MULTIPHOTON-INDUCED LUMINESCENCE FROM SUPERCONDUCTING NB3SN

We have observed multiphoton-induced visible luminescence from Nb3Sn i n the temperature range from 7K to 50K. The light source for excitatio n was a Q-switched Nd:YAG laser with light pulses of photon energy 1.1 65eV, Nb3Sn has a superconducting transition temperature at T-c=18K. T he luminescence intensity is roughly constant until the sample tempera ture is decreased from SOK to the superconducting transition. Then it increases rapidly below T-c. There is a dip in the luminescence intens ity at T-c. The rapid increase of the luminescence intensity below T-c reflects the transformation of the electronic states of Nb3Sn from th e normal to the superconducting state. The dip at the superconducting transition temperature seems to be related to the optical absorption o f bulk Nb3Sn that occurs at the phase transition temperature.