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In 1953, Charles Townes, along with his colleagues, produced the first coherent radiation in the form of microwaves. It was christened "maser," which stands for Microwave Amplification through Simulated Emission of Radiation.
These results were eventually extended to visible light, giving birth to the laser.
When it comes to lasers, you begin with a special medium that will transmit the laser beam. This could be a special gas, crystal or diode. Energy is pumped into this medium from the outside, in the form of electricity, radio, light or a chemical reaction. This sudden influx of energy pumps up the atoms of the medium so the electrons absorb the energy and then jumps into the outer electron shells.
In this excited and pumped up state, the medium is unstable. A light beam sent through this medium will have its photons hit each atom, causing it to suddenly decay to a lower state, releasing more photons in the process. This, in turn, causes even more electrons to release photons. This creates a cascade of collapsing atoms. Trillions upon trillions of photons are released into the beam. For certain substances, all of these photons are vibrating in unison, or, they are coherent.
Only certain materials have the ability to "lase." In other words, it is only in special materials, that when a photon hits a pumped up atom, a photon will be emitted that is coherent with the original photon. It is a consequence of this coherence, these photons vibrating in unison, that we observe a pencil-thin laser beam.
A simple gas laser consists of a tube of helium and neon gas. When electricity is sent through the tube, the atoms are energized. If the energy is suddenly released all at once, a beam of coherent light is produced. The beam is amplified using two mirrors:
1) The first mirror is completely opaque.
2) The other allows a tiny amount of light to escape on each pass.
This produces a beam that shoots out at one end!
Types of lasers
Gas lasers: This includes helium-neon lasers, which are very common, and create the familiar red beam. Gas lasers are energized by radio waves or electricity. Helium-neon lasers are quite weak. However, carbon dioxide gas lasers can be used for blasting, cutting and welding in heavy industry. They can create beams of enormous power that are totally invisible.
Chemical lasers: These lasers are more powerful and are energized by a chemical reaction, such as a burning jet of ethylene and nitrogen trifluoride. These lasers are powerful enough to be used in military applications. Chemical lasers are used in the U. S. military's airborne and ground lasers. These can produce millions of watts of power. They are designed to shoot down short-range missiles in midflight.
Excimer lasers: These lasers are also powered by chemical reactions. They often involve an inert gas, like argon, krypton or xenon, along with fluorine or chlorine. They produce ultraviolet light and can be used to etch tiny transistors onto chips in the semiconductor industry. They can also be used for delicate Lasik eye surgery.
Solid-state lasers: The first working laser ever made consisted of a chromium-sapphire ruby crystal. There are a large variety of crystals that will support a laser beam. This would be in conjunction with yttrium, holmium, thulium and other chemicals. They can produce high energy and ultra short pulses of laser light.
Semiconductor lasers: Diodes (which are commonly used in the semiconductor industry) can produce the intense beams used in industrial cutting and welding. These are also the lasers found in checkout stands in grocery stores. They read the bar codes of the grocery items.
Dye lasers: These lasers use organic dyes as their medium. These ultra short pulses of light are exceptionally useful. They often only last trillionths of a second.
Ray guns
We have an enormous variety of commercial lasers. We also have powerful military lasers. So why don't we have ray guns available for combat? Well, the short answer is that we lack a portable power pack. What would be required is a power pack that contains the energy of a huge electrical power station, yet still fits in the palm of your hand.
There is a second problem with ray guns: the stability of the lasing material. There is no theoretical limit to the energy one can concentrate on a laser. The problem is that the lasing material in a handheld ray gun would not be stable. To create an extremely powerful laser, one might need the power of an explosion. In that scenario, the stability of the lasing material is not that big of an issue, as it would be used only once.
Indeed, building a handheld ray gun is not possible by today's technology because of these two limitations. Ray guns are possible, however, only if they are connected by a cable to a power supply, Perhaps with nanotechnology, we might be able to create miniature batteries, that can store or generate enough energy to create the intense bursts of energy required of a handheld ray gun device.
Light sabers
Light sabers would suffer from a similar problem. Critics have raised these initial objections:
1) It is impossible to solidify light. Light always travels at the speed of light. It cannot be made solid.
2) Light beams do not terminate in mid-air, however, they keep going on forever. A real light saber would stretch into the sky.
Actually, there is a way to construct a kind of a light saber using plasmas or superhot ionized gas. Plasmas can be made hot enough to be to glow in the dark and cut through steel. This plasma light saber would consist of a thin, hollow rod, that slides out of the handle, like a telescope. Inside the tube, hot plasmas would be released, that would escape through small holes placed regularly throughout the rod. As this plasma flows out of the handle and up the rod, and through the holes, it would create a long glowing tube of superhot gas. This would be sufficient to melt steel. This device is sometimes referred to as a plasma torch.
So, it is possible to create a high energy device that resembles a light saber, however, much like the ray gun, would require a high energy portable power pack. You would either need long cables connecting your light saber to a power supply, or, you would have to create, via nanotechnology, a tiny power supply that could deliver huge amounts of power.
Death star
To build a Death Star laser cannon, that could destroy an entire planet, one would have to create the most powerful laser ever conceived. Some of the most powerful lasers on Earth are being used to unleash temperatures found only in the center of stars. Fusion reactors, may one day harness the power of the stars on Earth.
Fusion machines attempt to mimic what happens in outer space when a star first forms. A star begins as a huge formless ball of hydrogen gas. Gravity compresses that gas, and thereby heats it up until temperatures reach astronomical levels. Deep inside a star's core, temperatures can sore anywhere between 50 million and 100 million degrees centigrade. This is hot enough to cause hydrogen nuclei to slam into each other, creating helium nuclei and a burst of energy. This fusion of hydrogen into helium is the energy source of stars. Here, a small amount of mass is converted into the explosive energy of a star, via Albert Einstein's famous equation: E=mc^2.
There are two ways scientists are attempting to harness fusion on the Earth.
The first method is known as "inertial confinement." It uses the most powerful lasers on Earth to create a piece of the Sun in the lab. To duplicate the temperatures found in the stars, a neodymium glass solid-state laser is used. These laser systems are the size of a large factory. They contain a battery of lasers that shoot a series of parallel laser beams down a long tunnel. These high powered laser beams strike a series of small mirrors arranged around a sphere. The mirrors carefully focus the laser beams uniformly onto a tiny, hydrogen rich pellet, which is made of substances such as lithium deuteride, the active ingredient in the hydrogen bomb. This pellet is usually the size of a pinhead and weighs about 10 milligrams.
A blast of laser light incinerates the pellet, causing the surface to vaporize and compress the pellet. As the pellet collapses, a shockwave is created that reaches the core of the pellet. This sends it to temperatures soaring to millions of degrees. This is sufficient to fuse hydrogen nuclei into helium. These astronomical temperatures and pressures are able to satisfy Lawson's criterion, the same criterion that is satisfied in hydrogen bombs and in the core of stars. Lawson's criterion states that a specific range of temperatures, density, and time of confinement must be attained in order to unleash the fusion process in a hydrogen bomb, star or in a fusion reactor.
In the inertial confinement process, vast amounts of energy are released, including neutrons. The lithium deuteride can hit temperatures of 100 million degrees centigrade and a density 20 times that of lead. A burst of neutrons are emitted from the pellet. The neutrons then strike a spherical blanket of material surrounding the chamber. The blanket is heated up. The heated blanket boils water and the steam produced can be used to power a turbine and produce electricity.
The problem, however, is being able to focus such intense power evenly onto a tiny spherical pellet.
Shiva laser
Nova laser
The Shiva laser was the first serious attempt at creating laser fusion. This was a 20-beam laser system built at the Lawrence Livermore National Laboratory in California. It began operation in 1978. Shiva is the Hindu goddess with multiple arms, which the laser machine design mimics. Sadly, the performance of the Shiva system was disappointing. However, it was sufficient to prove that laser fusion could technically work.
The Shiva laser system was replaced by the Nova laser system, which had 10 times the energy. The Nova laser also failed to achieve proper ignition of the pellets. Nonetheless, it paved the way for current research in the NIF or National Ignition Facility, which began construction in 1997 at the LLNL.
National Ignition Facility
The NIF became operational in March 2009. It is a monstrous machine, consisting of a battery of 192 laser beams. This packs an enormous output of 700 trillion watts of power. This is the output of about 700,000 large nuclear power plants concentrated in a single burst of energy. It is a state of the art laser system, designed to achieve full ignition of the hydrogen-rich pellets.
Critics have also pointed out the obvious military use. This is since it can be used to simulate the detonation of a hydrogen bomb, and perhaps make possible the creation of a new nuclear weapon: the pure fusion bomb. This would not require a uranium or plutonium atomic bomb to kick-start the fusion process.
There is also "magnetic confinement." This is a process where a hot plasma of hydrogen gas is contained within a magnetic field. This method could actually provide the prototype for the first commercial fusion reactors.
The most advance fusion project of this type is the ITER or International Thermonuclear Experimental Reactor. In 2006, a coalition of nations, including the European Union, the United States, China, Japan, Korea, Russia and India, decided to build the ITER in Southern France. It is designed to heat hydrogen gas to 100 million degrees centigrade. It could become the first fusion reactor in history to generate more energy than it consumes. It is designed to generate 500 megawatts of power for 500 seconds. The current record is 16 megawatts of power for 1 second. As Of 31 October 2020, the ITER is 71.1% towards completion to first plasma. At a cost of $12 billion, the ITER is the third most expensive scientific project in history, behind the Manhattan Project and the International Space Station.
The ITER looks like a large donut, with hydrogen gas circulating inside, and huge coils of wire winding around the surface. The coils are cooled down until they become superconducting. Then a huge amount of electrical energy is pumped into them. This creates a magnetic field that confines the plasma inside the donut. When an electrical current is fed inside the doughnut, the gas is heated to stellar temperatures.
ITER is exciting to scientists because it is potentially a cheap energy source. The fuel supply for fusion reactors is ordinary seawater, which is rich in hydrogen.
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