# Dichroic mirror spectral range?

1. Mar 12, 2013

### geneiusxie

Hi guys,

I'm wondering about exactly if there is some sort of range that a dichroic mirror would reflect, like a green mirror would reflect between 532nm - 600nm or something. I'm pretty sure a green dichroic mirror doesn't only reflect only 532.00000 nm and not 533 nm or something.

But what is the typical wavelength range for dichroic mirrors? And would it be possible to make a dichroic mirror so precise that it would only reflect light that deviates no more than 1% from the design wavelength? For example, would it be possible to build a mirror that only reflects 530nm - 535 nm?
Thanks.

-Gene

2. Mar 12, 2013

### Staff: Mentor

I've seen filters that filter out all but a 5 nm range centered on the Hydrogen Alpha emission, which is 656.28 nm. I'd be willing to bet you can get smaller.

Also, the angle of the light has a drastic effect on this range. In any optical system, a smaller F/ratio, and thus a more sharply converging light cone will reduce the effectiveness of the filter more than a larger F/ratio system.

3. Mar 12, 2013

### geneiusxie

Huh. I was wondering if it was possible to make a mirror that would seem 100% transparent to the naked eye, but would reflect 100% of the light of a green laser.

If you stack 3 mirrors for red, green, and blue the size of a TV and put an activated carbon material designed to absorb 95% of the material that goes through the mirrors, and combine that with a laser projector, we could get a laser projector that offers much darker blacks than standard projectors in normally-lit rooms.

Of course, dichroic mirrors seem to be pretty expensive right now, so we'd need a cheaper way to make those mirrors too. We'd also probably have to use a gradient on the wavelength that the mirrors reflect due to some areas of the screen being at different angles than others. And we'd need a way to scatter the light so people can see it. And then if the light gets scattered, the dichroic mirrors wouldn't really work because of the different angles.

Wow never mind then lol.

4. Mar 13, 2013

### Andy Resnick

Spectral characteristics of dichroics (or any other dielectric mirror) can be designed with (AFAIK) nearly any spectral lineshape. The major companies are Omega Optical:
http://www.omegafilters.com/Products/Curvomatic

Chroma:
http://www.chroma.com/products

Semrock:
http://www.semrock.com/

Dielectric filters can have passbands as narrow as a few nm, AFAIK. If you want even more narrow passbands (say for solar observation), you have to go with a Fabry interferometer.