Your Comprehensive Guide to Laser Measurement & Laser Beam Analysis

It can be overwhelming to figure out how to set up your laser measurement system for the first time.

Let’s take a look at an article in which John McCauley, a Bus Dev manager at Ophir, revisits a product demonstration in which he had to confidently set up equipment to show a prospective customer. He used this experience to come up with a list of things to remember before setting up your equipment for the first time.

Before you even choose your equipment, it’s crucial to understand how your laser works.

Every laser has difference characteristics – is it continuous wave, or pulsed, for example. What is its power, energy, wavelengths?

How are you going to use the laser? What’s the application, and what does that mean for the laser?

If you’re using it for materials processing, you’re like to have a laser light coming out of a processing head, converging on a focused spot – the amount of light and the size of the focus spot are important things to know.

Once you understand your laser, it’s time to understand the whole laser system. Many times a measurement system is chosen after a laser system has already been designed and commissioned, so it has to fit in with the system and its limitations.

There are some characteristics that can create new challenges – glovebox welding lasers, for example, have a processing head at an offset, and a beam profiling system would need to be set up with this in mind.

The last thing you must remember is to know your measurement product limitations. Whatever happens - you mustn’t exceed your measurement product’s rated damage threshold by applying to high a power density. Measurements don’t need to be taken at the focus, where power density is highest – as laser power or energy will be the same whatever the beam size. The smaller the beam size, the higher the power density, the more chance of exceeding the measurement equipment damage threshold – which is not good for the equipment, or the measurements you’re taking.

Well armed with knowledge about your laser, laser system, and the laser measurement tools being used – setting up your laser system will be far less daunting.

Read the article for more details about this important information.

Selecting the right beam profiler is crucial for optimizing laser performance and ensuring accurate measurements.

You have lots of choices - CCD and CMOS cameras, scanning slit sensors, pyroelectric cameras, and knife edge sensors, just to name a few.

All other things being equal, Ease of use and absolute spot size dynamic range favors the scanning slit system.

But if you need to know the detailed 2-dimensional picture of the beam, including fine structure and possible hot and cold spots or the image of the beam, lean more toward a a camera-based beam profiling system.

Making an informed decision can be daunting, and we are here to help.

Here are 5 questions you need to ask yourself when searching for a beam profiler.

You first is - what wavelengths do I need to measure?

You next need to ask yourself - what beam width or spot size do I need to measure?

The third question is what’s the power of the beam?

Your fourth inquiry is whether the laser is continuous or pulsed?

Finally – and perhaps the most important question - is how accurate does the measurement need to be?

This might sound like a silly question because we all want accuracy.

But can you live with 98% accuracy?
But it’s not so simple – there will be many tradeoffs depending on the answers to the first 4 questions. Just as an example, the accuracy benefit of using a high resolution CCD camera might need to be weighed up against the accuracy loss due to needing attenuating optics.
The accuracy requirement final decision depends on the beam details, as well as what the data is used for, how the data is used, which application it’s used for, and the environment the profiler is in.

Take a factory floor.

Quality assurance needs a certain level of accuracy, but it also needs high throughput and ease of use. You also might need to embed a profiler into small piece of manufacturing equipment a manufacturing cell so that it performs measurements and communicates with other applications automatically and transmit results to other applications. All of these are considerations when selecting a profiler.

Determining the laser beam measurement environment and which specific measurements are most important to the success of your factory floor application are crucial questions when choosing a profiler.

Ophir’s knowledgeable product specialists can be helpful as you navigate the choices that best suit your needs.

We’d all like it if lasers always worked as they were supposed to – but that’s not always the case. So, like any process, we need some kind of process control – with lasers, you’ll want to be taking accurate measurements.

You might think measuring laser power is enough – but that leaves a lot of the story untold. Instead, laser beam profiling gives you more insight. Let’s explore Ophir’s blog post, and discover how to get started with laser beam profiling.

Let’s imagine a laser as a perfect, idealized beam of light – if something goes wrong, you’ll tweak the power and it will be fixed – right? Unfortunately, it’s not so simple. Lasers degrade with time, and that can change the beam’s spot and shape.

Increasing the beam’s power could even make the shape worse.

Beam profiling is the secret to monitoring laser beam size and shape, to ensure that the beam continues to look and behave exactly as designed.

So, how do you get started in implementing a profiling solution? First, you need to choose the right equipment – and to do that, you need to decide the measurements you’re planning to take. This could include beam width, overall beam shape, ellipticity, and M-squared – the beam quality factor. Most beam parameters are based on these measurements.

Then, it’s time to choose a beam profiler. Most profilers measure beam width – but in different ways. There’s a link in the blog post that explains this further.

Scanning slit profilers take tiny samples of the beam through two narrow slits, creating two one-dimensional profiles on the X-axis and Y-axis. You can use these to create a two dimensional image, but that doesn’t provide a full picture.

CCD cameras can product a full two dimensional image of the laser. But, they require that high power lasers have more attenuation, which can be a hassle. And very small lasers, such as those that are tens of microns, might do better with scanning slits - for higher resolution.

Both scanning slits and CCD cameras can be used to measure ellipticity and M-squared, although M-Squared requires the addition of an optical rail or mirror system to make measurements at multiple locations.

If you’re not sure where to start - visit the blog post and click on the link at the bottom to talk to an Ophir expert.

A VCSEL – a Vertical Cavity Surface Emitting Laser – is a semiconductor laser diode that can be packaged as hundreds of emitters on a single chip. This makes it useful for a whole range of applications – including face recognition, proximity sensors, and augmented reality displays – all features you may well find on your smartphone. To maximize device battery life, it’s crucial to measure VCSEL power consumption, and keep it low.

However, testing and a measuring a VCSEL has its challenges – the beams can be very wide, and are often used in pulsed mode.
Let’s dive into Ophir’s article, which explains the tools you need to measure VCSELs, despite these challenges.

First up – power consumption.
An integrating sphere is used for collecting light at high angles, often with a suitable port adapter to support the VCSEL’s wide beam angles. The sphere is coupled with a photodiode detector, which can measure even the lowest power lasers – down to under 1 microwatt!

You can also add other tools, such as spectrometers, to the sphere - and take multiple measurements at once.

For power levels above 100 milliwatts, you could choose a thermophile sensor instead - these are more compact and easy to use than integrating spheres.

Next - If the VCSEL is operating in pulsed mode - you may need to measure the energy per laser pulse – this can be done using pyroelectric and photodiode energy sensors.

For analyzing laser beam size, quality, shape, and divergence - beam profiling is essential. This is best done using a suitable camera, with Ophir’s BeamGage software for analysis. Why a camera? It’s the ideal way to get real-time, accurate measurements of the laser beam profile. See the article to find out about different methods for VCSEL beam profiling.

When it comes to measuring pulse shape and noise, you’ll need a high speed photodiode detector, which can be attached to an integrating sphere, or used in free space. Pair it with analysis in either the time or frequency domain.

Often, laser system manufacturers build measurement capabilities into their laser systems – Ophir offers these OEM solutions - to provide robust laser performance analysis and fast feedback for system control.

Visit the full article to read about Ophir’s VCSEL measurement solutions in further detail.

If you’re a serious laser user, you’ll know how important it is to measure certain laser parameters. Of those parameters, laser power is the most simple way to understand your laser. With the help of Ophir’s blog post – the beginner’s guide to laser power measurement, let’s talk about the first step in setting up a laser power measurement system – choosing the tools you’re going to use – the meter, or interface, and the sensor.

The meter, or interface, measures electric current, and displays the result. Ophir has a whole range of meters and PC interfaces, to suit any setup. There’s a link to the full list in the blog post.

Then – there’s the more complex choice – the sensor itself. The sensor must measure laser power accurately, and convert it to electric current – as that’s what the meter, or interface, reads.

If you’re looking for an easy way to make this choice – you’re in luck. There’s a link in the blog post to Ophir’s sensor finder, which allows you to enter your laser’s parameters and find the ideal sensor for your system.

What’s going on behind-the-scenes to generate these ‘best matches’?
Well, to start off with, there are two types of sensors to choose from – photodiodes, or thermopiles. What’s the difference?
If you have a low power laser, you’ll need a photodiode-based sensor, known as a PD sensor – for one simple reason – it’s the only type sensitive enough to measure lower power lasers.

And conversely, a thermopile-based sensor, or thermal sensor, is less sensitive, but can measure far higher powers – making it the choice for high power lasers.

When it comes to lasers with continuous wave beams, there are three crucial parameters that need to be considered, for either type of sensor.

First, the sensor must be able to cover the wavelength used by your laser. Secondly, the sensor must work well for your laser’s power range. And finally, it must be the right diameter, so that it can fit into the laser aperture.

For pulsed beams, things get a bit more complicated, but that’s a story for another day.

Did you know that a thermal sensor can be used for many years, without the need for a single repair?

Let’s take a look at Ophir’s article on avoiding thermal sensor damage - and find out what expert technicians have to say about keeping your thermal sensors in top condition for years to come.

According to the experts, thermal sensor damage comes from incorrect laser optical setup and usage. The articles discusses the most common causes of incorrect usage, and preventative measures you can use to keep your thermal sensors in pristine condition.

First up – surface contamination. It’s very common for thermal sensors to get dirty. It’s important to find our the source of this contamination – and take measures to prevent it. For example, in the metalworking industry – welding too close to a sensor can easily contaminate it, and should be avoided.

Preventing sensor contamination is easy – clean the sensor regularly, use a protective housing, store it in a clean, closed container when not in use - and avoid touching it with your bare hands.

Another common cause of issues is overheating the sensor.

If you use your thermal sensor at power levels that are too high, for a long period of time, you’re likely to see damage to the absorber layer.

And – if your sensor is one that uses thermal grease for thermal coupling – you’ll start to see grease contamination too.
Always keep to the power range and power density threshold listed in the sensor’s specifications.

Some high power sensors require water cooling. You should make sure the water you use meets quality requirements - otherwise it can cause significant damage.

Only deionized and filtered water should be used - the water should be clean, clear, and sediment free and for deionized water it’s also important to maintain a neutral pH level.

When it comes to a damaged sensor – it’s always worth getting it tested – some sensor damage is only cosmetic, and doesn’t affect the reliability of measurement results. Other forms of damage require full sensor disc replacement.

Take a look at the full article to see pictures of different types of sensor damage, and read more details about the measures you can take to keep your sensors in pristine condition.

They say that an ounce of prevention is worth a pound of cure.

And the same goes for your thermal sensors.

Sometimes, you can use your thermal sensors for years without the need for repairs.

But when we receive these sensors for calibration, we can often tell that misuse led to the sensor’s deterioration.

Here are 3 things that can help prevent deterioration of your thermal sensors from deterioration.

The first is a surface that remains clean from contamination.

Keep the sensor disc clean from foreign substances, such as process debris from often caused by welding industrial environments, or organic contaminants that can find their way to the surface by then be burned onto the disc by subsequent exposure to a laser beam.

So, keep the surface clean and store the sensor properly when it isn’t being used.

The second cause for of deterioration comes when the sensor disc is used at a power level higher than recommended specified, causing overheating.

Major overheating can destroy the detecting element, but even moderate overheating can cause damage to the absorber coating,; both will which requires replacement of the absorber disc.

Overheating can also cause grease contamination which requires disassembling, re-greasing and cleaning of the absorber.

So, avoid overheating by using the right power levels for continuous use versus those for short term use.

Finally, the third cause for of sensor deterioration is localized localized overheating of the coating. It’s the number one cause for disc replacement.

Every coating type has a specific power and energy damage threshold. The spec sheet for each sensor offers guidance on the limits for power and energy damage. Try to stay within those guidelines.

If you follow some of our this advice, early detection really will it can definitely help prevent deterioration of your thermal sensor from deterioration.