Improved femtosecond third-order nonlinear optical properties of thin layered Cu_3Nb_2O_8

摘要

Thin motif-layered triclinic Cu3Nb2O8 was prepared through solid-state reaction at 700 degrees C, 12 h and their nonlinear optical (NLO) properties with ultrafast [800 nm, 150 fs (fs) pulses, 80 MHz repetition rate] pulse laser excitation were studied. A peculiar shift from reverse saturable absorption (RSA) to saturable absorption (SA) at a peak intensity of 40 MW/cm(2) was observed. The involvement of excited state absorption (ESA) is confirmed from the decrease in the nonlinear absorption coefficient with increase in peak intensity and the observed nonlinearity is ascribed to a sequential 2 PA process (1 PA+ESA). Formation of layered structure in Cu3Nb2O8 acted as a transport layers which yielded high nonlinear absorption coefficient (7.8 x 10(-10) m/W), nonlinear refractive index (5.17 x 10(-16) m(2)/W) and nonlinear optical susceptibility (25.6 x 10(-11) esu) when compared to other known copper niobates. The observation of low onset-limiting threshold (78.79-26.26 mu J/cm(2)) renders Cu3Nb2O8 a prospective material for ultrashort pulse laser protecting device and biomedical microsurgery tools. A transition of mixed phase CuNb2O6-Cu3Nb2O8 into pure triclinic Cu3Nb2O8 along with change in morphology from pore to layered structure with increase in sintering time was confirmed from powder XRD, Raman, FESEM measurements and UV-Visible absorption studies.