What is Time-domain spectroscopy?
{{jargon|date=January 2024}} '''Time-domain spectroscopy''' is a type of [[spectroscopy]] that measures the power of [[electromagnetic radiation]] as a [[function (mathematics)|function]] of time. Normal spectroscopy is frequency-domain spectroscopy. It measures radiation as a function of [[frequency]] or [[wavelength]]. Time-domain spectroscopy usually requires the use of [[Fourier transform]]s. [[File:Wave addition1.jpg|thumb|Two slightly different frequencies plotted in time-domain and frequency domain. The bottom plot shows the addition of the frequencies in the time-domain]] Two [[monochrome|monochromatic]] lights of different frequencies can combine to show [[interference (physics)|interference]] patterns. At time t=0, the waves [[interfere constructively]]. This gives a maximum in the [[added plot]]. The waves get more out of [[phase]]. This leads to destructive interference and a minimum in the added plot. From one peak maximum to the next is a ''cycle''. So when looking at two monochromatic lights, they can be graphed as two lines in the frequency-domain (this plot shows power, P(ν), as a function of frequency). The same two lights can be plotted as the sum of their waves in the time-domain (this plot shows power, P(t), as a function of time). [[File:Wave addition2.jpg|thumb|Broad peaks in spectra are made of many wavelengths. These plots shows some of those wavelengths in the frequency and time domain.]] [[Absorption]]s in spectra usually look like broad peaks. This means that a peak may contain many wavelengths of radiation. These wavelengths can be plotted in the time domain. Notice that there are now smaller areas of constructive interference. This is because the closely spaced wavelengths quickly become more and more out of phase. == Getting time-domain spectra == Spectroscopy done with visible or infrared radiation involves wavelengths of 10<sup>12</sup> to 10<sup>15</sup> [[Hertz|Hz]]. [[Phototransducers]] (instruments that convert light to information readable by a computer)