High-Resolution
Spectrograph
Lab-worthy spectrum
analysis for cheap.
BY SIMON QUELLEN FIELD
A
Nearly 200 years ago, Joseph von Fraunhofer built the first spectroscope and saw dark lines in the spectrum of the sun. This led him to discover
that you can determine the chemical elements in things by analyzing the
light they give off. Each element has its own “signature” of lines in the light
spectrum. The lines correspond to the characteristic wavelengths that
electrons absorb and emit as they jump between lower- and higher-energy
orbits around the atom’s nucleus.
of wavelengths distinct. Each image of the slit, in a
slightly different color, is arrayed across the field of
view in a wide spectrum image. If any wavelength
is brighter or dimmer than the rest, it shows up,
respectively, as a bright or dark line in the spectrum.
The first spectroscopes used glass prisms to split
light into colors, but Fraunhofer found that an array
of closely spaced wires had the same effect. Today
we call these arrays of tiny slits diffraction gratings
(see sidebar on page 61).
After these discoveries, spectrographs (the
instruments used to record spectra) became a
standard tool for analyzing the chemistry of almost
anything, ranging from microscopic lab samples to
faraway galaxies.
The primary element in both spectroscopes and
spectrographs is a narrow slit oriented perpendicular to the direction in which the grating or
prism spreads the light. As with a pinhole camera,
the small aperture images the light source sharply
along the spectrum’s axis, which keeps the spread
Although spectroscopes have always been easy to
make, a homebrew recording spectrograph presented
more of a challenge. Building your own spectrograph
meant using microcontrollers and stepper motors to
move diffraction gratings past a light sensor — many
were planned, but few were actually built.
Today, digital cameras and online tools can turn
a simple spectroscope into a laboratory-quality,
high-resolution spectrograph. All it takes is a few
plumbing parts and other inexpensive materials and
less than an hour at your kitchen table.
Photography by Ed Troxell
58 Make: Volume 24
