Above-threshold ionization at intensity greater than 10²⁰ W/cm²

The ADK-PPT model of tunneling ionization is experimentally well-verified at intensity below 10¹⁹ W/cm². The relative simplicity of the tunneling model physics and the highly nonlinear ionization rate scaling with intensity make the detection of high ion charge states a promising method for directly measuring laser intensity. We present our progress toward the next generation of high-field atomic physics experiments, including modeling of the ion and electron dynamics in ultra-intense laser fields. We modeled the interaction of a highly-charged ion with a tightly-focused (f/1) laser pulse with a wavelength of 1057 nm and a pulse duration of 140 fs, characteristic of Nd:glass OPCPA laser facilities. We found that ponderomotive expulsion of the ions from the laser field necessitates new experimental methods for directly measuring or indirectly inferring the presence of high charge states. Our modeling showed ions will be accelerated to energies > 2 MeV/nucleon and ATI electron energies can exceed 1.4 GeV at the peak intensity of 3 x 10²³ W/cm² expected to be reached in the next few years. We also present our findings from two novel experimental campaigns on the Texas Petawatt Laser, an unsuccessful test of field-free ion time-of-flight and a successful detection of electrons produced by above-threshold ionization (ATI) of highly-charged neon states. We observed ATI electrons with energy greater than 10 MeV originating from the neon K-shell when laser intensity exceeds 2 x 10²⁰ W/cm².Physic

Plasma emission characteristics in laser-induced breakdown spectroscopy of silicon with mid-infrared, multi-millijoule, nanosecond laser pulses from a Ho:YLF excitation source

We characterized the plasma emission produced by the interaction of multi-millijoule, 40 ns duration, mid-infrared laser pulses with a silicon surface. The laser pulses were produced by a Q-switched Ho:YLF master oscillator power amplifier system. Using spectral measurements and a framing camera, we observed a spatial separation of the plasma plume, increased emission signal with low white-light generation, and a drop in the time- and space-averaged apparent plasma density with increasing pump energy. Our results can be explained by continuous heating of the plasma by the pump pulse due to the more efficient inverse bremsstrahlung absorption at longer wavelengths. (C) 2019 Optical Society of America1