Helium has the largest ionization potential of all elements; thus, it is difficult to ionization for measurement by mass spectrometry. In order to analyze He, a tunnel-ionization time-of-flight sputtered neutral mass spectrometry system (called LIMAS) has recently been developed. LIMAS uses a femto-second laser technique, and can ionize He to achieve ~10% ionization yields [1]. We quantified the effectiveness of this method for He analysis from a 2.5 × 4 µm 2 area of He-implanted silicon. The amount of He in a implant was quantified by measuring the ion-current, giving a nominal implant fluence per unit area. Thus, the fraction of total He measured by LIMAS during depth profiling could be quantified by comparison with the He-concentration of the reference implant. The He + intensities normalized by host ions of Si linearly correlated with the known He concentrations with a reproducibility of 10% at concentrations less than 10 21 cm -3 . The detection limit was down to 10 18 He cm -3 (20 ppm). For concentrations exceeding 10 21 cm -3 , the He intensities are smaller than those expected from the lower concentration range. This non-linearity may reflect the limit of retention of He in the Si lattice, since He is chemically inert.2