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Output Coupling Efficiency

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

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

Category: article belongs to category laser devices and laser physics laser devices and laser physics

Units: %, dimensionless number

Formula symbol: <$\eta_{oc}$>

DOI: 10.61835/m20 Cite the article: BibTex plain text HTML Link to this page LinkedIn

The power conversion efficiency of a laser is often reduced by unavoidable parasitic intracavity losses in the laser resonator. More specifically, such losses 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:

$${\eta _{{\rm{oc}}}} = \frac{{{T_{{\rm{oc}}}}}}{{{T_{{\rm{oc}}}} + {l_{{\rm{par}}}}}}$$

Here, the useful losses are given by the output coupler transmission <$T_\rm{oc}$>, and the parasitic losses are <$l_\rm{par}$>. (Both are the losses per round-trip, taking into account a possible double pass in a linear resonator.) A larger output coupler transmission always increases the output coupling efficiency; however, it also increases the laser's threshold pump power, and should therefore not be chosen too high.

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, and a more complicated equation is needed.

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.

More to Learn

Encyclopedia articles:

Blog articles:

The Photonics Spotlight 2007-01-21: “Laser Operation Far Above Threshold”
The Photonics Spotlight 2007-02-22: “Lossy Laser Cavities”

Suppliers

The RP Photonics Buyer's Guide contains 28 suppliers for output couplers. Among them:

OPTOMAN

Output couplers, as intracavity components, have to handle extreme energy densities. That is why OPTOMAN coatings are optimized for a high damage threshold, which exceeds 168 J/cm² at 1064 nm, 9.8 ns. OPTOMAN is able to make output couplers optimized for ultrafast lasers that feature negligible GDD, both in reflection and transmission.

Standard in-stock IBS coated optics can be found in OPTOSHOP.

EKSMA OPTICS

We offer a wide choice of laser output couplers designed for Nd³⁺ host lasers operating in the 1040–1070 nm range and for femtosecond Ti:sapphire or Yb:KGW/KYW lasers.

LASEROPTIK

LASEROPTIK offers partial reflectors, as are required e.g. as output couplers for lasers. We can address a wide range of wavelengths and use different coating technologies depending on your detailed requirements.

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