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  1. #1
    Power User
    Join Date
    Feb 2006
    MI / MA

    Default Laser Detector Diodes: How do they work?

    I haven't been able to find much technical explanation of this one, so I'll ask it...

    (1) How exactly does a laser detector work? (Other than they detect pulses of 904nm light...)
    (2) What factors determine the effectiveness of a laser detector? Is it in the sensor itself? Number of sensors? Hardware processor power? Software?

  2. #2
    Old Timer
    Join Date
    Jun 2005
    New Hampshire


    A laser detector is simply a photodiode (or multiple photodiodes) connected to a pulse detection circuit of some sort. The diode will generally have a filter over it to limit it to wavelengths around the 904nm that lidar uses.

    When a lidar pulse strikes the photodiode, it triggers the pulse detection circuit, which tells the microprocessor in the RD that an infrared pulse was detected. The processor counts and times the pulses to determine if they're lidar or not, and if it meets the criteria (minimum number of pulses at a certain constant rate) it sounds a laser alert.

    Sensitivity is a function of (a) the number of photodiodes used, (b) any collimating lens in front of the diode, (c) the quality of the diode, and (d) the circuit that "reads" the pulses from the diode. Software may be a factor too, as it may ignore weak pulses to minimize falses.

    The most sensitive laser detector is in the V1, which (in the 1.8 version) uses a large collimating lens in front of the diode. Plus V1 uses military grade components which offer a higher signal-to-noise ratio compared to lesser components, allowing for greater sensitivity.

    Bel and Escort use multiple photodiodes, 2-4 typically depending on the model, plus one for rear laser.
    If I'm passing you on the right, YOU are in the wrong lane!

    If speed kills, how come I'm still alive?

    Active Countermeasures: V1 3.858, Escort Redline, Beltronics STi-R+, LI Dual 7.1x CPU/8.7 Heads (front)
    Other/Backup Countermeasures: V1 3.813 (loaned to friend), Beltronics Pro RX65 M4 6.3
    Vehicle: 2002 Audi A4 1.8T Quattro
    LEO Toys: Kustom Pro Laser II & III
    Encounters/Saves August 2011: Radar 3/1, Laser 0/0

  3. #3
    Power User
    Join Date
    Feb 2006
    MI / MA


    Thanks, kpatz! That was very informative and answered all my questions.



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