Brillouin light scattering analysis of three-magnon splitting processes in yttrium iron garnet films

Wave vector and frequency selective Brillouin light scattering (BLS) has been used to measure the wave vector make up for the dipole exchange spin wave (DESW) modes which are parametrically excited by propagating magnetostatic surface wave (MSSW) pulse signals in a long and narrow yttrium iron garnet film strip through three magnon splitting processes. The signal frequency f(s) was 2.65 GHz, the input pulse width was 100 ns, and the in-plane applied field was 340 Oe. In addition, time and space resolved (TSR) BLS techniques were used to map the spatio-temporal propagation properties of the MSSW and DESW modes as they evolve as a result of three magnon processes. The film thicknesses were 5-10 mum. Specific data are reported for an 8.7 mum thick film. The DESW mode frequencies are at about f(s)/2. The DESW wave vector k directions form lobes at in-plane angles of 5degrees-15degrees relative to the field. The k values are in the 10(4) rad/cm range and are quantized. The frequencies and k values match those predicted from the dispersion relations and energy and momentum conservation. Specific critical powers are associated with particular k values. The TSR data show that the MSSW pulses propagate with a wedge shaped wave front and quench in such a way as to produce the ultra short 1-2 ns wide output pulses reported previously. The quench is connected with the appearance of a corresponding half frequency DESW wedge which is nearly stationary, has a response time of a few nanoseconds, and has a decay time in excess of the 100 ns MSSW pulse width.