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Need of Filter which blocks 400nm to 1500nm and allows above 1500nm - Reg

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prakashvenugopal

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Hi all,

I need a filter which blocks the 400nm to 1500nm wavelength and allows above 1500nm wavelength. kindly recommend the same.

Regards,
V. Prakash
 

BradtheRad

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Blocks visible light & the band named infra-red "A'.
Allows infra-red 'B'.

* Some types of IR photosensors are encased in dark purple translucent plastic.

* I looked at an automatic floodlight which had a milk-colored plastic sheet in front of the photodetector. It turned on when a warm-blooded animal walked nearby, and stayed off during daylight.

I imagine those are typical of the filter you want.
 

D.A.(Tony)Stewart

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1500nm wavelength.
These must have precision specs for passband and stop and attenuation with precise optical quality charactersistics and cost $k's thousands of dollars. But maybe you can find a surplus "Longpass Filter" here ( LPF ) for $250
 

FvM

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I'd check stock lists of other filter manufacturers and optic distributors, e.g.

1500 nm long pass isn't very usual, there isn't much stock in this range. You should specify the filter requirements, acceptable cut-off range and steepness.
--- Updated ---

Usual black plastic filters have near IR (e.g. 700 - 800 nm) cut-off wavelength and no continuous transmission below 1200 nm. That's no problem with Si sensors, but plastic filters are not suited for the requested application. It needs interference filters on IR substrate like fused silica.
 
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prakashvenugopal

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Hi,

I need a filter blocks UV and VIS wavelengths but allows IR from 1.6µm and above

Regards,
V. Prakash
 

FvM

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The question has been essentially answered by SunnySkygui. The specification (still not complete) can be met by an interference filter. If no stock filter available, it can be made according to your specification. Filter substrate defines the transmission range, e.g. up to 3-4 um with fused silicia, more with special IR materials.
 

prakashvenugopal

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  • Ir Filter specification.png
    Ir Filter specification.png
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FvM

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As clearly stated, it's a long pass filter. +/-35 nm is the tolerance. Substrate is Ge or Si, expect continuous transmission up to 15 or 20 um. In case of doubt, ask the vendor for a curve.
 

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