Laser-beam combination with dual-substrate dichroic filters

A system for combining three or more collimated laser beams, comprising:

• a series of instances of a dichroic beam combiner comprising:
• two substrates;
• and
• a dichroic thin-film filter coated at a nominally planar interface between the substrates, the dichroic thin-film filter being transmissive in a transmission-wavelength-range and reflective in a reflection-wavelength-range, whereby the dichroic thin-film filter is configured to combine, into a combined laser beam, first and second input laser beams that (a) have wavelengths in the transmission-wavelength-range and reflection-wavelength-range, respectively, and (b) are incident on the dichroic thin-film filter of the dichroic beam combiner from opposite respective sides thereof;
• wherein the substrates are configured to, when heated by absorption of the input laser beams in the dichroic thin-film filter, form a first lens for the first input laser beam and a second lens for the second input laser beam, the first and second lenses being either (a) both negative or (b) both positive;
• and
• for each pair of dichroic beam combiners adjacent to each other in the series, a respective reflector arranged to (a) collimate the combined laser beam produced by a first dichroic beam combiner of the pair and (b) reflect the combined laser beam toward a second dichroic beam combiner of the pair, whereby the combined laser beam produced by the first dichroic beam combiner of the pair forms one of the first and second input laser beams for the second dichroic beam combiner of the pair.