Corner Reflector
Step 1: Cut 3 pieces of plywood, One at 12”x12”, one at 12”x 12 3/4”, and one at 12 ¾”x12 ¾”.
Step 2: Glue mirrors to plywood.
Step 3: Screw the plywood with mirror to each other with wood screws.
Step 4: Attach clamp to the corner of mirrors.
Taken from from Exploratorium Cookbook III Recipe No. 170.