Just found this wideband thermal camera

[Ben321]

This https://www.ino.ca/en/products/3-14-microns-infrared-camera-microxcam-384i-mlwir/ is an MLWIR imager. That means it covers both medium-wave and long-wave IR bands. It's passband is 3um to 14um. Yet it uses a standard VOx microbolometer array. So I'm wondering, what material is the lens made out of, that allows such a wide passband? It can't be germanium, because that is only good for 7-14nm, and is used with standard LWIR images.

[Fraser]

Only the AR coating dictates the Germanium passband beyond its physical characteristics of transmission. Multi band AR coatings have been around for decades. Look at what Inframetrics used to produce.

[eKretz]

I was going to say that yesterday but wasn't sure of myself. It has always amazed me how just adding a simple microns thick coating can completely change the transmission to such a degree.

[RoGeorge]

It has always amazed me how just adding a simple microns thick coating can completely change the transmission to such a degree.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/antiref.html

[eKretz]

Outstanding, thank you.

[Ben321]

Only the AR coating dictates the Germanium passband beyond its physical characteristics of transmission. Multi band AR coatings have been around for decades. Look at what Inframetrics used to produce.

So uncoated germanium has about 45% transmission from 1.7um to 25um?

[eKretz]

Yup, close. See attached.

[Ben321]

Yup, close. See attached.

Interesting. When AR coatings are applied, that boosts the transmission in certain areas. However, does it also cut the transmission in other areas? Or does it leave it at the ~45% value?

Any idea what the transmission properties of an uncoated silicon window is? I'd be interested to see how that compares to uncoated germanium.

[eKretz]

From what I gather, multiple coatings of varying thickness can be applied to dial in whatever you'd like. I'm sure it's a trade-off sometimes or every lens would use the exact same recipe.

Silicon transmission graph attached.