Encyclopedia … combined with a great Buyer's Guide!

Sponsorship opportunity: support this popular resource, which serves the whole photonics community, and get recognition!

Output Coupling Efficiency

Definition: a factor influencing the power efficiency of a laser, taking into account intracavity losses

German: Auskoppeleffizienz

Category: lasers

Formula symbol: ηoc

Units: %, dimensionless number

How to cite the article; suggest additional literature


Unavoidable parasitic intracavity losses in the resonator of a laser tend to reduce the laser's power efficiency. More specifically, they can increase the threshold pump power and reduce the slope efficiency. The sensitivity of the slope efficiency to intracavity losses depends on the transmission of the output coupler mirror: the larger this transmission, the lower is the circulating intracavity power, and the lower is the effect of intracavity losses. The output coupling efficiency is defined as the ratio of the useful losses to the total losses:

output coupling efficiency

Here, the useful losses are given by the output coupler transmission Toc (or twice that value, if the output coupler is a folding mirror in a linear resonator), and the total losses contain both the useful losses and the parasitic losses lpar. This means that a larger output coupler transmission increases the output coupling efficiency; however, it also increases the laser's threshold pump power.

An underlying assumption of the above equation is that all optical losses involved are small, i.e. not more than a few percent. Otherwise, the order of the optical components would matter.

In simple cases, the slope efficiency can be calculated as the product of several efficiency factors, one of them being the output coupling efficiency. Depending on various quantities, a certain value of the output coupler transmission will optimize the overall power efficiency of a laser.

See also: output couplers, threshold pump power, slope efficiency, wall-plug efficiency, Spotlight article 2007-01-21, Spotlight article 2007-02-22
and other articles in the category lasers

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media: