Lumens don't make sense for lasers since they're not illumination devices, but it could in principle be computed from the output power and wavelength. That is, the output power measurement is basically the same thing as a lumen measurement. There is no integrating sphere involved since there is no uncertainty about the beam pattern (it's all in one spot), and there's no spectrometry as we normally think of it for flashlights, since the laser light is monochromatic.
