SF532+CO2 was designed for a Photonics West display. It attracted attention to the Lightwave Electronics tradeshow booth with its marvelous display of single frequency green laser light playing across condensation. The "sculpture" serves continuous duty by illuminating the glass globe when all of the dry ice has evaporated. SF532+CO2 met eye safety requirements, ease of use requirements, budgetary constraints and could work dynamically for 8 hours at a stretch.
How it all works:
At the base, sits a Lightwave Electronics model 142C ("Cinderella" Project) single frequency NPRO laser with an output of 200mW, 532nm. The laser is fed horizontally through a 1/2" diameter acrylic tube to a beam housing. Inside the housing a negative cylindrical lens fans the beam out just prior to hitting a 45 degree turning mirror. The turning mirror is aligned so that the fanned beam travels vertically up the main acrylic tube.
At the top of the acrylic tube rests a standard 9" frosted white glass globe. This globe rests atop a 4" diameter ABS fitting and is held in place by three 1/4-20 nylon screws. The globe must be removed to add chunks of dry ice.
At the bottom of the 4" diameter ABS section rests a coarse steel grate for supporting the dry ice. Slightly below this section (at the 4" to 3" taper joint) rests another fine mesh grate for catching smaller chunks of dry ice. The area in between the two grates is the air mixing chamber. The air mixing chamber has 1/4-20 holes for use in setting the total range of air flow possibilities, while at the base of the display tube is an easily accessable iris for use in controlling the desired air flow speed.
Creating a dynamic display that would survive 8 hours took iteration and effort. The air flow over the dry ice must be balanced for both speed of the downdraft as well as evaporation of the dry ice. Too little air flow and the upper air mixing chamber frosts over with water vapor and the "sculpture" locks up. Too much air flow and things become too turbulent and foggy, or the dry ice evaporates too quickly.
Because of the tendency of water vapor to collect at the top and drip, several tricks were used to prevent this water from landing on the turning mirror below. Just in case, a simple access port made cleaning of the turning mirror easy.
As air flows over the dry ice, condensation forms a fog that travels downward with the cold air. The laser beam illuminates a cross section of the miniature water droplets, showing the swirls and vortices of the falling fog.
Special thanks to Shannon Gomes and Wes Irwin, who contributed great amounts of effort to the SF532+CO2 project.