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I am buying a laser diode but cant understand some parameters

  1. Nov 19, 2011 #1
    i am buying Pulsed Laser Diode in Plastic Package 25 W Peak Power SPL PL90 and there is some parameters about semiconductors lasers....

    Forward current = 40 A why all this current ????

    then in the catalog Reverse voltage= 3 Volt

    then they say the Threshold current = 1A ??? what is the difference

    when i by the diodes what current should i apply 40 or 1 !!!!

    Attached Files:

  2. jcsd
  3. Nov 19, 2011 #2


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    The threshold current is the the minimal current you need to apply to achieve lasing operation. From that point on the emitted intensity depends on the current you apply. You find the curve showing this in the upper left corner of the fourth page of your data sheet. The x-axis denotes the current you apply and the lower of the two courves shown there gives your output power. Now you can choose the current such that it suits your needs. However, you should not go too high. Going above the indicated maximum value might damage your diode.
  4. Nov 19, 2011 #3
    thank you ...you helped me a lot ...but should the laser is amplification process ...but i am seeing that input power is mach higher than out put power ???
  5. Nov 19, 2011 #4


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    A laser operated far below threshold would basically just show spontaneous emission into many modes. Now the amplification means that one of these modes is preferred and amplified via stimulated emission at the expense of the other modes. So the benefit you get is huge emission from an amplified single mode. So you get some non-linearity in the input-output curve, but the power you apply to the laser as a whole is not amplified. If you got more out than you put in that would already violate conservation of energy. At room temperature the conversion efficiency from electrical energy to light output is usually not too high. While one can reach high values around 75%, typical values for semiconductor lasers that are actually on the market are way lower. 50% is already pretty much. Values below 30% are typical. However, that depends strongly on the wavelength range of interest.
  6. Nov 20, 2011 #5


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    What gets amplified is the power that is in the form of infrared radiation at 905 nm (or whatever the laser wavelength is). Total power does not -- and cannot, ever -- exceed the amount of power input to the device.
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