Laser tuned to atmospheric absorption

Has anyone ever.designed a laser to be absorbed by atmosphere?

I was thinking you might be able to knock air out of the way for a cannon style launch

Huh, you could heat air, I'm not sure how that would help you, since it's compressive heating that does most of the damage at those speeds, with a well designed craft. But yeah, long wave IR around 7 Micrometer wavelenth soaks into the water vapor, which would theoretically expand it, causing convection... Still not sure how that helps?

The thought was that you could use the laser to expand a pathway in front the ship.
In a high speed low altitude launch you could knock the thickest part of the atmosphere out of the way.

There are Russian rocket torpedoes that work exactly that way. See http://en.wikipedia.org/wiki/VA-111_Shkval. I'd imagine it would take alot of energy, though. Maybe if you put the laser on the ground?

But that torpedo works by pushing water out of the way using air (or other gases). If you push air out of the way using another gas, you're not going to improve your drag by much if anything. You'd need a way to replace the air with a vacuum in front of the ship, without pushing it aside directly.

The analogy would be to use a plasma to push the air, ostensibly a laser being the method of excitation to that state. It would still require a silly amount of energy.

So, you ionise the air in front of you. It'd still be in the way, just now consisting of charged particles. What am I missing?

By violently expanding air it is not in your way. If I could beam a laser that does not get absorbed by air into the ship from the ground. This could be converted into a different frequency and then emitted in a frequency that is absorbed by air.

The idea is to launch a very heavy ship with only ground based power and scramjets.

If a system like this could be made on a very small scale...... It could work on a very large scale.... If all launch energy is made on earth then the ship could be very light. A spaceport of a massive scale built by all nations would free us from earth and help ensure that humanity has back up colonies so extinction is very unlikely.

Heavy metal ships can shield radiation much better then light ones.

If I pulsed and electromagnet can't I pull or push ions?

I'd expand the air behind the ship, and skip the railgun, unless this was some sort of weapon. Cannons are really less useful for launching something you care about being destroyed in the process, and better for their classical use, destroying things.

Well, some stuff doesn't mind being instantaneously accelerated to mach 10. Rocket fuel, for example. Water, for another.

Mach 10 won't do it, think Mach 25 @ sea level, and with the drag associated with doing this in an atmosphere, probably a lot higher.

I agree, for the most part. Especially the Fuel, if it doesn't compression detonate from the gees. (Most substances that energy dense are sensitive to shock.) People aren't so hardy, though, so such a launch facility is best for cargo, or a weapon. You'd need something else to get crews up there.

A tuned beam could move the air out of the way, but I'm not sure how much this would help the muzzle barrier. Also, you're talking about a lot of energy, probably more than the railgun uses. At minimum depth, you're talking about a column of air as wide as the ship, and about 100 miles long. If your ship leaves at a constant LEO velocity, that'll take about 5 minutes to clear, while maintaining this tunnel against the entire atmosphere pushing back in the whole time.

So, you're using a railgun to save energy (in the form of fuel, which also has mass,) then multiplying the launch energy by at least an order of magnitude to minimize a side effect of using a railgun in an atmosphere. Then, you're talking about powering this ship with a Scramjet. In a column of pre-heated low density air created by the railgun, a ramjet would overheat, and suffocate, so that part of the combination at least is impossible. The trick of making the passage through the air makes the scramjet not work.

I don't see a point to adding a scramjet. It just adds extra weight, and you need a rocket at the other end of the flight anyway. Why not just launch a rocket with a railgun?