For a lot of people, lasers are small boxes that shoot red dots, which drive cats crazy. But in fact, laser systems are used in many manufacturing processes. They can be used for cutting metal or fabric materials or marking raw materials like aluminum ingots. They can also be used on finished components in automobile production as tracking codes for industrial traceability or for the measurement of part dimensions. There are numerous industrial applications that could benefit from the use of a laser, which is found in many industries. But before you can decide if a laser machine would be useful for one of your applications, it might be helpful to have an understanding of the components of a laser and how they work.
Lasers come at different power levels, colors and beam sizes, but they all rely on the same principles. Here's what an industrial laser is and how it works.
For now, let's just imagine that a laser is a magic black box with light coming out of it.
The Three Properties and Three Components of Industrial Lasers
Here are the three properties of that light:
- Single Direction
Laser light is monochromatic, meaning that the color of the beam has a single specific color. The color of the light is defined by the wavelength of the electromagnetic waves that it is composed of. The beam can be either visible, infrared or ultraviolet. For example, a normal incandescent light appears yellowish, but actually emits a mixture of green, yellow, red, blue and even in
frared light. Its wavelength ranges between 400 and 800 nanometers. On the other hand, a standard industrial red laser (helium-neon, for example) has a wavelength that ranges between 632.800 to 632.802 nanometers. Common incandescent light is polychromatic and a helium-neon laser is monochromatic. Monochromaticity is what makes laser light unique and allows for some of its special applications.
The laser beam has a single direction. Its direction is fixed and its beam diameter is small and almost constant over large distances. This concentration of light is what allows lasers to have very high power output. High-energy pulsed lasers, with power in the megawatts, are strong enough to cut through metal.
The beam is also said to be coherent, meaning that all the light rays in the beam are synchronized. They have the same phase and the same polarity. This coherence also helps the beam reach its high powers.
We now know the characteristics of what comes out of that magic black box. So now, what's actually in it?
Here are the three things you need in your laser cavity (the magic black box) to have a working laser:
- Gain Medium
- Energy Source
- Two Mirrors
The gain medium is the material you put in your laser cavity. It can be a solid (a ruby crystal), a liquid (a dye solution) or a gas (a helium-neon mixture). The important feature is that it emits light in the desired wavelength when excited.
The energy source is what causes the gain medium to emit light in the laser cavity. For example, simple electrical discharges can cause helium-neon gas to emit light.
This happens because by exciting the molecules (using a discharge) the electrons in the gas reach a higher energy state. However, electrons prefer being in their lower energy state (the ground state). So some electrons will spontaneously go back to that ground state by emitting light to spend their excess energy. In this case, light is randomly emitted in every direction though spontaneous emissions of light are rare. Both of these factors are problems for creating lasers. These problems can be solved by using the third component, the two mirrors.
The mirrors are put on both sides of the laser cavity with critical parallel alignment. The mirrors will bounce the light endlessly creating perfectly perpendicular light rays. The accumulation of light along the axis of the laser cavity eventually creates a high power laser beam. This solves the first problem of creating a coherent laser beam out of randomly emitted light.
The second problem, the rarity of spontaneous emissions, is solved by provoking stimulated emissions. When light waves pass near excited electrons, these electrons are stimulated and have a higher probability of going to their ground state thereby emitting light at the same wavelength, direction and polarization as the one that passed near it.
So now, we have a cavity filled with a gain medium that, when excited by an energy source, emits light. Two mirrors enable the selection of a specific direction, provoke the accumulation of light and stimulate the emission of even more light. So how does the light come out of the cavity? Well, actually, one of the mirrors isn't perfectly reflective. It let some of the light through and that’s how the laser beam is created. That beam has special characteristics that can be used for laser marking, cleaning, cutting or even welding.
You now know the basic principles behind creating lasers. Modern industrial lasers are optimized using more elaborate techniques to increase their power, precision, and robustness, but the principles remain the same. For the curious minds, this article in Photonics Media goes more deeply into the working of lasers.