Spectroscopy in which the electromagnetic radiation that interacts with the system is supplied by a laser. This has a number of advantages over spectroscopy that does not use lasers. For example, laser spectroscopy improves the accuracy with which the frequencies of spectral lines can be measured. High-resolution laser spectroscopy is also very useful for investigating the sizes and shapes of nuclei via the hyperfine structure of their atomic spectra. Ultrafast laser spectroscopy is a technique in which an ultrashort pulse (lasting about a picosecond) of electromagnetic radiation is used to investigate dynamics at very short time-scales.