That would require a lot of power (like an industrial CO2 laser with a
half a kW optical output), will before long blind and/or scar both
you, the cat, and every surface in the line of sight.
To remove feline adipose tissue it is much easier to use a purely
thermal approach, and apply the infrared beam to the cat surface
directly.
(Lunatics may wish to utilize UV or xRay lasers, but here "hand-held"
applies even less).
> floor or wall or other opaque surface in the vicinity of the cat, then
> moving the laser so as to cause the bright pattern of light to move in
> an irregular way fascinating to cats, and to any other animal with a
> chase instinct.