White Light Induced Near IR Fluorescence.

[colinbm]

From an inspiration from this recent post, http://www.ultraviol..._4897#entry4897

I will start the ball rolling, down this slippery slope...White Light Induced Near IR Fluorescence.

The Sun has gone down & the Moon is not yet up. I have powered up my reliably bright 24watt Mercury Vapour HID Flashlight, placing a Hot Mirror filter in front of the light to give an output below 660nm & placing a IR720nm filter in front of a Full Spectrum Sigma DP2 compact camera. The early results are perhaps the wavelengths are too close a match. I can see a reflection from a bathroom mirror.

Next I tried the S8612 filter in front of the flashlight to give an output below 680 to 600nm & placing a IR850nm filter in front of a Full Spectrum Sigma DP2 compact camera. The early results are perhaps there is some White Light Induced Near IR Fluorescence.

Around the inside of the house, bare stained woodwork is fluorescing, white enamel paint is fluorescing, yellow cream acrylic paint is fluorescing, BUT, I can see no reflection from a bathroom mirror.

Have I passed the test ?

Cheers

Col

 

PS, I have been outside & checked out the leaves of the difference plants in my yard & I can detect White Light Induced Near IR Fluorescence with all the leaves, though very faint, I will need at least 1 second of exposure, even with this bright light, though its beam is only a few cm wide.

I will need to set the camera & light on stable tripods & show my results tomorrow.

Col

[Andrea B.]

It will be cool to see your results, Col !!

 

What is the hot mirror you were using?

 

The 8612 passes UV and Visible light. Did you make a test exposure using a UV-Pass filter on the flashlight to verify that the flashlight passes no UV?

 

Remember the leaves IR fluorescence in chlorophyll is below 850nm.

[colinbm]

Hi Andrea

Yes, it will be cool to get usable results.

The hot mirror, I first used on the flashlight, was the Sigma original hot mirror, approx 420-660nm. I felt there was a slight over-lap with the R72 on the camera. I could see the reflection of the flashlight in the bathroom mirror. Then I tried the S8612 on the flashlight but was still able to see the flashlight in the bathroom mirror with the R72 on the camera. That is why I went to the ir850 filter on the camera.

I'll dig out some in-between IR filters & other hot mirrors etc...........

Watch this space :D

Col

[colinbm]

Preliminary results....

The leaves......I think are from a Tecomaria capensis (Cape Honeysuckle).

The set-up.....

The light source was a 24watt Mercury HID flashlight with the following filters to suppress the Ultraviolet & near Infrared light, Sigma original hot mirror (420-660nm), BG39 (360-680nm), MaxMax X-Nite CC1 (325-645nm). This gives the light source at approx 420-645nm.

The camera was a Sigma DP2 full spectrum APS-C compact camera with the following filters, R72 (>720nm) & a longer pass hot mirror (355-780nm). This gives a window on the IR fluorescence at 720-780nm.

 

The leaves showing IR Fluorescence

https://www.flickr.c...06/15370146400/

 

The lamp shining into a mirror, centre, with the same leaves on the right edge.

https://www.flickr.c...06/14935602193/

 

If this meets with satisfaction, I will get some more stable, in focus images.

Col

[Andrea B.]

I went there and clicked your photo and got a Hyundai ad !! I hate flickr !! Why do they do that?

Maybe you could upload the photos here?

 

The only thing I'm not sure about is whether there is any UV leak in the filtration. That depends on whether your Sigma hot mirror has any leakage. It would be a good idea to test it by mounting it with a UV-pass filter and making some exposures of varying length. Just to be sure.

 

Looks interesting so far. "-)

Carry on !!

[Andrea B.]

Finally found the link. Now I can see it !! Hope this is OK, Col ??

 

[colinbm]

Thanks Andrea

I will check for UV leaks.

I couldn't load the photos here as my allocation was full & it prevented me from loading them.

 

Col

[colinbm]

Hi Andrea

Just to be sure, I have added a L39 filter onto the flashlight stack. This will block below 390nm :D

I have added some better IR Floro images to my Flickr page....

Col

[nfoto]

When experimenting like this one has to keep a close watch on alternate explanations/sources of error.

 

First, try to establish the order of magnitude of spectral leakage in the filter(s). Then, convert this into exposure difference vs the light source alone. Remember the filters you have used are not very sharp-cutting ones. Thus, the 720 will actually transmit a large portion of deep red and borderline near IR. The L39 is just 1 stop down at 390 nm and so on. Can you deploy dichroic sharply cutting filters in your setup?

 

My first reactions to these images were they represent deep red leakage only. I would love to be proven wrong though.

[Andrea B.]

I couldn't load the photos here as my allocation was full & it prevented me from loading them.

 

Col, I added you to the Members+ group to give you more space for uploading photographs. :D

[colinbm]

Thanks Andrea & Bjorn

Yes Bjorn, I agree with your concerns.

I have used multiple hot mirrors to get the IR leakage from the lamp down as low as possible, this is why I showed the mirror shot of the light source next to the leaves. This has shown that the IR Fluorescence was much brighter then any red leak. Later the shot with the biro ink on my hand has shown the IR Fluorescence very well.

I will be getting a L42 filter soon.

"Can you deploy dichroic sharply cutting filters in your setup?" Can you elaborate on this further please, Bjorn, I have used all the suitable 'hot mirrors' I have.

Cheers

Col

[nfoto]

For example, the Baader UV/IR Cut filter is dichroic and cuts very sharply outside the range 420-680 nm (if memory serves).

 

With long exposures (in the seconds range), even 0.1% leaks might cause unwanted contamination.

[colinbm]

Thanks Bjorn

I don't know of any other Dichroic IRC that cut below 660nm like the Sigma original hot mirror ?

I have other Dichroic IRC like B+W 486 & 489, & the Tiffen Standard Hot Mirror, but these go beyond 660nm.

I guess I could stack them on the lamp too, just to add to the strength.

Cheers

Col