How to combine multiple laser beams into one laser beam
Here we combine 3 lasers into 1 laser, they are 532nm green laser, 660nm red laser, and 445nm blue laser . The 3 lasers will produce a RGB white laser. Check this video for BeamQ Powerful white laser pointer.
A partial mirror beam splitter can be used as a combiner with the two lasers at an angle, a cube beam splitter can combine two at 90°, when it is polarizing, and one of the polarized lasers are turned sideways. I use dichroic filters as frequency dependent beam splitter/combiners when adding RGB lasers.
There is also the “knife edge” method of grinding a knife edge on the backside of a first surface mirror and place them at 45° so it is JUST grazing (one goes past and one is barely hitting edge) this is more like stacking, than overlaying (the combined beam is larger). In the Old Days, you could make a “train” of laser tubes end to end, and make an extended cavity, to combine two gain paths into one long cavity with long focal length output coupler. This is the way they make the giant lasers at LLNL (hard to align, though). There are Ring lasers or Z fold, where multiple cavities are along one edge of of some polygon. There are really cool knife edge combiners taken from JVC video projectors, which are a linear array of small mirror segments that feed into one lens with diode lasers folded in. In confocal microscopes Olympus uses lenses to steer the beams into coincidence at specific near-spot, not long distances, these are tailored, wedged, and coated for that. Beam height is crucial in all of these schemes and fine laser tilt and rotate adjustments are needed. below are ebay examples of different methods. I have also used a “color cube” beamsplitter coated as a color combiner from a video projector. This worked pretty well and was compact. Prisms and Diffraction gratings also can work for color combining (converge at different angles) but not, if you are looking for more power. I have in mind a diamond shape, that I haven’t tried yet, for adding same color lasers.