4He third-sound pulse collisions -: art. no. 054524

We investigate the behavior of pulses of He-4 third sound that propagate and collide on a glass substrate. Third sound is created by a thermal source and detected by evaporated metal superconducting transition-edge thermometers. Two thermal sources located symmetrically on either side of a detector allow third-sound pulses to be created, propagate through each other, and be detected. By varying the delay of the pulse launch between the two sources, the collision can be placed at an arbitrary position on the substrate. We present detailed observations of the evolution of the amplitudes of the third-sound pulses in collision. We also report measurements on the effect of the pulse collision on the propagation time of Hight of the third-sound pulses. Experimental results for the time of flight change induced by the collisions are compared with quantitative expectations based on the two fluid model and a stronger effect is observed than expected.