JohnK on the holography forum had asked if I’d experienced any problems with delayed development of VRP-M.Â He’s been working on making holograms using a Coherent 315 and VRP-M film and was wondering VRP-M was sensitive to delays of several hours between exposure and development.
I normally develop right after exposure but did the following test to find out how VRP-M behaves.
Getting to the airport wasn’t bad. We were fairly close and made it in just about half an hour. I had printed my boarding pass ahead of time and breezed into the security line where it all went slightly pear shaped.
It’s time for another labcast and this time I’m experimenting with making a copy onto PFG-01 from a test "master" made using the 315M and VRP-M film.
The final test turned out pretty decent and was exposed for 12s, developed for 30s in TJ1 and bleached with EDTA.
The final image isn’t as bright as I’d want if this weren’t just a quick test but overall it’s not bad. I may have time tomorrow morning to try another test with fresh developer but then again all my time might be spent watching the lunar eclipse.
If you find yourself needing to take your laptop into the lab, you can make life simpler by making a safelight cover for the screen.
I know most of you who make holograms don’t carry around a tablet and those who carry around one probably don’t make holograms but for others who, like me, do both, here’s a way to take the computer into the lab without having to turn the screen off while film is out and about and you can save your "night" vision for what is probably a dimly lit lab.
On the face of it this doesn’t sound like much but the researchers hope to be able to use the results for optimize crystal growth.
Firing laser pulses into supercooled water creates ice crystals at specific locations in the liquid.
Using laser pulses to crystallise supercooled water into ice may seem counter-intuitive, but that’s exactly what researchers in Germany and the UK have achieved. Because the pulses can be focused to a specific point in the liquid, the researchers believe that their technique will be valuable for future material and crystal growth studies. (Physical Review Letters99 045701)
I don’t know how often I’ll do these but I had the urge to record what I was doing in the lab.
I’ve been trying to get good results with the coherent 315 laser and VRP-M film and haven’t had any luck. In each case where I’ve gotten any kind of image, it’s been extremely dim.
Unfortunately I found that my shutter was causing a full seconds worth of ringing in the table and had to build a new shutter. That was completed yesterday and this morning I’m doing some more exposure and development tests.
My apologies for the sound quality. Next time I’ll have to make sure the microphone is closer to me at all times.
Researchers at MIT’s George R. Harrison Spectroscopy Laboratory have developed a new use for laser interferometry that allows 3D images of the internal structure of cells to be created in just 0.1 seconds. Michael Feld and his team use the change in refractive index of a laser beam passing through the cell to create a series of 2D maps.
The researchers made their measurements using a technique known as interferometry, in which a light wave passing through a cell is compared with a reference wave that doesn’t pass through it. A 2D image containing information about refractive index is thus obtained.
To create a 3D image, the researchers combined 100 two-dimensional images taken from different angles. The resulting images are essentially 3D maps of the refractive index of the cell’s organelles. The entire process took about 10 seconds, but the researchers recently reduced this time to 0.1 seconds.
One major result of this research is we can now see the internal structure of cells without modifying the cells themselves through fixing or adding dyes.
"When you fix the cells, you can’t look at their movements, and when you add external contrast agents you can never be sure that you haven’t somehow interfered with normal cellular function," said Badizadegan.
The current resolution of the new technique is about 500 nanometers, or billionths of a meter, but the team is working on improving the resolution. "We are confident that we can attain 150 nanometers, and perhaps higher resolution is possible," Feld said. "We expect this new technique to serve as a complement to electron microscopy, which has a resolution of approximately 10 nanometers."
Well, it turns out that one of the problems I was having with my green laser and the VRP-M film is my shutter.
When it opened it set the table to ringing for at least a full second.Â My 2-4 second exposures were incredibly dim because they were getting fogged for the first second.Â I found this out after setting up an interferometer (shown above, click for a larger picture) opening and closing the shutter while it was going.Â The fringes really moved when the shutter closed but as no light would have been reaching the film, I didn’t care about that.Â Have it shake the table when opening was a problem though.
I tried all sorts of things to improve the isolation of the shutter and damp the vibrations it was putting out but in the end I had to give up and make a shutter from scratch.
I took a panel meter and attached a multi-layered piece of aluminum foil and used that reflect the incoming beam and create a beam dump on the inner surface of the meter housing.Â Painting the whole thing black created a nice little box to keep the beam in.
After putting a couple of beads of silicone where the meter arm rests against the coil I ended up with a nice quiet shutter that didn’t disturb the fringes at all.
It’s being put through its first hologram-making test right now.