Investigating Super Efficient Laser Propulsion Leads to Serendipitous UV effects

wvanhuffel writes "In this article from spacedaily the authors may be on the road to creating the impulse engine....then again, maybe not. It's life imitating art again!" The article details the exploration of the use of lasers and more importantly a new effect when certain materials (in this case lead) are struck by the laser, apparantly a predictable secondary explosion 50 millionths of a second after the target is struck, emitting UV light.

Lasering electrons off the particles.

[Nyphur]

Here's a little theory I thought up there now, while reading the full article on spacedaily:
Remember, I'm only 16 so I don't have enough grounding in particle physics to make a more solid theory.

The particles are ionised because the laser (a highly coherent beam of focused photons) interacts with the electrons in the lead atoms. The photons literally knock the electrons in the atoms of the lead further back into the lead by giving them energy and raising the resistance back towards the laser.

A lot of energy is, at the same time, given to lots of particles of lead. The particles of lead given energy are those in the direct path of the laser and thus are those which have had their electrons removed by the laser, thus producing the ionised lead cloud.

With all this energy stored up in the electrons, which have no atoms to return to, it has to go somewhere! The electrons cannot enter the outer electron shells of the lead atoms, so they are bounced around the lead, attracted by the gravitational pull of the atoms but repelled by the electrons, while possibly forcing electrons with less energy than them out of the outer electron shells and replacing them.

When an electron is forced out of its shell (as in the first case 1millionth of a second after the laser discontinues) it emits the energy it had stored in the bond, like splitting the bonds in an actual atom, but with less intensity. When the electrons are forced out in the second case (50 millionths of a second after the first wave), energy is used in making the new bonds and the same ammount is used in breaking the old bonds, BUT the electrons making the new bond and breaking the old ones already have a lot of energy from the laser, which is released when the electrons enter the outer electron shells of the atoms, because the energy released from breaking the bonds cannot enter the energy-saturated electrons and the energy taken in from making the bond is already present in the electrons entering the shell.

Re:Lasering electrons off the particles.

[Nyphur]

Oops, sorry about the bold bit, I used a b tag instead of a br tag. I was typing too quickly again ^_^

Re:Lasering electrons off the particles.

[Bob_Robertson]

Never appologise for your age. You'll find that peoples aparent "written" age has nothing to do with their years since being born.

Photons are sometimes released when an electron drops from a more excited state to a lower state or "shell".

It could be that the lead atoms "absorb" the laser pulse energy by having some electrons energy level raised. The "pulse" of the laser is echoed by the time it takes for the electrons to rise, then fall and release their energy.

This would not require ionization, or a sonic echo as someone else suggested, but there is no reason to believe that any hypothisis is wrong until it is demonstrated to be false or the "real" answer proven. Or it may be an interaction of all those effects at once.

So relax, Nyphur, and voice your ideas. It's the only way anyone really learns.

Bob-

Re:Lasering electrons off the particles.

[Nyphur]

Thanks for your support. I do know that my mental age is far beyond that of the number of years since my birth, as can be said for a lot of those who post on slashdot.
And, jsut a little reference, although you said that your explanation does not require it, the report clearly stated that there is always ionisation. (The inital ion cloud expanding at 20km/s which occurs 1 microsecond after the laser-pulse). I agree that the photonic pulse is probably the result of electron-"shell-shifting", which I happen to know is not only caused by an inward shift, but also an outward shift. So, as you see, the shift MAY be caused by electrons with more energy pushing themselves onto already full particles, thus forcing the other electrons to push out at a greater velocity, OR it may be caused by the existing electrons gaining so much energy that they break the bond and move outward from the particle.

In either case, knowing the charge of the initial ion-cloud would help with the theories. Anyone know it?

I bet it's a mechanical effect

[ka9dgx]

I bet the laser creates an acoustic shock wave is transversing the lead, reflecting back, and hittle the already excited atoms again, 50 microseconds later.

They should try thicker/thinner films.

--Mike--

Re:I bet it's a mechanical effect

[Nyphur]

They would need to test different thicknesses to test this, yes. I'll wait for them to do that before rethinking about this.

Re:I bet it's a mechanical effect

[Winged Cat]

What, you mean like the basic mechanism by which a laser operates? ;)

Re:I bet it's a mechanical effect

[Winged Cat]

Pulse sparks at one point, travels down the guide exciting the material along its path, reflects off the end, travels back down the guide re-exciting the material along its path, reflects off the other side...repeat until the pulse becomes coherent. Weaken one of the reflectors so the pulse, once it is coherent (i.e., in one big burst), overwhelms the reflector at the end and breaks out. "Mechanical" or not, that's how lasers operate.

It's BIG!

[gnovos]

Sorting through this unexpected discovery is a secondary concern. The main goal is testing different materials under different lengths and strengths of laser pulses to see what might give the most efficient result.

I have been watching the discover and history channels lately, and one thing that seems to stick out like a sore thumb in science is people finding incredible discoveries, and then shelving them or ignoring them becuase it isn't part of the expierement that was being performed. Then maybe 5, 10 or even 100 years later someone will stumble on to it and change the world.

If these guys are just going to table this really intruiging discovery for a few years while they work on ho-hum materials testing, then is has GOT to be big...

Re:It's BIG!

[Doctor Fishboy]

I have been watching the discover and history channels lately, and one thing that seems to stick out like a sore thumb in science is people finding incredible discoveries, and then shelving them or ignoring them becuase it isn't part of the expierement that was being performed. Then maybe 5, 10 or even 100 years later someone will stumble on to it and change the world.

It could also be that they repeated the experiment many times, subsequently realised that it was a known side-effect that they hadn't taken into account the first time around, and then carried on as normal.

The difference is that the History and Discovery channels rarely do programs on "Incredible discovery of the millenium turns out to be misunderstood version of the photoelectric effect".

Please don't misunderstand me, I'm just as excited about new, interesting and unexplained phonomena too. It's just that the media hypes up the unexplained whilst dismissing it as 'boring' if scientists then find out an explanation using known physics.

Dr Fish

Impulse Engine it's not

[Rick the Red]

This is a reaction engine. Lead may be the reactant, and lasers may be the energy source, but the propulsion is still caused by tossing mass away from the direction you wish to move.

A true impulse engine does not lose mass, just energy, and is still a fiction. That's not what these folks are working on.

Re:Impulse Engine it's not

[dlakelan]

E = mC^2, mass is energy according to current theory. Therefore losing energy IS losing mass (albeit a small amount, because E/C^2 = m).

But I know what you meant...

Doesn't the "solar sail" concept essentially react to the momentum of photons?

Re:Impulse Engine it's not

[geekoid]

I thought it was called an "impulse engine" because it would be used as a plot device when ever the director had the impulse to use it...

Energy Has Mass

[inKubus]

When something is moving, it has a larger mass than when it is stationary. General theory of relativity. This energy mass must come from somewhere. So, of course a pure impulse drive is impossible. Mass must be lost by something and given to the object you want to move in the form of energy. Energy does not weigh much, so if they could develop a 99.99% efficient reaction drive, it would begin to function almost like an impulse drive.

Ion engines?

[olman]

Say, didn't one of those recent experimental NASA probes have an Ion engine? IIRC, it didn't work very well or at least it died very quickly after firing.

But the principle is/was to charge "space dust" electrically which will then propel the vehicle forward. A little bit like jet engine, really. The drive doesn't use it's own mass as a reaction source, but I'm rather sure that's not what the original technobabble engine principle was all about.

Space-based lasers?

[whoisthatdog]

My favorite part of the article is the closing paragraph: giant ionizing lasers in space! Sounds like a good excuse for a hack-a-thon. I've always wanted to write my name in hundred-mile high letters...

giant ionizing lasers in space

[Spamalamadingdong]

I've always wanted to write my name in hundred-mile high letters...

You, and Chairface Chippendale.

so what you're saying is...

[corbettw]

You just want a frickin' laser beam.

A superior engine

[spike hay]

A better engine than this one is the VASIMR. It is a plasma engine that is under development. It ionizes hydrogen with microwaves an then accelerates them with magnetic fields. While it doen't provide thrust like a chemical rocket, it certainly has many, many times more thrust than a ion engine. It has some oomph to it. I really don't think that the ablative engine that this article was about would be good to launch vehicles into space. You would need a fscking huge laser to propel the ablative rocket into space. The cost of the giant laser would outweigh the cost savings of not using a huge amount of rocket fuel.
For cheap launches, you really need somthing like the x-42 scramjet spaceplane. That would cut costs of launching by a factor of 10 with no giant lasers.

VASIMR will get a specific impulse of 30,000 seconds compared to 500 seconds for the shuttle's engines. A specific impulse is the number of seconds 1 kg. of fuel could produce 1 kg. of thrust. The specific impulse of the VASIMR is 60 times better than the shuttle. That's even better than this ablative engine.
That would allow cheap interplanetary voyages anywhere in the solar system, using very little fuel. Using these engines, you could get to Saturn in less than a year. It would also allow slow intersteller trips of around 1% the speed of light.
Also, VASIMRs could be easily, cheaply, and quickly refueled for more missions.Interplanetary travel could become cheap. I bet each ship would cost around 5 billion dollars initialy. After that, it's cheap. After each trip, an X-42 could come and restock the ship with fuel and supplies. That would only cost around 50 million. We could send tens of thousands to colonize Mars.

BTW: On this article, it says the VASIMR gets 10,000 seconds. It can reach 30,000 with further development.
Read about the VASIMR here [space.com]

Re:A superior engine

[Omnibus]

High impulse also means low thrust. It is great for continuous thrust, like for space probes and such that have time to spend thrusting to gain speed. In the long run, it's vastly more efficient. But when you need to haul ass from the ground to orbit, that type of engine is going to be totally useless. Gravity is much stronger than the thrust of VASMIR. This new doodad seems to be aimed at launch vehicles, not long distance space travel.

Re:A superior engine

[spike hay]

Yeah. I know the VASIMR is worthless for launches. But I also think this ablative thing is worthless for launches. You would have to have a mega-billion dollar laser to launch it. That would eliminate any cost savings over say, a spaceplane.

Re:A superior engine

[Omnibus]

Don't forget - we have several multi-billion dollar space shuttles, that cost well over a hundred million per mission. Over time a 'mega-billion dollar' laser would pay for itself.

The question is how much would the lift vehicles and ablative materials cost. I think a single stage to orbit solution using less exotic technologies like ram/scramjets and rockets would be more intelligent for now.

what about ultrasonics ?

[dario_moreno]

the femtosecond pulse might induce an
ultrasonic wave of roughly the same frequency,
which bounces off the other side
of the slab...did they try varying
the lead thickness ?

the timescales would be coherent with that.