Computational and Raman studies of phospho-tellurite glasses as ultrabroad Raman gain media

Molecular orbital calculations of two phospho-tellurite model clusters were performed to clarify the origins of the Raman bands in the Stokes region of over 1000 cm^− 1 in phospho-tellurite glasses. The Raman bands could be attributed to two components of 900-1050 cm^− 1 of symmetrical stretching vibrations of PO₄ units and 1050-1200 cm^− 1 of anti-symmetrical stretching vibrations of PO₄ units. It was also clarified that the top of the valence band of phospho-tellurite glasses consists of the lone pair electrons in a TeO_4 + 1 unit and the bottom of the conduction band of the glass consists of the antibonding hybrids of Te 5p and O 2p orbitals in the equatorial plane of a TeO₄ unit.We have developed new phospho-tellurite glasses which have the Raman gain peak of 30 times as large as silica glass or the Raman gain bandwidth of more than 1200 cm^− 1.