In reflection mode, the holographic microscope can create images of dense, opaque materials, such as water filters. (a-b) Laser light from a laser diode ("LD" in the diagrams) is projected through a pin hole ("PH") and then split into two beams by a beam cube (labeled "BC"). One beam of light hits the sample; the other does not. The beams are then reunited to form an interference pattern, which is recorded on a CMOS image sensor. (c) This photograph shows the microscope in reflection mode, with its cover removed. (The inset shows what the microscope looks like with its cover on.) The device weighs about 200 grams and is 15 cm long, 5.5 cm high, and 5 cm wide.