Hearing carrier-envelope offset frequency and phase in air with a microphone*

Attosecond science and frequency metrology rely on the precise measurement and control of the laser pulse waveform, a feat traditionally achieved using optoelectronic techniques. In this study, we conducted a laser-induced acoustic experiment in air ionized by carrier-envelope offset phase (CEP)-stabilized sub-4 femtosecond pulses. Our findings reveal that the acoustic intensity in the frequency domain is dependent on the CEP of the driving light pulses, mainly corresponding to an amplitude modulation of the acoustic waves in the time domain. Moreover, we measured the carrier-envelope offset frequency of optical light pulses in the acoustic spectrum with a microphone. These observations enable an application of pulse characterization through these acoustic waves. Our study highlights the potential of laser-induced acoustic waves for advancing frequency metrology and ultrafast science.