What's the difference between a laser diode and ordinary LED?
Laser diodes use an optical resonant cavity which when injected with light above the "Lasing threshold" generates orders of magnitude more light than injected by the high Q resonance.  A integrated PD detects the output so that it must be regulated to avoid out of control heat rise.  A thick metal case is essential to dissipate the heat and higher power.

Natural effects of high Q emission of photons include coherence of the light with low jitter, whereas LEDs are low Q vibrations of band-gap vibrations resulting in incoherent phonon emissions of light.

Lasers are currently about 30% efficient whereas LEDs are currently up to 70% efficient.