Upconverted lasing

Figure 3.105 shows the emission output by comparison of OP and TP excitation. A clear threshold behavior and linear increase of the intensity with increasing pump power can be seen in both cases. However, the threshold for TP excitation upconverted lasing is about 300 times larger compared to the threshold for OP excitation. Despite these superior properties one still has to keep in mind that the optical feedback has to be properly sealed in order to avoid photodamage during the excitation cycles. 

Figure 3 Two-photon upconverted emission. Two photons of frequency <>> are absorbed by a medium, thus populating an excited state. A higher energy photon w is emitted. In some circumstances lasing can be achieved.

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