Spectroscopy (greek „Ghost seeing“) is the interaction of light and matter. The literal translation is quite appropiate, because with the use of these techniques, not the real molecules/atoms can be seen, but only their images and „shadows“ they produce.
The result is a chart, where energy, time, frequency,…. are related, this we call a spectrum. If spectra are recorded along a line or square or whatever shape, then images can be composed, this is then called imaging approach i.e. Raman imaging.
The advantage of using such techniques is that they are essentially an advanced form of the human view. For us, the sun is the radiation source, its light gets reflected on objects (these are the samples) and then passes on to our detector, the eye. In a similar fashion, our equipment has radiation sources, which radiate on the samples and the absorption (Infrared) or scattering (Raman) is measured.
The advantage is clearly that the sample can be measured in its natural condition, no chemical treatment, heating etc. is needed – just like you would look at it. The difficulty however lies in the interpretation of the resulting data. This requires both expertise and statistical programs and is the real challenge in spectroscopy.