(1+1)-photon absorption for 3D laser printing

2-photon absorption mediated by short laser pulses provides an optical nonlinearity that is highly desirable or even mandatory for various forms of volumetric (3D) laser printing. Here, we review and compare different approaches that replace 2-photon absorption by some sort of cascaded 1-photon absorption processes. Such “(1+1)-photon absorption” processes can be accomplished by inexpensive continuous-wave lasers at comparably low powers. We present recently published and unpublished results, including screening of molecules suitable for one-color and two-color 2-step absorption. In addition, we investigate the possibility of optical depletion processes at a laser wavelength that is distinct from the excitation wavelength.