= Semiconductor laser
A <semiconductor laser> uses a <semiconductor> as its <laser gain medium>. Pumping produces carrier populations that permit <stimulated emission> between suitable electronic states. An <optical resonator> supplies feedback, and oscillation begins when the gain compensates round-trip losses.
A <laser diode> supplies pumping by electrical injection; other <semiconductor lasers> can be optically pumped. The <band gap>, confinement and resonator determine the possible emission range. A measurement of optical output versus pump strength helps locate the <laser threshold>, while an emission spectrum tests the modes involved. Increasing output alone does not establish that the device has entered coherent <laser> oscillation.
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