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Thread: Why is infrared diode so powerful ?

  1. #1
    Join Date
    Jan 2005

    Default Why is infrared diode so powerful ?

    Soh.. I just start thinking (when i was playing with my superduper powerful RED luxeon LED) ...
    WHY... why is there not a RED laserpointer so powerful as the green one (yea the green light is more wisible for the eye) but the red stuff is so cheap today..

    And a red one is more easy to make than green one....

    So why is it that a IR-LED... (IR diode?) is soooo damn powerful, and not the green,red,blue,amber... and so on...

    To make a example, when ONLY using a IR and a night vision cam, you can se the light from the IR maybe 100-200 meters away on a building... THAT is not possible with using a LED is it ??

  2. #2
    Join Date
    Jun 2005


    Well the first issue is that you're mixing several technologies and issues...

    For any given DPSS (Diode pumped solid state) green laser's power level
    you can easily match with a DPSS red laser... They're not common
    because demand for high power red lasers is low. But the gernam
    "showlaser" unit is a good example of a high power DPSS red in action

    There are no commerically produced green laser diodes that put
    out any appreciable amount of power. So when you're talking raw
    technology, you're right. Red is significantly easier to produce than green.

    IR laser diodes are a hair bit more efficient than red laser diodes so
    at a given current level, the IR laser will put out a bit more...

    For example:
    For 800-900nm wavelengths, output power facet density is around
    20-30 mW/μm of emitter width.
    Red diode lasers achieve about 5 mW/μm of emitter width,
    Lasers of 1400nm or longer achieve 10-15 mW/μm.

    Lengthening the cavity of the emitter can also enhances its power output.
    Cavity lengths are typically in the 0.6-1 mm range.

    The problem lies in the fact that there is a maximum energy density
    that the semiconductor can handle so the solution is to create "bar" diodes
    which basically make the emitter wider. In general, output power scales
    linearly with increasing emitter width.

    The problem for entertainment users is that the minimum beam thickness
    of a well collimated beam is exponentially related to the point size of the
    original source light. This means that the wider you make the emitter
    the larger the minimum beam diameter becomes and the harder it
    gets to collimate correctly...

    To be technically corrent, laser diodes can and do regularly exceed
    LED power output levels, but the problem is that the ones that do are
    certainly not cheap and they tend to be water cooled... I'd imagine the
    market for water cooled LEDs to be fairly low

  3. #3
    Join Date
    Jan 2005


    hey yadda

    I had hoped you did answer, as you are loaded with VERY informative stuff in your brain hehe :P :P
    Thanx for your answer....

    Yes you are true... not so much marked for watercooling LED.. (but, I sure want one) :roll:

    But i`m still some confues about LED diode and a IR diode.. and a RED laser diode... but i dont think i will understand that...

    When I was i child i did belive a red LED was the same as a red laser
    So i did take out the lence from my broken laser and tryed to aim it to the LED, but i was sadly dissapointed when i did not get a blue\red 1miles long 1mm thick beam out of the LED haha..

    And my brother did tell me that "laser" is a bounch of atoms and more stuff going in in a wave and directions.. and not as a LED..

    But why is the red laser only a LED (how can they make laser beam directly out of a LED)
    Well.. that stuff about splitting atoms and produce waves i never will understand lol

    Anyway, thanx for your post yadda, much helpful info there that i DID understand

  4. #4
    Join Date
    Jun 2005


    As you've noticed, there are noticable similarities between Light Emitting
    Diodes and Laser Diodes...

    Laser Diodes are in fact actual LEDs with very special characteristics to
    allow lasing at sufficient power densities (more accurately, lasing when
    "carrier population inversion" is attained). In fact, most laser diodes will act
    as simple LEDs (emit non-coherent light) until the lasing current is reached.

    The primary thing that seperates Laser diodes from LEDs, is that
    a laser possesses a "resonant optical cavity" which is basically an
    optical gap with mirrors on both ends (typically polished cavity ends
    on lower power lasers or dielectric coatings on higher power lasers)
    The other difference is that the "depletion layer" (where the current flows)
    is narrower than on a LED (to in order to concentrate the carrier)

    Now I'll point out that a LASER is different from normal light in that
    it possess an attribute called "coherence" that means all the waves of
    the light from a laser travels in lockstep like soldiers... This is primarily
    noticable in the diffraction off the point on the wall...

    The second difference is that a LASER is monochromatic... that means
    when it lases, it emits light in only one frequency... 532nm for example
    for green DPSS lasers... (the number 532nm is actually the physical
    distance between the waves measured in billionth of a meter)

    Note: A lot of laser heads are "multi-line" (thanks spec) which means they emit multiple
    laser beams at different frequencies (usually just refered to as laser lines)...
    These heads still follow the monochromatic rule since each line is
    monochromatic, its behaves just like multiple lasers in the same optical cavity.

    An LED is not a laser for the simple fact that it fails both requirements.

    A red LED emits light from the range of 600nm though 680nm...
    An IR LED typically emits light somewhere in a range from 660nm to 1600nm
    A red Laser Diode will emit light in a specific frequency, such as 657nm...

  5. #5
    Join Date
    Jan 2005


    thank you

    very easy understanding answer

    There is so much to learn.... :roll:

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