Let's start with the reason:
Most form 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 form of light beams, the wavelength is between 700nm to 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 it's potential mates it's presence and location, but also serves to communicate with the potential mate about it's 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 purpose, usually to benefit his/her own survival. Ants touch Antennae to exchange information about location of food, Fireflies blink to tell whether it's a male of a female, Bees does figure 8 dances to alert others of it's colony the location of a discovered food source.
Problems with broadcasting
###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 tries to communicate with, the weaker the signal intensity your target will recieve for a same beam profile. In order to combat this, we can either Increase the beam Power, which is impratical 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 satellies. Lasers were used, because the have a short wavelength compared to radio waves, and because of that, it's possible to focus a laser into a very colliminated, narrow beam; thus decreasing 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 tends 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 suffers 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 colliminated 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 colliminated, 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 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 it's excitation energy as a photon. Once the luminescent substrate have 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 seems 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 an 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 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 emmission. 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 it's 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 it's light signals in a primitive, omindirectional 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.
