We have conducted an experimental and theoretical study of the desorption, by 25 ns ruby laser pulses, of hydrogen implanted at ∼25 at. % concentration in c-Si. The evolution of the hydrogen depth profile was monitored by elastic recoil detection. The implantation or laser-induced damage was observed by optical microscopy. The heat and hydrogen transport were modeled with a finite-difference code. Desorption sets in at a very sharp threshold of (0.50±0.05) J/cm2 as a function of the laser energy fluence, corresponding to a peak temperature of ∼1000 K, and to minimal laser damage. The rate limiting process is detrapping with an activation energy of 1.2–1.5 eV, and an effective diffusion energy ≤0.1 eV.