High-resolution third harmonic order imaging line for measuring laser focal spot size in laser-solid interactions*

In high-intensity laser-solid interactions used for high-harmonic generation (HHG), measuring the laser spot size on the target during the interaction is useful for reducing uncertainty in HHG intensity calculations. Furthermore, when such interactions are desired to occur at the edge of the target, a method is required to determine if the laser hits the edge of the target or the full target. For these purposes, I will report on the development of a high-resolution imaging line of the laser focal spot, which is achieved by imaging the third harmonic order. Imaging of the third harmonic offers advantages over X-ray imaging – a reduction in background noise and an emission spot closer to that of the incident laser – leading to a greater certainty of the laser spot size. The third harmonic is also straightforward to extract from other harmonics generated, allowing for a relatively simple imaging line.