The desorption of pairs of chlorine atoms influenced by the tip of a scanning tunneling microscope is achieved at preselected sites on the Cl-saturated Si(100)-(2X1) surface using nanosecond laser pulse irradiation of the tip within the tunneling range. Bright features observed for the empty state topographic images after a laser pulse sequence are interpreted to be due to bare Si-Si dimers formed by laser induced desorption of two Cl atoms underneath the tip. The Cl desorption mechanism involves the enhancement of the sample-tip interaction due to laser pulse induced tip heating and tip expansion.