COHERENCE LENGTH TESTING 2013

Spurred on by conversations on the Holography Forum, (http://holoforum.org/forum/viewtopic.php?f=11&t=662) I decided to check the coherence of some of my workhorse lasers. Traditionally the set up for a coherence length hologram was in the transmission mode. Back at the first reports of coherence length holograms, circa 1967, there were no really good silver halide holographic recording materials capable of recording decent reflection holograms. Plus the transmission hologram case relaxes the vibration requirement with its lower spatial frequency, and with an unbleached hologram it can be the thriftiest with light.

Three functioning Helium Neon lasers were chosen from my museum for the survey: Unphase 1145P, Melles Griot 05-LHP-165 and a Uniphase 1 mW, whose model number is hidden behind the side walls of its enclosure. Also tested were a Coherent Compass 315M, and a Melles Griot BLD 605, both of which are of the Diode-Pumped Soid State persuasion.