Applications and Surprises of Laser Physics
Ah, lasers. Can we say enough about them? They offer so much entertainment and are beautiful to behold. Therefore, for those who just cannot satisfy their laser cravings, read on for some even cooler applications of lasers as well as derivatives of them. Who knows, you may develop a new craze yet!
Lasers stand for Light Amplification by Stimulated Emission of Radiation, so it should come as no surprise that Saser is Sound Amplification by Stimulated Emission of Radiation. But how would that work? Lasers use quantum mechanics by encouraging materials to emit photons rather than absorb in order to get a single frequency of light out. So how we do the same thing but for sound? You get creative like Tony Kent and his team at the University of Nottingham. They created a “thin, layered lattice mode of 2 semiconductors” with one of them being gallium arsenide and the other aluminum arsenide. Once some electricity is applied to the lattice, specific frequencies in the Terahertz range can be achieved but for only a few nanoseconds. Kerry Vahala and his group at Caltech created a different saser when they developed a thin, almost membrane-like piece of glass that can vibrate fast enough to produce frequencies in the Megahertz range. Sasers could have applications in detecting product defects (Rich).
Laser Jet Engine
Here we have a truly ridiculous application of a laser. In this system, a mass of deuterium and tritium (both isotopes of hydrogen) are fired upon by lasers which increase pressure until the isotopes fuse. Through this reaction a bunch of gas is produced and is channeled through a nozzle, creating thrust and therefore the propulsion needed to act like a jet engine. But a product of the fusion is high velocity neutrons. To ensure that these are dealt with and don't destroy our engine, an inner coating of material that can combine with the neutrons through fission is layered. This does generate heat but through a dissipation system this too can be dealt with, using the heat to generate electricity that powers the lasers. Ah, its so beautiful. Its also unlikely, because the isotopes and fissionable material would both be radioactive. Not so good to have it on a plane. But someday...(Anthony).
Would you believe that lasers have been proposed to help us get into space? Not through intimidation of space-faring companies, but by means of propulsion. Trust me, when it costs over $10,000 per pound to launch a rocket, you would look into anything to elevate that. Franklin Mead Jr. of the Air Force Research Lab and Eric Davis of the Institute for Advanced Studies at Austin Texas have devised a way to launch a low-mass craft by having the bottom of it exposed to a high-power laser. The material on the bottom would become plasma as it burned away and create thrust, thus eliminating the need to carry fuel aboard. According to preliminary calculations by them, the cost per pound would be reduced to $1,400. A prototype by Leik Myralo and his team at the Reusselaer Polytechnic Institute was able to go 233 feet with a potential for 30 times that amount if the laser was made more powerful and wider. Now, to achieve low-Earth-orbit you would need a Megawatt laser, over 10 times the strength of current ones so this idea has plenty of growth to go (Zautia).
Plasma and Lasers
Now this idea for space propulsion relied on plasma to generate thrust. But recently plasma and lasers had another link besides this concept. You see, because lasers are just electromagnetic waves that move up and down, or oscillate. And given a high enough number of oscillations it will disturb a material to having its electrons striped and forming ions a.k.a. plasma . The electrons themselves are excited by the laser and therefore as they jump levels they emit and absorb light. And electrons not attached to an atom tend to reflect because of their inability to jump levels. This is why metals are so shiny, for their electrons are not so easily swayed to jump levels. But if you have a powerful laser, then the leading edge of the material you are vaporizing develops many free electrons and therefore reflects the laser back, preventing any more of the material from being vaporized! What to do, especially for our potential rockets? (Lee “Hairy”).
Scientists at Colorado State University and Heinrich-Heine University looked at ways to help a compound along in this process. They created a version of nickel (normally quite dense) which had a width of 55 nanometers and a length of 5 micrometers. Each of these “hairs” was 130 nanometers apart. Now, you got a nickel compound which is 12 percent the density it used to be. And according to the number crunching the electrons generated by a high-power laser will stay close to the wires, allowing the laser to continue unimpeded on its destructive path. Yes, the free electrons are still reflecting but they are not hindering the process enough to stop the laser. Similar setups with gold have yielded comparable results to the nickel. And on top of that this setup generates 50 times the X-rays which would have been emitted with the solid material and with shorter wavelengths, a huge boost in X-ray imaging (for the smaller the wavelength, the better the resolution can be) (Ibid).
Lasers in Outer Space
Alright science-fiction fans, we talked about using lasers to boost rockets. Now comes something you have been dreaming about…sort of. Remember from high school physics when you played with lenses? You shined light into it and because of the molecular structure of the glass the light would be bent and leave at a different angle than it entered. But really, that is an idealized version of the truth. Light is the most focused at its center but it becomes diffuse the further along the radius of the beam you go. And because the light is being bent it is having a force exerted on it and it to the material. So what if you had a small enough glass object so that the beam of light was wider than the glass? Depending on where you shine the light on the glass it will experience a varying force due to momentum changes. This is because the light particles impact the glass particles, transferring momentum in the process. Through this transference, the glass object will move towards the greatest intensity of light so that the forces balance out. We call this wonderful process optical trapping (Lee “Giant”).
So where does outer space come into this picture? Well, imagine a lot of glass balls with a huge laser. They would all want to occupy the same space but can’t so they do their best and flatten out. Through electrostatics (how charges work on non-moving objects), the glass beads develop an attraction to one another and so will try to come back together if pulled apart. Now you got a huge reflecting material floating around in space! While it could not be the telescope itself, it would act like a giant mirror (Ibid).
Small-scale tests by scientists seem to back this up. They used “polystyrene beads in water” along with a laser to show how they would react. Sure enough, the beads congregated in a flat surface along one of the sides of the container. Even though other geometries should be possible besides 2D, none were attempted. They then used it as a mirror and compared the results to using no mirror. While the image was not the best work out there, it did indeed prove to be an aid (Ibid).
Tiny, Tiny Laser
Now that we have fulfilled everyone’s giant laser dreams, what about thinking small? If you can believe it, scientists at Princeton led by Jason Petta have built the smallest laser ever – and likely will be! Smaller than a grain of rice and running on “one-billionth of the electric current needed to power a hair dryer,” the maser (microwave laser) is a step in the direction of a quantum computer. They created nano-sized wires to connect quantum dots together. Those are artificial molecules which contain semiconductors, in this case indium arsenide. The quantum dots are just 6 millimeters apart and are inside a miniature container made of niobium (a superconductor) and mirrors. Once current flows through the wire, single electrons are excited to higher levels, emitting light at a microwave wavelength which then reflects off the mirrors and narrow down into a nice beam. Through this single electron mechanism, scientists may be closer to transferring qubits, or quantum data (Cooper-White).
So, hopefully this satisfies the appetite for lasers. But of course if you want more, leave a comment and I can find more to post on. After all, this is lasers we are talking about.
Anthony, Sebastian. "Boeing Patents Laser-Powered Fusion-Fission Jet Engine (That's Truly Impossible." arstechnica.com. Conte Nast., 12 Jul. 2015. Web. 30 Jan. 2016.
Cooper-White. “Scientists Create Laser No Bigger Than A Single Grain.” HuffingtonPost.com. Huffington Post, 15 Jan. 2015. Web. 26 Aug. 2015.
Lee, Chris. “Giant Laser Could Arrange Particles into Enormous Space Telescope.” ars technica. Conte Nast., 19 Jan. 2014. Web. 26 Aug. 2015.
---. “Hairy Metal Laser Show Produces Bright X-Rays.” ars technica. Conte Nast., 19 Nov. 2013. Web. 25 Aug. 2015.
Rich, Laurie. “Lasers Make Some Noise.” Discover Jun. 2010. Print.
Zautia, Nick. “Launching on a Beam of Light.” Discover Jul./Aug. 2010: 21. Print.
© 2015 Leonard Kelley
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