The thin disk laser (TDL)

The thin disk laser (TDL) is normally a diode-pumped, high-power, solid-state laser. A thin-disk laser with a multi-pass pumping configuration was first introduced in the 1990’s by the Adolf Giesen group at the University of Stuttgart, Germany.  The thickness of a thin disk laser crystal is typically only a few hundred micrometers.

Figure 1.  The heat sink on the backside of the disk normally uses water to remove heat caused by pumping.  Source: Encyclopedia of Laser Physics and Technology http://www.rp-photonics.com/

                                                                                                                                                                                                                                               

The thickness (100~300 mm) is small compared to the diameters of the pumped area and the laser beam (usually a few millimeters). The disk has a highly reflective coating on one side and an anti-reflective coating on the other side for both pump and laser wavelengths. The reflective side is mounted directly onto a water-cooled heat sink and the disk acts as an active mirror. The thin disk is sometimes called an “active mirror”, because it is like a mirror with laser gain. It can be cooled very efficiently and the heat flow is mainly one-dimensional towards the heat sink, i.e., co-linear with the direction of the laser beam. The thermal gradients in the transverse direction are weak, and thermal lensing is therefore strongly reduced compared to a rod or slab design. Pump absorption in a single pass through the thin disk is low. However, highly efficient operation is achieved by arranging multiple pump passes through the disk (typically 16 to 24 passes).

  Our Applied Energetics “Wild Cat” line of laser amplifiers uses Yb:YAG (Ytterbium-doped yttrium aluminum garnet) thin disk laser (TDL) gain media. Ytterbium (Yb) is a chemical element belonging to the group of rare earth metals (Lanthanides) with atomic number 70.  Ytterbium is often used as a doping material (Yb3⁺) for high powered and wavelength-tunable solid state lasers.

  Ytterbium was discovered by the Swiss chemist Jean Charles Galissard de Marignac in the year 1878 and named it for Ytterby, the Swedish village near where he found the new mineral.

Figure 2.  Atomic energy levels of Yb3+ ions in Yb:YAG, showing the 940nm pump and 1030nm laser transitions.  Source: Encyclopedia of Laser Physics and Technology http://www.rp-photonics.com/

                                             

Ytterbium-doped YAG lases at about 1030 nm, with a broad, 18 nm wide absorption band at 940 nm. The energy levels are of the form ^(2s+1) L_J  such that the ground state manifold ²F_7/2 means that spin quantum number S=1/2, F corresponds to orbital quantum number L=3, and total angular momentum J=7/2. At Applied Energetics, we use InGaAs (Indium gallium arsenide) laser diodes at 940nm to pump our Yb:YAG thin disks.


For more information go to  www.appliedenergetics.com