Editing Tunable laser (section)

===Single line tuning===
No real laser is truly [[monochromatic#In physics|monochromatic]]; all lasers can emit light over some range of frequencies, known as the [[linewidth]] of the laser transition. In most lasers, this linewidth is quite narrow (for example, the {{formatnum:1064}}&nbsp;nm wavelength transition of a [[Nd:YAG laser]] has a linewidth of approximately 120&nbsp;GHz, or 0.45&nbsp;nm<ref>Koechner, §2.3.1, p49.</ref>). Tuning of the laser output across this range can be achieved by placing wavelength-selective optical elements (such as an [[etalon]]) into the laser's [[optical cavity]], to provide selection of a particular [[longitudinal mode]] of the cavity.