Editing Coherence length (section)

==Lasers==

Multimode [[helium–neon laser]]s have a typical coherence length on the order of centimeters, while the coherence length of longitudinally single-mode lasers can exceed 1&nbsp;km. [[Semiconductor laser]]s can reach some 100&nbsp;m, but small, inexpensive semiconductor lasers have shorter lengths, with one source<ref>{{Cite web|url=https://www.repairfaq.org/sam/laserdio.htm#diobcc4|title=Sam's Laser FAQ - Diode Lasers|website=www.repairfaq.org|access-date=2017-02-06}}</ref> claiming up to 20&nbsp;cm, although multi-mode diodes will have even shorter coherence lengths. Singlemode [[fiber laser]]s with [[Laser linewidth|linewidths]] of a few kHz can have coherence lengths exceeding 100&nbsp;km. Similar coherence lengths can be reached with optical [[frequency comb]]s due to the narrow linewidth of each tooth. Non-zero visibility is present only for short intervals of pulses repeated after cavity length distances up to this long coherence length.