Ruby laser system was developed at PSI

I believe that there are some inaccuracies in your article "Ruby laser captured munitions impacts" (June, p. 40). I was formerly employed by Physical Science Inc. (PSI) and was the principal investigator for both the pulsed ruby laser illumination development program and the Nd:YAG illumination program. Both of these programs were contract awards to PSI and not Continuum, although they played a critical part in the success of each program.

In particular, the last paragraph in your article states that the Nd:YAG system was developed by Continuum as a result of the success of the pulsed ruby system. This is incorrect. The system contained (eight) individual Nd:YAG lasers, was developed first and by PSI. My colleagues at PSI and I developed the specifications. The system utilized "off the shelf" Nd:YAG systems purchased from Continuum by PSI. The system was integrated and characterized at the PSI facilities in Andover, MA. The ruby development project was a result of the success of the Nd:YAG program.

The specifications for the ruby laser program were again developed by myself and my colleagues at PSI. The laser itself was a custom-built "free-running" laser made by Continuum. The laser was built specifically for this program at PSI's request and was integrated with the hardware required for the pulsing, obtained from a separate vender, at the PSI facilities in Andover. The characterization measurements of the pulse train were also carried out by PSI.

Chuck Goldey
5ESS Business Developer
Special Customer Operations
Lucent Technologies Inc.
[email protected]

Laser TV still has obstacles to overcome

I read with interest "Laser displays move from the amphitheater toward the living room" (May, p. 91). Having worked in the field of laser video projection with both Dwight-Cavendish and LCI during the 1980s and 1990s, I was interested to note the same degree of optimistic enthusiasm of your writer about laser TV as I received from many viewers of our equipment years ago.

The relatively slow-moving beams of a laser show provide intense and spectacular effects. This leads to the assumption by many that laser video projection will provide "far greater light output" compared with other projection technologies.The mere mention of "laser" in connection with video .projection seems to suggest .extremely intense images.

The fact is that to make a video raster, a laser video projector has to scan the laser beam much faster and further than a laser show projector. And, unfortunately, the red, green, and blue laser wavelengths add up to only about 250 ANSI lumens per optical watt of laser light, due to the photopic response of the eye. Thus, an 18-W laser video image is the equivalent of less than 5000 ANSI lumens, achieved with ease by modern low-cost LCD projectors. Even greater intensity is available with DMD-based projectors.

There are health and safety issues with the use of powerful laser beams in public displays. Under current ruling (CDRH in the USA, HSE in England), the use of an 18-W laser for public display requires inspections, permissions, and operation only by a licensed laser technician. Compare this with the ease of placing an LCD projector onto a table and projecting a 5000-lumen image without restrictions and with a minimum of fuss.

Mainly as a result of these issues we were forced to abandon our laser video project and although I enjoyed the fascinating development of the technology, in the end practical and commercial reality had to be accepted. So, while I admire your writer's enthusiasm, the reality is rather less exciting.

Tony Clynick
Consultant Engineer for AV and Laser Applications
London, England
[email protected]

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