Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Overpowering my laser makes it dimmer, why?

  1. Sep 9, 2015 #1
    I bought some laser diodes on amazon. They're the typical small red 5mW lasers. Just wanted to see if the diode handle more power so i put about 20 - 30mW through it. Nice bright red dot on the wall, but then it dims and dims. The diode didn't get super hot it just got a little hot. But I've never seen such a dramatic change in resistance with so little thermal energy. Would someone mind explaining why?

    I know the basics behind a diode, I don't know much about the physics behind lasers though, but since it is called a laser "diode," if i treat it as a diode, which is a semiconductor, wouldn't thermal energy just put more charge carriers in the conduction band?
  2. jcsd
  3. Sep 9, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The circuit board may have a limit circuit built in. From here: http://www.teamwavelength.com/info/laserdiodedrivers.php

    Limit Circuit: One way to damage a laser diode is to drive too much current through it. Each laser diode datasheet will specify a maximum operating current. Exceeding this current will damage the laser diode. To avoid this, a limit circuit is included in the laser diode power supply. The user determines the maximum setting and the output current is kept from exceeding that level. Some limit circuits cap the current at the max level and keep operating. An Active Current Limit circuit will disable the laser diode driver current.
  4. Sep 19, 2015 #3


    User Avatar
    Gold Member

    Actually, laser diodes are very sensitive to overloading. Even a very short spike in the forward current can destroy them or greatly shorten their lifetime.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook