesting and I think it could be a new avenue beyond scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) for retinal imaging.

  • Wide-field AOSLO imaging

Until recently, the only way to image a large region of the eye and gain any perspective on where you were imaging was to use a fundus image and take the small-area images from the AO imaging system and line them up with key features:  Not an easy task.  This year, Steve Burns unveiled his newest instrument where he was able to scan over multiple areas using an adaptive optics SLO and create a composite wide-field image of the retina.  While this task is equally difficult, it offers a new exciting approach to this process and holds promise for advances in imaging the retina.