Low-Frequency Vibrational Excitations in a Niobium-Phosphate Glass for Raman Gain Applications

Raman gain for all-optical amplification depends significantly on the cross section for spontaneous Raman scattering. We present measurements of the Raman spectrum of binary niobium-phosphate glasses in the frequency range from 5 – 1300 cm. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (‘Boson peak’) suggesting a significant gain profile for application in Raman amplifiers as well as providing an additional mechanism for Raman gain. To separate the effects of density of states from the lightvibration coupling we carried out an inelastic neutron scattering investigation of 40 Nb2O5 60 NaPO3 using the time-of-flight spectrometer (TOF-TOF) at the FRM II neutron source in Munich. The Boson peak appears between 40 and 70 cm as an increase of the reduced density of states over the flat Debye approximation. Possible mechanisms contributing to the low frequency excitations such as disorder-induced irregular vibrational states are discussed.