Abstract
The spatio-temporal and polarisation properties of intense light is important in wide-ranging topics at the forefront of extreme light-matter interactions, including ultrafast laser-driven particle acceleration, attosecond pulse generation, plasma photonics, high-field physics and laboratory astrophysics. Here, we experimentally demonstrate modifications to the polarisation and temporal properties of intense light measured at the rear of an ultrathin target foil irradiated by a relativistically intense laser pulse. The changes are shown to result from a superposition of coherent radiation, generated by a directly accelerated bipolar electron distribution, and the light transmitted due to the onset of relativistic self-induced transparency. Simulations show that the generated light has a high-order transverse electromagnetic mode structure in both the first and second laser harmonics that can evolve on intra-pulse time-scales. The mode structure and polarisation state vary with the interaction parameters, opening up the possibility of developing this approach to achieve dynamic control of structured light fields at ultrahigh intensities.
Highlights
The spatio-temporal and polarisation properties of intense light is important in wide-ranging topics at the forefront of extreme light-matter interactions, including ultrafast laser-driven particle acceleration, attosecond pulse generation, plasma photonics, high-field physics and laboratory astrophysics
An ability to dynamically vary these laser properties at high power could have a transformational effect on topics at the forefront of ultraintense light-matter interactions, plasma photonics and radiation generation
We begin with results from an experiment performed to explore changes to the polarisation of light transmitted through ultrathin foils expanding to near critical densities and undergoing relativistic self-induced transparency (RSIT)
Summary
The spatio-temporal and polarisation properties of intense light is important in wide-ranging topics at the forefront of extreme light-matter interactions, including ultrafast laser-driven particle acceleration, attosecond pulse generation, plasma photonics, high-field physics and laboratory astrophysics. The laser pulse propagating through the aperture can directly accelerate electrons (See reference[37] for a discussion of direct electron acceleration in sub-critical density plasma) This case of an ultrathin foil undergoing RSIT is of particular importance for the acceleration of ions to high energies[38] and for the generation of bright attosecond pulses of XUV radiation[39]. It is shown that measured changes to the polarisation and temporal properties of the light result from the generation of first and second harmonic radiation in high-order transverse electromagnetic modes It is shown that the polarisation and degree of conversion to a given mode varies with the energy of the light detected at the rear of the target, making this both a diagnostic of the intra-pulse time at which RSIT occurs and a potentially tunable approach to producing high-order modes of relativistically intense laser light
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