The primary reason for holography to move into the realm of flashes was - first and foremost - to facilitate imaging of people. Sadly, ruby laser portrait holography was almost instantly recognized as severely wanting. Not quite right sums it up quite rightly - the images have been described (even by those responsible) as wax-like; a descriptor that begins to describe something full of life being reduced to something lifeless. The reason for the ruby portrait shortcomings can be traced to the color of the laser light - red (bordering on infrared) at 694 nanometers. If you could light yourself up from within (the way you did as a kid when you put a flashlight in your mouth, you would produce the same kind of eerie effect as did the ruby laser portraitists. The people seemed to glow in sort of surreal fashion and even though there were some recognizable attributes of the subjects - the images were definitely not the subjects. In particular, the eyes just didn’t pack it. It was as if the subjects had gone through a sort of alien transformation that might fool an outsider but one that would never fool mom. Still, it was professed to be state of the art in 3-dimensional realism and a group of avid practitioners remained (at least outwardly) steadfast to their belief that the public would one day appreciate their efforts - that all things new take time to gain acceptance. Their somewhat en masse denial effectively soured the viewing public to the idea of serious display holography - in particular as it applies to imaging people. While several high-profile artists (among them Salvador Dali, Bruce Nauman and Chuck Close) used the ruby portrait technique – it was typically in surreal, almost tongue-in-cheek fashion.
When I first saw display holography and in particular portrait holography I started asking the obvious question: why a ruby laser? The answer, it turned out, was as previously mentioned: because it was the only game in town. True… to a point. Whereas you couldn't (until recently) buy a commercial pulsed laser specifically for holographic portraiture – with the right background you certainly could build one from commercially available components. Unlike CW lasers with their large plasma tubes and imposing black-boxish nature, Q-switched solid-state lasers are in no way monolithic - they actually invite tinkering along the lines of old car parts in a small town garage or a storeroom full of computer hardware. The components you need to build even a big laser like ours are available as recycled hardware (there are several web sites specializing in laser resale) and old lasers can be reconfigured into any number of very specific applications like punching holes in steel; looking at combustion processes; or producing holography. The particular hardware kit that we bought as government surplus spent its first lifetime measuring the distance between Tranquility Base and a lonely mountaintop in Texas. Obsoleted for lunar ranging (and following a modicum of fiddling) it became an absolutely state of the art laser for holographic portraiture.
My background was in custom lasers - one-of-a-kind systems designed and built to customer specifications. I knew from experience which laser parameters to concentrate on for our application.
Wavelength (color): I chose green light (532nm) because of its ability to reflect cleanly off skin and eyes and because it’s easy to produce in copious amounts
Pulsewidth (shutter speed): it turns out that 10 nanoseconds is a good overall number and it's where frequency doubled Neodymium YAG lasers like to operate
Energy (when combined with film speed):1 Joule turns out to be the energy our imaging system needs to expose ~1 meter x 1 meter holographic film (our maximum format as dictated by film suppliers)
Laser Repetition Rate (minimum time between shots): our laser is virtually single shot - firing one pulse every two minutes - but that's OK because we deal with single exposures and it takes that much time to load film
Coherence which we established as being at least 2 meters. Coherence length to holography is akin to f-stop in photography in that it defines the available depth of focus.
I spent a grand total of about 2 months and $5,000 reconfiguring and fine-tuning our laser and light delivery system in the summer of 1990 and have since been in continuous production ever since.