Attosecond metrology

The generation of ultrashort pulses is a key to exploring the dynamic behav iour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, whi ch lasts somewhat longer than one femtosecond (1 fs = 10(-15) s) in the vis ible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic pr ocesses occurring on an attosecond (1 as = 10(-18) s) timescale. Here we tr ace electronic dynamics with a time resolution of less than or equal to 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible ligh t pulse. Our measurement indicates an attosecond response of the atomic sys tem, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchr onism of the soft-X-ray pulse with the light field. The demonstrated experi mental tools and techniques open the door to attosecond spectroscopy of bou nd electrons.