All New Focus tunable lasers start out as commercially available semiconductor-diode lasers. These diodes typically operate with several longitudinal modes lasing simultaneously, leading to low coherence and large linewidths. To ensure high coherence, we anti-reflection (AR) coat the diodes so they act only as gain elements. The diode can then be placed in an external cavity that contains wavelength-selective optics so that only a single mode lases at any given time. Click Simply Better™ Tunable Lasers for a complete overview of our tunable lasers and additional info including Selection Guides, Technical Notes, Application Notes, and Definitions of Characteristics