read before Wednesday

http://www.integraf.com/a-Types_of_Holograms.htm

http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/holog2.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/holog.html#c2

FYI:

http://www.integraf.com/a-holography_medical_applications.htm