Optical mouse and laser safety.

[Balthisar]

@scr4

OK, so can someone here explain why they use a laser diode instead of an LED? I’d read the marketing blurb (the one you quoted) and it doesn’t explain why a simillar wavelength LED wouldn’t do the job.

I can explain a “probably.” A laser is brighter in the tested frequency band than a common LED given the same power consumption.

Meaning, aside from the laser to generate light, there must be a photoreceptor (photodiode, phototransitor, etc) to receive the reflection. Photoreceptors will react to a certain band of frequencies only. So by using a 716μW laser in the correct frequency band, you avoid the need to use a 5mW LED that’s bleeding across the entire spectrum. That is, the 5mW (this is just an example value) is substantially stronger than 716μW, but the power at the photoreceptor’s reaction frequency may only be 716μW.

[dakravel]

Don’t most LEDs really only emit across a fairly small range of wavelengths though? From my understanding, the main difference between an LED and a laser diode is that the laser diode is more heavily doped than a typical LED would be.

So Balthisar, I don’t see that your example holds since it’s not the case that an LED would be ‘bleeding across the entire spectrum’. I can sorta imagine that an LED because it is more lightly doped, it could indeed be emitting a larger range of wavelengths, and because a laser diode is so heavily doped, that it emits light over the same range, but much more at a main frequency. However, I don’t think that’s the case. Am I wrong in the way I’m thinking about this?

[Walker_in_Eternity]

@dakravel

Don’t most LEDs really only emit across a fairly small range of wavelengths though? From my understanding, the main difference between an LED and a laser diode is that the laser diode is more heavily doped than a typical LED would be.

…I don’t think that’s the case. Am I wrong in the way I’m thinking about this?

A laser diode is also cleaved so that the faces of the diode act as mirrors to form a laser cavity, I don’t think normal LEDs do this. Basically one cleaved faced has a reflectivity close to 1 and the other slightly less so that as the intensity of the light builds up it is only emitted in one direction.

We did a theoretical exercise at uni as to whether a laser pointer would damage the human eye, the upshot was that if the blink rate was fast enough you could avoid damage. I must point out that this was purely theoretical and I would not recommend pointing laser pointers at your eye.

[Balthisar]

@Stryfe

We did a theoretical exercise at uni as to whether a laser pointer would damage the human eye, the upshot was that if the blink rate was fast enough you could avoid damage. I must point out that this was purely theoretical and I would not recommend pointing laser pointers at your eye.

Laser classes are partially based on aversion response. That laser pointer wouldn’t be available if the average aversion response were longer than 0.25 seconds. So, don’t do anything stupid as you say (like repeat the experiment 100 times), but your natural tendancy to protect yourself will protect you.