Measuring Photons as a Signal

In the previous section we defined several characteristic properties of electromagnetic radiation, including its energy, velocity, amplitude, frequency, phase angle, polarization, and direction of propagation. Spectroscopy is possible only if the photon s interaction with the sample leads to a change in one or more of these characteristic properties. 

The attenuation of photons as they pass through a sample (A). 

A graph of a sample s absorbance of electromagnetic radiation versus wavelength (or frequency or wavenumber). 

The release of a photon when an analyte returns to a lower-energy state from a higher-energy state. 

Ultraviolet/visible absorption spectrum for bromothymol blue. 

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