output coupling efficiency (original) (raw)

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

Units: %, dimensionless number

Formula symbol: ($\eta_{oc}$)

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

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What is an Output Coupling Efficiency?

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

Here, the useful losses are given by the output coupler transmission ($T_\textrm{oc}$), and the parasitic losses are ($l_\textrm{par}$). (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.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is output coupling efficiency in a laser?

The output coupling efficiency is the ratio of the useful losses (power transmitted through the output coupler) to the total round-trip losses in the laser resonator. It is calculated as (${\eta _{{\textrm{oc}}}} = {T_{{\textrm{oc}}}} / ({T_{{\textrm{oc}}}} + {l_{{\textrm{par}}}})$), where ($T_\textrm{oc}$) is the output coupler transmission and ($l_\textrm{par}$) are the parasitic losses.

Why is a very high output coupler transmission not always better for a laser?

While a larger output coupler transmission increases the output coupling efficiency, it also increases the laser's threshold pump power. Therefore, the transmission must be optimized to achieve the maximum output power, balancing these two effects.

What is the relation between output coupling efficiency and slope efficiency?

The output coupling efficiency is one of the factors determining the laser's slope efficiency. A higher output coupling efficiency generally leads to a higher slope efficiency, assuming the laser is operating well above its threshold.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains 27 suppliers for output couplers. Among them:

⚙ hardware

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.

⚙ hardware

Output couplers, as intracavity components, have to handle extreme energy densities. That is why OPTOMAN coatings are optimized for a high damage threshold, which can exceed 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.

⚙ hardware🧩 accessories and parts🧴 consumables🔧 maintenance, repair📏 metrology, calibration, testing💡 consulting🧰 development

Off-the-shelf and custom output couplers are available in Shalom EO; these partially reflective mirrors are optimized for extracting laser beams from laser cavities, while they can also be used as optical attenuators. We can provide diverse shapes, plano-plano, plano-concave, plano-convex, and wedged. The output couplers can contain arrow markings or indications to show the partially reflective surface.

Various reflection/transmission configurations and design wavelengths are accessible to suit the applications of your laser systems. The standard modules include:

Nd:YAG laser output couplers with various reflection/transmission ratios (532 nm, 946 nm, 1064 nm)
Other laser output couplers with various reflection/transmission ratios (716 nm, 808 nm diode laser, 1030 nm ytterbium laser, 1645 nm Er:YAG

⚙ hardware

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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