In its simplest form, lasers consist of four components
- Excitation source (red)
- Gain media (orange)
- Total reflector (mirror) (purple)
- Output Coupler (partial mirror) (blue)
Depending on the laser type, the gain media can be a Gas (CO2, HeNe, Ar+), liquid (dye) or a solid (glass, fiber or semiconductor).
The excitation source is some form of energy that is used to pump the gain media. It is typically electrical (sometimes optical) and establishes the population inversion required to create the stimulated emission events. In the case of an RF excited CO2 laser, the excitation source is a radio frequency electrical generator that breaks down the gas mixture in the tube (vessel that contains this gas). Where as in a fiber laser, the excitation source is usually a set of pump diodes and the gain media is an Yb doped optical fiber. Below is a list of some of the more common lasers and their emission lines.
|Laser media||wavelength (µm)||wavelength (nm)|
|CO||5 to 6||5000 to 6000|
|Argon||0.457 to 0.528||457 to 528|
|XeF||0.353 or 0.459||353 or 459|
|XeCl||0.308 or 0.459||308 or 459|
As shown is in the table above, CO2 has three wavelengths which are commonly used in materials processing. The predominant line is at 10.6 µm, with another at 10.2 µm and a third at 9.3 µm. In reality, these are not individual lines but groups of lines that are called branches. The 10.6 µm branch is referred to as the P branch and actually consists of over 20 discrete decay states ranging in wavelength from 10.4 to 11 µm. The 10.2 µm line corresponds to the R branch (again with over 20 discrete emissions of its own) and varies in wavelength from 10.1 to 10.3 µm. There are shorter wavelength variants of both these branches in the 9.6 and 9.3 µm region as well.
As with any task, there is always a best tool for completing it. This holds true for lasers as well. CO2 lasers operate far into the infrared and absorb in practical all materials. That makes CO2 laser great for processing clear substrates like glasses, plastics and acrylic. CO2 also has advantages in organic materials like wood, paper, cardboard and stone. High power (>kW) CO2 lasers had been the work horse for cutting metals for years. Today, fiber laser technology has been scaled to similar power levels with higher efficiencies and are displacing these systems. When marking and cutting metals at lower power (<kW), fiber laser have advantages on metals also due to the absorption increase at 1 um wavelength. As you move to shorter wavelength, spot size and thermal effects tend to be significantly less and allows for things like micromachining and other high precision work. The disadvantage of these shorter wavelengths are the costs and the difficulty obtaining higher output powers.