My most important point:
lasers are awesome! There is a surprising amount of DIY geeky physics that you can do with a laser pointer and some bodged together diffraction slits and holes.
Using two razor blades held a few tenths of a millimetre apart and a red and green laser pointer you can get some pretty good
diffraction patterns.
It even behaves as expected! The increase in wavelength gives a corresponding increase in fringe spacing.
Laser diffraction patterns are a perfect test ground for
fourier transform analysis, the fourier transform of the diffraction pattern gives the shape of the diffraction slit used.
This is the
aperture I hacked together from a piece of 1mm aluminium and a drawing pin. The ruler markings are 1mm apart.
The diffraction pattern encodes the information about the aperture shape in the positioning of the fringes. The roughly circular diffraction pattern shows that the aperture is approximately circular.
Calculating a 2D fourier transform of the diffraction pattern gives the above image, an accurate reconstruction of the shape of an aperture only a few tenths of a millimetre across.
Software used:
Fourier transforms:
ImageJImage management:
Paint.net
Using random walks in this way has some interesting side effects; a "momentum" effect has to be included to prevent the walks getting stuck in local minima. Without the momentum effect the random walk effectively acts as a low frequency Fourier filter... To get the above effect a momentum effect of 0.4 (a 0.4 chance of just continuing in the same direction) was used.
This was made using ImageJ's powerful macro abilities; see the image's Wikipedia page for the macro used.
Using two razor blades held a few tenths of a millimetre apart and a red and green laser pointer you can get some pretty good diffraction patterns.
It even behaves as expected! The increase in wavelength gives a corresponding increase in fringe spacing.
This is the aperture I hacked together from a piece of 1mm aluminium and a drawing pin. The ruler markings are 1mm apart.
The diffraction pattern encodes the information about the aperture shape in the positioning of the fringes. The roughly circular diffraction pattern shows that the aperture is approximately circular.
Microscopes are fun... Small things are cool! This is paper in all its fibrous glory; illuminated in ultraviolet paper autofluoresces at blue wavelengths and looks amazing! This was created from a 3x3 array of images, see the links below for higher resolutions:
