# Can a biological laser exist?

We know that Earth creatures can generate high-voltage electricity (your nearest electric eel can attest to that). We also know that ordinary air at Earth atmospheric pressure can be used as a laser gain medium -- this is used in Transverse Excitation at Atmospheric pressure (TEA) laser designs. While not capable of CW output, such a laser can produce pulsed output at a high enough frequency to be practically equivalent to a CW laser, in addition to being operated in a single pulse mode.

This leads me to the question, similar to this but for land-bound creatures: could a creature on land generate a laser pulse without the need for assistance from non-biological structures (such as the finely spaced optics used in the chemically pumped GFP-laser cell)? Furthermore, how much power could they feed such a bio-laser with?

• There were several examples in Foster’s Sentenced to Prism. – JDługosz Oct 18 '16 at 21:45
• @JDługosz -- interesting, although it seems like you could do it on a much more Earth-like world, with carbon based lifeforms – Shalvenay Oct 18 '16 at 21:48
• One of the examples in that novel is a modified human, with laser in the arm bones. Bringing the elements into alignment fires a shot. – JDługosz Oct 18 '16 at 21:50
• These types questions need a general answer somewhere people can be pointed to because it's the same everywhere. "Any structure can be done via biological means, but whether it would ever develop is another question entirely and for most of these questions it is a not likely to occur status" Perhaps even have a 10pt scale of unlikeliness where 10/10 means next to impossible given all known strictures of the universe no matter how much time passes and 1/10 means somewhere in the cosmos it probably exists, but any random civilization probably will never run into it. – Durakken Oct 18 '16 at 23:27
• Try green florescent protein in micro high Q cavity and amazingly in vitro testing the organism survives the ordeal! – user6760 Oct 19 '16 at 0:51

## Bioluminescence, refined, could lead to the evolution of lasers. But is it worth the implications?

1) Creating a powerful beam within the electromagnetic spectrum requires energy.

Any organism with a laser will have to eat nutritious food, constantly, to meet the energy requirements of such an organ. The exact amount of energy required depends on the size of the laser and the organism that wields it. When an organism finally does eat enough to maintain a laser, however, our next problem arises:

2) If an organism has excess energy, it will use it practically.

Unless a laser is exactly what your creature needs, it will use the energy it gets to maintain existing systems, or it will evolve a more efficient, more reasonable way of defending itself, and channel energy to that organ instead. Why would humans evolve lasers that aren't likely to do much damage when they could instead evolve sharper teeth, or spit acid?

## Assuming an organism meets the energy requirement, how can a practical laser evolve?

An organism with prexisting bioluminescence, such a firefly, that controls when it releases light, is an ideal candidate to evolve a laser-bearing species from. However, fireflies use their lights to find mates and communicate, which lasers will not help them with. Then what is a practical use of a laser that a creature would want to evolve?

Going on the offensive is not practical. A laser will not evolve if a firefly tries to kill its enemies with blinking lights. You will only end up with lots of dead fireflies.

Using lights for defense? Why not. If blinking lights stun or confuse predators, and your creatures become dependent on this as a species, then the individuals with the most effective, concentrated, and blinding lights will survive to reproduce or be favorited by mates. Over time, this could lead to extremely concentrated beams of light similar to lasers. Not exactly a traditional laser, but technically, it still is one. After your lasers are concentrated, your organisms may discover that they can do damage with them, too. It depends on how concentrated, and I don't have the math or means to say.

A) You want a land creature, but I used fireflies as an example. No problem! As long as your land creature has evolved bioluminescence, my steps to evolving lasers should still work.

B) Wouldn't heat and self-damage cause problems? Nope, and here's why: bioluminescence is efficent. Fireflies do not heat up when they shine their lights because their process is extremely productive. This could go for your organism as well. Finally, self-damage would only occur if the lasers evolved to be extremely powerful. At this rate, a large organ shaped like a dish, that concentrated all beams in one direction, would likely stop any tissue from taking too much of the radiation.

• Perhaps evolving from an omnidirectional setup to a sort of lens that concentrates the entire body's glow into one spot would be a possible progression. – SPavel Oct 19 '16 at 16:02
• "Over time, this could lead to extremely concentrated beams of light similar to lasers. Not exactly a traditional laser, but technically, it still is one." I think that, technically, a highly concentrated beam of light that doesn't involve stimulated emission is not a laser. https://en.wikipedia.org/wiki/Laser – Nathan Hinchey Aug 28 '18 at 19:54
• The question isn't whether evolution of a biological laser is feasible, but whether it could exist. It could have been created by genetic engineering. – Infrisios Aug 30 '18 at 11:03

## "Human cell becomes living laser"

In June of 2011, scientists for the first time created a laser light using living biological material: a single human cell and some jellyfish protein.

"Lasers started from physics and are viewed as engineering devices," says Seok-Hyun Yun, an optical physicist at Harvard Medical School and Massachusetts General Hospital in Boston, who created the 'living laser' with his colleague Malte Gather. "This is the first time that we have used biological materials to build a laser and generate light from something that is living."

Building a laser requires two things: a lasing material that amplifies light from an external source (a 'gain medium') and an arrangement of mirrors (an 'optical cavity'), which concentrates and aligns the light waves into a tight beam. Until now, the gain medium has only been made from non-biological substances such as doped crystals, semiconductors or gases, but in this case the researchers used enhanced green fluorescent protein (GFP) — the substance that makes jellyfish bioluminescent, which is used extensively in cell biology to label cells.

The team engineered human embryonic kidney cells to produce GFP, then placed a single cell between two mirrors to make an optical cavity just 20 micrometres across. When they fed the cell pulses of blue light, it emitted a directional laser beam visible with the naked eye — and the cell wasn't harmed.

The width of the laser beam is "tiny" and "fairly weak" in its brightness compared to traditional lasers, says Yun, but "an order of magnitude" brighter than natural jellyfish fluorescence, with a "beautiful green" colour:

Two points of interest here in regard to your question:

• it was a human cell, so this might eventually be possible in living humans
• it's brightness is "fairly weak" compared to a traditional laser, but perhaps future developments could produce output great enough to rival traditional lasers
• The mirrors were provided by the experimenters and aren't biological. – jknappen - Reinstate Monica Oct 19 '16 at 13:13
• Hmm. Well, if they can get the cells to laze at all, my guess is they will eventually be able to figure out how to make an optical cavity with biological mirrors. – Thom Blair III Oct 19 '16 at 17:36
• Couldn't the tapetum lucidum act as a mirror for a laser...it's the organ at the back of dogs eyes that make them shine. Our organic laser could use a similar construct et voila! – Michael Brown Aug 30 '18 at 20:22
• Ooo! That's awesome...great idea! – Thom Blair III Aug 31 '18 at 4:18
• So they injected a cell with lasing material, gave it an energy source, and put it in a laser cavity, and it lased? Not surprising given that they've just assembled a laser using a cell as scaffolding. The only surprising fact could be that the cell wasn't harmed, but then again, it was a weak laser. – user253751 Dec 15 '18 at 6:08

I'm surprised nobody's argued this way yet, but I think it's crucial:

### Laser = repeated (coherent) amplification of light

Yes, we use the stimulated emission mostly for generating light (often not collimated BTW, it's the coherence that's most important), but also for amplifying a given light source. And that would probably be the biological motivation for evolving tissue that can act as a gain medium: to sense very weak light stimuli, e.g. luminent predators or prey.

This would probably happen in the eye of a cat-eyed creature, between the retina and the tapetum lucidum. The latter is already a reflector, which is the other thing you need for a laser. Once all of this is in place, it would be advantageous for another semi-reflecting layer to develop in front of the retina: though this would block some of the incoming photons before they even get to the retina, it would also send the ones that are already there another time through the amplifier, which generates even more photons... and so on. This is most efficient when the spacing between the mirrors is tuned to the frequency of emitted light: that's how a resonant laser cavity works.

This way, the eye would become extremely sensitive. The downside is that it also becomes very nonlinear, and is readily saturated – it can only detect that there is light, but is bad at making out details. Thus, our creature would evolve an asymmetry, with only one eye developing ever-increasing gain. The side effect of this is that the one eye would actually light up in response to an incoming source. This light then would reflect off the predator and could thus be used by the other eye to see more details. You've developed an automatically-triggered torch!

At this point it's clear that ever stronger pumping of the gain medium is an advantage, to make the flash-light more useful. And whilst the predators or prey haven't adapted to this, they would probably be confused and/or blinded by the flash, giving you time to escape or catch them, respectively. This further incentivises evolution to make the laser stronger. In the end, it might get to quite formidable power (evolution is great at optimising quirky features to surprising strength – consider hagfish, chameleons or pistol shrimps), probably not enough to hurt anything but certainly to blind it. Our creature's laser-eye would by this point not be useful as an eye anymore itself (because every firing scorches its own retina), but that's not important anymore because the other eye has been hugely upgraded through the laser.

Clearly, all of this would be most likely to work out in a deep-sea environment, where there's never sunlight and lots of luminescent animals.

Sure. Not just humans, but all manner of creatures on Earth have very sophisticated highly evolved eyes and even partially inorganic bodies (e.g. shellfish) at all manner of wave lengths.

I don't think they could get very powerful (biological systems aren't known for sustained high voltage high ampere electrical output outside anything more realistic than the Flinstones) - at best some sort of bio-capacitor might allow for short, high intensity bursts. But, while bio-lasers might not be fully appropriate to weaponize, they could be useful for line of sight communication, fire starting, accurate measurements, temporarily (or even permanently) blinding predators or prey, and any number of other applications.

I think it's totally possible but the chances of this organism evolving on Earth is pretty slim. This hypothetical laser would likely be used for attracting mates, or to stop predators and other threats in their tracks. How would it come to be? Likely in an environment with a lot of light with the organism taking on similar traits to the high light environment. Predators that push for this laser to come to be. An example could be smaller predators hunting in swarms with the organism effectively killing them all with the laser, or a fairly powerful predator that otherwise the organism cannot fight back against.

The issue in my opinion would be self damage. Could the creature control how powerful this laser is? How long can it activate the laser for? How much energy does it require? Will it die once it uses it? Termite soldiers can explode themselves as a last resort against enemies (usually ants) to stop enemies, but obviously they themselves die. If so, it would be practical for this creature to have other means for defense before using the laser.

Another concern would be if it's against the environment. An animal with a relatively destructive laser could be disastrous towards an environment. It could potentially start a fire which alone is a huge threat. If this organism can use this deadly laser at its leisure with little consequences, there's a chance that humanity would try to destroy this species. Just imagine birds with the ability to breathe fire. That would be an incredibly dangerous species.

Most forms of radiant energy obeys the Inverse Square Law, which means that, for any given point source, the total amount of energy that passes through a surface that is of the same angular size from the perspective of the source stays unchanged, or, the intensity of the radiant energy at any given distance from a source is proportional to the inverse of the square of the distance to the source.

### Beam formation and spot intensity

For any application of energy at a given distance, for a given amount of energy, the narrower the radiated beam you can radiate your energy for, the more energy density you can apply to a target of a given size.

It is possible to focus the applied energy to a single beam, but there is always a limit of the highest energy density you can apply to a given area at a distance.

$$d=\frac{4 \lambda D}{\pi Da}$$

where d is the diameter of the spot or the size of the focal point of the beam, D is the distance from the aperture (the hole/window of which the beam came out of), Da is the diameter of the Aperture, and

$$\lambda$$ is the wavelength of the energy beam

The spot intensity, then, is just the ratio between the beam power and the area of the spot:

$$I=P/(pi*d^2/4).$$

For a sound beam, the wavelength is about 1/10m to 1m. For most forms of light beams, the wavelength is between 700nm and 400nm.

## Why lasers?

Communication, or information exchange, plays an important role within groups/colonies of many types of organisms. For example, a bird's tweet is not only just for alerting its potential mates to its presence and location but also serves to communicate with the potential mate about its fitness and condition, information that will be used for the selection of mate from potential candidates. Humans talk to each other, not just for alerting others of his/her existence and location, but also to exchange information that will be used for a variety of purposes, usually to benefit his/her own survival. Ants touch Antennae to exchange information about the location of food, Fireflies blink to tell whether it's a male of a female, bees do figure-8 dances to alert others of its colony to the location of a discovered food source.

### The signal to noise ratio:

The signal to noise ratio is simply the ratio of the power of the signal at a given location to the power of background noise at that location. a signal-to-noise ratio that is smaller then 1:1 will prevent the signal from being properly analyzed, stopping communication completely. Given a specific background noise level, the Signal to Noise ratio is directly proportional to the local intensity of the signal, which is inversely proportional to the square of the distance to the source for any given point source. The intensity of a directional source at a distance is given as:

$$I=\frac{4\pi P}{r^{2}S}$$

P is the power of the source, r is the distance, S is the spread of the beam, in steradians.

from this equation we can see, the smaller the spread of a given beam, the more intense the beam's power is for a target at a given distance for the same amount of total beam power.

### Freespace Laser Communications: Why we use lasers for long-distance communications.

The farther the target you try to communicate with, the weaker the signal intensity your target will receive for the same beam profile. In order to combat this, we can either increase the beam power, which is impractical for handheld devices and/or living organisms, or we can decrease the spread of the beam, which is how satellite dishes and megaphones work. A high-speed communications system, using lasers across empty space, is currently being employed by SpaceX's Starlink satellites. Lasers were used because they have a short wavelength compared to radio waves, and because of that, it's possible to focus a laser into a very collimated, narrow beam; thus decreasing the beam's spread and increasing range for a limited power supply(the solar panels of the satellites)

## Evolution of a laser-using organism

For an organism that lives sparsely in a noisy environment, which a need for long-distance communications between individuals are needed due to whatever reason(Sexual selection tends to disproportionally favor a certain trait, such as the ability to send information of high complexity at a high speed, like the songs/tweets of many birds for mating)(but also for certain colonial organisms of which intracolonial communication is favored by Kin selection, benefiting the colony as a whole), the ability of accurate, long-distance communications are heavily selected for, and the logical mean of achieving that is to both shorten the wavelength of the signal used, and improve the directionality of the method of communication used to increase peak spot intensity and conserve energy.

If the environment is exceptionally noisy, vocal, or sound-based communication is no longer feasible at extended distances, especially because sound waves tend to make poor beams due to the long wavelength of sound waves.

So light-based communications, likely based on bioluminescence, is the preferred method for these conditions.

Because light waves also suffer from the inverse square law when unfocused, the logical next move for the organism is to produce a structure to focus the bioluminescent light into a collimated beam, using, for example, a structure that is the inverse of an eye, with a lens in front of the luminescent substrate to focus the light into a collimated, long-range beam. Due to Conservation of Etendue, the maximum apparent intensity for any point on a light organ can not exceed that of the luminescent substrate used within the light organ used to give out the light. Therefore, there is significant selection pressure for light organs whose substrate have a high luminescent intensity for a given surface area--It is better to have a small amount of Very Intensely glowing substrate than to have a large amount of Weakly glowing substrate, even if the total luminescent power of the two light organs are identical.

Due to the nature of bioluminescence--a conditionally irreversible chemical reaction produces a product in an excited state, whose decay releases its excitation energy as a photon. Once the luminescent substrate has it's light intensity, hence it's reaction rate increase past a certain threshold without the fluorescent lifetime of the product degrading correspondingly, there will be a spatio-temporal point in that reaction where the concentration of the excited product exceeds that of the ground state product, causing a population inversion--the luminescent substrate became a gain medium.

For the organism, it probably won't seem to matter much--as the quest for higher light intensity per unit area of substrate continues, the bioluminescent light first changes from phosphorescence to fluorescence, then from fluorescence to superluminescence, while the unit area intensity increases largely linearly, biological eyes being too sluggish and far too slow to notice the differences in mechanism. Then, because a biological optic system tends to contain many layers of materials with different refractive index, the superluminescence become more and more intense as light that would otherwise be lost are reflected back using what is known as a distributed Bragg reflector (the same layers of material is largely responsible for animal eyes to glow in the dark when a light source is carried by the observer, being a mechanism to reflect light that passes through the retina back onto the retina, therefore nearly doubling the efficiency of night vision).

Finally, the different phase(temporal) modes of the light emitted by the light-producing organ collapses to a single mode, as enough light that exits the gain medium is reflected back to be amplified again and again in a process of resonant electromagnetic oscillation through amplification by stimulated emission. A true laser has been formed.

With a true laser, the area intensity for the luminescent medium is no longer important, as the gain medium can now generate a very low entropy, coherent beam with an infinitely small etendue, the efficiency of long-range optical communication through bioluminescence is no longer limited by the maximum unit area intensity of the luminous substrate, and is now entirely dependent on the wavelength of the light used and the aperture size of the light organ, the organism is able to save more energy during its communication with other individuals by being able to focus the beam down to the diffraction limit(like most eyes are capable of). thus no longer require as much energy as if it was broadcasting its light signals in a primitive, omnidirectional manner.

### As for offensive uses of lasers in the sense of burning the target alive? probably not.

Though the same long-range communication organ can probably be used to dazzle predators/small prey like insects or birds, causing them to be blinded and stunned/fall from the sky, conferring a nutritional advantage in the sense of being able to hunt at range/being less likely to be eaten.

• A good first post! Let me know if I missed or screwed up something with my copy editing, BTW – Shalvenay Nov 2 at 2:49

Sure it can!

For nitrogen laser you need gaseous nitrogen. But our atmosphere is pure enough if you don't care about efficiency. It needs to be between few milibars and few bars. Again, atmosphere can do! You need a high voltage supply. Can do, too. Some fishes sure can. Spark gap is most problematic, but with graphite electrodes why not? No optics required.

Transversely Exited Atmospheric pressure laser is really simple device, and no reason you couldn't bioengineer it into a species, or at least into creatures. For homework, I suggest building one.

• By the way, I helped building one. It's really, really simple stuff. – Mołot Oct 18 '16 at 23:15
• Me thinks a dye laser makes much more sense. However. I do not think it would be a solvable problem to "grow" an optical resonant cavity... – Aron Oct 19 '16 at 5:41
• @Aron By "dye", you mean solution by Zxyrra? May be, can't tell. Both lack any evolutionary pressure, as far as I know, so both would need to be bio-engineered. And when it comes to such things, it's human fantasy and whim, not probability ;) – Mołot Oct 19 '16 at 6:39
• No I mean "Dye laser". They were much more common in the past, using organic dyes, usually in solution. They had wide bandwidth which allowed for tuning (via the optical cavity). en.wikipedia.org/wiki/Dye_laser – Aron Oct 19 '16 at 6:44
• @Aron that would be an answer I'll gladly upvote. – Mołot Oct 19 '16 at 7:29

My guess is that they already do exist, just not in the super-powerful-laser form you have in mind. Nature seems to have discovered and utilised a remarkable range of capabilities, so much so that I would be amazed if there wasn't some niche (even on a microscopic scale) where synchronised electromagnetic radiation didn't arise.......

No. I’m not saying that a biological laser could not evolve, just that they would need precisely spaced and shaped optical elements. That’s a principle on how lasers do what they do.

• Did you mean to make this a comment? – Shalvenay Oct 18 '16 at 21:49
• No, it's a suitable answer for a realiy-check question, and the question is « could a creature on land generate a laser pulse without … finely spaced optics…?» – JDługosz Oct 18 '16 at 21:51
• BTW -- a laser with enough medium gain doesn't need end optics (TEA nitrogen lasers certainly lase quite happily without them) – Shalvenay Oct 18 '16 at 21:58
• Evolve, probably not, but exist? I can't think of a single reason why not. Sufficiently advanced bioengineering should be able to make anything we need. The question is, what biological equivalents or hypothetical equivalents could we use? – Kronimiciad Oct 18 '16 at 22:03
• I disagree. It does provide an answer to the specific question as asked «could a creature on land generate a laser pulse without … finely spaced optics…?»: I literally answered that question, so how can it be accused of not answering? And in any case, challanging the premise is OK for an answer on a Q with the reality-check tag. – JDługosz Oct 19 '16 at 1:06

In contrast to the many optimistic answers here, my answer is no.

While there are many ways to produce biological light, an optical cavity of good quality for a laser is almost impossible for a biological system. It needs to have two parallel mirrors in a resonant distance. Both traits are difficult to achieve. Only small deviations will make the whole laser fail completely.

P.S. For me, there is a difference between a Laser and superluminescence without a resonator.

EDIT: Also a superluminescent organ is highly implausible; it needs to be in a straight geometrical line. Biological structures aren't like this.

• Most folks who work with TEA lasers would send a few laser pulses your way for that P.S. of yours, just sayin'... – Shalvenay Oct 19 '16 at 22:16
• "Only small deviations will make the whole laser fail completely." could you not say the the same for any organ? – Bryan McClure Oct 20 '16 at 20:34
• @BryanMcClure: No, most organs are really robust against deviations of many kind (loss or gain of weight, growth of the body, movement, and even physical injuries). – jknappen - Reinstate Monica Oct 20 '16 at 23:40