A system for forming a micro-truss structure including a reservoir having walls and a flat bottom configured to hold a volume of a liquid photomonomer configured to form a photopolymer when exposed to light, a partially transparent mask secured to, or being, the bottom of the reservoir, a release layer on the mask configured to resist adhesion by the photopolymer, and a blocker positioned a first distance below the mask. The system also includes a light source positioned below the blocker configured to produce collimated light suitable for causing conversion of the photomonomer into the photopolymer, and to which the blocker is opaque, and a first mirror, oblique to the blocker, configured to reflect the light from the light source around the blocker and through the mask and into the reservoir. The blocker is positioned to block a straight path of light from the light source to the mask.