Why does a laser diode need a heat sink?

Laser diodes dissipate typically 50–70 % of the electrical power as heat – only a fraction becomes light. A 1 W laser diode therefore generates 1.5–2 W of waste heat in the semiconductor chip. Without a heat sink the junction temperature climbs to critical levels within seconds and the diode fails thermally. Consequences: drastic wavelength shift (red-shifted), efficiency collapse, irreversible destruction. Rule of thumb: every additional 10 °C in junction temperature roughly halves the service life. Practice: mount the diode in a massive metal holder (brass or aluminium), the holder on a heat sink with thermal compound, and add a fan or thermal convection for > 1 W.