I am investigating plastic optical parts that could be produced by injection molding, hot embossing, or other techniques, in order to work between 7 and 14µm (long wave infrared - LWIR).
PMMA and other optical plastics used in the visible are opaque at around 10 µm, unless they are made very thin, which is not suitable to making lenses !
Christophe
- You should try polyethylene, polypropylene or possibly polymers containing only carbon and hydrogen (not oxygen, which is the case for. PMMA}. But also here the transparency will depend on the thickness necessary for your lenses.
Thank you Pavel. Polyethylene is probably the simplest polymer containing only C and H atoms (very simple structure, no oxygen).
It is actually used for making very thin infrared lenses working at 10 µm. However, this is not a very transparent material (about 10 or 15% aborption per 1/10 mm). The transmission coefficient of a 0.5 mm foil of PE is about 50%.
Any idea about how to enhance the infrared transmittivity of PE ? Or another type of suitable material ?
Regards,
Christophe
What you are searchiong for are infra-red glasses. There are a couple of materials available. So called chalcogenide glasses may be the weapon of choice. They are mainly composed of the elements Ge-As-Se.
Searching the internet for these keywords you should easily find suitable materials.
Thank you Jan.
Yes, chalcogenides are well known for making infrared optics. But they are way too expensive for applications in building automation. This type of application requires very low cost materials and processes. I am considering a cost of just a few $ for infrared optical elements. This is the reason why I am looking at polymers. Maybe chalcogenide elements can be mixed with organic polymers to improve their mediocre transmission ?
ChristopheAdd your answer
That makes it more tricky.
How is your applicagtion designed so far? Would it be an option to use your standard components and use dichroitic filter elements (depending on the precision of your set-up) to gate out unwanted parts of the spectrum? Such filters can be bought as cheap foil filters? Not sure whether they cover the required range, but might be an idea...
Not sure about polycarbonates. They have at least a good transmissivity in the NIR...
Jan
Chalcogenides could be produced somewhat inexpensively in very large quantities - you would have to talk to the materials vendor and also consider the molding costs. A major issue will be size - if your lenses are very small (think cell phone camera), then the molding process could be done with dozens of elements per run and the materials cost would be small. As siize goes up, costs go up exponentially. For larger lenses, the comment about diffractive lenses is a good one - but you will be limited in the MTF quality you can expect.
Hi Dean,
Chalcogenides are certainly well adapted to mass production, especially small elements (multiple cavity molds). However, chalcogenide lenses are still much more expensive than injected lenses made with polyethylene for instance. For an application using a small single lens, with a modest aperture, a low cost chalcogenide could be used. However, my application requires a rather large field of view and an f/1 aperture. A 2 or 3 lens system is probably needed. In this case, chalcogenide lenses will be too expensive...
Thin plastic lenses could be used with large refractive Fresnel zones or smaller diffractive zones. The limiting factor is still the transmittance at 10 µm.
Christophe
Sure ! Military applications doesn't really need low cost materials... That 's the difference with mainstream applications in building automation. No missile involved, just millions of cheap IR modules to detect, count and locate people !
Christophe
Hello Christophe,
I understand this a very old thread, but I was wondering whether you were able to find a solution. I am dealing with some automation and trying to increase the range of an IR thermopile for my project, with typical target wavelength of 12um. The cost of the conventional lenses is too high for my project. Any ideas will be appreciated.
Thanks
Saptarshi
Dear Saptarshi,
You can check the website of Kube Electronics in Swizerland. They sell many low cost IR parts for pyroelectric an thermopile sensors.
Good luck with your project.
Christophe
PS. In my lab, we offer testing services for low cost infrared detectors used in automation. Our customers are the manufacturers of occupancy sensors, motions detectors, alarm systems, lighting controls, etc.
Hi Christophe,
Are you still interested in LWIR transmitting polymers? I may have a solution for you.
Hi Darryl,
I am interested in such a material as well. Can you please provide a reference?
Thanks
@DanielTulbert, here's a good place to start:
DA Boyd, CC Baker, JD Myers, VQ Nguyen, GA Drake, CC McClain, ...
Chemical Communications 53 (1), 259-262
DA Boyd, VQ Nguyen, CC McClain, FH Kung, CC Baker, JD Myers, ...
ACS Macro Letters 8 (2), 113-116