Laser induced boron doping of silicon is studied as a function of the laser pulse number and energy density, in a special configuration where the precursor gas (BCl3) is injected and chemisorbed on the Si surface prior to each laser pulse. In-situ optical diagnostics, based on the transient reflectivity at 675 nm, allow to control the evolution of the dopant concentration and of the doped layer thickness during the laser doping process. Samples are characterized by the four-point probe method, atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS). As the laser pulse number is scanned from 10 to 200 at a constant laser pulse energy, the junction depth increases from 21 to 74 nm while its sheet resistance decreases from 220 to 17 Ω/. Moreover, boron concentrations well above the solubility limit (up to 31021 cm-3 for 200 pulses) and very abrupt box-like dopant profiles are obtained. So, laser doping, in this dopant gas injection configuration, seems to be a very attractive technique to meet the International Technology Roadmap for Semiconductors (ITRS) requirements for ultra-shallow junctions.