Projector AR window

[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. (visualy estimated, it seems quite a lot and so im worried.)
So i am wondering how much of reflection is still safe for blue diodes, because i dont want to fry them

[steve-o]

Just make sure that the beam is not reflecting directly back to the diode(s) output aperture window (adjust your AR window angle at lowest possible diode power).

[planters]

I have the same VIS zero degree coating and measured the 445 reflectance to be 1-2%. It looks brighter and I discovered that some of this appearance is due to anything less than scrupulous cleanliness at this wavelength. This is a good argument for First Contact or the Stanwax product (I have no affiliation).

[andy_con]

I don't have this issue and I use ar windows from edmund

[norty303]

Have you got it the right way round? Some are only coated one side.

[kecked]

I used their windows for years. A bit thin but they work well. If you really want to waste money buy a sapphire window or such though I think those are for IR.

[dilbert]

I use a 1mm AR from edmunds with no problem on 445

[andy_con]

get the 3mm thick window then

[Heavyen]

Well AR coating is on both sides, so there shouldnt be a problem with orientation.
About placing it at angle, im afraid im little too short on space to use such technique.
well at specifications its written that at blue wavelenght the reflection should be around 5% could this be enough to damage diodes?

[dilbert]

Which window did you use?? Mine has 0.3% reflection and 96% transmission on 445 and blue is the worst - its 99% for red & green.

[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:

22.5 445 Windo_2.JPG22.5 445 Windo_1.JPG

..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