David:
It's a halftone dot pattern. There are ways to achieve this effect, but there's no simple click on a filter that will do this. The closest I can get to a simple click is this (In a RGB mode document):
1. Draw a circle, hit Ctrl-C (Copy, but don't paste yet);
2. Apply a radial gradient to it, black in the center to white on the edge;
3. Set the document raster effect settings to 300dpi;
4. Effect>Pixelate>Color Halftone, set all channels to the desired angle (in this case, 0 degrees), and pick a number for the radius (you can alter any settings live later on from the appearance palette item);
5. Ctrl-B (This pastes the previously copied circle in the back) and fill with desired orange;
6. Select both, Make Opacity Mask, then Invert.
It's all live, so you can control everything from the appearance palette if need be.
The result should look something like this:
Bert Philippus