摘要：

Thulium-doped crystals are considered for programmable filtering. Such a filter can be achieved by Spectral Hole Burning (SHB). One optically pumps the active ions into a long-lived shelving state, opening a narrow transparency window in the crystal absorption band. We investigate a new shelving scheme in Tm:YAG where the thulium ions are pumped into a ground state nuclear Zeeman sublevel, instead of their natural 10ms-lifetime metastable state. The shelving time is increased to several seconds, reducing the residual population in the transparency window by orders of magnitude. This should enhance the filter's dynamic range, which is essential in demanding filtering applications like ultrasound optical tomography.

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