What are Lasers?

Understanding lasers necessitates a grasp of atoms and their energy states. Atoms comprise a nucleus surrounded by an electron cloud. This cloud is populated by electrons held to the atom by electromagnetic forces, and these electrons exist at various energy levels. When an electron is in its lowest energy state, it is considered to be in the ground state. When an atom is energized by heat, light, or electricity, electrons in the ground state can be excited to higher energy levels.

However, these higher energy states are not the most stable for electrons. Since energy cannot vanish, electrons must release energy to transition back to lower levels. This energy is emitted in the form of photons—massless light particles. Each photon carries an energy equivalent to what the respective electron lost when moving down to a lower energy level. Lasers operate by stimulating atoms to emit photons through this process. The term "laser" is actually an acronym for "light amplification by stimulated emission of radiation."

All laser systems contain a lasing medium, which is a collection of atoms that generate laser light. This medium is subjected to intense flashes of light or electrical currents to excite its electrons. The resulting excited-state atoms eventually release photons, collectively forming a beam of laser light.

Though incandescent and fluorescent light sources also produce light through atomic photon emissions, their outputs differ significantly because the atoms radiate energy randomly. Each atom emits photons in various directions and energies, leading to diffuse white light. In contrast, laser photons are emitted uniformly in one direction, possessing the same energy and wavelength, which results in a concentrated beam of light. Laser light is also coherent; the electromagnetic waves align perfectly, a result of stimulated emission.

Stimulated emission occurs when a photon emitted from one electron encounters another electron in the same excited state. This interaction causes the second electron to return to its ground state, releasing a photon identical in energy, wavelength, and direction to the first. In laser systems, mirrors are placed at both ends of the lasing medium, reflecting emitted photons back and forth among the excited-state atoms to maximize stimulated emission. One mirror is half-silvered, allowing some light to escape as a laser beam—characterized by its unidirectional, monochromatic, coherent light.

Now that we've explored the fundamentals of lasers, let’s discuss why Aoyama’s sparkly blasts do not qualify as laser beams…

Aoyama’s Beams vs. Real Lasers

The first discrepancy with Aoyama's beams is their visibility. Laser light travels in a linear direction; hence, a typical laser pointer's beam is often invisible in open air unless aimed directly at an observer. While introducing particles like smoke or dust can enhance scattering, Aoyama's beams are visible from any angle regardless of lighting conditions. For a laser to scatter in this manner, it would need significant energy, and indeed, Aoyama's beams are highly energetic.

A more significant issue is the presence of twinkling lights within Aoyama's beams. In a true laser beam, one would not anticipate areas of varying brightness. All photons in a laser beam have uniform energy, and their electromagnetic waves are synchronized, avoiding destructive or constructive interference. Some degree of twinkling may occur when particulates pass through a laser beam and scatter light, but the lasers themselves do not exhibit inherent sparkles.

Additionally, Aoyama's beams exert force on their targets, generating recoil that pushes him backward. For these beams to impart force or momentum, they must transfer momentum to objects. While this is theoretically feasible with lasers, it is exceptionally challenging.

As previously mentioned, photons are massless. This fact initially seems to contradict Einstein’s mass-energy equivalence principle, which states that a system's rest mass is equal to its energy divided by the square of the speed of light. At first glance, it may appear that light should possess mass simply due to its energy. However, this equation only describes the mass of a system at rest. The comprehensive version of this formula incorporates momentum, which photons do possess. Thus, massless light can still carry energy. In fact, the absence of mass in photons means their energy can be calculated using their momentum.

In summary, while photons have momentum and can apply force to objects, generating significant force through light is impractical. For instance, a one-kilogram object moving at one meter per second has one newton-second of momentum, while a laser with equivalent momentum would require 299,792,458 joules of energy—an enormous amount.

Above all, the most significant distinction between Aoyama's beams and genuine lasers lies in speed. Light travels at an astonishing speed of 299,702,547.2 meters per second, which is over 99.97% of the maximum speed at which information can travel in our universe. This speed is far too rapid for any character to evade, even in a universe where individuals frequently react swiftly enough to dodge electrical arcs. Nonetheless, characters in My Hero Academia routinely evade Aoyama's beams. In the above clip, Bakugo clearly dodges Aoyama’s “laser” after it has been shot. This is the final nail in the coffin. There must be an explanation for Aoyama's beams that circumvents these issues while still involving lasers in some capacity. Fortunately, there is: laser-induced plasma.

Plasma: The Secret Behind Aoyama’s Quirk

Plasma serves as a viable alternative to laser light for the blue beams emitted by Aoyama's quirk. For those unfamiliar, plasma is a state of matter formed when a gas is heated or electrified to the point of ionization. Similar to a lasing medium, injecting energy into the gas's atoms excites its electrons. These electrons become so energized that they leave their atomic clouds entirely. Once liberated, they traverse the space between atomic nuclei until they bond with new atoms. This ongoing process of severing and reattaching electrons and atomic nuclei results in a chaotic mixture of swiftly moving charged particles. The recombination, in particular, produces light, as electrons release energy to re-enter atomic clouds in the form of photons.

If Aoyama's beams consist of plasma, this clarifies their observable characteristics. Plasmas emit photons in all directions, rendering them visible from every angle. They also possess mass, meaning that transferring momentum requires significantly less energy. Kinetic energy, or energy of motion, is represented by the formula KE=mv², while the momentum of a mass-bearing object is expressed as p=mv. Consequently, the correlation between kinetic energy (KE) and momentum (p) for a plasma with constant mass (m) is KE=pv, where v denotes velocity. This formula bears resemblance to the E=pc equation that relates light's momentum and energy. The key distinction is that mass-bearing objects can never exceed the speed of light (c). Therefore, plasmas can provide greater momentum per energy unit than light, making them more effective for transferring momentum to objects and to Aoyama himself. Moreover, plasmas can move slowly enough for characters in My Hero Academia to realistically dodge them.

While plasmas are indeed beneficial, they do not paint the entire picture. As mentioned earlier, I believe that lasers play a pivotal role in Aoyama's quirk, specifically in generating and propelling plasma.

How Lasers Create Plasma

The tiny 3D pixels, or voxels, illustrated above are made of plasma. These voxels are generated through the intersection of numerous lasers at specific points. While these voxels are quite hot, they can still be safely touched due to their brief existence. The laser pulses that create them last only for a femtosecond—1/1,000,000,000,000,000 of a second. This brevity prevents the plasma from transferring substantial thermal energy. However, similar technology can also produce longer laser pulses that extend the lifespan of the plasma. The longer the plasma remains active, the more heat it can impart.

Returning to the glittering sparkles observed in Aoyama's beams, I believe these represent plasma being generated at the intersections of intense laser beams. Each sparkle denotes the initial flash from thousands of laser pulses colliding to ionize the air at that location. Once these pulses conclude, the plasma cools and dissipates, contributing to the dimmer blue mass of the beam.

In addition to emitting photons, plasmas can absorb them. This absorption poses a challenge for Aoyama if he intends to send laser pulses through the existing plasma to generate additional plasma and enhance his beams. Fortunately, there are workarounds. Depending on the plasma's temperature and other characteristics, it may not absorb certain light wavelengths. Aoyama's laser beams might exploit one of these wavelengths. Alternatively, he could simply move the existing plasma away before creating new plasma, thus avoiding the need to send his ionizing lasers through it.

Regardless, any laser light that does penetrate the plasma and strike a target would be less intense than the light at points where plasma is generated. Consequently, they would inflict far less damage than the plasma itself. The same principle applies to any laser light scattered by the plasma or the gas from which it originates. This explains why characters in My Hero Academia are not immediately scorched by laser light when Aoyama's beams approach them.

This leads us to the method Aoyama employs to propel his plasma beams. Once again, lasers are involved…

How Lasers Push Plasma

The illustration above depicts a ring of plasma contained within its own magnetic field. The high density of charged particles in plasmas renders them exceptionally responsive to electromagnetic forces. Experimental fusion reactors employ magnetic fields to compress plasmas to the point of atomic fusion. These examples underscore two essential truths: magnetic fields can confine plasma in tight spaces and maintain its temperature. Additionally, magnetic fields can be generated using plasma itself.

Specifically, magnetic fields can be produced by striking plasma with the appropriate laser type. Research indicates that these magnetic fields could soon reach multi-gigagauss levels—billions of times stronger than Earth's magnetic field. In contrast, the most powerful superconducting magnets currently achieve only 45.5 tesla. While the magnetic fields generated by laser-energized plasma would exist for only brief moments, weaker secondary magnetic fields would persist for much longer after each major pulse.

A specific type of laser light creates these magnetic pulses: circularly polarized light. This light consists of two perpendicular transverse waves, which can accelerate charged particles in plasma, prompting them to emit their own light. This effect, known as radiation friction, generates potent magnetic fields.

To achieve multi-gigagauss magnetic fields, lasers would need to produce petawatts or even exawatts of power. We already possess circularly polarized lasers capable of outputting around 10 petawatts, so achieving multi-gigagauss magnetic pulses may be within reach. However, the typical magnetic fields used to contain plasmas are much weaker. For instance, the ITER plasma-shaping magnet system only operates at 15 tesla. Aoyama's lasers must confine plasma into a narrow beam, propel it at high speeds, and maintain sufficient heat to inflict damage on targets. Based on our calculations, his lasers might require less energy to achieve this than currently available systems.

I propose that, in addition to the myriad small lasers generating his plasma, Aoyama could utilize several circularly polarized lasers to accelerate and magnetize the charged particles within the plasma. These lasers would fire in rapid succession, and the resulting magnetic pulses would pull the plasma along with them, while also keeping it contained in bright, hot beams.

To maximize the speed of magnetic field generation, Aoyama would need to accelerate the charged particles in his plasma over the shortest possible distance. This can be achieved through wakefield acceleration, where lasers create waves in plasma that enable electrons to "surf" these waves. This technique can drastically reduce the distance required to accelerate electrons to high velocities, from miles to mere centimeters!

Given that plasma is not particularly dense, Aoyama must propel it to extreme speeds to generate the forces exhibited in the anime. According to Newton’s third law, pushing the plasma to such high momentum would result in an equivalent force acting on Aoyama, potentially propelling him through the air as seen in the series.

Moreover, launching the plasma beam at higher speeds ensures that numerous plasma voxels traverse the entire beam's length before cooling and dimming. Consequently, the flashes of newly generated plasma would be distributed throughout the beam rather than solely at its origin. This effect intensifies with longer ionizing laser pulses, resulting in a more powerful overall plasma beam. Essentially, the more Aoyama's beam sparkles, the greater its strength.

As his hero name suggests, Aoyama embraces this wholeheartedly:

However, it is crucial to acknowledge that this method of plasma propulsion does not resolve the photon momentum challenge. According to the conservation of momentum, the momentum imparted to both the plasma and Aoyama must equate to that of the photons from his magnetizing lasers. The light emitted from Aoyama is ultimately what propels him backward, just as it pushes the plasma forward. Generating substantial forces with his lasers would still necessitate an extraordinary amount of energy.

For this reason, Aoyama would be prudent to rely on heat-based attacks whenever feasible. Heating plasma to damaging temperatures using light requires significantly less energy than imparting damaging momentum. Nonetheless, in a world where characters frequently unleash overwhelming energy, Aoyama's seemingly inefficient photonic propulsion fits right in.

With a solid understanding of how lasers can both create and manipulate plasma, let’s summarize how Aoyama's quirk operates…

How Does Navel Laser Work?

To experience the recoil from his beams, Aoyama must generate them from within his own body. The laser light cannot originate from the quirk megastructure, as with Todoroki’s ice or Ashido’s acid. However, the energy for his lasers can indeed be supplied by the megastructure. His midsection likely houses multiple small lasing media that the megastructure energizes through either light pulses (via photon tunneling) or electrical discharges (via electron tunneling).

One set of lasers ionizes the gas in front of Aoyama, while another set strikes this plasma to accelerate its charged particles and create magnetic pulses. The latter lasers would need polarizing filters over the half-silvered mirrors to achieve the necessary circular polarization.

If the gas in front of Aoyama were air, his beams would appear more violet than blue, suggesting that the quirk megastructure likely delivers argon or xenon gas to him, as both elements emit blue light when ionized.

Aoyama can control the thermal damage of his beams by adjusting the duration of his ionizing laser pulses.

Similarly, he can increase the velocity and momentum of his beams by enhancing the power (and thus momentum) of his magnetizing laser pulses. This adjustment amplifies the force exerted by his beams on both their targets and himself.

Before we conclude, let's examine a few special abilities and support items…

What Does Aoyama’s Belt Do?

Aoyama faces challenges with inadvertently activating his quirk. To mitigate this issue, he wears a specialized belt. Every unintended beam he releases appears to be less destructive than those he emits deliberately. This implies that accidental laser pulses carry more energy than intended ones. High-energy photons also have longer wavelengths. I suspect that Aoyama’s belt features a filter that absorbs wavelengths associated with accidental laser light while remaining transparent to wavelengths tied to intentional laser light.

Depending on the belt’s construction, the absorbed light is likely converted into heat and/or electricity. If the filter is merely a passive material, all energy would convert to heat. If it functions as a photovoltaic cell, a portion of the light energy would convert to electricity while the rest becomes heat. Aoyama could then utilize this electricity for various purposes, potentially competing with Kaminari for the title of Class 1A’s top phone charger. Meanwhile, the heat could be dissipated via heat sinks. The belt may even incorporate small fans or cooling mechanisms, powered by Aoyama in the case of a photovoltaic filter.

How Does Aoyama’s Buffet Laser Work?

Aoyama’s hero outfit enables him to execute Buffet Laser, a special move where he fires beams from his shoulders and knees. This function likely utilizes fiber optics, which are cables that reflect light internally to transport it from one point to another along curved paths while minimizing energy loss due to photon absorption. When wearing his costume, Aoyama's lasing media could connect to optical fibers designed to withstand high-powered laser pulses.

I will not delve into the challenges of channeling high-intensity light through optical fibers here, but an article from Stanford provides excellent insights:

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<h2>Fiber Optic Power</h2>

<div><h3>Fig. 1: Output powers of forward beam and backward beam as a function of input power into a 13.6km long single-mode…</h3></div>

<div><p>large.stanford.edu</p></div>

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How Does Aoyama’s Supernova Work?

Aoyama’s most powerful technique, Supernova, generates a large, bright beam from his midsection, complemented by smaller beams emitted from his knees and shoulders. These secondary beams curve toward the target midair. Such behavior would not occur if Aoyama's beams were straightforward lasers; the presence of plasma alters the dynamics entirely.

Aoyama can widen his primary beam by generating a greater number of plasma voxels and distributing them over a larger area in front of him. Meanwhile, the secondary beams specifically curve toward the primary beam's target. This indicates that the magnetic pulses from the primary beam attract the plasma in the secondary beams. To prevent the secondary beams from deviating too far, Aoyama likely avoids propelling them with his magnetizing lasers. Instead, he ionizes the gas around his shoulders and knees, providing just enough magnetism to maintain the plasma's coherence, allowing the primary beam's magnetic fields to guide them.

For this to succeed, the magnetic fields of both the primary and secondary beams must be calibrated to attract rather than repel each other.

Conclusion

Yuga Aoyama embodies a free spirit filled with self-affirmation and resolve. We could all benefit from adopting some of his traits. I eagerly anticipate his future developments and the evolution of his quirk. I am also grateful for the opportunity to address prevalent misconceptions regarding lasers in pop culture and how the incorporation of plasmas can remedy these inaccuracies. Who knows? We may soon see actual lasers and plasma weapons capable of replicating the mesmerizing effects of Aoyama’s abilities. Let’s hope they are used for positive ends. Next up: The Physics of Mr. Aizawa’s Erasure! Go Beyond! Plus Ultra!

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