Cells of Escherichia coli labeled with an amino-specific Alexa Fluor dye and examined with a fluorescence microscope. By using pulsed light (strobed laser illumination at a smaller average intensity) and an ordinary CCD camera, one can see what flagella do as swimming cells run and tumble.
Turner, L., Ryu, W.S. & Berg, H.C. Real-time imaging of fluorescent flagellar filaments. J. Bacteriol. 182, 2793-2801 (2000)