Ordinarily, this approach would work well in only two dimensions. That's because even If we focused the laser deep into the resist, photons would he absorbed not only close to the focal region but also throughout the entire beam cone, below and above the focus. To make the curing process work in three dimensions, we alter the strategy slightly, pairing the “photoinitiator”-the part of the photoresist that absorbs photons-with a longer-wavelength laser. If the combination of the two isju.st right, we can create a system in which the photoinitiator must absorb two photons instead of one to become excited.