Archive for the ‘Show-n-Tell’ Category

In our last post we discussed the goal and methods around capturing the birefringence found in frozen soap bubbles.   The good news is that we established a solid method for capturing birefringence, but so far have yet to see any real noticeable birefringence on soap bubbles.

Along the way we did capture some amazing photos of soap bubbles in several different states of frozen, and finally just shot some images of just ice crystals forming.  We have some videos of the growth of crystals which we might post later.

In order to capture images such as these, you need to polarizing sheets.   One covers your light source (flash, led, etc), the other over your camera. It is important that the polarizing sheet is the last optical element before the subject you wish to photograph.

First, more photos of "ice crystals we really wished showed birefringence ".  We have a few theories about why this doesn't work (including: thin film from glycerine causing scatter, too many layers of ice, etc).  At this point it's still unknown, any comments welcomed!  The good news is that the soap is showing it's lovely colors!

Well, that sure was neat, but we didn't really get the birefringence in water crystals we wanted. So it was time to just try old fashioned ice crystals and liquid nitrogen. The results where spectacular:

Here's where it got interesting. By rotating the polarizing film different parts of the crystals would show birefringence based on the changing angles interacting with each other.



Frozen bubbles!

Posted by 3ricj on 3 February 2013

Transparent solids can show birefringence when they are under mechanical stress. This stress can be present in a part after it's manufactured (in the case of plastic) or present due to thermal expansion. You can view these birefringence patterns if you view it between two crossed polarizers.

These patterns can also be found in ice. I decided, on a whim, that would attempt to photograph birefringent (cross polarized) crystals in frozen soap bubbles. This is what is hopefully going to be short set of posts with attempts to do so.

For starters, making frozen bubbles has it's own challenges. When air cools, it compresses. This would likely lead to a fracture of the bubble. The first attempt to make frozen bubbles confirmed this - if you inflate a bubble using (warm) air from your lungs, it pops the moment it gets close to something cold. In this case, we tried this with a pool of liquid nitrogen - -  it fractured well before hitting the liquid. We did manage to make some 'broken half bubbles', which floated around on the gaseous nitrogen. I don't have any photos of this, but let's just say it didn't work so well. After some trials and tribulations we developed the following method to make frozen bubbles:

  • Take a short (12") copper pipe
  • dip one end into a "bubble solution", adding additional glycerin may help.
  • Make sure that there is bubble solution coating the outside of the pipe; a thin film will work fine.
  • Submerge the other end into a cup of liquid nitrogen.
  • The warm copper will cause a phase change in the nitrogen, which will inflate the bubble with chilled nitrogen.
  • Before it pops, gently shake the pipe such that bubble 'slides' down to the pipe.
  • Take the pipe and hold it carefully over a pool of liquid nitrogen. There will be a thermal gradient there which enables the bottom of the bubble to freeze.
  • With some luck and skill, you can "thaw" and "refreeze" your bubble many times before it bursts.

Here are some photos of our first round of testing.  At the time we didn't have a good setup for capturing the birefringence in the crystals then we ran out of liquid nitrogen!. We will have to try again. On the next post I'll provide more information about how to capture birefringence using a camera.

A nitrogen filled bubble:

Frozen bubbles!

A shot of an old fashioned ice-cube under cross polarization (you can see birefringence!!):

Drip Drip goes the funding.

Posted by 3ricj on 30 August 2012

Our friends over at shift labs are seeking funding for one of their projects. Ya'll should go fund their product they are building for the developing world. No lasers, but it's still bad-ass. Even if they are excessively smiley on video. Go give them money. kthx.

http://www.indiegogo.com/shiftlabs

Photonic Beam: Results

Posted by ratha on 15 August 2012

The laser was successfully deployed at Toorcamp. We operated it on Friday and Saturday nights (August 10 and 11, 2012). Design and construction of the laser is documented in previous posts here and here.

Here is the laser in operation:

H1kari took the following amazing photo of the laser punching through above the fog:

Joe FitzPatrick took this futuristic photo proving once and for all that we implement science fiction:

The Yurt

The yurt on which the laser was mounted was built by Ratha in 2008. It provided a stable, 8' tall platform (above eye level) and it made the phrase "laser yurt" possible.

Safety interlocks

We had a bit of trouble with the motion sensors detecting motion *outside* the yurt (through the open lattice). On Saturday, Kyle attached cardboard blinders to the sides of both motion sensors, and this helped quite a bit.

We also found that a number of people couldn't resist hitting the emergency stop buttons.

Future improvements

We could make the software much fancier for a future deployment. At Toorcamp, we simply operated the arduino microcontroller over PC USB, and interacted with it using keyboard commands over the Arduino IDE serial interface. What would be awesome would be to develop a graphical interface with continuous monitoring of the safety components and red/yellow/green display of their status.

Budget status

We are accepting donations through the end of August to cover budget overruns, which mostly occurred due to the cooling system. The array of 24 diodes we used came from a projector which was not designed to run the lasers at full power for any sustained period of time, so it was very difficult to extract the heat from the tiny module fast enough. The cooling system had to be rebuilt several times, with substantial enhancements and new parts each time.

To read more about this and to donate, please go here: https://www.wepay.com/donations/tip-jar-for-photonic-beam

Thanks

- h1kari and company from toorcamp for motivating the project and offering the grant.
- Owen Trueblood, Pierce Nichols, Phil Rutschman and Myles Conley for their work on the laser drivers.
- Ratha Grimes for majority of the electronics and software.
- Nathan Pegram for his work on the coolant system.
- Kyle Drosdick and Brian Campbell for setup and operations on site.
- DKP for software and making stuff happen, despite barely even going to toorcamp.
- Sirus for modding the OSPid so it works great with the TECs.
- Brett Beauregard for providing the OSPid and software and support.
- All of the folks offering support in various forms. Thank you!
- The fine members of hackerbot, who continue to do amazing shit.

The introductory post on this project mentioned most of the high level considerations for safety and compliance when shooting a laser into the sky. Here, we will go into the gory details.

Read the rest of this entry »

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