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In a magic system that allowed the manipulation of energy by sorcerers, what would a bystander observe during such an attack? Some details are relevant:

  1. As I understand it, lasers are visible due to scattering of light, therefore a lot would depend on the air (dusty, clear) and possibly even the time of day. This is evidenced by the fact that lasers are invisible in a vacuum. Therefore, if the laser is observable, what would its color be, presuming it is within the range of lasers "hot enough" to cause fatal damage to the target? I've read that blue lasers are apparently hotter than others.
  2. What would be the observable effect on the target at the point of impact? Would we observe charring, or something more explosive as liquids are super-heated? Apparently, lasers "ablate the surface and create a small amount of exploding plasma". This source also supports an explosive reaction. However, as stated in this medical article, mid-infrared lasers with long wavelengths cut by burning (breaking down chemical bonds holding tissue together). Shorter wavelength lasers in the near-infrared, visible and ultraviolet range create a series of micro-explosions that break the molecules apart i.e. plasma is created at the laser focus. "At the end of each laser pulse, the plasma collapses and the energy released produces the micro-explosions".
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if the laser is observable, what would its color be, presuming it is within the range of lasers "hot enough" to cause fatal damage to the target? I've read that blue lasers are apparently hotter than others.

If the laser has a wavelength in the visible spectrum of light, as a consequence of the scattering you will see that very color, like in the picture below for a green laser. If it is outside of the visible spectrum, i.e. IR or UV, you won't see a thing, unless it is so energetic to excite light emission from air.

Nd-YAG laser

For a laser the concept of "hot enough" is not dependent on the wavelength, but rather on the energy. If you deliver enough energy to the target, you have significant effects on it.

What would be the observable effect on the target at the point of impact? Would we observe charring, or something more explosive as liquids are super-heated?

Back in my university days, while I was working with a 10 mJ, nanosecond pulsed, frequency-doubled Nd-YAG laser (the one you can see in the photo), I was so sloppy to put my forearm in the beam path and catch few pulses on it. I immediately felt like I was stung by a wasp and the smell of burnt hair saturated the air. Later, for work, I have seen the footage of a chicken breast being hit by an IR pulsed kW laser: the thing drills a hole into the breast in a matter of moment, in a cloud of smoke.

Despite the difference related to the wavelength of the photons interacting with the matter, what you end up seeing is a puff of smoke and hearing a sound. In my case, whenever a used the beam trap on the beam path of the laser, or adjusted the metal slit to cut the beam, I heard like someone was whipping on the metal, and could later see cuts in the metal itself.

The smoke is the result of either the evaporated material diffusing in the air around the point of interaction, or of the plasma interacting with the surrounding. The sound comes from the resulting shockwave, so with different materials you can have a stronger or weaker sound.

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  • $\begingroup$ If, as you said, it is outside the visible spectrum but energetic enough to "excite light emission", what would the color of that emission be? $\endgroup$ – Red Robin Apr 4 '19 at 13:09
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    $\begingroup$ @RedRobin, it depends on the excited atom and its electronic transition. $\endgroup$ – L.Dutch - Reinstate Monica Apr 4 '19 at 14:03
  • $\begingroup$ @RedRobin - NIST has a database for atomic spectra and emissions wavelengths. You're looking for the strong lines (for example, most ions of copper, when excited, have several strong lines between 520 and 560 nm (ie. green light). $\endgroup$ – jdunlop Apr 4 '19 at 17:29
  • $\begingroup$ It's also worth noting that the dustier the air, the more likely something bad happens to innocent bystanders. Laser scattering for weapons-grade lasers can easily blind onlookers unless they're wearing appropriate protection. $\endgroup$ – jdunlop Apr 4 '19 at 17:31
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  1. Every color is fine, but blue has the most energy per photon. There can always be more photons and the energies within visible spectrum are not that different. https://en.wikipedia.org/wiki/Electromagnetic_spectrum

  2. Depends on the lasers strength and the material it hits. Thermal capacity and energy required for phase transition will be different between materials. Also some material absorbs more light of a different wavelength. Some may evaporate and some may melt, boil, create plasma, or even freeze (not for visible lasers).

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If the laser in question emitted UV at a high energy, it may create a UV-emitting plasma in the beampath, which can secondarily induce photodissociation of oxygen and high temperature gas-phase reactions. Plasma channels in open air (in laser labs they fire these in argon atmosphere tubes to prevent this) are dangerous (think semi-stable linear lightning) and there was some research being done here in the US, and in Russia, and in Europe into weaponising this - you can, it turns out, control the duration of these plasma channels and use them to create and control high-voltage discharges... Laser-Induced Plasma Channel weapons.

So one possible appearance of your sorcerous laser wielders is semi-linear lightning.

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