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FAQ: BMC Deformable Mirrors for Laser Applications:Power

Posted by Angelica Perrone on Wed, Apr 02, 2014 @ 12:00 PM

Tags: deformable mirror, adaptive optics, boston micromachines, Boston University, laser beam, laser science, BMC, Mirrors, pulse, pulse width, peak power, laser pulse shaping, ultrafast lasers, laser pulse compression

About half of our customers use our deformable mirrors for laser applications, such as beam shaping or steering. We get a lot of questions pertaining to laser power and handling for both our deformable mirrors and modulators.  Below is a summary of the guidelines we use when discussing our technolgy.

The most important specification to note immediately if you are working with lasers is the damage threshold of our DM's. There are two mechanisms of failure to consider: mirror damage due to heating and coating delamination.  The first failure mode is largely governed by the average power experienced by the DM. The rule of thumb that we follow is maximum average power of 20W/cm². For the second failure mode, the peak energy is of greatest concern.  In this case, the threshold that we use is that of a standard thin-film gold metallic coating, in this case, 0.4J/cm². Depending on the DM system, the calculations may be slightly different. In order to ensure a DM is suitable for your application, we typically need to know as many of the following properties as possible: the pulse width of the laser, peak power, frequency, wavelength and beam size. This last pameter will help to determine which aperture size is required and if you need to change your beam size at all. Additional information on laser power can be found on our previous blog here.

From a power threshold standpoint, our modulator technology works similarly to our deformable mirror technology. However, it may have a slightly lower damage threshold due to the fact that the exposed surface is a thin layer of silicon nitride as opposed to the thicker polysilicon surface used for our deformable mirrors. Honestly, we do not have much experience testing the devices.  If you are interested in carrying out testing, we would be glad to lend you some modulators to test.

If you are interested in learning more about customers' experience with high-power lasers used on our DM's, please click here to read Andrew Norton's paper on laser test performed using our DMs. Also, please visit our website or contact us for questions or additional information on how to obtain a device for testing.

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

Posted by Michael Feinberg on Tue, Jan 11, 2011 @ 12:37 PM

Tags: deformable mirror, adaptive optics, boston micromachines, resolution, response time, laser beam, SLM, spatial light modulator, turbulence, pulse, pulse width, peak power, CW, average power

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!