Size of the light-emitting region in a sonoluminescing bubble

The size of the light-emitting region is a key parameter toward understanding the light-emitting processes in a sonoluminescing bubble. Here we present measurements of interference effects from particles with a diameter of approximately 2 microm situated 6-10 microm from a sonoluminescing bubble. From the angular size of the pattern and from an estimated distance to the particles we conclude that the light-emitting region of a sonoluminescing bubble is smaller than commonly believed [see, e.g., Nature (London) 398, 402 (1999)]. We argue that an upper limit of the size of the light-emitting region is approximately 200 nm.