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Composite Laser Crystals

Definition: laser crystals consisting of several parts of different materials or with different chemical compositions (e.g. doping concentrations)

Alternative terms: hybrid laser crystals, core-doped rods

More general terms: laser crystals

Categories: optical materials, lasers

How to cite the article; suggest additional literature


Composite laser crystals (sometimes called hybrid laser crystals) are laser crystals which have been fabricated by combining different parts. Typically, adhesive-free diffusion bonding of carefully prepared crystal surfaces is used, e.g., to combine an Nd:YAG or Yb:YAG crystal with an undoped YAG crystal. The same can be done e.g. with Nd:YVO4. Another possibility is to bond a Cr:YAG crystal (a saturable absorber material for passive Q switching) to Nd:YAG. In other cases, a nonlinear crystal material for nonlinear frequency conversion is bonded to a laser crystal. Composite gain media can also be made of glasses and from ceramics.

The optical quality of bonded interfaces is essential. Different processes have been developed for obtaining high-quality bonds. Some of these operate at high temperatures, while others can be performed also at room temperature. One may, for example, use irradiation with high-energy ions in a vacuum to remove any disturbing surface layers before bonding. In any case, preparing very flat surfaces is essential.

In the following, some examples of the use of composite gain media are given:

composite laser crystal with undoped end caps
multi-segmented laser rod
core-doped laser rod
thin disk crystal with undoped cap

In other situations, undoped end caps can help to suppress parasitic laser oscillation, and when they are properly shaped (e.g. conically) they can act as ducts for pump radiation. In some single-frequency ring lasers, an undoped section at a point of beam reflection can eliminate spatial hole burning effects.

Note that composite gain media can also be made of ceramics. The fabrication techniques for ceramics introduce a lot of freedom for composite structures, including doping gradients. It is also possible to combine single crystals and ceramics, e.g. to grow undoped ceramic around a doped single crystal.


The RP Photonics Buyer's Guide contains 12 suppliers for composite laser crystals.

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[1]R. Zhou et a l., “Continuous-wave, 15.2 W diode-end-pumped Nd:YAG laser operating at 946 nm”, Opt. Lett. 31 (12), 1869 (2006), doi:10.1364/OL.31.001869
[2]R. Wilhelm et al., “Power scaling of end-pumped solid-state rod lasers by longitudinal dopant concentration gradients”, IEEE J. Quantum Electron. 44 (3), 232 (2008), doi:10.1109/JQE.2007.911702
[3]Y. T. Chang et al., “Comparison of thermal lensing effects between single-end and double-end diffusion-bonded Nd:YVO4 crystals for 4F3/24I11/2 and 4F3/24I13/2 transitions”, Opt. Express 16 (25), 21155 (2008), doi:10.1364/OE.16.021155

(Suggest additional literature!)

See also: laser crystals, gain media, ceramic gain media, neodymium-doped gain media, ytterbium-doped gain media, thermal lensing, high-power lasers
and other articles in the categories optical materials, lasers

Dr. R. Paschotta

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