In order to obtain the spatial distribution of hydrogen desorption by ultraviolet (UV) laser pulses from a hydrogen terminated Si (H-Si) surface, optical second harmonic (SH) intensity images of the surface have been observed in ultra high vacuum. The observed SH signal included both contributions of the hydrogen deficiency on the H-Si surface and the surface damage. The spatial distribution of the hydrogen deficiency has been obtained from the difference between the SH intensity images before

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... nd after the hydrogen re-termination. The hydrogen desorption occurred above the threshold fluence of ∼40 mJ/cm 2 , and the total amount of the hydrogen desorption increased monotonically as a function of the UV laser pulse energy. It is suggested that the observed hydrogen desorption may have resulted from the laser induced thermal desorption (LITD) mechanism.