Do concentrated forms of light, such as a laser, have mass?
laser has no difference from normal coherent light (like the one you'd get through a slit).
and light has no rest mass.
Depends what you mean by the term mass. Do you mean mass in terms of a material concept, or in terms of an inertial concept?
Fargoth is right, light has no rest mass, but then again, light is never at rest. Given that light can be bent by gravitational fields, one could argue that light does in fact possess some inertia. E=mc^2 would also suggest that light posesses some inertial mass since it posesses energy.
Note however that this applies to 'ordinary' light as well as laser light.
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