What parameters of my laser do I need to measure?
Friday, June 16, 2023
When you purchase a new laser, it always comes with a long list of specifications. Some parameters might not be useful to you, but others might be important to your application.
Let me present different laser parameters that can be measured and examples of applications that require them to be measured.
Wavelength
Wavelength is a key parameter of any laser process because absorption, transmission, and reflection all depend on it. Every material from metals to organic tissues will absorb a different fraction of light. This fraction will depend on the wavelength. The material used in your application usually determines the wavelength of your laser.
One example is CO2 lasers used in skin laser resurfacing. Skin is made mostly of water and water absorbs a high portion of light emitted at 10.6 um, hence why you would use CO2 here.
In most applications, the wavelength does not need to be measured, because it is a stable parameter. Even if the central wavelength changes a bit from one laser to another, the fraction of absorption does not change a lot between two wavelengths a few nanometers apart.
Wavelength measurements can be used in some applications like manufacturing the lasers themselves or precise measurement methods that rely on wavelength shifts.
Power
Power is a parameter that always needs to be measured. Many processes like cutting, welding, and additive manufacturing need to control the power level.
A power level too low would mean a weld or cut not deep enough, or a 3D-printed model that is not entirely melted together. A power level too high can simply be a waste of electricity or at worst create unforeseen damage to your manufactured item.
You also need to measure the power of medical lasers because of norms and/or regulations. Even at low power, it is crucial to know the power level because it can differentiate between the protective equipment needed.
Learn more about laser power measurement solutions.
Laser specifications change over time for many reasons and it causes problems accross all industries. Learn about how laser output measurement solves numerous problems in YOUR industry. Download the guide below. Gentec-EO's high-accuracy laser beam measurement instruments help engineers, scientists and technicians in all sorts of laser applications from the factory to the hospital, laboratory and research center. Learn about our solutions for these measurement types:
Energy
Energy measurement requires a pulsed laser as it cannot be done with a CW laser. However, energy measurement is not required for all pulsed lasers, sometimes power is enough.
There are lasers with repetition rates so slow that you will not be able to measure the average power because the power detector will never stabilize. For these lasers, energy measurement is recommended. Energy measurement is also recommended in delicate applications where it is important the energy of every pulse remains the same or to find if there are any missing pulses.
Find your laser energy measurement solution.
Repetition rate
Repetition rate is the number of pulses in one second of a laser. Only pulsed lasers can have a repetition rate. It is usually interesting to measure this parameter when the repetition rate is on the slower side and you need to know exactly when the pulse will be emitted.
In many cases, this parameter can be found from the energy and power measurements since Power = Energy x Repetition Rate. If you can measure power and energy accurately, you can easily find the repetition rate.
Pulse duration
Pulse duration or pulse width is how the power of some lasers is controlled. This process is often referred to as the duty cycle or pulse width modulation (PWM). This value is often a percentage that refers to the pulse duration divided by the period between each pulse.
Pulse width measurement can be useful if you want to calibrate a modulated laser. You can also measure its power since the average power will be directly related to the duty cycle of a modulated laser.
Divergence
The most common need for divergence measurements is in free-space laser communication. Since these lasers need to travel a long distance in free space, you need to know the divergence to know the beam size of the laser at the sensor that receives the communication.
Knowing the divergence of a laser can also be useful to predict the exact position of the beam waist and the distance to place a surface if you want a larger beam.
Beam profile
Beam profile measurement is useful to know the power distribution of the beam. This measurement can show if you have a Gaussian profile or a flat-top one. It can also show if you have hot spots in your beam profile.
It is important to know if hot spots are present in applications like 3D printing. If we take LPBF (Laser Powder Bed Fusion) as an example, you do not want to overheat the metal and create defects in the metal piece.
This is why you want a predictable beam profile where you know the exact distribution of the laser. Then, you can accurately predict the melt pool's heat distribution and avoid any defects caused by overheating or underheating metals.
Explore our laser beam profiling solutions.
Beam size
Beam size is one of the most often measured parameters of a laser. Most people want to measure the size at the beam waist meaning the location where the beam size is at its smallest. If you have a laser manufacturing application, you want to know the beam size at the waist because it will give you the size of the laser cut, mark, or weld.
The same is needed for medical applications. If you have a laser system for eye surgery, you want a beam size that is small enough to correct all the aberrations needed, but not too small that it will take too long to do the surgery.
Two beam size measurements of the same laser can also be used to calculate the divergence.
Many other laser parameters can be measured, but these are the most common and useful ones. I hope this helped you decide which one you should consider measuring in your application. Measuring your laser parameters can often help to troubleshoot your laser process.
