Femtosecond Laser-Induced Ablation – Quadrupole Mass Spectroscopy (fs-LIA-QMS) experiment for the detection of trapped hydrogen-isotopes and helium in nuclear fusion relevant materials

We present a novel instrumentation using ultrashort pulsed laser induced ablation in combination with a Quadrupole Mass Spectrometer (QMS) for the detection of gaseous species captured in tungsten (W) and other metallic substrates. In particular, we demonstrate the potential of this technique for the investigation of plasma-facing components in fusion devices. Our fs-LIA-QMS experiment is capable of detecting deuterium (D) and helium (He) in W samples simultaneously with high sensitivity down to 0.004 at.%, depth resolution in the order of 31 nm, and high lateral resolution better than 20 µm. Our study highlights the importance of using sub-picosecond laser pulses for an accurate depth-resolved detection of gaseous species trapped in metallic substrates. The use of ultra-short, near UV laser pulses (400 fs, 343 nm) reduces heat affection compared to nanosecond and even picosecond ablation processes. Our results are in good agreement with other diagnostics applied in this context, such as Nuclear Reaction Analysis (NRA) for the D depth profiling, and numerical predictions of the He distribution with SDTrimSP. We also discuss the limitations of the technique, including the influence of heat diffusion initiated by the fs-laser and the characterization of loss-channels in the system that restricts the limit of detection.