Is there a formula to measure the strength of the magnetic field of magnetically polarized laser light? Or some way to "guesstimate"?

yeah, well if you tell us the wattage of the laser. the average energy density of an electromagnetic field is proportional to the square of hte magnetic field.

could you please work that out for a 200 watt laser system? Thanks I'm a dumbass -

well i think the formula for energy density is u=1/2\mu₀B². so then Wattage = A*c*u, where A is the cross sectional area, c is the speed of light, and u is energy density. i think that should work, no? solve for B? this assumes a uniform EM field, which i think is a pretty good assumption for a laser

What do you mean by "magnetically polarised" light?

so according to the formula i gave, a 200 Watt beam, with a cross sectional area of 1 square millimeter would give you a magnetic field of 1 mT. not bad.

i hope you realize though that this is an oscillating field, so you can t go moving magnets around with it. it has a positive RMS, but if the average of the field vector is 0.

lethe, is there any way that you know of to turn the laser into something that can move magnets?

i think i should probably add a factor of root two, from averaging out the sinusoidal magnetic field amplitude squared.

won t change your answer much though.

Originally posted by G Fresh
lethe, is there any way that you know of to turn the laser into something that can move magnets?

well sure... one thing you could do with the magnetic field of a laser is find some atoms that have the same resonance frequency as the frequency of the laser. then the laser will oscillate the atoms at that frequency. this is the basis of NMR (like when you get an MRI from the doctor), only they don t use lasers, they just use non coherent radio waves.

you have to understand, G Fresh Prince Mac Daddy, that the magnetic field in a laser (or any other electromagnetic source), is oscillating rapidly. it is not a constant field. so the best you could hope to do is oscillate magnets, not move them. and only very small magnets.

if you want a magnetic field to move things, then you need some coils. their not hard to come by. you could probably even make some. helmholts coils make the most uniform fields. that s two short coaxial coils seperated by the same distance as their radius.

OK! get to work on your coils, G Funk Master!

By oscillating what do you mean? Is the polarity still in one direction, so it'll be pulling the magnet along at different rates of speed?

Originally posted by G Fresh
By oscillating what do you mean? Is the polarity still in one direction, so it'll be pulling the magnet along at different rates of speed?

OK, so polarized means that the magnetic field stays in one direction, throughout the whole electromagnetic region. right?

but electromagnetic waves are waves. so just like the waves in the ocean, the magnetic field rises and falls. it crests up to a maximum, then descends to zero, and keeps going down to the exact opposite, along the negative axis. the average is zero. with me so far?

just like the average height of the ocean is zero. the waves go up, they go down, but they average to zero. you asking me to move magnets with a laser is a lot like me asking you to lift a ship up into the sky by hitting it with normal water waves.

it doesn t happen.

lasers, and all forms of electromagnetic radiation, are waves.

Thanks lethe

Originally posted by lethe
you have to understand, G Fresh Prince Mac Daddy, that the magnetic field in a laser (or any other electromagnetic source), is oscillating rapidly
LeThe, hope U will soon deliver the much awaited grand unified theory. Wish U all the best and advance congrats..! yeah really i hope man..

Originally posted by everneo
LeThe, hope U will soon deliver the much awaited grand unified theory. Wish U all the best and advance congrats..! yeah really i hope man..

i hope you guys don t think my name is Le The, as in the french word for "the" followed by the english word "the". cause that ain t it.

and, everneo, i don t know about unified theory. i ve been thinking that i made a mistake switching to physics, and i want to switch back into math. indecision, indecision.. but anyway, thanks for the good will.

U don't know UT.! joking.. anyway u have the attitude and ground so eventually u will endup there..! have a nice spring break..!

Hi,

"so according to the formula i gave, a 200 Watt beam, with a cross sectional area of 1 square millimeter would give you a magnetic field of 1 mT. not bad."

With the electricity used to generate an optical beam of that wattage, and with all the water needed for cooling, you'd be off a lot cheaper just using some superconducting magnets... You can get 10T without problems, over a much larger area aswel...

Bye!

Crisp

One more question lethe: Assuming I had a magnetic field generated via laser by the NMR technique, and I held a magnet up to the beam: would the magnet move the laser or would the light just steadily attract the magnet?

Originally posted by G Fresh
One more question lethe: Assuming I had a magnetic field generated via laser by the NMR technique, and I held a magnet up to the beam: would the magnet move the laser or would the light just steadily attract the magnet?

remember, the magnetic field of a laser is oscillating, because the laser is an electromagnetic wave. therefore if the magnet were the right size (like the size of an atomic nucleus), then the laser would oscillate the magnet back and forth. under no circumstances would the laser steadily attract the magnet. you would nead a steady magnetic field for something like that. and in no cases would the magnet attract the laser. the laser is presumably electrically neutral, and has no magnetic moment.

Allright, I'll just say what this laser is for: an interstellar
spaceship.

Plan on projecting a laser out the front of a craft and having the craft pulled along by attracting to the laser. The craft will be made out of niobium-titanium, 14 or 15 Tesla in strength.

Actually, I'm not going to do this. A company is just designing the ship. The company is called UNITEL Northwest.

Here's an excerpt from the book they have:

"At low temperatures excitons are less able to penetrate the narrower, higher-energy parts of the wire; thus, these narrow areas become de facto barriers along the wire. They wall off sections of the wire creating a string of dots. In addition to this fixed magnetic field backdrop, NMR procedures also utilize varying electromagnetic fields. By applying an oscillating field of just the right frequency (determined by the magnitude of the fixed field and the intrinsic properties of the particle involved), certain spins can be made to flip between states. This feature allows the nuclear spins to be directed at will.

For instance, protons (hydrogen nuclei) placed within a fixed magnetic field of 10-Tesla can be induced to change direction by a magnetic field that oscillates at about 400 megahertz - that is, at radio frequencies. While turned on, usually only for a few millionths of a second, such radio waves will rotate the nuclear spins about the direction of the oscillating field which is typically arranged to lie at right angles to the fixed field. If the oscillating radio-frequency pulse lasts just long enough to rotate the spins by 180 degrees, the excess of magnetic nuclei previously aligned in parallel with the fixed field will now point in the opposite, anti-parallel direction. A pulse of half that duration would leave the particles with an equal probability of being aligned parallel or anti-parallel.

In this fashion we can control the strength of magnetization by manipulating the alignment of all particles, along with feathering the signal to slow the attraction down for instant response of the vehicle to projected field interactions."

-Qunatum Electromagnetic Laser Propulsion

i was with you up until this part:


Originally posted by G Fresh
along with feathering the signal to slow the attraction down for instant response of the vehicle to projected field interactions."

i m not really sure what this means... can you explain that a little more?

Feathering: to turn (an oar blade) almost horizontal when lifting from the water at the end of a stroke to reduce air resistance b (1) : to change the angle of (airplane propeller blades) so that the chords become approximately parallel to the line of flight; also : to change the angle of airplane propeller blades of (an engine) in such a manner (2) : to change the angle of (a rotor blade of a rotorcraft) periodically in forward flight

So presumably they would be moving the laser in an analgous fashion to control the propulsion. Although it seems like they could just modulate the beam's power more easily.

Using a laser attached to ship to pull it along is akin to trying to push a sailboat along using a fan attached to the back of the boat. It won't work.

Why not? Is there a physics law that says so?

It seems to me it could be more efficient than shoving propellant out the back of the ship.

Keep in mind the magnet that will be used is over 300,000 times the strength of the Earth's magnetic field, and the laser will have much more than 1 mT of attraction. All that's needed is a good power source, perhaps a nuclear power generator.

<i>Why not? Is there a physics law that says so?</i>

Yes. Newton's third law.

Originally posted by James R
<i>Why not? Is there a physics law that says so?</i>

Yes. Newton's third law.

Newton's third law (action & reaction) does not prevent the ship from flying.

If the laser is attached to the ship that the sails are attached to, isn't that, in effect, a closed system?

Please explain why it isn't.

Originally posted by one_raven
If the laser is attached to the ship that the sails are attached to, isn't that, in effect, a closed system?

Please explain why it isn't.

Yeah it's a closed system, just like your car's a closed system.

I'm not a physicist, I'm not affiliated with the company. I'm just using common sense.

If I'm wrong here please let me know.

Your car isn't a closed system because the wheels are in contact with teh ground, and it is the rotation of the wheels on the ground that causes motion.

Think of it this way.

If your car breaks down and you have to push it.
So you sit in the driver's seat and push on the steering wheel.
How far would it get you?

The force (you) is attached to the car (your but in the seat).
Like James said, it is like bolting a fan onto a boat, and aiming it at the sails.
How far would you get?

I am not sure what would come into play with "feathering".
I suppose if the fan's air stream is directed nearly parallel to the sail, it would cause a sligh change in pressure (like an airplane wing) but I can't imagine how efficient that would be, and how that would apply to light.

Can anyone address that better than I can?

It's not a closed system. The laser does have effects on the environment: it creates a "flux tube" vacuum to fly through.

<i>It's not a closed system. The laser does have effects on the environment: it creates a "flux tube" vacuum to fly through.</i>

I don't know about the flux tube thing, but you're right that it isn't exactly a closed system. Your spaceship with a laser mounted on the front might accelerate very slowly backwards due to all the photons it is shoving out the front, but it won't be dragged forwards as you seem to be saying.

I wouldn't expect that James since laser light is an electromagnetic wave.

Here's the patent:

http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='4,817,102'.WKU.&OS=PN/4,817,102&RS=PN/4,817,102

Maybe I'm simplifying too much.

"The lens will emit coherent monochromatic laser light from the three separate Red, Green, and Blue sections forming an overall white light. The parabaloidical curve serves as the base or point of attachment for a light string. This curved lens provides the uplifting path for parallel transport superconducting mechanism that attaches the light beam to the vehicle. this is the fiber bundle connection of the projected light string to the vehicle. The dielectric and ZPE forces play an important role in producing the particle pair mode from this arrangement so as to become a gigantic electron-hole or electron-positron pair at macroscopic scales. The glass mixture will provide the ruggedness required for aerospace propulsion."

-Quantum Electromagnetic Laser Propulsion, pg. 70

And don't go shooting your mouth off about ZPE if you don't know what it is.
"The Zero-Point energy of the atom is the kinetic energy when it is at this lowest energy level" (Scientific American)

Your extract uses lots of physics terms, but it doesn't actually seem to be coherent.

BTW, to get a patent, your invention doesn't have to work.

No way.

Could explain why emitting light out the front will pull the ship forward. And why is this more effective then an ion engine?

Is it not better to have the laser on the ground and push the ship away?

i know about action+reaction and how both could cancel out any motion forward nor backward in a closed system, hence the comparison with a shipsail and a ventilator. BUT just really how much pressure is generated at the moment the fotons leave the laser, would that be equal to counteract the pressure generated on the sail??


Even if this is true, we wouldn't need a lasersail in the first place, but just a giant laser as foton exhaust on the rear side of the ship to deliver the necessary propulsion.

Maybe, due to the wavenature of the laserbeam, newtons third law mainly applies at the moment fotons hit the sail and act like matter and kinetic enegy ???? in that case a sail would make sense.

you could point the laser at a mirror on a planetary body and use the photons emitted as a sort of propulsion, and reflect it back on a sail, capturing it twofold