# What’s M-Squared, again?

Here’s a surprising statistic: Nine out of ten laser technicians have no idea what M² is.

Most laser beam characteristics are easy to put your finger on:  laser beam width, position and divergence angle are generally known to those that work with lasers – and if not, can be learned quickly.

M² is a little more obscure and abstract.

### So…What is M²?

M2 takes a look at your beam caustic (the curve of the laser beam as it focuses and diverges again) and compares this to an ideal Gaussian beam caustic.

So if your beam is perfectly Gaussian, you’ll get M²= 1.  For high quality beams, M² might be 1.1 or 1.2, for lower qualities you can get up to 3, 4 and even double digits for some low quality high power lasers.

How is M² measured?

M² cannot be determined from a single beam profile measurement. The ISO/DIS 11146 requires that M² be calculated from a series of measurements. M² is measured on real beams by focusing the beam with a fixed position lens of known focal length, and then measuring the characteristics of the artificially created beam waist and divergence.

To provide an accurate calculation of M², it is essential to make at least 5 measurements in the focused beam waist region, and at least 5 measurements in the far fields, two Rayleigh ranges away from the waist area. The multiple measurements ensure that the minimum beam width is found. In addition, the multiple measurements enable a “curve fit” that improves the accuracy of the calculation by minimizing measurement error at any single point. An accurate calculation of M² is made by using the data from the multiple beam width measurements at known distances from a lens, coupled with the known characteristics of the focusing lens.

All this is to say that M² measurement can be a little complicated.  Here are a few tips to help you get the most, based on some customer questions we’ve gotten recently:

### M² Q&A

Q: How can I maintain high repeatability from one bench calibration to the next?

A: You should try to use consistent optical setups, enable statistics and remove outliers.  (You can remove them automatically with the M2-200s software.)  Also, an optical table will be useful to minimize vibrations.  With the M²-200s, you should be able to achieve reproducibility of all parameters within 5%, except for beam waist location, which is ±12%.

Q: What is the optimal beam size for M² measurements?

A: The beam should be as collimated as possible with an unfocused diameter of 1-10 mm.  This will allow the focused beam waist to cover at least 20×20 pixels on the camera, which yields a fair resolution.

Q: What is the optimal laser power for M² measurements?

A: Power of the laser should be on the order of milliwatts or less.  If the camera saturates, add attenuation.  Be careful to make sure that the focused power density is below the camera’s damage threshold.

Q: What is the noise of M² measurements?

A: It depends which beam width calculation method is used (there are several – see the Beam Width Measurement Accuracy article for more on that).  The D4σ method, which is the ISO standard and default in our software, is most sensitive to noise.  You can use the knife edge (90/10) technique to increase accuracy.

Q: How can I avoid smearing (where one axis is very different from the other?

A: Smearing (or blooming) is a hardware glitch that occurs when the laser light leaks through the CCD and affects the layers underneath the Silicon.  This usually happens with longer wavelengths in the NIR range.  Adding exposure typically minimizes this effect.  (Make sure to reduce the laser power or add more attenuation when lengthening exposure time.)  The M²-200s has recently been updated with a new USB camera which further minimizes this blooming phenomenon.  If you are still experiencing this problem, fill out an RMA and we’ll try to get you a better camera.

I hope this will give you a jump-start on your M-Squared measurement mission.  For more info. go to:  http://www.ophiropt.com/laser-measurement-instruments/beam-profilers/knowledge-center/tutorial/what-is-m2

And If you have other questions, feel free to leave a comment!

# Why does measuring your laser beam help you maintain quality processes?

Much like a light ball that degrades over time, a laser beam at the work surface has to be maintained and preserved in order to keep it’s high & precise performance.

Why does measuring your laser beam help you maintain quality processes?

# New laser fails to perform according to specifications – What can you do about it?

Just imagine the following situation: you’re a well trained and experienced manufacturer engineer.
Your company had just purchased a laser to heat-treat metal parts but something was happening during the use of the laser that was causing the treated parts to fail the quality control checks afterwards.

# OPHIR’S 2018 CATALOG IS HERE!

If you have a laser, you need to measure it.

As in every year – Ophir’s 2018 new catalog covers a wide range of laser power and energy sensors, meters and laser beam profiling systems for medical, industrial, defense, and research applications.

# THANK YOU FOR VISITING US AT THE 2018 Photonics west Trade show!

We would like to dedicate this blog post to all of  you who came by our booth (#507) at the 2018 Photonics west Trade show.
Among many other  exciting products, we were glad to introduc the new Centauri laser power meter for the very first time!

# This is why you need to Visit Ophir Next Week at Photonics West 2018

With less than a week to go, the team at Ophir Photonics is getting ready to pack their bags and head off to San Francisco to attend the SPIE Photonics West Conference.

Use a laser? You won’t want to miss our booth (#507) at Photonics West.

Why?

Well, here’s a taste of what you will see there:

# MKS Announces Ophir® LBS-300s, New Beam Splitter Finds Focus Spots with Shorter Working Distances

Andover, MA – December 12, 2017 – MKS Instruments, Inc. (NASDAQ: MKSI), a global provider of technologies that enable advanced processes and improve productivity, has announced the Ophir® LBS-300s, a compact, portable laser beam splitter for handling small beam diameters and a wide range of powers.

# MKS Announces Ophir® BeamWatch AM, Non-Contact Laser Beam Monitoring System for Additive Manufacturing

Andover, MA – November 20, 2017 – MKS Instruments, Inc. (NASDAQ: MKSI), a global provider of technologies that enable advanced processes and improve productivity, has announced the Ophir® BeamWatch® AM, the industry’s first non-contact laser beam monitoring system for additive manufacturing.

# Beam Profiling 101: Intro to laser measurement

One of the most common questions Mark S. Szorik, Pacific Northwest Regional Sales Manager at Ophir Photonics is being asked, is “Why do I need a beam profiler and what tools and methods do I need to profile my beam?”

1 2 3 15