  Simultaneous measurements of hard X-ray by a Geiger counter and audible sound
(10 Hz-20kHz) by a microphone from a thin water film in air were carried out
under intense single and double pulse irradiations of femtosecond laser (35 fs,
800 nm, 1 kHz). Emission profiles of X-ray and sound under the single pulse
irradiation by changing the water film position along the laser incident
direction (Z-axis) show the same peak positions with a broader emission in
sound (403{\mu}m at FWHM) than in X-ray (37{\mu}m). Under the double pulse
irradiation condition with the time delay at 0 ps and 4.6 ns, it was clearly
observed that the acoustic signal intensity is enhanced in associated with
X-ray intensity enhancements. The enhancements can be assigned to laser
ablation dynamics such as pre-plasma formation and transient surface roughness
formation induced by the pre-pulse irradiation. For the acoustic signal under
the double-pulse irradiation with the time delay, there was a weak dependence
observed on the pre-pulse irradiation position at the laser focus. It is
consistent with a long breakdown filament formation which makes the
microphone-detection less position-sensitive.
