IR Cutoff filter

I'm looking for a IR cutoff filter that is quite a bit cheaper than what Edmund Optics sells. OCLI wants 21 dolars, I'd like to find something
cheaper. I need to pass wavelengths from 420-660nm, though if it attenuated light on each end a bit, it would still be fine for me.
I'm putting it in front of a silicon photodiode, and need to kill the IR response on this part.
Can anyone recommend some material/manufacturer? (I know devices like the BPW21 already have this, but I need to use a different part).
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attenuated
I've extracted what I guess is infrared filtering glass from a photocopier. It's light blue colour seem just like a dilute solution of copper sulphate, which I once saw used as an infrared filter to prevent heating of liquid helium while it's photographed. I guess it's intended to give a response closer to the eye.
Scrim
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the
photocopier.
sulphate,
The heat filters used on slide projectors are made of a phosphate glass. They might be the best source, if you can find an old one.
A light blue colour doesn't sound very promising, but you never know. If you can get it put on a spectrophotometer and check the absorption spectrum in the visible and near IR, that will tell you if it's any good.
--
Terry Harper
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http://www.science-info.org/micro/docs/waterfilter.pdf gives the spectral properties of copper sulfate solution as well as other dye solutions.
--
Gordon
Gordon Couger snipped-for-privacy@couger.com
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in
Spectra in solution and spectra in glass are not necessarily the same, mainly because there could be other species present. Cu2+ is likely to absorb too much of the visible for him. If it was a pale green it would be more promising.
--
Terry Harper
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Leeper wrote:

By far, the cheapest way to do this is to pick a photo diode that incorporates such a filter. What diode are you using. Perhaps someone knows of a similar one that includes the filter.
As to filter materials, Schott KG series filter glasses are made for this purpose.
http://www.noao.edu/kpno/filters/sgt/131t_sm.gif
The BG series has more red attenuation.
http://www.noao.edu/kpno/filters/sgt/123b_sm.gif
http://www.noao.edu/kpno/filters/sgt/123t_sm.gif
--
John Popelish

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I agree with John, with this addendum: If you're trying to improve signal to noise ratio by reducing photocurrent due to ambient light, this often proves to be an elusive goal. The reason is that shot noise is proportional to the square root of bias current. So, you will typically need to reduce ambient photocurrent by more than the square of the passband transmittance of any filter. An example will make this clear. Supposing that you reduce ambient photocurrent by a factor of 2, for a shot noise reduction of about 40%. If your passband transmittance is 60%, you will not have gained anything.
Paul Mathews
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I'm trying to reduce the IR response, so that the sunlight IR doesn't mask the visible light I am trying to measure.
Modulation and all that will not work, I need to know the amplitude of each Red, Green, and Blue device.
I'm using a reversed biased BPW34, and a the speeds I need to measure at, it's 50pf (or whatever the datasheet said) is wonderful, it helps me maintain 400nS rise response, to make amplitude measurements 100 nS later, of the R, G, & B sources rather easily. It only lacks a filter.
Something like the SFH2430 (?), has too much capacitance and internal resistance for the method I am using.
The BPW21 isn't bad, but it's cost of 4.55 is a bit high for me, plus it is not in a surface mount package.
I found one device from Hamamastu that might possibly work, it's marginal, I'll have to wait for it to arrive to actually test it.
Any advice is greatly welcomed, thanks.

what
attenuated
IR
the
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Leeper wrote:

(snip)
Have you looked at any photo diodes that have narrow band visible filters built in like: http://www.photonics.com/spectra/newprods/XQ/ASP/newprodidnl.6444/QX/read.htm http://www.photonics.com/spectra/newprods/XQ/ASP/newprodidd.3114/QX/read.htm
--
John Popelish

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----- Original Message -----
Newsgroups: sci.materials,sci.optics,sci.electronics.design Sent: Sunday, May 02, 2004 7:49 PM Subject: Re: IR Cutoff filter
: Leeper wrote: : > : > I'm trying to reduce the IR response, so that the sunlight IR doesn't mask : > the : > visible light I am trying to measure. : > : > Modulation and all that will not work, I need to know the amplitude of each : > Red, Green, and Blue device. : (snip) : : Have you looked at any photo diodes that have narrow band visible : filters built in like: : http://www.photonics.com/spectra/newprods/XQ/ASP/newprodidnl.6444/QX/read.htm : http://www.photonics.com/spectra/newprods/XQ/ASP/newprodidd.3114/QX/read.htm : Or only sampling the AC of the switched light source and letting the DC component the sun light fall out you only get the LED reading with none of the back ground noise from the sun. Do a 180 degree phase shift at the sensor and amplify to signals exactly the same and combine them at the end and any thing you have left is the common mode error. Go back and find the schematic for an old Instorn amplifier using vacuum tubes to see how this is done. Gordon
Gordon Couger Stillwater, OK www.couger.com/gcouger
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There are many kinds of 'modulation'. The simplest, in concept, involves sampling just before a pulse, sampling during a pulse, then subtracting the first sample from the 2nd. This works wonderfully well, and it can be done with analog or digital electronics, in hardware or software. Of course, it's best to optimize the optics first. One of the easiest ways to reduce the ambient contribution is to narrow the field of view, using lenses and/or baffles, to just what you need and no more. Perhaps contrary to intuition, lensing can actually reduce ambient photocurrent if it narrows field of view (and, if your optics don't 'look' into the sun or an image of the sun).
Paul Mathews

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Remember rubylith sheets? Charettes still sells them.
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Sorry, don't recall rubylith.
I do miss the 5 cent bottles of pop.
wrote:

attenuated
the
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Its a red masking film sold in art supply stores. You can get a 30"x40" sheet for about $6.00 (us). Used to use it to make pcb long ago...
http://www.misterart.com/store/view.cfm?group_ide6&store 1
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maxfoo wrote:

I doubt it would be a stable IR filter. Its chromophores aren't designed for long-term stability.
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Unless I've slipped up here, strange that it should be red - kind of implies it lets that end of the spectrum through. An infra red blocker whose range extends into the visible will have a lack of red in its passed light, which makes it look blue.
Scrim
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You can make a cheap optical low pass filter for testing purposes out of photographic film negative. Take some Kodak Kodacolor ASA 100 film, remove it from the roll, expose it to light for a minute or so, then wind the film into the roll again. Tell the person doing the developing that you just want negatives and that you overexposed it on purpose (you don't want them trying to lighten the negative/darken the print!) The processed color negatives can be used as a low-pass optical filter. It should stay stable for about as long as negatives last unless you hit it with a lot of light (direct sunlight or a laser). It's fragile and easy to scratch so I ususlly use two layers with the scratchable sides facing each other.
Also see: http://members.misty.com/don/irfilter.html http://www.amasci.com/amateur/irgoggl.html http://www.x-raycameras.com/kodak_wratten_87_range.htm
--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
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Not sure what wavelength you really need to pass. If you are on a tight budget, colored plastic or colored glass works well. The bandpass is fairly wide, but probably not from 420 to 660 nm. It does block IR well.
Any hobbly shop will sell colored glass (sometimes sold in broken pieces for those doing stained glass windows). They also sell colored plastic for the same purpose.
Cellophane is even cheaper, but it's thin and has more loss.
Are you doing free space laser communication??
A

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attenuated
I have read that over-exposed films can be used as an IR filter Or use (a piece of) the reflector of 'cold' halogen lamp.
Wim
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Over exposed film is used to block visible and pass IR. I need the opposite.

the
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