Joe F said:
One thing I would like to measure is the actual power of the spread beams, going from the center outward. I want to measure the power (using a LaserCheck) in the center, and then every 1 centimeter, going outward, until the light stops. I suppose there are graphs showing this, but I want to do it directly.
The business with measuring every centimeter across the spread beam is not such a bad idea to use up some lab time and see how good you are with taking data. The end result of the project would be a graph looking like The Bell-Shaped Curve, which is another name for the Gaussian Distribution Curve, which is what the laser’s intensity profile should look like.
Put a piece of graph paper in your spread beam to coordinate your detector head positions. Make it normal to the spread beam for starters, you might get carried away and see what tilting the target gets you after this test. (You might prove the cosine law!)
You might want to tape your detector’s active area down to a slit. This is for finer resolution when graphing, for if your detector is a one square centimeter square, each side is a centimeter, and moving it a cm could cause some overlap.
The slit should be at right angles to the sampling direction, and you could sample first in one direction then the other to see if the profile is symmetrical. This type of sampling that you would be doing manually is done automatically by mechanical/digital beam profilers like these:
http://www.ophiropt.com/laser-measureme ... slit-based
Ideally after measuring all these points and graphing them, you should see the classic Gaussian distribution. But then again, you may not. I have a Compass 315M and its distribution doesn’t look as Gaussian as a He-Ne’s, more flat topped, when they are combined, and the Melles Griot BLD 605’s beam is neither round nor Gaussian looking either. If I didn’t have an insane project hanging over my head to play in the lab...
As far as how much less bright should the edges be in illuminating the hologram, you can usually see a photographic stop’s (doubling or halving of light intensity) difference in exposure in the typical silver halide holographic material. I try to go less than a half-stop, or .7 approximately. (Square root of two over two, to be exact.) With the tolerance for DCG you guys are the experts. But I would be running exposures with 50 in the center and 45 at the edges!
