There are a variety of lasers. For instance, diodes, crystals, gas discharge, etc. For purposes of cutting silicone steel sheet to make something like a VIC core, a high powered laser is needed. High power means a few tens of watts to a couple hundred watts, not mW. And the operation should produce a Continuous Wave output (CW), rather than a string of pulses. It turns out that this type of system is fairly easy to build, using thermal pumping, in the form of a Gas Dynamic Laser.
Gas Dynamic Lasers operate in the IR part of the spectrum. They usually involve two gasses, usually CO2 and Nitrogen, one of which is hot. (A few thousand degrees.) When the two gasses pass through a nozzel, a region is formed which is refered to as a lasing medium. The cold gas takes energy from the hot gas, producing the required population inversion among the molecules which have suddenly been cooled, or heated, depending on the specific reaction. A set of laser mirrors then extract the energy in the form of a coherent beam of light.
In the 70's, I had a copy of a patent from France which talked about 200kW, CW mode, depending on the size of the nozzel. That system burned two organic gasses whose product of combustion was strictly Carbon Monoxide. The exhaust nozzel had an aspirator tube where cold Nitrogen was pulled in. One way to produce CO is to burn graphite under a stream of hot CO2. (Charcole may also work.) Otherwise, an electric arc would have to be used to get the required temperature.
Improvements in the nozzel design have simplified the need for machining. For instance, several closely spaced parallel rods will work. A pressure cooker fitted with an 'easy' nozzel element, followed by an exhaust fan, would form the basic unit. The catalyst gas can be cooled by running it through some tubing immersed in a tub of alcohol chilled by dry ice. And a focussing lens would be helpful, for thin line detail.
The output of this kind of laser is extremely dangerous. Even a reflected fragment of the beam will instantly cause permanent blindness. The beam, and the work piece, should always be contained in a completely light tight enclosure. Monitoring cameras are usually mounted on a mechanism which keeps moving the camera around a little every second or two, to prevent burning the CCD chip.
I've attached a couple of drawings taken from some patents, to make it easier to visualize.
