This Small Business Innovation Research Phase I research project will develop a fabrication simulation tool for theoretical modeling of three-dimensional micro and nanostructures formed by Two-Photon Absorption (TPA) fabrication. This work will focus on development of a theoretical model for prediction of feature size using TPA quantifying exposure time and optical flux with optical beam writing speed and the validation of the model. Once structural geometry control has been validated this simulation tool will form the base of a device and fabrication modeling tool that can expedite optimization of designs using TPA. The tool will enable geometric structuring and ultimately serve as a validation tool for device performance by coupling additional elements appropriate to each application and translating the structural and materials properties into device characteristics (i.e. photonic device performance and mechanical engineering performance models). Integrated Circuit (IC) technology and silicon micromachining has benefited greatly from the incorporation of simulation and modeling tools into the design, development and evaluation of the components, devices, and systems. This has provided a rapid means to deterministically evaluate new wafer components and designs cost effectively, and avoid the expensive, empirical optimization through physical design iterations. TPA technology will allow for the world's first truly 3D maskless, fabrication platform for micro and sub - micron components devices and systems, and much like traditional IC fabrication requires modeling tools that can optimize fabrication performance.