Electro-optic Kerr effect measurement based on carrier-envelope phase demodulation

A precise control of the electric field nodes relative to the maximum of the intensity envelope is a prerequisite for attosecond pulse generation and experiments in high-field physics. Many carrier-envelope phase (CEP) stabilization schemes start with stabilization of an oscillator, which is nevertheless often difficult to obtain as the CEP has proven highly sensitive to environmental parameters, including temperature, air pressure, and humidity. This very high susceptibility to environmental changes is considered more of a nuisance than anywhere useful. Here, we show that the extreme sensitivity of the CEP can be exploited for quantitative measurements of the electro-optic Kerr effect in atmospheric air, i.e., an extremely weak effect that has previously only been measurable by combining effective path lengths of 100m with tens of kilovolt voltages. In contrast, we can obtain a measurable effect by placing an 8 cm long high voltage capacitor into the intracavity beam path of a mode-locked few-cycle Ti:sapphire oscillator, and we only require rather moderate driver voltages of less than 5 kV.