High-dynamic-range laser waveform measurement using tunneling ionization

Abstract

Ultrafast lasers have opened new frontiers in study of relativistic electromagnetic phenomena, as their peak intensity now exceeds 1023 W/cm2. At such extreme field strengths, light-matter interactions exhibit a wealth of nonlinear and relativistic effects, including relativistic high-harmonic generation from plasma mirrors, laser-driven electron acceleration of electrons and ions, and the X-rays and gamma rays. To fully exploit these extreme interactions, precise temporal characterization of femtosecond and sub-femtosecond laser pulses is essential. In this thesis, we explore two complementary approaches for laser pulse characterization: 1） single-shot methodology and 2） high-dynamic-range measurement in a delay-scanning type. Both methods are based on Tunneling Ionization with a Perturbation for the Time-domain Observation of the Electric field （TIPTOE）. In the single-shot methodology, the ionization-yield modulation is extracted from plasma fluorescence emission, enabling direct pulse characterization at the interaction point. By employing a noncollinear geometry and line-shape focusing configuration, the plasma fluorescence modulation encodes the spatially mapped temporal waveform of the laser pulses. Laser waveforms measured under different dispersion condition––positive, zero, negative chirped––show excellent agreement between the single-shot scheme and the conventional delay-scanning type TIPTOE technique. These various chirp conditions, induced using an Acousto-Optic Programmable dispersive filter （AOPDF） system, were successfully reconstructed by both two TIPTOE methods. In the high-dynamic-range temporal characterization study, multiple electrodes were employed to suppress measurement noise and enhance sensitivity. By utilizing ten electrodes, the dynamic range of the TIPTOE measurement was significantly improved, reaching 89 dB through effective suppression of the background noise of the detection unit. This performance was further enhanced to 102 dB by incorporating the Kerr-lens effect. Owing to strong nonlinearity of tunneling ionization, the reconstructed waveforms exhibited high fidelity with substantially reduced post-pulse gating artifacts, which often require careful interpretation in conventional characterization techniques. These results demonstrate a substantial advancement in the performance and versatility of the TIPTOE technique, establishing it as a powerful and broadly applicable tool for ultrafast laser pulse characterization under extreme light–matter interaction conditions.