Selecting The Right Deformable Mirror Part 2: Beam Shaping

By Michael Feinberg, director of marketing and sales, Boston Micromachines

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 are on the path to obtaining great results in your research or manufacturing application. This list, combined with our previous recommendations, will help to get the total picture of what’s needed. 

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 telescoping/focusing optics. Before doing research into your alternatives, you should figure out what your limitations are in relation to this.

2. 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. 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 are trying to move the beam multiple degrees, a fast-steering mirror is probably a good place to start. If you are 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. Many customers have asked about using our entire mirror surface to steer a beam. For those looking for larger angles, we unfortunately have to turn them away. Some, however, want to steer it a very slight angle at high levels of precision, and MEMS technology is able to do that.

3. Speed:  Do you want to make fine adjustments? Are you looking to phase-wrap?
To shape a beam that is pretty much static, some low-cost solutions will work. However, if you are looking to change the profile at high speeds with high precision, MEMS solutions are a great fit. The stroke is sufficient to accomplish phase-wrapping using our SLM model (segmented surface) at visible and near-infrared wavelengths up to 3 m. With sub-nanometer precision, very precisely-shaped beams are possible. 

Light wavelength chart

4. Power
This is particularly important. If you have a high-powered laser, your options become limited very quickly as most of the extremely precise devices are a bit fragile.  Lots of research is being conducted to steer big, powerful lasers, and the bulk of the technologies out there fall short due to 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:

• Peak energy (in J/cm²)
• Average power (in W/cm²)
• Pulse width (if applicable)

Most manufacturers probably cannot 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 about not fry mirrors when you fire things up. Obtaining 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.

Michael Feinberg is the director of marketing and sales at Boston Micromachines Corporation.  Michael currently oversees all product sales, marketing, and business development activities.

For more information, please visit www.bostonmicromachines.com.