• Ultraviolet Photography
  •  

Melting snowflakes in SWIR [video]

Infrared SWIR
12 replies to this topic

#1 Andy Perrin

    Member

  • Members+G
  • 4,247 posts
  • Location: United States

Posted 21 January 2021 - 20:05

As previously discussed, ice and water have different spectra in SWIR. You can see this pretty graphically demonstrated when you watch a snowflake melt.





Edited by Andy Perrin, 27 January 2021 - 20:38.


#2 Stefano

    Member

  • Members(+)
  • 2,018 posts
  • Location: Italy

Posted 21 January 2021 - 20:18

Andy, fascinating as always. In the first video you really see this well. Are there substances that change color like that when changing phase in the visible spectrum?

How did you upload videos here? I imagine this aren't links.

#3 Andy Perrin

    Member

  • Members+G
  • 4,247 posts
  • Location: United States

Posted 21 January 2021 - 20:30

Make YouTube video, get an embed link, then you use the media tag inside of the embed tag with the url inside the media tag.

#4 Bernard Foot

    Bernard Foot

  • Members+G
  • 722 posts
  • Location: UK

Posted 21 January 2021 - 20:56

Fascinating, indeed!
Bernard Foot

#5 Cadmium

    Member

  • Members+G
  • 4,193 posts

Posted 22 January 2021 - 05:09

Andy, really cool! :smile:

#6 Andy Perrin

    Member

  • Members+G
  • 4,247 posts
  • Location: United States

Posted 22 January 2021 - 05:54

Thanks guys! Rather hard to do -- I had to capture a snowflake on the mitten, FIND the snowflake on the mitten with the camera, which is easier said than done since the mitten has to stay outside on the window sill where it's cold, and the camera is large and heavy (2 kg = 4 lb or so), and you have to find the snowflake before it melts while also keeping the camera from falling out the window, and get it the right distance to be in focus.

By the way, this is a Thorlabs FB1450-12 (1450nm, 12nm FWHM) filter, which is the peak of the water absorption curve (within the range of my camera), so this is the best I can ever do. The water is a little ink blob, though, so I'm happy.

Edited by Andy Perrin, 22 January 2021 - 06:00.


#7 dabateman

    Da Bateman

  • Members+G
  • 2,895 posts
  • Location: Maryland

Posted 22 January 2021 - 09:30

Looks very cool, or warm. As its water now, not snow.

Can you do the same with ice shavings from an ice cube or does it need to be snow, which has a different crystalline lattice?


#8 dabateman

    Da Bateman

  • Members+G
  • 2,895 posts
  • Location: Maryland

Posted 22 January 2021 - 09:35

I have also wondered if the different ice lattices have different absorption. Like ice ix. But not the Vonnegut ice ix, that just causes the end of civilization.

#9 Stefano

    Member

  • Members(+)
  • 2,018 posts
  • Location: Italy

Posted 22 January 2021 - 11:52

David, probably different ice types have (slightly) different absorption spectrums. The difference between water and typical ice is already not a lot, although enough to see visually (with a camera), as Andy already showed. So I guess the difference between ice types is even less.

You could even test deuterium water at this point. This opens a lot of possibilities.

Andy, you eventually got the SWIRiest SWIR filter. I would take a selfie with that filter to have super dark skin. You already took a selfe, but it was full-spectrum I think: https://www.ultravio...dpost__p__27663

#10 Andy Perrin

    Member

  • Members+G
  • 4,247 posts
  • Location: United States

Posted 22 January 2021 - 15:46

No, that one was a 1500nm long pass Stefano. Full spectrum looks almost normal because that would include 350-1600nm and visible has the highest gain.

I’m not sure the 1450nm would make my skin all that much darker — once all the light is absorbed it doesn’t get any blacker. The only reason skin isn’t completely black in that photo is surface reflection.

Re ice cubes, I could try but I bet it’s the same thing. Not sure how I would shave ice? Do you use a knife? But it would melt instantly in my apartment.

#11 Stefano

    Member

  • Members(+)
  • 2,018 posts
  • Location: Italy

Posted 22 January 2021 - 17:39

Andy, thanks for clarifying.

I think the only ways you can have dry ice shavings (I think it is important for you not to have them covered in inky water) is to either do the "grinding" outside (since you probably have snow where you live given the videos you posted above, I think the temperature outside is around 0°C, ± some degrees), or to do this quickly inside, put the shavings in the freezer and then break them apart since they will all stick together. Not easy in both ways.

#12 dabateman

    Da Bateman

  • Members+G
  • 2,895 posts
  • Location: Maryland

Posted 22 January 2021 - 18:39

Yes use a knife or a cheese grater.

#13 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 8,941 posts
  • Location: UVP Western Division, Santa Fe, New Mexico

Posted 22 January 2021 - 21:46

Those are just the coolest vids !!!!
Thank you, Andy, for posting this experiment.
Andrea G. Blum
Often found hanging out with flowers & bees.