Some optical material, when illuminated with a certain wavelength, emit light at different wavelengths. Light emitted often has a lifetime, where emitted intensity decays over time, and the decay time can be used to characterize the material. A distinguishing feature of laser light is its long coherence length compared to natural lighting. Coherent light is when light waves at different spatial positions move in unison, and therefore can be made to interfere. Interferometry is enabled by interfering two or more coherent light waves. Holography is the science of recording phase and amplitude in an optical media, recording of three-dimensional images in two-dimensional media, or recording of very large amounts of data in a very small volume. Holograms are generated by interfering coherent light. Spectroscopy is the field of optics that involves characterizing an incident broad spectral light by producing data that indicates intensity variation with respect to optical wavelength.