Hi.

Thank you for reading my post and now on to the questions:

I want to make a seventy thousand watt(seventy millon milliwatts is the same as seventy thousand watts? ) visible light laser beam in the green spectrum.

I want to use either one thousand Coherent or Laser System Europe lasers that are single mode green beam visible spectrum and combine these beams to form that seventy thousand watt beam.

Another question is:

How can I cool the final beam to prevent mirror meltdown since I was told that anything over sixty watts will light a cigarrette?

And why do visible laser beams do this since i was under the idea that a laser beam with no infrared and no UV components was supposed to be cool?

Thank you.

Russ.

Being that this is an Astronomy forum, and 5mw lasers work fine for star pointing, why do you need a laser that is 14 million times more powerful than this?

Are you sure?

Lawrence Livermore National Labs: Environmental Safety and Health Manual: Class 4 Lasers

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Yes, since a seventy thousand watt laser beam is new technology versus a rocket.

So how do I combine the beams?

Thank you.

I am exploring alternatives to todays rockets.

Also if I form the beam into a tube shape, then what is the behaviour of gas molecules inside this laser tube when hitting the walls(laser beam tube wall)?

If I activate this laser array in a remote area and point it at the moon then what will be the behavior of gas molecules inside the laser tube walls since vaporized water tends to be reflective and so subject to thurusting pressure from the laser.

How can I calculate how much thurust pressure a seventy thousand watt beam has?

My guess would be that the tube wall would cause expansion, and cause higher pressures inside the tube. This in turn would force more into the beam and expand, all the time being dissipated outside the tube, and quickly reach equilibrium.
And even if the expansion occurs within the tube wall, then the only thing you would have to expand would be the portion of the tube within the atmosphere, so the atmosphere would only be extended a portion.
(again, I'm no scientist, just an an interested person)

I would think that your first problem to solve is how you're going to power this thing. 70KW's of power is alot of power.

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Yes. Lasers usually aren't fantastically efficient, but they get a lot less efficient at higher powers. Im currently using a .5W laser in my practicals. It has a 300W power supply. You'll need the power supply of a (small?) country to power this thing.

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Russell Burrows. In answer to your query, " How do I make a 70,000 watt laser?". Very carefully.

Three students asked to move a paraboidal mirror, salvaged from an old lighthouse, from one school to another on a sunny day in the winter were a little careless. The tarp covering the mirror was loose. So, when it arrived at the second school, they picked it up,uncovered, and one of them unintentionally walked through the focal point while it was facing South. It was about a meter and a half in diameter. Sunlight is ~ 1000 watts per square meter, concentrated to ~0.1 cm squared...young man walking not quite at focal point received a third degree burn. Your potential laser risk is enormously higher, should you tinker with them. That's why the lab signs......"Danger. Laser". Ciao. Pete.

A 70,000 watt laser definitively qualifies as a weapon.

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Uhm, yes. I think the first step to building one would be to get the money. This isn't going to be a cheap project. The next step is to talk to the government and work through the legal process that would allow you to build one - unless you want some federal agents showing up, shutting you down and possibly arresting you. You'll need to hire some people to help you with the negotiations, and this will take time, luck, and money. Then hire some people to build it ... and did I mention the money issue?

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Buy 70,000, 1000 miliwatts laser modules at $6000.00 a piece;$42,000000.00 get mirrors to redirect the beams to 1 focal point. your focal point should then be at your required enrgy level.

Alexian

And just how are you going to power this monster array? Even at 100% efficiency (Yeah, right!) that's 70 KW! You're looking at something in the megawatt range!

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T. Anderson

There is also the problem of aiming 70,000 lasers at a single point. Aiming a single laser at a specific point is very difficult, aming 70,000 would be next to impossible.

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I don't know about next to impossible. All you would need to do is have every laser mounted on a movable base controlled by a cluster of computers. Of course, you'd have to build the mounts, and write the software to control 70,000 seperate acuators. Shouldn't cost more than a million or two or ten to build.

The there's the problem of finding a place where you can calibrate the focus. Not too sure if people would like something around that would flash fry their new puppy, or the whole neighborhood for that matter.

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Another problem that has not been brought up: Phase cancellation!

Seventy thousand lasers, each emitting independently, are going to have 70,000 random phase orientations. Result - net output (near) zero!

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Oops.
Should've thought of that.

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I thought of it just before I posted it, In an alternate universe, "you" thought of it first and "I" said:
"Oops.
Should've thought of that."

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T. Anderson

We are talking about 70,000 beams each probably about a millimeter in diameter. Walking around too heavily will mess up their orientation. One of the most difficult things about lasers is lining up all the equipment perfectly. We are talking about 70,000 of them, you would need a very large room just to have them all, and they will have to be a ways away from the target so that the hardware from one laser does not interfere with another laser's beam. Assuming each laser is 3 inches tall and 3 inches wide, we are talking about a wall over 20 meterslong and 20 meters tall just to hold them all. You could use optic fibers, but then you have the problem with maximizing the coupling of the laser to the fibers which isn't easy even for one fiber (even then the coupling will be incomplete) and attenuation in the fibers, so you would need well over 70,000 lasers if you used fiber optics.

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Sorry, should have used a smiley, but I can never seem to get them to work on this site.

I was just trying to prove a point that a project like this would require a massive amount of support technology to theoretically make it work.

Yes, setting up and aligning 70,000 lasers would be next to impossble. The hurdles that would have to be overcome building this thing would be enormous. Not to mention extremely expensive.

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Since you plan to use the 70,000 watt lasar to thrust a space craft, my guess is you don't need a mirror to make a tight beam, nor is it important that the many separate lasars be phase locked. I don't think cancelation reduces your thrust much, if any. The dangers mentioned by the posters are real and I'm quite sure the feds and or local authorities will confiscate your equipment unless you get permission.
My guess is you need megawatts to produce 70,000 watts average output, but the array will only produce a few pounds of thrust = not nearly enough to be useful. See www.liftport.com These people are planing to use about that much power, but infrared, to beam energy from Earth's surface to photovoltaic cells on the lifter = climber on the space elevator. They also have a good forum simular to this one. Neil

Cancellation has NO EFFECT WHATSOEVER on the beam energy. Think about it from a conservation of energy point of view--if the beam energy is reduced by cancelation, where did the energy go?

What actually happens when multiple beams which aren't in phase are overlapped is that an interference pattern is formed. You can see this effect by pointing a laser pointer at a nonsmooth surface (like a white wall). Instead of a solid red spot, you will see something splotchy with bright and dark spots. The red light bouncing off of a nonsmooth surface is like a bunch of point sources of red light which are randomly out of phase with each other. Some places, the interference is constructive. Other places, the interference is destructive. But the total amount of energy remains the same.

So, what it the benefit of a coherent in phase source? The benefit is an improvement in beam tightness. By putting all of the beams in phase in just the right way, you can acheive constructive interference in a tight circular spot while acheiving destructive interference everywhere else. This is the principle used by a phased-array radar. Each beam emitter in a phased array radar has a beam "tightness" of emitting over the entire hemisphere. By putting them in the appropriate phase delays, the beams constructively interfere in only a very narrow beam.

If you have a bunch of lasers and don't do anything to coordinate their phases, then you can overlap as many as you like and still linearly improve thrust and power. However, your beam tightness is exactly the same as the tightness of any single laser.

For a target far away enough to be much smaller than the beam size, a hundred non-coordinated lasers have only 100x as much power as a single laser. A hundred phase coordinated lasers would have 10,000x as much power as a single laser. Where did the extra power come from? In this case, it came from tightening up the beam--it came from the energy which was otherwise "wasted" on a wider than theoretically possible beam.

Hmmm.

A few interesting responses.

At most it takes LESS than one thousand lasers since Laser Systems Europe and Coherent both have one hundred WATT visible light lasers ready for sale.

The FEDs?
U.S law ends at the nations borders since there are many more nations than just this one.

I was wondering about the performance of gas molecules since it is sometimes required to pump a gas and a laser tunnel sounded interesting.

I really, really need some input as to the performance of a gas when inside a laser tunnel and hit with either a microwave beam or another laser.

Will the gas be pumped when hit by the laser or microwave beam?

Will the laser tunnel being coherent light serve to constrain the reflective vapor gas plasma and serve as a conduit from one place to another?

Thank you.

Russ.

How about just one like Lightcraft Technology Incorporated. They claim; "A Lightcraft is a 1kg launch vehicle, made from high temperature ceramic materials, that flies into space on a megawatt laser beam."

I thought they were using a smaller laser they borrowed from the air force.

Nanosatellites?
Publiusr will go apoplectic if he sees this.

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Exactly where are you going to try to do this? I would like to make sure the bulk of the planet is between us when you fire it up.

I will try to give you some more help tho. You should be able to find the scattering cross section for the different air molecules and use that to find the mean free path for the photons in the beam. Off hand, I would say that you would have extreme problems with beam scattering losses just off the air. That would give you even more problems as the beam is chaotically refracted by heated air convecting thru the beam. I dunno if this is controllable, and if I remember right, it is what killed a ground based laser defence system.

As for collimating the beam, even at 99.9% transmission, you are depositing 70W of heat into the final lenses and mirrors. Again, heating will do bad things to the focus, no matter how you cool. The thermal expansion in the beam would throw the focus off.

This really is a 'do not try this at home' sort of thing. Someone could very easily be killed at this sort of power.

Convected super heated air tends to rise creating a low pressure zone at its center in nature this results in a hurricane.

In a laser tunnel this aspect of super heated convected air may be the precise feature that makes the tunnel work for plasma pumping or for a micro miniature craft where the super heated plasma creates a thurst vortex.

However I am wondering of the reflectivity index of super heated plasma as the higher index the better the tunnel walls will perform at pushing the super heated plasma inside the tunnel and since any water dropletts expand by a factor of 1600 times or more to superheated steam this results in an interesting factor.

Since any air on the outside contacting the walls will flash vapor to plasma creating a vacume so this presents an interesting aspect as to what goes on meanwhile on the inside of the tunnel.

And my original model was for one thousand watts of visible energy to make the tunnel but if we add losses and other bad things we get the 70 K numbers to make it work in the real world.

Primitive technology is complex and advanced technology tends to favor no moving parts.

Bi-Frost Bridge.

Back on topic where can I get reflectivity indexes for super heated plasma?

Anyone know where to get a plasma simulator or an app that runs on MAYA?

Thanks.

Russ.