Measuring Distance with Lasers: From Micrometres to Kilometres

Published July 30 2025

By Shawn McSorley 

From manufacturing tiny precision components to helping your phone figure out exactly where on Earth it is, the ability to measure distance (and measure it well) underpins much of the modern world. Across industries and applications, the demand for precision is growing. 

One of the most powerful tools we have for this is deceptively simple: Lasers. 

A tightly controlled beam of light, with optical wavelengths smaller than a few micrometres, can offer us incredible precision when it comes to measuring distance.  

But how does it actually work? 

Using Light as a Ruler 

At its core, a laser is a stream of tiny electromagnetic waves moving through space. These waves have a well-defined and measurable wavelength, which makes them useful for measuring distances.  

Think of it like using a ruler: the optical wavelength is your scale, and by counting how many of these ‘light waves’ fit between two points, you can measure distance. Scientists can even subdivide these wavelengths to achieve resolutions at mind-bogglingly small scales, down to the picometre.  

For context, that’s one trillionth of a metre. 

With this technique, we can detect tiny changes in distance with remarkable precision. 

The Precision Problem 

But precision isn’t the same as accuracy. Here’s the catch: light waves repeat themselves. 

This periodic nature, the way light waves repeat over and over, means that while we can measure changes over small distances incredibly well, it becomes tricky to measure an absolute distance, especially over large scales. 

A good analogy is this: Imagine knowing that a car is travelling at 80km/h, you can measure its change in position perfectly but not knowing how far away it actually is from you at any given moment.  You have precision about its movement, but not accuracy about its location. 

Another way to think about it is, imagine trying to use a ruler that doesn’t have a clear ‘zero’ mark (we’ve all got one) and repeating the same pattern. You could measure changes along it perfectly, but you’d struggle to say with certainty where you started or ended.  

That’s essentially what’s happening with lasers optical wavelengths. Without a clear ‘zero’ point, those repeating wavelengths make it difficult to tell how many full waves you’ve counted over a long distance. 

As distances grow longer, this problem gets worse. It becomes harder to keep track of how many light waves (or fractions of them) you’ve crossed and impossible to get an accurate absolute measurement without some clever workarounds.  

A Clever Solution: Synthetic Wavelength Interferometry 

While challenging, it’s not impossible to achieve long range distance measurements when tracking the optical wavelength of a laser. And thankfully, physics offers a neat solution. 

It’s called synthetic wavelength interferometry, and it works by using two lasers with slightly different optical wavelengths. When you measure the difference between them, you create what’s called a synthetic wavelength, a new, longer ‘wave’ formed by the interaction of the two originals. 

Unlike the tiny original wavelengths, the synthetic wavelength can be stretched or compressed as needed.  

For a short lab measurement, it might only span a few millimetres.  

For a long-distance application, like a 500 kilometre link between ground and satellites in low Earth orbit, it could stretch to several hundred or even several thousand metres. 

This approach provides something we were missing before: a clear reference point, or ‘zero’. 

It allows us to anchor our measurements and achieve accurate absolute distances, even over long paths. 

By combining the precision of optical wavelengths with the flexibility of synthetic ones, we can build a ‘ruler’ that works at both microscopic and macroscopic scales. 

The Big Picture 

These precision laser measurement techniques are helping pave the way for more accurate long-distance measurements.  

This is a key consideration for applications like optical ground stations and secure communications. It’s an area where there’s still plenty of room for exploration, and it continues to be an exciting space for research and innovation. 

If you’re interested in the deeper technical details (and there’s plenty of them), this work is published here: Digital multi-wavelength optical absolute ranging.  

More to come soon as this research develops further.