Hi. I'm Fran, and this is the diffraction apparatus. A diffraction
apparatus consists of three parts. First, there's a red laser, 635 nanometers, plus
or minus 5 nanometers. Second, there is a set of precision slits, metal film on
glass. Third, a combination high-sensitivity light sensor and linear
position sensor. The high-sensitivity light sensor has a selectable aperture, so
you can control how much light gets into it. It also has three settings for 1, 10,
or 100 microwatts of power. The linear position sensor has an internal optical
encoder, and has a resolution of about 40 micrometers, and that lets you do this
experiment without having to use a micrometer screw. I'm going to show you
two different slit patterns that you can collect data with, with this apparatus.
First, I need to adjust my laser to make sure that it's going to be actually
pointing through the slit, and there are two screws at the back that let me turn it
and get it centered. If I put this in the center, I can use that to help me guide
getting the diffraction pattern to the right location. Now, I'm going to select a
double-slit pattern, and I'm going to choose one where the separation is 0.25
millimeters and the slits have a width of 0.04 millimeters. To begin data
collection, I'm going to move the linear position sensor all the way over to the
right of the carriage. That means that when I push it to the left, I'm going to
get positive position values. I'm going to zero my sensors,
and then once I start collecting data I'll have about 30 seconds
to move the carriage all the way across over 15 centimeters.
Now, it doesn't matter what rate I go at, I am not looking
at the intensity versus time. I'm looking at it versus position, and that means that
I can even pause while collecting data and it's not going to affect
how that comes out.
It also does not matter if I finish data collection a little bit early.
So here's my data, and let's look at that auto-scaled graph. You can clearly see
maxima and minima, and the extra fringes from that two-slit diffraction pattern.
The other one I'd like to show you is a multiple slit pattern with five slits that
are also 0.04 millimeters wide, but which are separated by a distance of 0.125
millimeters. There they are. Once again, move the carriage all the way to the
right, zero sensors.
And you'll see that this diffraction pattern is different
because of the multiple slits.
So you can use the Examine function to look at the
locations of the maxima and minima for the diffraction pattern, and use that for
mathematical calculations regarding the wavelength of the laser or the slit
separation of the slits. There are many experiments that you can do with this. As
always, more information is available at our website, www.vernier.com. Thank you.