GERD GUENTHER / SCIENCE PHOTO LIBRARY GERD GUENTHER / SCIENCE PHOTO LIBRARY
Light microscopy of the colours in a thin soap film. The bands of intense colour occur when the thickness of the soap film is comparable to the wavelength of visible light. Light rays reflect from the top and bottom layers of the film, causing specific wavelengths to be removed or enhanced in the reflected light by destructive and constructive interference. The distance between the top and bottom of the film determines which colours are seen. The fifth order interference occurs at a thickness of over 790 nanometres, producing pink and green colours. At 680nm, bright grass green is produced. As it thins more, the light appears bright red (542nm), purple (396nm), crimson (371nm) and violet (216nm). At its thinnest, some 6nm, it appears black, and after this the film pops. The constant movement of the film is due to it being mounted vertically, with gravity making it thicker at the bottom, and also through evaporation of the water. Blowing on the film produces tiny bubble-like regions, and dust particles form concentric spots of colours as the dust attracts the film. Filmed with incident lighting, with a captured field width of 0.8 millimetres.
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