Lasers

__Laser and Quantum Mechanics__

__Table of Contents__

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= = =Quantum Mechanics: = Quantum mechanics are used to describe how particles that are extremely small, such as atoms or electrons, behave. The beginning of the study of quantum mechanics had to do with the behavior of electrons, and light. According to physics, electrons can behave both as a wave, and as a particle. The pre-1900's view of electrons was that they orbited around the nucleus in a consistent path, at different energy levels. However, Max Plank, a German scientist, proved that light could only exist at certain energy levels. The "quantum" part of quantum mechanics comes from this theory, as quantum essentially means "can only be at certain numerical levels and not every single one".

When electrons behave as waves, they are acting as standing waves. A standing wave is one that has a constant position, and nodes. At the nodes, there is a 0% chance of finding an electron. Therefore, electrons can be found only in certain spots around the nucleus. These spots are called orbitals. The problem with this is that electrons would have to move through a node to get to a different orbital. This would be impossible if electrons were particles, therefore they must act as waves. Since they act as waves, electrons could be in many places at once, as a wave would be.

Electrons can also behave as particles though. If light was shined at a recorder, and it put a dot whenever an electron hit, there would be interferance patterns, similar to waves, but there would be separate dots where electrons hit, showing that electrons do behave as particles. These particles are called photons, and can only exist at certain energy levels.

Quantum mechanics and lasers are related. Later, it will go more in depth into how a laser works, but the basics of the laser, stimulated emission, is quantum related. To get the laser to work, the electron must be excited, and moved to a higher energy state. Then, because of the Aufbau Principle, which states that electrons will always move to a lower energy position, if possible, the electron wants to jump back to its ground state. When it does, energy is lost in the form of light, or a photon. This will be covered more in depth later on, but that is the quantum component to a laser. = = = = =How Lasers Work: = A laser is a little device that controls the way energized atoms release their photons. The word "Laser" means **L**ight **A**mplification by **S**timulated **E**mission of **R**adiation. Lasers are made using atoms. Atoms are made up of protons, which have a electrical charge of +1, neutrons, which have a electrical charge of 0, and electrons, which have a electrical charge of -1. In an atom the center is composed of protons and neutrons, which make the nucleus. Atoms are always in motion and everything is made up of the​m. Atoms stay at their ground-state energy level, unless they are excited by something. Atoms can be excited by light, heat, or electricity, when atoms are excited they can gain energy and move from lower energy levels to higher energy levels.

When a electron goes up in an energy level, it always wants to return to the ground-state energy level, and when this happens, a photon is emitted (A photon is a particle of light that is always moving). This emission is called [|spontaneous emission]. The energy released can be calculated by taking the difference of the two energy levels (. While the electron is releasing energy, stimulated emission will occur where a photon will hit the electron, and an identical photon will be released that is the same wavelength, frequency, and color . The second photon moves in the same direction as the first. For a laser to begin to work, more excited atoms must be present in the laser than atoms in the ground state. So to excite the atoms, one must use a light, heat, or electricity. Once there are more excited electrons than ground state, which is called [|population inversion]. When the electrons get excited, two things can happen. One is stimulated emission as stated above, and the other is [|absorption], which is when a photon passes an atom at ground state, the photon causes the atom to become excited.

There are three main components of a Laser, which are the [|pump source], the [|gain medium], and the [|optical resonator]. The pump source is what excites the atoms in the laser, this can be a light, chemical reactions, or even other lasers. The pump source normally depends on the gain medium. The gain medium is the source of the atoms in the laser. Gain mediums can be liquids like methanol or ethanol and then chemicals are added like fluorescein. Depending on way the chemicals line up, it creates different wavelengths. Gases can also be used as gain mediums along with solids like glass, and even Jell-o. The last component of laser is the optical resonator, which is normally just two mirrors placed on each end of the gain medium. One of the mirrors does not allow any of the photons out and the other is permeable. About half of the electrons are let out, in the form of the directed laser beam, and about half are bounced back. As more and more photons are created more leave the laser as light. This light is different from normal light, because it is all from stimulated emission, so it is all the same wavelength, frequency, and color. The light is also focused in one direction, and not a range, such as sunlight, making the laser in a straight line. = = =History of Lasers: = Albert Einstein first came up with the idea of stimulated emission in 1917 which made making Lasers possible. The first Laser was based off a [|maser] (**M**icrowave **A**mplification by **S**timulated **E**mission of **R**adiation) which was created by Charles Townes and Arthur Maser in 1954. Charles Townes and Arthur Maser published papers about their work in 1954. They continued to work on developing the maser throughout the 1960s and 70s. In 1958 the concept of the maser was analyzed by Schawlow, Townes, and Lebedev Institute. They realized that they could create a laser by utilizing the Maser in the optical region. This in turn created a laser. That same year the concept of laser spectroscopy was developed by Schawlow and his workers a Stamford. Another scientist named Bloembergen further investigated laser spectroscopy and discovered nonlinear optics which is a unique type of laser spectroscopy. Nonlinear optics allows two or more lasers beams to be joined together. The lasers then chemically react with each other. Finally in 1960 the operating laser the Ruby Laser was made. It created red light. In 1963 a special property of modern day lasers was created. The concept of the semiconductor heterostructure was investigated by both Alferov and Kroemer. This property is used in the most popular lasers of today; semiconductor lasers.

=Applications in Real Life: = Lasers have many uses in the modern world. Uses of lasers range from military uses to eye surgery. The of Lasik eye surgery was not tested until the 1970s by the Russians, but the Chinese had been playing with the idea of using lasers in eye surgery since the 1930s. After the Russians experimented with the use of lasers in eye surgery, American scientists learned the procedure and began researching how it could be performed safely. By 1987 the use of lasers in eye surgery was brought to practice on the public.

Today, millions of people have drastically improved their vision through the use of Lasik eye surgery; but how does it work? [|Lasik] stands for **L** aser **A** ssisted **I** n **S** itu **K** eratomileusis. In this case, the Lasik eye surgery utilizes a excimer laser which alters the cornea. Laser keratome cuts a flap in the cornea which is pulled back. The next layer of the eye is the stroma; this is where the laser comes into play again. The laser sends shocks into the stroma and this replaces the flap of the cornea that was pulled up. Aside from lasers being used in eye surgery, the military has been using lasers to neutralize unexploded ordnances. The military has been researching and working with lasers since the 1960s. The military had focused on chemical lasers one of which had the ability to incinerate helicopters and vehicles. The laser named [|MIRACL] is deemed as being as strong as some power plants. One laser, the Mobile Tactical High Energy Laser has been utilized on fighting jets to track down and destroy artillery projects during flight. = =

One of the coolest uses of lasers in society is by NASA. NASA has been using a laser to track the [|Lunar Reconnaissance Orbiter]. The laser is fired through over 250,000 miles of space from a telescope. The telescope sends out laser pulses that upon getting to the Lunar Reconnaissance Orbiter make the Lunar Reconnaissance Orbiter send microwaves from an electrode in a vacuum tube back to the earth giving information on its whereabouts .  Along with laser eye surgery, there is also other surgery's that use lasers rather than scalpels. This type of [|cosmetic laser surgery] does not cause bleeding because there is no penetration into the skin. This surgery consists of removal of acne scars, stretch marks, age spots, sun damage, and even creases around the mouth and nose. Lasers can cut through tissue without affecting other tissue that is near. The lasers can help produce Collagen which is what gives skin its texture (the new skin will not have wrinkles and marks like the skin before it did).

=Cool Stuff: =

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This is Stephan Hobly's laser harp. Instead of strings, it uses lasers. By moving his hand through the beam, or disrupting it, he can make music. A sensor detects the disruption, and sends a message to software on a computer than plays a harp sound specific to each beam. In this picture, the lasers are more visible because of mist in the room. The video shows the laser harp in action.

Lasers are also commonly used at techno and trance music performances, as they can create amazing effects with lighting. They are often used as background lighting as well. Laser light shows can be very cool to look at.



Hanyoung Lee, a production designer has created a virtual barrier that will indicate pedestrian crossing zones. The model utilizes red lasers that indicate pedestrian zones in the street to bring more awareness to vehicles. Hanyoung Lee named the model the [|Virtual Wall].

NASA created the first [|Laser-powered (remote control) aircraft]. Before this aircraft, others were only made from battery, solar, gas, and sometimes human power. The power of this aircraft is a laser beam and could keep the plane in the air until the beam is interrupted. The aircraft has a 5 foot wingspan and only weighs 11 ounces! To keep the plane in flight, the plane is made of photovoltaic cells, which convert the energy from the laser wavelength to electrical power to run a small motor with a propeller.



The PhaSRis a non-lethal laser weapon for the military. The name stands for Personal Halting and Stimulating Response, and it has been around since the end of 2005. The laser gun works by the shooter aiming at the targets eyes, and the laser, which is two wavelengths, not one, temporarily blind them. Permanent blindness is illegal, so it is only temporary, but the weapon would be great for riot control, or situations where there could be friendly fire.



Recently Boeing Corporation made a laser named the [|Advanced Tactical Laser] that will be available for military use. The laser is immensely powerful and extremely precise. Precision was the main goal in mounting the laser in military planes. While a missile would create damage to not only its target and the target's surroundings, the Advanced Tactical Laser accurately only hits its target. The laser can hit targets five miles away and unlike a missile; it can't be shot down. The laser has the ability to incinerate tanks, radio towers, and moving vehicles...all from the belly of military plane. Other versions of the laser will also be made to mount on smaller vehicles than Boeing's C-130 plane.

​ =__Works Cited:__ =

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