Wavelength Detector

Hey! I'm using photodiodes to detect the light emitted from a laser diode, however I would like to cut off the ambient light intervening with the laser's light. Are there IC's to detect a certain wavelength or is there a way to build a frequency/wavelength detector circuit?

Thanks.

Hi,

Often an optical filter would be used. You can also use a 'hood' that blocks out ambient light coming in from the top and sides which can be a simple pipe with the inside painted flat black. The laser is then aimed so that it shines down the pipe to the sensor.

Are there IC's to detect a certain wavelength or is there a way to build a frequency/wavelength detector circuit?

No. Not a circuit. You can build an optical interference filter tuned to the laser's wavelength if you have a vacuum deposition chamber.

However, if you modulate the laser you can put the signal from the sensor through a band pass filter with gain tuned to the frequency of that modulation.

You can use a diffraction grating to measure the wavelength. No need for electronics.

Turn the laser on and off in a defined pattern. Observe that the detector output has the same pattern. Now you are synchronised and you can detect the laser reliably in the current ambient light condition. If the detector doesn't have the same pattern then either the path is blocked or your ambient light is too bright and the detector is stuck at max.

Perhaps you find some ideas here: https://www.youtube.com/watch?v=PIn00-qW5WI&t=18s

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Custom optical narrowband filters are very expensive. But cruder optical filters will help a little (ie a red filter for red laser, even if its not a narrowband red).

Modulation is probably the way to go, you just need a frequency that's not present in the ambient illumination (ie not a harmonic of the mains frequency).

islamkarim95: Hey! I'm using photodiodes to detect the light emitted from a laser diode...

Sounds like an XY problem. What do you really want to do. Beambreak? A laser might not be the answer. Leo..