Resonant laser sputtered neutral mass spectrometry can greatly enhance the ionization efficiency of specific neutral sputtered atoms through resonant excitation using tunable laser(s). However, the laser beam cannot irradiate the entire volume where sputtered particles are moving, because the laser beam is focused. In contrast, for an extremely low concentration of target elements, it is necessary to increase the laser irradiation efficiency. Irradiation efficiency depends on both spatial coverage and resonance wavelength matching. The former can be increased by increasing the laser path length within the sputtered neutral plume. The latter depends on the relationship between the laser spectral linewidth and the Doppler broadening width caused by the velocity of sputtered neutral particles. The authors have developed a new method to improve the ionization probability of neutral particles by reflecting the laser using mirrors to increase the ionization efficiency based on the concept mentioned above.