Spectroscopic properties of Cr3+ ions in KTP single crystals

The possibility of creation of self-frequency doubling laser crystal based on crystal KTP (KTiOPO4) doped with chromium ions is investigated. The spectral (fluorescence and absorption) properties of Cr3+ ions are researched. The magnitude of emission cross-section (sigma(lambda) similar to10(-20) cm(2)) at the wavelength of 833 nm corresponding to the maximum of vibronic transition (4)T(2-)(4)A(2) of Cr3+ ion is estimated. The excited state (T-4(2)) lifetimes at room (tau(300) = 3.5 musec) and liquid nitrogen (tau(77) = 90 musec) temperatures are determined. The spectroscopic investigations show that impurity Cr3+ ions in KTP crystal are placed in positions with weak crystal field: Dq=1507 cm(-1), B=652 cm(-1), C=2800 cm(-1). The configuration diagram model with one excited state is discussed. The main features of fluorescence spectra and the expected laser emission in the near IR range from 700 to 1000 nm are considered.