Lasers: Guns and Forcefields

How do lasers work (including an attempt to explain an Einstein theory using the word “tickle”)? What’s the latest on laser weapons? Is it possible to construct a laser forcefield that lets some things pass through but not others (and if they try the get blown up)? In which I continue to build the setting of my novel.

First, what is a laser, exactly? A very simple and elegant way to put it is:

Lasers organize particles of light into coherent beams

– Michiko Kako on The Science Channel

The word itself came from an acronym that stands for:

light amplification by stimulated emission of radiation

Now, what does that mean?

Stimulated Emission of Radiation: Tickle an Atom

It all started with Albert Einstein, who in 1917 introduced the world to the idea of stimulated emission (Laserfest has a nice overview of the history of lasers).* Matthew Weschler explains this concept as part of his piece on lasers at How Stuff Works. However, it’s still a bit difficult to follow, especially if someone doesn’t have (or remember) a physics or chemistry background. So I will attempt to explain using a rough exercise in imagination.

First, imagine this in slow motion:

You have a guy named Atom.* You tickle him. He guffaws: his belly rises, but because that’s tiring and unstable, his belly falls back to its resting state. In doing this movement, Atom emits a loud “Ha!”

Now, the connection:

First you excite, or stimulate, an atom by applying intense flashes of light, electrical discharges or heat (tickle Atom). An electron moves to a higher, excited, state of energy (belly rises). This excited state is unstable, so the electron moves back to a lower-energy state (belly falls). In doing this movement, the atom emits a photon (the “Ha!”), which is light. And that’s stimulated emission of radiation in an atom. Light is both particles and a wave (it’s complicated). Radiation is the transmission, very simply, of electromagnetic waves (which are not necessarily toxic).

Of course, it’s not an exact analogy, but it illustrates (I hope) the concept for the purpose of explaining lasers. But that’s only half of the story.

Light Amplification: Mirror, Mirror

The next half is straightforward and doesn’t need an analogy.

A tube holds many of these excited atoms. A pair of mirrors cap both ends of the tube. One mirror is full (like a household mirror) and one is partial (it lets some light through, but not others). Light (photons from the excited atoms) bounces around the tube. Any light that hits the full mirror gets bounced towards the partial mirror. Only one type of light can leave through the partial mirror. And that’s your laser.

In sum, you contain atoms of some chemical element in a tube capped by two mirrors, and light comes out of one end in a “laser beam”. These beams can be as harmless as a presentation pointer (unless used directly into eyeballs) or as harmful as weapons of destruction and murder.


Offense: Laser Guns

Laser weapons are closer to now than we think. Erik Schechter and Dave Majumdar talk about Israel’s Iron Beam and recommend that the US build a laser-cannon in this Wall Street Journal article. Here’s a video of the Iron Beam in action (at least in CGI):

It can shoot up to 100kW of energy at an incoming projectile. Schechter and Majumdar reckon that the US military could develop a 300-kW laser cannon within the next ten years. I’m finding it difficult to find a good comparison to put it into perspective for Your Average Joelle (household appliances and light bulbs run on energy in the order of watts or hundreds thereof, not typically in the hundreds of kW).

I need a handgun, though (at least as far as First Draft is concerned). I can’t find any information on how any of the above weapons work, exactly (for obvious reasons) and hence can’t extrapolate into the world of personal firearms.

So I will use my imagination and some sense. Given the basic mechanics of a laser, I imagine I’d need to have:

  • some energy source with which to excite an element
  • encased in some sort of shielding material
  • with some sort of barrel (to which the partial mirror is affixed at the far end)

to arrive at a personal firearm (or at least a vaporizing laser that is smaller than the Iron Beam). A small cannon, even.

The closest I can get to ultra-mobile laser damage is this cool portable laser cutter – the subtractive counterpart to the 3D printer’s additive approach. It is, by the way, a KickStarter project cutely called “Origami” that I wouldn’t mind funding. (Not for destruction but for construction, and they have put special emphasis on safety.) Maybe one day, someone from the team will let me pick his or her brain (figuratively).

Now I know that the weaponry is possible. My next step is to determine the type of high-energy laser, element(s) to excite and appropriate shielding material. For First Draft, I’m using gamma rays, an unidentified isotope, and lead. But all of that is for another post. On to the defensive play.

Defense: Force Fields

At the time of writing First Draft, my notion had been to use plasma – somehow – in a forcefield. I did some cursory research in the midst of last year’s NaNoWriMo and found temporary plasma shields used for tank defense in the works. There are no links here because I can’t seem to find those articles and videos now. I had a deeper look at other sources, though, and plasma doesn’t seem to be the way forward for what I need.***

Last week, in a productive conversation over coffee and water, my Techno Advisor suggested a laser fed into a magnetic field similar to the Earth’s (an axial magnetic field), which is naturally curved. So lasers might just be the ticket. Dr. Michio Kaku, author of a book about the physics of celebrated sci fi (The Physics of the Impossible), has described how to make a laser force field.

You take trillions of Watts and power up a laser lattice – basically, a doily of lasers, Entrapment-style – using dozens of mirrors and thousands of lasers. The laser beams would heat any incoming projectiles to thousands of degrees Fahrenheit and vaporize them instantly. Add beneath this laser lattice a doily of carbon nanotube fibers coated with photochromatic material (material that can change the color of light) to counter any laser beams with which your ship might be attacked, and badabing badaboom – you’re safe.

But Dr. Kaku is talking about a spaceship – I need a forcefield on Earth (not in a vacuum, though he didn’t get very specific on this). And the ship would have to peel back its nanotube cage to be able to fire out. I need my forcefield to hold its structural integrity at all times.

On a January 2012 thread in a science and philosophy forum, user Percarus responds to the question of lasers acting as force fields that repel matter and gases:

the intention in constructing a laser field would have to involve ‘tractor beam’ concepts which would necessitate gravity impulse beams to control gases – through pressure differences and heat, as provided by a laser.

That was in 2012. Today, physicists at Australia National University created a reversible (can attract or repel) laser tractor beams, which Michelle Starr explains beautifully at cnet. Sigh. Again, not fit for my force field purpose (though, maybe, for my optogenetics purpose – later on that). I need my forcefield to blow things into smithereens upon entry, not be denied entry altogether.

My last, small yet sliver-of-light hope comes from the seventies. In a 1979 paper, Kwan and Dawson seem to find that in theory, a strong electromagnetic field can guide a free electron laser. I can only read the abstract, which is sometimes Greek to me and everyone else (there’s omega and tau), and I’d have to pay to get the full paper. Also, the magnetic field of which they speak is helical (coiled), not axial (like the Earth’s) in shape. But never mind. I don’t even know if it makes a difference.

So I’ll leave it at that. Possible and just about right is good enough for me on this one. I’ll go look for experts.

It’s My ForceField, I’ll Make Stuff Up If I Want To

After this exhausting trawl through free and freely available mind-bending material and multiple dead ends, it is time for me to stop. As my Venerable Techno Adviser says, roughly translated through time and language,

Not every element in sci fi need have roots in science today – it just has to be internally consistent in the book.

It is fiction, after all. And when writing sci-fi, you need to know what science you need for the story and focus on how your fictional science affects your characters.****

So I have the formula for my forcefields:

electromagnetic field + laser + FUTURE MAGIC SAUCE = a dome

that lets some things in and out freely, but not others, fries those other things that try to pass through to bits, kind of like this:

and repels rain and negates the force of oncoming storms, kind of like a far more powerful version of this:*****

To make this all happen, I will look for some MAGIC FUTURE SAUCE: a bit of quantum physics, a lot of imagination, and a dash of suspension of belief. What’s important for First Draft and beyond is that the special forcefield and laser gun technology have profound socio-political consequences – both intended and unintended in SFT.

Thank you lasers, Mr. Einstein and Dr. Evil. I sure hope whoevermightbewatching doesn’t have too close a look at my Google search history today.

Now. Off to find some physicists…

* I know a guy named Atom – an emcee with an incredible voice that sounds like honey. I tried to get him to host my wedding, but Atom was, unfortunately, all booked up.

** The root of Einstein’s idea echoes further back into history, and he must have been influenced by previous works. A big one is Titus Lucretius’s “De Rerum Natura” (“On the Nature of Things”) available for free online. I read it curled up awkwardly in a foldout armchair in Dad’s freezing hospital room last year and it blew my mind. Stephen Greenblatt made the 2000-year-old poem famous relatively recently with his novel, The Swerve, discussed in this Harvard Magazine article. I bring this piece up because in the very first comment, I stumbled upon a nugget of gold. But even better, though I’m pretty sure it’s a denser read: Lüthy, Murdoch, & Newman’s Late Medieval and Early Modern Corpuscular Matter Theories (Brill, 2001).

*** This is TROPHY, a tank defense system. If you watch the whole video and the Fox News report, you’ll probably agree with me and DrDoom514, who says, “The anti rpg Trophy is just a shotgun with radar even [though] news anchors [like Fox’s Mike] called it a force field.” Drakkith seconded that: “They call it that because it’s a creative way of describing it to grab peoples attention. It is in no way similar to a force field except in the vaguest sense possible.”

I browsed that entire thread on whether Star Trek-style plasma shields were physically possible and I’m convinced by its bottom line: “Short version: Plasma shields are fiction. They don’t work in real life.” (Neither do laser ones at the moment, but I think that’s closer to my sci fi than plasma.)

There was, however, a good piece by David Hambling from 2007 with interesting elements on plasma aerodynamics, but that doesn’t work for my purposes either because they repel, they don’t vaporize (although because of repellent forces they can blow things up). I’ll leave plasma for my energy and fusion post.

**** The air umbrella idea’s not quite that new. A French student won a design competition with the concept last year.

***** The concept of “edge of ideas” or “carrying extrapolation into daily life” in the genre (a compilation of sci fi criticism lexicon here). Thanks to author Massimo Marino for his post pointing me this way!

****** I discovered another very, very cool recipe for a forcefield (but again, not suited for my story) using a phase conjugate mirror, pumping beams and a brilliant explanation using pool table bumpers. Unfortunately, the much-celebrated link to a superb explanation of phase conjugation and details on the pumping beams is broken.

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