Ophir Photonics Blog
Laser Power & Energy Sensors

How Precisely Can You Measure Laser Power?

A measurement is only as good as its accuracy.

Take height, for example.

As a kid, you probably had yearly checkups at your doctor’s office.  Among other things, he measured your height.  Imagine, you’re 12 years old and you can’t wait to see if you’re finally five feet tall.  So your doctor has you stand very straight and tells you that you’re 5 feet ± a foot.  What a waste of your time!  The measurement didn’t tell you anything you didn’t already know.  If he tells you that you’re 5 feet ± a quarter of an inch, then we’re getting somewhere.

The same is true for any measurement, not least of all laser power measurements.

Most laser power sensors at Ophir are calibrated to ±3%, but this is just the baseline.  The error can increase when the sensor is used to measure a laser that differs from the calibration laser – in wavelength, power or energy, or pulse frequency.  Since errors are summed by the root of the squares, this adds less than you might think, but it could easily amount to 5% or more.

This is often acceptable, but depending on your application and industry standards, you might need something better.

Ophir offers a service for customers that need a very high level of accuracy.  We can reduce the total error to almost ±2%.  But how does this work?

There are two components to Ophir’s “special calibration service”:

First, we use a laser as close to identical as the one that you’re using (and measuring).  This eliminates all those extra sources of error, such as linearity with power, frequency, etc.

Of course, we don’t have every possible laser; this table has the calibration lasers available for each sensor:


So if your wavelength fits on this chart, you can get a special calibration at a power (and pulse repetition rate, if applicable) that’s similar to your own laser.  This reduces the total error back to the baseline, ±3%.

Furthermore, we do a double calibration on your sensor, which means the statistical error is reduced by the square root of two.  This brings the uncertainty down to about ±2.1%.

For more information about special calibration, contact your local distributor or post a comment here and I’ll try to help you out.

Flickr creative commons image via Mauro Cateb



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