Abstract

Deep-red (or far-red) light is the emission at the extreme red end of the visible spectrum, at 660 - 750 nm. It is hardly visible by a naked eye but plays a key role in many aspects of the plant development (falling in the spectral range of photo-biologically active radiation, PBAR). Deep-red laser sources find applications in biomedicine (e.g., photodynamic and photoimmune therapy), live cell imaging and UV generation via frequency doubling. Deep-red laser emission can be directly generated using several rare-earth ions such as Pr³⁺, Ho³⁺ and Eu³⁺. In particular, trivalent europium (Eu³⁺) ions provide emission at ~700 nm due to the quasi-four-level ⁵D₀ → ⁷F₄ transition [1]. Due to the lack of cross-relaxation processes affecting the ⁵D₀ Eu³⁺ metastable state, heavily doped laser materials can be used benefiting from increased pump absorption efficiency. In the present work, we report on the first laser operation of a heavily Eu³⁺-doped CsGd(MoO₄)₂ molybdate crystal in the deep-red spectral range.

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