So, here's the projection system that you just saw a schematic for. Over here, we have our LED. You can see light coming out. This is a 405 nanometer LED. And this aperture right here is going to be a field stop for the system. We'll see how that works in a little bit. As we follow the image here, little breaks you can't quite see but the image of the LED is right at this aperture. Send the light through this lens, and this puts the Fourier transform of that image over here onto a mask that I have. So, now, we have a very, very uniform illumination on our mask, and this is all just the illumination system. We're going to spend a little bit more time talking about that in the next unit. But this is one way we can get a nice uniform illumination onto our mask that we then, want to image onto a sample. So, now let's take a look at our imaging system. This is my uniform illumination. Can see our mask is sideways here, so you can't see it so well. This is just a diffraction grating. We have a number of different diffraction gratings on our mask of different periods, so that we can project those. This is a two lens system right here, and this is our imaging system. We have a one-to-one one system and our aperture stop is right here in the center. There's an Iris here. We see image of our mask on the sample plane. So, this is where the image of your mask is. You can't see the diffraction grating lines because they're so small, but you can see the edges there. We then, for alignment purposes, take this and we image it to another two lens system onto a camera. So, this way we can look at the image and then, we can align our field stop, and align our mask so that we know it's in the sample plane. Let's take a look at what that looks like right now on the camera. So, that looks like an image of that diffraction grating on a camera. So, on the background here, we have the raw image and then, in each of these we're looking at a line. This is a horizontal- this is a vertical line, sorry. This is a vertical line through a diffraction grating. So, it's only getting a few of our periods and this is a horizontal line where we see many periods. This is 10 micron pitch diffraction grating and we're viewing this on our camera. S let's see what happens when we change some of the stops. First of all, I'm going to close the field stop, that's what we discussed earlier. That's right after the LED. So, we see as I close the field stop, I changed the field of view. So, this is an Iris in our field stop and it comes down, and it cuts off our field of view. So, that's not changing our resolution, our contrast of our image, it's just changing how much the image we're seeing. So, I'm going to leave that closed and then, I'm going to move the aperture stop. So, the aperture stop is wide open right now. So, next, we're going to close that and see what that does to our image. So this aperture stop is between the two lenses in the imaging system and as I start to close this we see that we lose contrast. So, we still have the light getting through. You can still see a bit of a signal. We have lost some of the light as well. But we can no longer really resolve these 10 micron lines anymore. We've lost that resolution by limiting the number of angles that make it through our system. As I open up the aperture stop, we get our diffraction grating back. So, I close it, you start to lose contrast. Here we can see as we close it we use it slowly until it's all gone. We still have light but I can no longer resolve those 10 micron lines. I can open that back up, and I get my image back. So, this shows the effects that field stop has on your image as well as the aperture stop in an imaging system.
