I would like to use a laser beam to weld small metal parts that are located within an air tight enclosure but want the laser head to be located outside the enclosure which would require the laser beam to pass through a glass window. Can laser beams used to weld metals pass through glass?
Most weld optics have a protective glass that shields the (more expensive to replace) focusing lens from welding spatter. So there are definitely glasses that exist and can be used for this.
When designing your enclosure and/or the location of the metal parts during welding operation, try to let the laser beam propagate through the window as soon as possible after the focusing lens. The greater the distance, the higher the power density on the glass. Your design choices here of course depend on the focal length of the weld optic.
You might also need active cooling for the window, depending on the power of your laser.
The actual material depends on the wavelength of your laser and the power range, for simple (low power) applications, it is often BK7, for higher power quartz glass.
Important: Such a laser protective glass is a special optical component that is particularly picked for power and wavelength. Do not use a random piece of window glass or similar without checking the absorption, transmittance and reflectance of the material at that wavelength. You don't want to direct a 2 kW disk laser on your protective glass and have half of it reflected back into the resonator or even worse, into the room you are standing in.