1. Active laser medium
2. Laser pumping energy
3. High reflector
4. Output coupler
5. Laser beam
An output coupler (OC) is a partially reflective mirror used in lasers to extract a portion of the laser beam from the optical resonator.
Lasers operate by reflecting light between two or more mirrors which have an active laser medium between them. The medium amplifies the light by stimulated emission. For lasing to occur, the gain of the active medium must be larger than the total loss, which includes both unwanted effects such as absorption, and the intentional release of energy through the output coupler. In other words the laser must attain threshold.
There are two important properties of the output coupler:
- Radii of curvature
- The output coupler may be either flat or curved, depending on the design of the optical cavity. The face of the output coupler facing into the cavity is the side with the applied partially-reflective coating. This is the side which partially determines the laser modal properties. If this inner surface is curved then so must be the outer surface. This will stop the OC performing as a lens. The curvature of the outer surface can be designed to give a collimated laser output. This outer surface generally has an anti-reflection coating applied to maximise the output power.
- Depending on the gain of the medium, the amount of light the OC needs to reflect back can vary widely. Helium-neon lasers require around a 99% reflective mirror to lase, while nitrogen lasers have an extremely high gain (they are "superradiant") and do not require any OC (0% reflective). The reflectivity of any OC will vary with wavelength. A particular mirror may have a tuning range as low as a 10nm or so. For this reason the spectral properties of the OC are important to consider when a laser cavity is being assembled.
See also
Open source encyclopedia content modification information:
Authorship and Review
Open source encyclopedia content provided here is not reviewed directly by PediaView.com. Content is authored by an open community of volunteers and is not produced by or in any way affiliated with PediaView.com.
Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Output coupler", which is available in its original form here:
http://en.wikipedia.org/w/index.php?title=Output_coupler
All Wikipedia text is available under the terms of the GNU Free Documentation License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.