Scientific Photographs
Scientific photos, taken years ago well before I retired. Some date from the years I taught optics, some go back to the junior lab course I was involved in, some came out of a course I gave in “Scientific and Technical Photography”, some just came..
Browse down the page you can find diffraction, the solar spectrum, resolving power, strobe, bows, x-rays, chambered nautilus, Schlieren, and the liquid drop.
Diffraction
Refraction is the bending of light rays as they pass from one medium into another. This is due to the change in the speed of light (a different index of refraction) as it passes across a boundary. Diffraction is the bending of light around obstacles and into shadow regions due to the wave nature of the light. It often gives rise to “fringes”, alternating regions of light and dark.
A circular aperture. If light only went in straight lines, this would look like a uniformly illuminated disc. |
An irregularly shaped aperture |
 Another irregularly shaped aperture. |
 Rectangular aperture. 2-fold symmetry, of course. |
 Triangular aperture. Almost 3-fold symmetry, so I guess the triangle was not quite equilateral. |
 Diffraction pattern of two narrow slits |
 Diffraction pattern of two slits, not so narrow |
 Difffraction patterns, a single slit. These are very narrow slits, so that if the slit is narrower, the pattern is wider. Thus the top pattern is produced by the narrower slit. The bottom pattern is produced by the widest slit. |
 Fringes from a Michelson interferometer. The pattern of fringes can be thought of as the pattern resulting from in interference between two point light sources, one in front of the other. |
 Pinhole camera. If the pinhole is too small, light diffracts into the “shadow” regions, blurring the picture. In the first picture, the pinhole was extremely small. Not only was the resulting photograph fuzzy due to diffraction, but the exposure was very long (several hours) so that figures in the room appear ghostly. |
 Here the pinhole was a bit too large, so the picture is fuzzy. The exposure time was quite short, just a second or so. |
 The pinhole was just right for this photograph. |
 Diffraction pattern for a straight edge. In order to see this pattern, a point source of monochromatic light is needed. That’s why we don’t usually see this. Lasers make this easy to do. |
Diffraction by a circular object. In 1818, Fresnel presented his theory explaining diffraction of light. Poisson denied the truth of the theory, and argued that a consequence of the theory would be that there would be a bright spot right in the middle of the shadow of a circular object. The spot, shown above of the shadow of a ball bearing suspended on a needle, was promptly discovered by Arago. This was a lot harder to do before lasers were invented! |
The diffraction grating. This shows the diffraction pattern of one slit, then two, then three, four, five, six, and more. When there are many slits, we call it a diffraction grating. The more slits, the narrower the pattern becomes. The pictures above were taken with monochromatic light. If there were different wavelengths present, then the interference maxima would occur at different spots, and we would be looking at the “spectrum” of the source. |
 Solar spectrum. The spectrum of sunlight has missing wavelengths due to absorption of the light as it passes through the solar atmosphere, which is significantly cooler than the solar surface where the light was produced. In the picture above, the solar spectrum is compared to the emission spectrum of sodium. Yes, there is sodium in the sun! |
 Another small part of the solar spectrum (lower) compared to the emission spectrum of iron (top). There is iron in the sun. |
 Zeeman Effect. Here is a very high resolution spectrum showing the yellow lines of the mercury spectrum, taken when the mercury atoms were in a strong magnetic field. This splitting into three lines is the “normal” Zeeman effect. Most lines are not “normal”. |
Resolving power. Images formed in a telescope of two small close sources with various sized apertures. Large apertures at the top, small ones at the bottom. Images at long wavelength (red) on the left, short wavelength (blue) on the right. The ability of a telescope to resolve objects depends on both the aperture and the wavelength used. This principle holds true not only for optical telescopes, but for radio telescopes, microscopes, electron microscopes, and all kinds of imaging instruments. |
 |
 |
| Babinet’s Principle | |
 |
 |
| … and the screens used to produce the diffraction patterns above.. | |
Circular aprertures, Fresnel diffraction. (Not plane waves incoming; distance from aperture to screen is not large) |
Single slit, Fresnel diffraction. Not the same as the single slit patterns shown above, because the distances are smaller. Put another way, not plane waves in a nd out. Top: theoretical intensity versus position |
| Strobe Photos |
 Bouncing ping pong ball |
 Conical pendulum, seen from below. Styrofoam ball on a string. |
| Bows – in the sky |
 Rainbow. Maine, Penobscot Bay |
Fogbow. Same thing, but the droplets are much smaller, so diffraction takes place. |
| Xrays |
 In Laue patterns, x-rays with a continuous spectrum are scattered from a single crystal. The film formed a cylinder around the target crystal. A continuum spectrum of x-rays on a single crystal. |
 2-fold symmetry, 110 axis |
 4-fold symmetry, 100 axis |
 |
 |
| 3-fold, forward scattering, 111 axis | 3-fold, back scattering, 111 axis |
Forward scattering from an aluminum wire (many small crystals). The dark circle in the center was from a lead plug used to stop the direct x-ray beam. The “X” patterns in the center are due to a partial alignment of the crystals of aluminum in the extrusion process when the wire was formed. |
Forward scattering from finely ground NaCl. No x-patterns in the center, of course. |
Powder patterns, cylindrical camera. Scattering from “powder” Ag, Al, Au, and Cu. The film is wrapped around the sample, and so forms a cylinder. The x-rays |
Backward scattering (the x-ray entrance hole) detail. The resolving power gets very high in the backward direction, the “doublet” patter is from the fine structure in the x-ray spectrum: the copper K-alpha-1 and K-alpha-2. |
 Wrap-around powder patterns for NaCl and KCl, similar but not the same. KCl is about as close as you can get to a simple cubic pattern! |
| Logarithmic spiral: |
 X-ray of chambered nautilus shell |
 Chambered nautilus shell, cut in half |
| Schlieren photography |
 It’s all done with mirrors and a straight edge. |
| Interference |
 Biprism and bimirror to produce fringes similar to the double slit. |
| Liquid Drop
Liquid drop falls into a liquid… |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
| … and wait for the next drop to fall. These were still photographs, each of a different drop, but the events are very much the same from drop to drop. A bit of milk was added to the water to make the drops more visible. That worked fine, except it got stinky after a while. The falling drop interrupted a laser beam, which triggered a variable delay circuit, which triggered the strobe. |
