The laser and the blizzard

[Andy Perrin]

With ominous forecasts of a substantial blizzard approaching my home in Boston, all of which later came to pass, I began to consider the photographic possibilities of a large snow storm. As I was looking through my equipment, it hit me that I had several 405 nm lasers, all equipped with Powell lenses that spread the beams into a sheet. These were used previously for my laser-induced fluorescence experiments, but I realized that here was the perfect way to photograph a SLICE of the blizzard, as snow passed through the beam.

 

So I set up my 200mW laser in the window and projected it horizontally on the trees behind the apartment. (With such an intense blizzard, at 2am, there was no chance of any human being in the path of the beam, which was, as you can see below, well above people's heads in any event.) I used the Sony A7S with a BG38 2mm filter to record some video and stills.

 

This geometry produced the occasional speckle, but it was hard to get much feel for the way the snow was blowing around.

 

 

Next, I tried taking a lot of photos and combining them by taking the maximum value of each pixel, giving the following picture:

 

Maximum at each pixel of 30 pics, each one is F/22, 0.5sec, ISO1600, with BG38 2mm on the camera

 

While this was neat, it didn't give any sense of motion really, especially since the majority of the motion was vertical. So I rotated the beam vertically for the next shots. By now it was 3am or later, and I was not concerned about anyone getting hit by the beam. I also realized that I owned a 405BP20 filter, which is the same wavelength as the laser. Unfortunately it is only 12mm in diameter, which meant I had a lot of vignetting. However this allowed me to remove the majority of the background light and get a much better signal to background ratio. 

 

I got some nice speckle patterns. This one was 30 seconds long. Lens was the Sony Zeiss FE 55mm/1.8 at F5 ISO1000. It was a struggle to keep things in focus.

 

This was F/9, 1 second, ISO3200, filter 405BP20

 

F/7.1, 2.5sec, ISO2000, filter 405BP20

 

F/7.1, 2.5sec, ISO2000, filter 405BP20

 

So that's what a slice of a blizzard looks like! Finally, I went outside with a ziplock bag around my camera and photographed the scene from the side:

 

F/2.5, 25 sec, ISO2500, filter 405BP20

If you were previously confused about the geometry, hopefully that picture makes it clear. It's also my favorite of the lot!

Incidentally, without the 405nm filter, the laser was quite invisible outdoors when seen from the side - I could not see the beam reflecting off the snow until after I took the photo. I could see the line of the beam projected on the trees (not shown here, but like you can see it in the movie) above my head though. 

 

[colinbm]

Very weird & strange, I can sort off imaging the scenario with rain, as I have never experienced snow, but snow is less weight. 
Probably best with no one around, lest you get a heavy knock on the door....ha ha

[nfoto]

Snow makes wonderful patterns, so nice to see these laser images.

 

Basically the heavier the snow fall, the easier it is to capture patterns. Here is from my porch with the 40cm f/5.6 Noflexar, IR with Z6.

[photoni]

they look like science fiction
i also really like the latest IR it is a perfect combination of exposure time (0,3"-3200Iso) to give a magical texture

 

[Nate]

Neat shots and great idea. I like the side shot. I can't imagine a 200mW beam, my 5mW green laser is bright at night.

[Andy Perrin]

Nate, when you spread the beam into a sheet, it’s actually hardly more intense than a 5mW once you’re a few feet away. 
 

Also, green light is WAY WAY (1000 times or so) brighter than 405nm at the same intensity. This is just because of human eyes not being sensitive to violet. 

[Nate]

@Andy Perrin That's right I never thought of that. Just out of curiosity, what determines the wavelength of a laser output beam?

 

 

 

 

[Andy Perrin]

10 minutes ago, Nate said:

@Andy Perrin That's right I never thought of that. Just out of curiosity, what determines the wavelength of a laser output beam?

 

 

 

 

Depends on what kind of laser it is. For laser diodes, the size of bandgap of the material will determine the output wavelength. Electrons in semiconductors live in either the valence band, which is lower energy, or the conduction band, which is higher energy. In between there is a region of energies where nothing is allowed called the bandgap. To make a photon, an electron falls from the conduction band to the valence band. 

[Nate]

Good info, thanks Andy

 

[Doug A]

@Andy PerrinCool idea! Like #4 and the side view best. The side view is exceptional. 

 

@nfoto super IR snow image. 

 

Thanks for sharing,

Doug A

[dabateman]

Interesting Andy.

Your last photo with the laser shooting out the window,  like a film projector is my favorite. 

 

[Andrea B.]

Andy, these were really *fun* !! Thanks for making these during an actual blizzard!!

 

I had visions of you tying a guide rope to the door in order to find your way back. Hah!

[Andy Perrin]

Andrea, you have no idea how close you are to the truth on that! It was really coming down out there, and with the wind-tunnel effect between the buildings there were points where I was thinking, "Yeah, I really AM out of my mind." On the other hand, this was a real testament to the sturdiness of the tripod!