Visualiser of two-micron laser radiation based on Ho:CaF2 crystals

The anti-Stokes luminescence spectra of Ho:CaF₂ crystals corresponding to the ⁵G₄ → ⁵I₈, ⁵G₅ → ⁵I₈, ⁵F₃ → ⁵I₈, ⁵F₄(⁵S₂) → ⁵I₈, ⁵F₅ → ⁵I₈, ⁵S₂ → ⁵I₇, ⁵I₄ → ⁵I₈, ⁵I₅ → ⁵I₈, ⁵F₅ → ⁵I₇, ⁵F₃ → ⁵I₆, ⁵I₆ → ⁵I₈, ⁵F₅ → ⁵I₆, and ⁵I₅ → ⁵I₇ transitions upon excitation of the ⁵I₇ level of Ho³⁺ ions are studied. A method for visualisation of IR radiation in the two-micron range using Ho:CaF₂ crystals is proposed. The energy efficiency of conversion of two-micron laser radiation to radiation in the red spectral range 620 – 690 nm by a 1 mol % HoF₃:CaF₂ crystal is estimated to be no higher than 0.02%.