Abstract
We report on experimental results in a new regime of a relativistic light-matter interaction employing mid-infrared (3.9-micrometer wavelength) high-intensity femtosecond laser pulses. In the laser generated plasma, the electrons reach relativistic energies already at rather low intensities due to the fortunate lambda^2-scaling of the kinetic energy with the laser wavelength. The lower intensity suppresses optical field ionization and creation of the pre-plasma at the rising edge of the laser pulse efficiently, enabling an enhanced efficient vacuum heating of the plasma. The lower critical plasma density for long-wavelength radiation can be surmounted by using nanowires instead of flat targets. In our experiments about 80% of the incident laser energy has been absorbed resulting in a long living, keV-temperature, high-charge state plasma with a density of more than three orders of magnitude above the critical value. Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate.
Highlights
Solid density,keV-temperature plasmas open new perspectives for realizing tabletop, high-brilliance x-ray sources [1–3], laser-induced nuclear physics [4,5], and experiments on laboratory astrophysics [6,7]
We report on experimental results in a new regime of relativistic light-matter interaction employing midinfrared (3.9-μm wavelength) high-intensity femtosecond laser pulses
Our results pave the way to laser-driven experiments on laboratory astrophysics and nuclear physics at a high repetition rate
Summary
Solid density, (multi-)keV-temperature plasmas open new perspectives for realizing tabletop, high-brilliance x-ray sources [1–3], laser-induced nuclear physics [4,5], and experiments on laboratory astrophysics [6,7] Such plasmas can be generated when relativistically intense, high-temporal-contrast femtosecond laser pulses interact with solids. For a given laser pulse energy, higher intensities can be reached easier with short-wavelength laser sources by entering the so-called λ3 regime, defined by focusing the shortest possible pulses (given by the length of a single cycle) to the diffraction limited spot given by the wavelength [8]. Such single-cycle, short-wavelength ultraintense pulses will only interact with an extremely small volume of plasma. It is worth mentioning that pulse compression down to a single cycle becomes extremely challenging with a shortening of the laser wavelength
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