What are diode lasers and where do we use them?
Monday, October 17, 2022
For most people, when you ear the term diode, it automatically refers to LED lighting. Indeed, thanks to the Nobel prize winners of physics in 2014 for their work on blue LED, this mental association could keep becoming even stronger.
Although, most of the time you might probably be right, diodes don’t have to emit light and can be used in a multitude of devices. When you use them in a way to stimulate coherent lighting emission and combine then with a resonator, what you obtain is what we call a laser diode.
Terminology
First, you should know that, despite frequent misuses of the terms, diode lasers, laser diodes and semi-conductor lasers generally refer to the same thing. Let’s sort this out and clarify these terms a little.
A laser diode, just like a regular diode, is made of a PN junction. What makes it different is that we added a layer in it that is capable of spontaneous emissions.
A diode laser, is a laser based of laser diodes. So, the laser can be made of only one diode, but it may also contain several of them combined. It can also incorporate many other optical components.
A semiconductor laser, as the name suggest, is based of semiconductors. Its internal structure doesn’t have to be the one of a diode. That being said, in real life it just happens that, in most cases, it is.
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What makes a diode laser a diode laser?
You have to understand that, in the laser world, despite lasers being made out of several different components, we tend to classify them based on the gain medium. The main types you will find are fiber, solid-state, gas, liquid and semiconductors. Semiconductors and fiber lasers are actually specific cases of solid-state lasers that have grown enough to get a category of their own. Diode lasers differentiate themselves from solid-state lasers mainly because of their PN junction.
The energy source of laser diodes is an electrical current going through that PN junction. That’s why we say that they are electrically pumped (opposed to optically pumped when the population inversion is reached through a light source instead). Actually, diode lasers are often used as an optical pump themselves for other lasers.
Like a diode, the intensity of a diode laser tends to correlate linearly with the current input. As a matter of fact, diode lasers are quite popular regarding their high electrical-to-optical efficiency, meaning that they are good at converting that current flow into laser power. Typically, this ratio is around 50%, but it can reach up to 80% in ideal conditions.
Why use them and why not
Electrical-to-optical efficiency aside, diode lasers have other advantages. They tend to have a good lifespan and are pretty reliable (when properly used). They can be suited for both low-power and high-power applications. They are cheap and are quite compact compared to other laser types.
On the other hand, this type of laser has generally poor beam quality and very high beam divergence, making them less useful at a distance. Also, the beam quality tends to vary a lot according to power. Despite having high divergence, some low-power diode lasers can still display good overall beam quality. But when you think about high power diode lasers though, things get messy. These beams tend to exhibit high asymmetry and astigmatism, making them much harder to work with without the proper optical components.
Diode laser applications
All these properties predisposed diode lasers for some applications and kept them away from others.
Like mentioned before, they are an efficient optical pumps for other lasers.
Low power diode lasers with high-quality beams are widely used to read and write data on different medias like CDs and BLU-RAY discs for example. So, your gaming console probably has a diode laser inside it!
Paper is becoming less and less useful these days, but you probably have vaguely heard of a thing called a laser printer or a laser scanner. Well, guess what? Diode lasers again.
When you go back deep into your childhood and think about the first time another kid came to school with a small red laser pointer… chances are: diode laser.
You will also find them in the medical industry (as you will probably find every other type of laser though). Mostly in surgeries and in dermatological treatments. Yes, you read right, your next epilation treatment might just be done with a diode laser.
You are thinking about modernizing the metal welding step of your factory? You might take a look at diode lasers as they are energetically efficient and cheap. Also, by being really close to the metal pieces, even though diode lasers have poor beam quality, the end result will generally not be affected at all.
And last but not least, they are widely used in optical fiber communications.
So, as you can see, diode lasers are way more common around us then what you could expect. And if you intend to use an high-power one, either in research or in industry, it might be a good idea to check its profile using a camera like our BEAMAGE-4M or characterize its beam quality with our BEAMAGE-M2.
