Calculating laser wavelength/power to cause emission of light in a gas? I've become interested in volumetric displays. In particular I'm looking at a pair of lasers scanning a volume of gas such that the intersection of the lasers would supply enough energy to cause the gas to emit visible light. Since this is the start of my research I would like to investigate a number of gases in order to determine a number of gases which might be suitable for this application. I have, however, forgotten how to determine the amount of energy needed to cause an outer shell electron to emit a photon, and then trying to back-calculate the required wavelength(s) and power requirements of the laser emitters.
I'm looking for some information on how to identify the required information for a given gas and how to calculate the energy required to cause visible light emission, and also information on how the wavelength of laser light impacts the ability of the gas to absorb the energy with the intended effect of emitting visible light. Links to introductory texts are always helpful, as are answers which help me get the terminology correct so that I can improve my searches for this information.
 A: Are you thinking about resonant light absorption i.e. using a laser frequency that matches an energy level in the gas atom? If so I'm not sure this will do what you want. The resonant absorption, and therefore emission, is just proportional to the light intensity so where the lasers cross the spot on only twice as bright as the rest of the beams. Your display would have a very poor contrast.
On the other hand you might be able to heat the gas and generate light. The beam crossing will only heat twice as much as the rest of the beam, but if you get the heating correct this might be enough to trigger emission only at the crossing point. However I suspect you're going to need a gas mixture e.g. one gas to absorb the laser and heat up and a different gas to respond to the high temperature by emitting light.
I did the obligatory google for "volumetric display", and I note that the Wikipedia article on it gives an example of a laser being used to heat air until it forms a plasma and glows. However that's done with a pulsed laser not crossed beams. Are you trying to build some already existing design of volumetric display, or are you thinking of inventing one?
