Could you make a bar of metal glow by forcing the charge density on the surface to oscillate? Since light is just a changing electromagnetic wave through space, could you create light by changing a charge density at a certain frequency?
 A: Changing the charge density at optical frequencies is hard to do, but suppose we wind the frequency down a bit to FM radio frequencies. The question is then whether changing the charge density at FM frequencies would cause radio waves to be emitted, and of course the answer is yes because that's what a radio aerial does.
Well, EM waves would only be emitted if there was a dipolar component of the charge density that was changing, but in practice unless your aerial is a perfect sphere I think there will always be some oscillating dipole present and hence your bar of metal will glow (at radio frequencies)
A: Subjecting a charge density to a hight frequency EM field produces a wider spectrum EM through Bremsstrahlung (any accelerated charge radiates). This property is used in laser plasma interaction or in free electrons laser. There are many complex phenomena involved in laser plasma interactions ranging from particle acceleration to frequency doubling, you will find more information if you look at this link:
http://en.wikipedia.org/wiki/X-ray_laser
An other approach is the free electrons laser where once again the charges are accelerated in an EM field to produce light.
http://en.wikipedia.org/wiki/Free_electron_laser
