My red dichro reflects green

[carmangary]

I bought a red dichro from Edmund and received it today. It is the 25mm red one. I tested it out and it reflects all of the red. But when I shine green through it, although it passes most of the green, I get two beams bouncing off of it and end up with two very bright dots. I turned it around to make sure it only passes green in one way but it didn't make a difference. So what's the deal? Is this normal?

[ajohnson30]

If you are talking about the dicro here:

http://www.edmundoptics.com/onlineca...=2433&search=1

Its supposed to reflect 98% of the red and pass > 90% of other colors. What does not pass will get reflected, meaning you should see a reflected dot of green thats < 10% of your greens power.

If that sounds about like what you are experiencing, then yes, it's normal

[carmangary]

OK, thanks. I had assumed that the remaining 10% would get absorbed or diffused but I guess I was wrong.

On a seperate note... has anyone tried the green led trick to measure green laser power? I just tried it and it sort of works. It said my 30mw laser is 65mw. Considering it is a cheap chinese laser it could be telling the truth, though.

[allthatwhichis]

Don't forget the IR it is leaking... You got it from Aixiz correct?

[carmangary]

Yea. I don't think green LEDS pick up IR though, do they?

[carmangary]

A couple of observations:

1) I just realized that it is very cool that the dichro reflects a little green because it just so happens to be in a usable direction. Meaning, I can use it for other effects. I think I will put a shutter and lumia wheel in it's path somehow. That will be cool!

2) You probably know this but I Did some research and LEDs will only detect light very near the wavelength of the color of the LED. So, a green LED will only detect green light. I think that's pretty cool. There is a website that says to sand the tops of the leds to make them flat but that is pretty silly since you can buy those rectangular ones with flat tops already on them. There is a formula to detect power (uA/2.8 I think). Does anyone know if it varies from LED to LED or if it is a set formula? Seems like it would vary but I am no LED expert.

[Pangolin]

One thing to keep in mind about all dichros. They "block" more efficiently than they "pass". You need to take a very close look at the specifications. Even for wavelengths they are supposed to pass, they will still block some light from those wavelengths.

The implication is that when you are using these to combine multiple lasers for RGB, you need to arrange the lasers so that your least powerful laser passes through the fewest number of optics (especially dichros) and that this "least powerful" laser is BLOCKED by the dichro.

Best regards,

William Benner

[ajohnson30]

The led power method does vary from LED to LED. All it can really do is give you relative brightnesses, i.e. Laser A is brighter/dimmer than Laser B by amount C. It's pretty much useless unless calibrated against a laser of known power, possibly even two of different power to check the range. If you can manage that, then you could calculate how much power an unknown laser had, as long as it's power doesn't exceed the specs of the LED.

[yaddatrance]

One last thought is try mounting it at a brewster angle, on some coatings this
minimizes the "work" the AR coating needs to do to pass...

[steve-o]

What about a poor-mans power meter where you stand 4 meters from the laser (to eliminate any ir) hold your hand in the beam and measure the time it takes to feel the burn..