Measuring the Raman spectrum of water with a smartphone, laser diodes and diffraction grating

Abstract

We show how low-cost apparatus based on the use of commercial laser diodes, inexpensive diffraction transmission gratings coupled with a smartphone camera, can be assembled and employed to quantitavely measure the wavelengths of photons scattered inelastically as a consequence of the Raman effect. In particular, we measured the Raman shift of water stimulated by violet and green laser radiation.

Low-cost measurements of the ‘resonant’ wavelengths reflected by a compact disc under skimming light rays

“…The first involved taking pictures of the CD with a smartphone camera, using a 100 lines/mm diffraction grating put in front of the lens, placed as close as possible to the projector. This allowed for direct images of the spectral lines, which were then analyzed using the free app Tracker [10,13] according to a procedure described in [14]. To calibrate the measurements, three different LEDs of known peak wavelength were placed behind the CD/DVD, so that their spectra were included in the photos.…”

“…The calibration is performed by using the two-point calibration in Tracker on the 395 nm and on the 510 nm LED to set the scale (the calibration is performed taking as reference the peak of the emission, with uncertainty given by the full width at half maximum), then checking that this scale agrees with the third LED (which it does within 5 nm), and finally performing the measurement on the lines. Details on this procedure can be found in [14]. (Right).…”