Methods including a combined light sheet and apparatuses

A method of forming an object in a volume of a composition comprising a photohardenable composition, the method comprising:

• (a) forming a combined light sheet including a first wavelength at a selected location in the volume of the composition comprising directing a generated light sheet along a light sheet illumination axis at the selected location through the volume of the composition;
• and reflecting the light sheet exiting the volume of the composition back through the volume of the composition;
• (b) projecting an optical image including a second wavelength into the volume of the composition to intersect with the combined light sheet at the selected location in the volume, the optical image being projected into the volume along a projection axis perpendicular to the light sheet illumination axis, the projected optical image being perpendicular to its projection axis and the combined sheet being orthogonal to the direction in which the optical image is projected into the volume, wherein the composition comprising the photohardenable composition is at least partially hardened at the intersection of the optical image and the combined light sheet;
• and
• (c) optionally repeating steps (a) and (b) until the object is partially or fully formed, wherein the intersection occurs at the same or a different selected location in the volume.