High-repetition rate ion acceleration driven by a two-plasmon decay instability

Intense laser plasma driven ion acceleration is typically based on a target normal sheath acceleration scheme. This demands short density scale length plasmas and relativistic intensity laser pulses. Parametric instabilities driving electron acceleration in long density scale length plasmas have seldom been considered in this context. We provide the first experimental evidence for ion acceleration driven by parametric two plasmon decay (TPD) instability. In this regime, laser pulses with intensities hundredfold below relativistic thresholds are enough to produce MeV energy hot electrons. This allows mJ energy laser pulses to drive ion beams up to 0.6 MeV energy with <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mn>20</a:mn><a:mo>∘</a:mo></a:msup></a:math> angular width. Ion source size <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mo>&lt;</b:mo><b:mn>15</b:mn></b:mrow></b:math> <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mo>µ</c:mo><c:mtext>m</c:mtext></c:mrow></c:math> are observed via ion radiography, steady over thousands of shots.