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Michael Feinberg is the Director of Product Marketing at Boston Micromachines Corporation.  He has over 10 years of marketing and engineering experience in various technology fields.  He can be reached at mrf@bostonmicromachines.com  and welcomes any comments about the content presented herein.

 

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Deformable mirrors in space???

Posted by Michael Feinberg on Thu, Jul 21, 2011 @ 11:14 AM
  
  
  
  
  

250px Crab Nebula

Boston Micromachines has been awarded US$ 1.2M in contracts by NASA's Small Business Innovation Research Program (SBIR) to support space-based astronomy research.  Now, one might wonder, considering this is astronomy, “why is anyone spending any money to develop deformable mirrors for use in space telescopes looking out at the stars?  I thought that deformable mirrors were used to remove aberrations introduced by the atmosphere.  There’s no atmosphere up there!”

Well, you’d be right:  There is no atmosphere up there.  But, there are aberrations:  In the optical system.  When systems are designed, none of them are completely perfectly aligned. There’s no such thing.  But, when you’re looking for planets around stars in other galaxies, you need things to be well aligned.  VERY well aligned.  So, to compensate for any misalignments introduced either during transit to space or thermal variations in the instrument, you can use a deformable mirror as part of an adaptive optics system.  So, for this, we are designing a 1021 segment (3063 actuator), tip-tilt-piston deformable mirror.  It is the largest ever designed of this type and is expected to be used as part of a coronagraph telescope for exo-planet research.

Two other things to worry about are power and weight.  In satellites, there is a very limited amount of power, and the weight greatly affects the cost to put the satellite into orbit.  In terms of the mirror, MEMS has that taken care of:  The power is extremely low and the weight is many orders of magnitude lower than traditional piezo-electric-based mirrors.  So, the other half of the equation is the drive electronics.  As part of this research, BMC is designing multiplexed drive electronics which will reduce the size and weight significantly and lower the power even further.

You put the two parts together, mirror hardware and drive electronics, and you have a low-cost, low-power, lightweight solution for the most cutting edge astronomy research going on right now.

If you have any questions, please contact me directly:  I would be happy to talk about these products or refer you to the folks who are attacking this challenging problem.

Link to press release.

(Image credit:  A giant Hubble mosaic of the Crab Nebula, a supernova remnant)

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How to select the right deformable mirror for you Part 2: Beam Shaping

Posted by Michael Feinberg on Tue, Jan 11, 2011 @ 11:37 AM
  
  
  
  
  

Laser spotIn our second installment of this series designed to boil down the questions that need to be answered before selecting the right mirror, we will review some of the past categories with alterations specific to laser beam shaping and introduce a few new ones that pertain only to beam shaping.  We plan to focus on pulse shaping applications in our third and final installment of this series.

So you have a beam (CW or pulsed) and you want to control it.  Below are the fundamental questions that need to be asked in order to ensure that you’re on the path to obtaining great results in your research or manufacturing application.  This list should be combined with Part 1 of this series to get the total picture of what’s needed.  I have left out the “pitch” and “response” categories, assuming that you have read the previous installment.  Click here, in case you haven’t.

1)      Aperture:  How big is your beam?

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)      Control:  Phase control? Beam steering?

This will greatly affect the basic type of mirror you will need.  For phase control, most modern phase-only mirrors will work, depending on your requirement of resolution (see “2. Resolution” from Part 1 of this series).  However, if you get into beam steering, the amount you need to move your beam will greatly affect the type of mirror you need.  For example, if you’re trying to move the beam multiple degrees, a fast-steering mirror is probably a good place to start.  However, if you’re looking to only make very fine adjustments (milliradians), you can benefit from MEMS-based solutions which are usually referred to as tip-tilt-piston (TTP) devices or piston-tip-tilt, if you’re from one other particular company out there (you know who you are J).  Many customers have come to us asking about using our entire mirror surface to steer a beam.  For those asking for big angles, we unfortunately have to turn them away, but some want to steer it a very slight angle at high levels of precision and we can do that.  

3)      Speed:  Do you want to make fine adjustments?  Are you looking to phase-wrap?

If you’re shaping a beam that is pretty much static, then some low-cost solutions will work.  However, if you’re looking to change the profile at high speeds with high precision, MEMS solutions are a great bet.  The stroke is sufficient to accomplish phase-wrapping, using our SLM model (segmented surface). With sub-nanometer precision, very precisely-shaped beams are possible.

4)      PowerVisible laser

This is a biggie:  If you have a high-powered laser, your options become limited very quickly as most of the very precise devices are a bit fragile as well.  Lots of research is being conducted to steer big, powerful lasers and the bulk of the technologies out there fall short due the fact that they are made of thin-film surfaces and temperature-sensitive materials. My recommendation for this is to make sure you know the “big three” properties and contact individual manufacturers to see what their experience is. They are:

1)      Peak power (in W/cm2)

2)      Average power

3)      Pulse width (if applicable)

Most manufacturers probably can’t guarantee much, but if your application has beam characteristics close to some of the data points they have, then it will make you much more comfortable that you won’t be frying mirrors when you fire things up.  BMC has a database that is constantly being updated with new experience that we would be happy to discuss.  Also, see this paper for the latest published results from our friends at the UCO/Lick Observatory.

As I mentioned before, this is not exhaustive, but if you have these questions answered, your first conversation with either us or one of our competitors will be a pleasant one which will make you more confident of your purchase.

Please chime in and let me know what you think of this series!   Again, stay tuned for the final installment where I will talk about pulse-shaping and the different ways that deformable mirror technologies can be used to create the perfect pulse!

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How much freedom does your deformable mirror have?

Posted by Michael Feinberg on Thu, Sep 30, 2010 @ 09:39 AM
  
  
  
  
  

FREEEEEEDOOOOOM!!Brave mel resized 600

Although William Wallace shouted this in the movie, “Braveheart,” as he died in the hopes to inspire others to join his fight against tyranny, our interest here at Boston Micromachines is related to “degrees of freedom” rather than individual rights. I chose this as a post because numerous times we have come across customers who miscalculate the minimum number of control points (re: actuators) needed to satisfy their wavefront control needs because the forget about this simple concept. Here’s an example:

A customer recently came to us insisting that they needed one of our advanced tip-tilt-piston devices over a continuous surface deformable mirror.  Their reasoning was that with the same number of actuators, to correct for their wavefront, tipping and tilting the individual segments would give them more control than using the simple piston mechanism of our continuous device.  This is true if you compare the number of segments (with three actuators) to the number of single actuators of a continuous DM.  However, if you choose to use a tip-tilt-piston device over a continuous surface mirror, you actually need more actuators (if you work out the numbers, 1.8 times more) to achieve the same level of correction capability. This has been explained and presented very well by Claire Max at UC Santa Cruz.  See the presentation materials here (Slide 47 goes over the equations).

If we step back from the equations and look for the basic concept behind this, it boils down to the ability to change the profile of the surface in many more ways using a continuous membrane as opposed to stiff, separate segments.  Even more simply put: If you want to approximate a curvy line using only a few points (five, let’s say), would you prefer to use a slightly less curvy line, or a series of straight lines? 

The figure below illustrates this concept.

Deformable Mirror Degrees of Freedom
 So, the next time you’re considering wavefront control, keep this in mind before hitching your wagon to a particular architecture. THINK FREEDOM!!!!! 

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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 @ 01:10 PM
  
  
  
  
  

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.

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