Products > Thermal Imaging

Protective window for thermal camera - coatings

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Mike_91:
Hi all,

I'm looking for a protective window (sacrificial lens) for a thermal monocular (Hikmicro LE10S, spectrum of 8-14 um), the cheaper the better, but it has to have good transmittance.

The purposes:
1) protect the monocular's lens in airsoft games against a possible hit from the BB (assuming kinetic energy to be <1 J) - even if the sacrificial lens itself gets damaged in such case, it should not shatter into pieces to protect the monocular
2) the second use case is protecting the monocular from road debris - I have an idea where I would use the monocular as a "night drive assistance" mounted on a car (a couple of ideas how to mount it on the outside) and transmit the image over wi-fi to my phone (or via CVBS cable which LE10S supports since there is a lag on the wi-fi, to a compatible screen), to help spotting wild animals when driving on wooded roads at night time.

I'm aiming at germanium windows, diameter of approx. 20 mm (twice the size of the monocular's lens dia) and thickness of 2 mm - I think this should be sufficient. Coating type is still to be determined, as uncoated Ge lens has transmittance of around 50% in this spectrum, which is too low.
But I'm also considering ZnSe windows, which are usually cheaper, however it's a softer material, so I gather not as good as Ge for these purposes.

Now, as for the coatings - it can be either AR/AR or AR/DLC.
Is the "standard" AR/AR coating good enough in terms of scratch resistance?
I know the diamond-like carbon (DLC) layer on top of the AR coating adds extra protection, but at a cost of slightly lower transmittance and higher price.

I'm also looking for a supplier where I can buy such thing, and found a few of them (so far best looking one is https://www.uqgoptics.com/material-category/germanium/ ), but some make such windows on custom request and when ordered in larger volume only.

Bill W:
Standard AR/AR is not going to last long outdoors.  It is vulnerable to water which will get in via micro scratches.  It is really only suitable as an 'indoors' / internal coating.

You can get 'durable' coatings which are close to AR in transmission and stand up to civil use OK - but won't pass military 'sandy windscreen wiper' type tests.
The downside is I'm not aware anyone selling windows with AR/DUR singly.  The DUR side is a specific coating run that costs 1000's could make in the multiple 100's of windows.

A lot of the catalogue sellers like Edmunds are at stupid prices, at least 10x volume pricing.

If you are not too fussy cosmetically I could look out and check some of my used windows from Argus cameras - drop me a PM
26 or 33mm dia

Bill

Mike_91:
Thank you, Bill :)

What is the DUR coating? I searched the internet but didn't find any references. Isn't the DLC the type of coating protecting Ge lens from scratches, abrasion and chemicals? I base my knowledge on UQG's spec - they claim their AR/DLC (the side with DLC must be on the outside of assembly, of course) conforms to MIL-C-48497A.

Bill W:
DLC (Diamond-like-carbon) is a very high spec coating which as you have found is not so great on transmission.  However it meets all the MIL-specs for abrasion and water resistance.

Classic 'AR' (HEAR, High efficiency anti-reflection) is great on transmission but not so on resistance to wear / water.

The 'durables' sit in between.  They are an 'on request' coating, only viable if you are buying 1000's and want the extra 15% transmsission.  That said DLC is getting better on transmission now anyway.

Bill

bap2703:
Would Kitchen plastic film + rubber band be durable enough?

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