Laser Sniping Rifles

Karl-Heinz said (my replies marked with [Tomb]):

The noticeable effects of Ionization depend on the intensity and
frequency of the beam. From the low to the high end, this would be:
- - slight electrical charges in the athmosphere. Minimal effects like a
faint vapour trail in humid air.

[Tomb] Minimal, except for nicely backtracking the origin of the shot.
An important consideration perhaps...?

- - light emission by the ionized atoms. Depending on intensity, this
may be either only detectable with electrooptic light intensifiers or
with the naked eye

[Tomb] Or some form of Laser warner systems. How much energy would a
laser have to emit to leave a glow in the air showing its passage? Come
on, Physics geeks! You're always impressing me with your grasp of
vacc-head motion and physics.... try this closer to the ground problem
on for size. Would this be something that would happen with a man
portable rifle laser, a tank laser main gun, or only if you got FT sized
batteries into play?

- - Extreme heating of the air passed through. Only this would produce
something like a thunder.

[Tomb] Rapid expansion could produce a bit of thunder. Air less
superheated but rushing in to fill the pathway the laser burnt through
would probably make a "pop". 

Other effects:
- - light scattering off dust /smoke in the athmospere. This is what
make a visible light laser beam visible in the athmosphere. In clean
air, even a visible light beam cannot be observed.

[Tomb] Smoke would surely get you a bearing on the firer even more
pronouncedly than a bullet potentially. Or maybe not... maybe the shot
is so short of duration that a hole in the smoke is all that could be
seen?

The sound from the weapon itself is hard to guess, but is probably low.
There could some cracks from thermal effects produced by waste heat.
Also the weapon may be visible to IR detectors.

[Tomb] Maybe a snap like an electrical arc generates? Air rushing back
into the laser's pathway making a small crack or pop. If the laser was
powerful enough, maybe it would be a ripping or hissing or even a small
thunderclap. And the weapon would stand out like a sore thumb to some
kinds of sensors. And of course would be blocked by most aerosols,
unlike bullets.... 

[Tomb] And the wounds.... I've heard some people suggest small burnt
holes, deep wounds. I've heard others suggest superheating of
intracellular fluids could result in a kind of mini explosion blowing
chunks out of the target. I'm not sure which is actually the case, or it
may depend on laser energy levels.