Field and excitation dependent ultrasonic attenuation in 3He-B

Sound absorption of 3He-B at 0 bar was studied at a frequency of 10 MHz. We performed pulsed experiments with different pulse lengths (4 to 15 μs) and pulse powers (0.1 to 160μW) in the temperature range 0.2 < T/Tc < 2. For pulse power less than pth∼50 μW, and in the temperature range 0.4 to 0.8 Tc and zero field, the attenuation coefficient a decreases monotonically at about 0.2 cm-1 per decade of power. Above pthα increases up to values of 3.5 cm-1 and 1.9 cm-1 at highest power for temperatures of 0.8 Tcand 0.4 Tc, respectively. At pulse power around 100μW and at the lowest temperatures, the attenuation changes within the first 200 μs after the application of the pulse; α also increases with increasing field. In the normal fluid α decreases with increasing power. All of our observations are lacking a rigorous theoretical understanding