Essential laser beam parameters to know about your laser system
Wednesday, September 07, 2022
Ease-of-use was top of mind when we created our Product Finder. To ask only the most essential questions to help you get where you’re going.
Below, we explain what those essential laser beam parameters represent, beyond the number on the spec sheet.
Beam profile (gaussian, flat-top & irregular)
If you shine a laser and look very closely at its laser spot, you’ll see that certain regions are more brightly lit than others.
Exactly how the laser’s intensity is distributed is what we call the beam profile, which can be viewed with a laser beam profiling camera such as this one:
Flat-top lasers
The laser is either on or off, with a clear boundary in between. No gray areas.
This is good for certain applications, however, flat-top beams do not stay well-defined when propagating. Flat-top lasers combine multiple wavefronts, which get out of sync as the laser travels, hence a blurrier profile.
Gaussian lasers
An ideal Gaussian laser beam profile will have an intensity distribution like a bell curve (i.e. a Gaussian distribution). The M2 factor indicates how closely the beam resembles a perfect Gaussian.
Gaussian beams provide these notable advantages:
- Profile is preserved as it propagates
- Tightest possible focusing
- Lowest beam divergence
- Cost-efficient
Irregular
The name says it all.
These beam profiles are either completely irregular, or approximately Gaussian/flat-top, but with hotspots.
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Beam Size (beam diameter, in mm)
Because Gaussian and irregular beams do not have a clear-cut boundary where the laser spot “finishes”, laser professionals have had to agree on a few different ways to determine the beam’s spot size (FWHM, 1/e, 1/e2, D4σ).
The definition used in our Product Finder is the 1/e2 definition. The spot “ends” when its intensity has decreased to 1/e2 of its maximum value. For a Gaussian beam, the intensity at the 1/e2 diameter corresponds to roughly 13% of the maximum intensity.
Wavelength
The wavelength parameter determines how much energy each photon carries, and how tightly the beam can be focused.
The shorter the wavelength, the “bluer” and more energetic it is. Shorter wavelengths can be focused to smaller sizes. Extremely short and energetic wavelengths, like UVs, can be harder to handle, requiring special rugged optics.
There is no universally “better” wavelength. It really depends on the application.
Laser type (CW & pulsed)
Lasers can emit light either as a continuous wave (CW) or in short bursts, called pulses.
Average power (nW to kW)
Average power describes how much energy is transmitted by the laser per unit of time, regardless of exactly how the power gets dished out (continuously or in pulses).
CW lasers can be described fairly well with just the average power.
To describe the details of individual pulses, other laser beam parameters are required: pulse energy, repetition rate and pulse duration.
Pulse energy (nJ to kJ)
The pulse energy (or single-pulse energy) states how much energy is in each individual laser pulse.
Repetition Rate (Hz, pulses/second)
The frequency at which the laser pulses are emitted.
The faster the repetition rate, the more pulses are shot within a single second. This in turn means that higher repetition rates are associated with a higher average power.
Pulse width/duration
Pulse width refers to the “width” of time between a pulse’s beginning and its end.
Because power is energy divided by time and pulses exist only for a brief instant, their peak power can be gigantic. For instance, a 1 mJ, 10 picoseconds pulse has 100 megawatts of peak power!
The laser parameters presented in this article are the most essential ones when it comes to measuring a laser beam power or energy. Feel free to give our Product Finder a try if you know your laser beam parameters or get in touch with a Gentec-EO representative.
