Projector AR window

[steve-o]

You only have to tilt it a couple of degrees to avoid the beam reflection from hitting the diode window .. maybe 1/16 inch on 1 side or a couple of mm. That must be a tight build . Got any pix?

[Heavyen]

Well the transmission shhould be around 95%, i wrongly assumed that would mean 5% reflectance... Its this type of window: http://www.edmundoptics.com/products...Num=1#Products, 3mm thick, 50x50mm.
So it should be safe at such power of reflected beam?

About angle... the scanners are +-20° so this means i should tilt window for at least 21°... or maybe i misunderstood something.

[dsli_jon]

Hi Heavyen -

I have bought Anti-Reflection (AR) Coated High Efficiency Window from edmund optics and i have noticed it has high reflection for my blue lasers.

Astute-question... I've been wanting to post this for a bit, but... sigh, never enough time for everything...

The 'CDAR' windows from Edmunds are, imo, the 'best-overall' solution, AR-wise, for a window - even the 1mm-thick stuff it tough, fairly scratch-resistant, and has a preeety-sweet AR-curve, overall:



..however, as you can see, the coating-efficiency starts to 'wane', below 450nm - right where our beloved-blue sits - so, yeah - you might see a 'bit more R' at 445.. remember, a lot of these 'mass-market optics' were designed in the 'ion-reign days', where there wasn't typically a lot of power-goin-on below 457nm, say, out of an Argon, etc.. thus, this 'CDAR' was likely designed / optimized for those more 'typical' laser-lines... However...

..I did a little testing, and found that by tilting these ..(..and, thanks, Steve, for mentioning that - yes, 10˚ or more 'rake' is a great-way to avoid back-reflections - not so-critical for these Blues, but some Reds, etc - but that slight-rake also avoids that nasty 'ghosting' off your galvo-shafts, double-bounce off the Y, etc - best to 'rake' the window back, and 'up', ie: \ ) - but, continuing - by tilting the CDAR to about 22.5˚, you get a 'brewster-effect', and this lowers the R% to about 1% or less, vs the ~4-5%, at 90˚... Here's an 'example' of a window / mount I recently did for a m8, here:



..just band-sawed a 'tube' at the ~22.5%, (..and, not 45˚, not 10˚, etc - ~22.5 (1/2 of 45˚..) seems to be the 'magic' ˚...) and epoxied-up the windows, and voila.. ~0.5% of R @ 445... much-improved... and with the back/up rake ( \ ) you can terminate inside your projector-cover, etc.. just 'watch-it', when-removed...

..532 and 640 are both still pretty-'efficient', R-wise, at the 22.5˚, but I did not measure the R% of R/G, so... if someone wants to test / post some data / curves,
@ 22.5˚, that'd be sweet..

---
---hey Sire -

I have the same VIS zero degree coating and measured the 445 reflectance to be 1-2%.

You got *windows* with the VIS 0˚?? I know you can 'spec' them, but, I'd love to get a link to 'stock' windows (..like the CDARs) that have the VIS-0..cause, then - Yes - VIS-0 has a slightly-broader curve.. from Edmunds: VIS-0 - "AR Coated to Provide <0.4% Reflectance per Surface for 425 - 675nm, at 0° Angle of Incidence.." - we always get any Edmund-lenses coated with this, vs the Mag-Fluo, but I hadn't seen the windows, w/ the VIS-0... well, other than the 'super-thin' stuff, which is N/G for 'typical' projector-window.. waaay-too fragile...

Share, please?

fwiw, ya'll.. ..feel-free to post your own-findings / tell me I'm full of guano...
j

[djpsych]

Can these Edmund Anti-Reflection (AR) Coated High Efficiency Windows handle 4W of laser power?

[dilbert]

Yes no problem!