Ophir Photonics Blog
Laser Beam Profilers

How to Measure M-Squared – Two Choices

“When you come to a fork in the road – take it.”

Unfortunately, Yogi Berra’s sage advice has not worked well for most people.

There’s an age-old decision when it comes to getting a job done: difficult, but quick or slow and steady.  As Phil Keoghan likes to say about “speed bump” challenges in The Amazing Race: “Challenge X is very difficult, but those who get the hang of it might find themselves speeding ahead.  There’s nothing hard about Challenge Y, but it may take longer to complete.”  It’s easy to claim that one or the other is the right way.  In truth, though, it usually depends on the specific situation.

The same choice comes up when deciding how to measure M2 In this case, one must choose between an instantaneous measurement and a fully automated one.  The question is: do you want to take the time to carefully set up the device or would you prefer to let the machine do the work for you (sacrificing time later on)?  I’ll outline both approaches so you can see how and why they’re different.  However, you might want to refresh your memory about M2 in general first.


ModeScan 1780 – The quick fix:

This revolutionary device saves not only time, but also expense and space.  Most M2 measurement instruments contain an optical train for the sensor to move on, since multiple measurements along the beam are required to calculate M2.  Photon’s clever solution with the M2-1780 was that carefully placed mirrors can measure different parts of the beam instantaneously and without any movement of the detector.  This simultaneously saves a lot of time (measurement takes seconds instead of minutes) and space.  Additionally, as moving parts are unnecessary, this model is lighter and less expensive than most others.

The trade-off here is that it’s a little harder to set up than other methods (see below), and good results depend on a proper configuration.


M2-200S – Take it easy:

One will need to wait a couple of minutes for a result, since this device actually measures M-squared at physically different spots on the beam.  He will be rewarded, however, by results whose accuracy is second to none.  Additionally, the M2-200s is fully automated, so you don’t need to worry about setup at all.

Just like in The Amazing Race, you will need to decide between easy and fast.  What would you choose?

Perhaps what Yogi meant was that either direction must take you somewhere, so don’t worry too much about which way to go.  Just take the fork.  Although there are pros and cons to both choices, there’s ultimately no bad decision.  What do you think?  About M2 measurement, not about Yogi Berra!  Okay, fine.  You can also tell me what you think about Yogi.

You might also like to read:

3 Ways to Keep Track of Your Laser Beam’s Divergence

What Is M2 And Why Is It Important?



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