Thin Disk Gain Media
Thin-disk lasers typically utilize ytterbium-doped yttrium aluminum garnet (Yb:YAG) crystal as the gain medium. Compared to neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal, Yb:YAG displays several benefits. Firstly, it provides a shorter emission wavelength at around 1030 nm. Secondly, it has a lesser degree of quantum defect, which provides improved efficiency with regard to the conversion from pump photons to laser photons. Thirdly, Yb:YAG has a longer upper-state lifetime, which is beneficial for energy storage regarding Q-switching.
Furthermore, Yb:YAG thin disk gain media provides a larger gain bandwidth, which aids in short or ultra-short pulse generation (mode-locking). Another benefit derives from the ability to utilize higher doping concentrations. For example, the maximum dopant rate for neodymium is approximately 1.5%. Anything greater than around 1.5% doping with neodymium leads to excess material strain. However, the maximum dopant rate for ytterbium is much greater (up to ≈ 25%). A higher percentage of doping allows for stronger overall pump absorption. This increase does come at somewhat of a cost, as ytterbium is a quasi-three-level laser gain medium. This means it exhibits significant reabsorption at the laser wavelength, requiring greater intensities from the pump source. However, thin-disk lasers are particularly well suited for this situation.
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