I tested several different IR pass filters.
My set up includes 2 850 NM IR lasers in a sunlight filled room.  The camera is a Creative Labs VF0070 Webcam Live! Ultra (IR blocking filter removed).  The surface is a 19” LCD panel which blocks a substantial amount of visible light.  I’m not using any acrylic nor any compliant surfaces.  The white marks above my hand are incomplete plaster repairs on the ceiling.  Any marks below my hand are reflections from the floor and camera.

Here is the first test with NO filter shooting up at the LCD panel.

A single piece of exposed film negative.  This does very little to reduce the ambient light.

A single piece of floppy disc.  This reduces ambient light but also darkens the blobs.

An inexpensive 850nm IR pass filter.  It allows all light greater than 850 nm to pass.  This was a waste of money.  It is not much better than the negative.

A used ultra high-end Coherent 850 nm IR Narrow Bandpass filter.  This is by far the winner.  It blocks out almost all ambient light and does not diminish the blobs.  The filter is designed to only pass 850 nm light.  You can see the precision from its test chart.  I paid $35 for the filter on eBay.  I think this would retail for much more. 

The filter case includes the following info:
Part# 35-4480-000
Coherent 25.4 MM, 850.0 NM CWL
For service call 530-888-5062
UK 01923242261
U.S. 530-889-5365

The test chart has the following company info:
Ealing Electro-Optics, Inc
89 Doug Brown Way
Holliston, MA 01746
800-343-4912

Great results rdagger. A bandpass filter will always work the best! =) I’m interested in seeing this setup directly next to a window with daylight (basically as much daylight as possible directly coming on the table aside from it being outside). If you could get a picture of it also, that would be great. Many times people say they have their tables in direct daylight, but it’s better to see the exact atmosphere if we see where the table is placed in the room and where the light is.

Rdagger, great to see more people testing laser setup .

About your bandpass filter, does the company have a website ?
Thornlabs filters are 3 times more expensives ...

Could you test this outside? I would like to see it done right outside. full sunlight. Maybe this could be used in store windows?

Great post rdagger… just question what are your upper and lower cut off frequencies for the filter you are using?

Taha

Taha - 05 July 2008 04:43 PM

Great post rdagger… just question what are your upper and lower cut off frequencies for the filter you are using?

Taha

From the specs he posted:
Coherent 25.4 MM, 850.0 NM CWL

I’m assuming the Coherent 25.4 MM spec is the bandpass width, 25.4 NM

So, 25.4 / 2 = 12.7 NM on each side of 850 NM center.

So the freq to freq is 837.3 NM - 862.7 NM

...if my assumptions are correct mind you…

hmmm ive tested 880BP12 and i’ve got to say that the results weren’t like this… and btw im using SHF485’s which has a peak output at 880nm my blobs are a lot darker but that maybe because i tested my setup in the basement.

Gonna go try out my BP12 again…

Taha

Tinkerman - 05 July 2008 06:34 PM

Taha - 05 July 2008 04:43 PM

Great post rdagger… just question what are your upper and lower cut off frequencies for the filter you are using?

Taha

From the specs he posted:
Coherent 25.4 MM, 850.0 NM CWL

I’m assuming the Coherent 25.4 MM spec is the bandpass width, 25.4 NM

So, 25.4 / 2 = 12.7 NM on each side of 850 NM center.

So the freq to freq is 837.3 NM - 862.7 NM

...if my assumptions are correct mind you…

Tinkerman,

I think that 25.4 MM refers to the filter diameter (which is excactly 1").

From the test chart I can see that:
CWL=851.1 (Filter’s center wavelength)
HBW=11 or 12?? (this is not clear since the image was cut, but this is the filters bandwidth)
XT=57% (filter’s transmittance)

From the chart I can also see that filter cuts almost all the light outside of 840-860nm range, so it seems that filter’s bandwidth is 20nm.
So I’m curious what the HBW number from the test chart is as this will tell us how narrow the filter is.

~Alex

AlexP - 06 July 2008 08:16 PM

I think that 25.4 MM refers to the filter diameter (which is excactly 1").

From the test chart I can see that:
CWL=851.1 (Filter’s center wavelength)
HBW=11 or 12?? (this is not clear since the image was cut, but this is the filters bandwidth)
XT=57% (filter’s transmittance)

From the chart I can also see that filter cuts almost all the light outside of 840-860nm range, so it seems that filter’s bandwidth is 20nm.
So I’m curious what the HBW number from the test chart is as this will tell us how narrow the filter is.

~Alex

AlexP is correct the 25.4 is the diameter and the chart shows that pass falls quickly as you near 840 or 860.
I took a vacation to see the D.C. Air & Space Musuem.  When I get back I will post all the specs from the chart. 
cerupcat & Justin: I will also perform an outdoor test and include pics of my set up.

jimihertz - 05 July 2008 05:55 AM

Rdagger, great to see more people testing laser setup .
About your bandpass filter, does the company have a website ?
Thornlabs filters are 3 times more expensives ...

The filter is used and I bought it on eBay.  I posted all the company information that was on the box.  Sorry no website listed.  The date on the test chart is 9/26/2000 so the filter is around 8 years old.  You might want to try Edmund Optics.

AlexP -

So I’m curious what the HBW number from the test chart is as this will tell us how narrow the filter is.
~Alex

Here is a better scan of the test chart.  The half band width = 11.9.

Seems like the filter is 850BP20 making the lower cut off 830 and the upper cut-off 870

Taha