Lasers & Holography

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."

Thanks to ScottY for the link.

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.  My 2-4 second exposures were incredibly dim because they were getting fogged for the first second.  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.  The fringes really moved when the shutter closed but as no light would have been reaching the film, I didn't care about that.  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.  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.

This is pretty cool and something that even hobbyist holographers could make.

Laser Focus World is reporting that researchers at New South Wales University have developed a holographic astigmatism test that's faster to use than the lens-flipping "how does the chart look now?" test we've all endured when having our eyes checked.

The current method of looking at a distant object through a number of lenses to prescribe corrective glasses is at best cumbersome. In an alternate approach, the researchers recorded the wavefront emanating from various sunburst patterns located at different distances from the eye in a hologram. When a subject views through this hologram (illuminated by a plane wave), he or she will see the images of various sunburst patterns located at different distances from the eye.

Unfortunately there's no additional information at the university site.  Perhaps they'll put something up soon.

Optics.org has a bit more information and a few extra photos available.

I don't have one of these babies yet but you can bet they'll be on my Christmas list.

Laser tag is sweet. R/C helicopters are sweet. When you combine the two only good things can happen. That's why I'm pretty amped about the news that a Chinese toy maker has armed its new R/C chopper with an IR transmitter and sensor, allowing for two to have laser dogfights in midair. If one gets hit, its power gets cut, sending it crashing to the ground. Cold blooded!

Oops.

IT was not quite a Star Wars death ray, but air force Top Guns accidentally focused high-powered lasers on to a civilian car in May this year - potentially endangering the eyesight of peaceful earthlings.
RAAF F/A-18 fighters from the Williamtown base north of Newcastle were conducting exercises near the NSW mid-north coast town of Forster when the incident happened.

The pilots thought their laser targeting system was turned off for the training flight.

Unfortunately it wasn't and the powerful light beams, known as class four lasers, were shone twice on to a road intersection for a total of 43 seconds.

Guys, remember to put your equipment into O.F.F mode first.

It's taken way to long to get the new Coherent 315M integrated in my lab (insert excuses here) but that's now been completed.

The power and shutter controls have been wired up, the software has been updated to control a third laser and it's been tested and is ready for use.  One thing I seriously need to do is refactor the HoloController source so that it's simpler to control an arbitrary number of lasers.

The layout shown above is the one I used to create a transmission master for a professor at A&M.  I was surprised to see that the beads which I'd painted fluorescent orange show up yellow under green light.  It'll be interesting to see how they come out when shot with green-sensitive film. 

The red in the background is from my copy layout which uses a HeNe.  The red dot in the middle-right is the beam from my red mastering laser.  Ordinarily it would be shining on the subject in the foreground but it's being blocked by the transfer mirror used to "inject" the green beam into the mastering path.

Click on the image for a larger version.