Abstract: A 3D printing apparatus for manufacturing a workpiece has a first radiation source to carry out a non-linear absorption polymerization and a second radiation source to carry out optical coherence tomography. A first beam path is traversed by the first radiation and a second beam path is traversed by the second radiation. The first and second beam paths are formed completely independently of one another. Further, a 3D printing method for manufacturing a workpiece, another 3D printing apparatus, and methods for analyzing the quality of a raw material of a non-linear absorption polymerization; checking an orientation of a substrate to be printed by non-linear absorption polymerization; determining a spatially resolved degree of conversion of a non-linear absorption polymerization; analyzing a structural sharpness of a structure produced by non-linear absorption polymerization; and for three-dimensional reconstruction of a workpiece manufactured by non-linear absorption polymerization are disclosed.