output couplers (original) (raw)

Definition: partially transparent laser mirrors, used for extracting output beams from laser resonators

Alternative term: output coupling mirrors

Categories: photonic devices, laser devices and laser physics

• mirrors
  • laser mirrors
    * output couplers

Related: output coupling efficiencymirrorsdielectric mirrorslaser mirrorslaserslaser resonators

Page views in 12 months: 1349

DOI: 10.61835/zcz Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

Content quality and neutrality are maintained according to our editorial policy.

📦 For purchasing output couplers, use the RP Photonics Buyer's Guide — an expert-curated directory for finding all relevant suppliers, which also offers advanced purchasing assistance.

Contents

What are Output Couplers?

An output coupler is usually a semi-transparent dielectric mirror used in a laser resonator. Its function is to transmit part of the circulating intracavity optical power to generate a useful output of the laser.

As for basically all laser mirrors, the reflecting coating of an output coupler mirror is on the inner side, i.e., on the side of the mirror substrate which is oriented towards the laser resonator. This is because otherwise one would have a serious impact of losses by parasitic reflections on that inner side, which is exposed to the full circulating optical power.

In lasers with unstable resonators, the output coupler is sometimes a highly reflecting mirror, where output coupling occurs at an edge. It is also possible, although not common, to do output coupling in a laser with other optical elements, e.g. with diffraction gratings.

Output Coupler Transmissivity

An important property of an output coupler is its transmissivity (the degree of its transmission of optical power). A low output coupler transmissivity leads to a low threshold pump power, but also possibly to a poor laser efficiency if the losses due to output coupling do not dominate over other (parasitic) losses in the laser resonator (low output coupling efficiency). The output coupler transmissivity is often chosen to maximize the output power, although its optimum value may be lower or higher if there are other design goals, e.g. minimizing the intracavity intensities or suppressing Q-switching instabilities in a passively mode-locked laser.

Flat and Curved Output Couplers

Output coupler mirrors are often mirrors with a flat surface, since it is often convenient to obtain a collimated beam at the output. (For a linear resonator, the wavefronts of the resonator modes must match the mirror surface, so that a flat output coupler results in a focus at that place.) Also, misalignment of any optical element other than the output coupler itself will then lead only to a parallel shift of the output beam, but not to a change in direction (→ beam pointing fluctuations). In the case of an output coupler with a curved (e.g. concave) surface, one also has to take into account that the mirror substrate will usually have a focusing or defocusing effect on the output beam.

Reflections from the Backside

Note also that the backside of the glass substrate of an output coupler mirror has some reflectivity, which may have an effect on the laser performance. Even the residual reflectivity of an anti-reflection-coated backside may create an interference (etalon) effect (if the surfaces are flat and parallel), which modulates the effective transmission of the device as a function of wavelength and can thus influence the laser bandwidth. In a mode-locked laser, such effects (even at a very low level) can cause instabilities. A way to avoid such problems is to use a slightly wedged output coupler, so that the reflected light from the backside does not interfere with the laser modes.

Variable Reflectivity Mirrors

In the case of stable optical resonators, the output coupler mirror usually has a spatially constant output coupler transmission (see below). Output couplers of unstable resonators can be very different: they are often variable reflectivity mirrors, having a transversely variable reflectance e.g. with a Gaussian or super-Gaussian profile, possibly even with total reflection within some radius and total transmission outside that radius.

Suppliers

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

⚙ 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.

⚙ 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

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.

Questions and Comments from Users

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.