LASER vs. Atmospherics

1. Jul 2, 2006

Intuitive

Question.

If we had a tuned LASER, at what level of Energy would be required for a tuned LASER beam to spontaneously ignite the Air around its Beam just as a Bolt of Lightning ignites the Air around itself.

2. Jul 2, 2006

Staff: Mentor

A bolt of lightning does not ignite the air! A bolt of lightning ionizes the N2 and O2 molecules and atoms, and the recombination results in the formation of some NOx. The frequency of a laser would have to match the binding energy of N2 and/or O2, and perhaps one would need two lasers of different frequencies, and the intensity would determine the amount of molecules ionized.

3. Jul 3, 2006

Intuitive

My Apologies Astronuc.

I used the word ignite because of the process

When exposed to oxygen, NO is converted into NO2. This conversion has been speculated as occurring via the ONOONO intermediate. In water, NO will react with oxygen and water to form HNO2. The reaction is thought to proceed via the following stoichiometry:

4 NO + O2 + 2 H2O → 4 HNO2

Which to me the entire process of ionizing the N2 and O2 to form NO and the rest of the chemical reaction to be a form of ignited cumbustion, I was taught that Lightning ignites the Air and that's where I used the term.

And thanks again for the useful information on the LASER.

I am working on a concept that uses a LASER that will emit through a highly reflective pipe that has an Inside diameter(ID) the same diameter as the LASER Beams width, The objective is to intensify the LASER Beam so that Air inside the Pipe evacuates by reaction although I don't believe a low power LASER can do the job even if properly tuned, That's why I wanted to know about the power level required to react with Air.

I wished to take this further for my own Linear LASER particle accelerator on a small scale.

4. Jul 3, 2006

Staff: Mentor

Interesting - a related concept was envisioned during the development of SDI (Star Wars).

In a pipe, I don't believe a significant vacuum would be achieved based on 4 NO + O2 + 2 H2O → 4 HNO2. The reduction in molecules from 7 to 4 would produce a reduction in pressure, but only upon cooling. During the laser pulse, with the dissociation, one would achieve a transient increase in pressure. Remember that the sound of thunder is due to a pressure wave expanding outward from the lightning bolt.

To determine the energy requirements, one needs to look at the number of moles of air (N2 and O2) that would have to be dissociated in the path (column) of the laser, and determine the energy and determine the pulse shape in order to determine the power.

$$E\,=\,\int\,P(t)\,dt$$