The Front End Test Stand (FETS) at Rutherford Appleton Laboratory (RAL) has been developed to demonstrate a high current (60 mA) H− beam with the energy of 3 MeV that will be required for future proton drivers. At such high power beam machine a non-invasive diagnostics is required. To measure the emittance of the ion beam a laserwire scanner is being developed. A high power laser will scan across the H− ion beam. The H− particles will be neutralized via a photo-detachment process producing a stream of fast neutral hydrogen atoms bearing information about the phase space distribution of the initial H− beam. To design an effective detection system and optimize its parameters a simulation of the processes at the interaction point is required. We present recent simulation results of theц FETS laserwire system. Simulations were performed using measured data of the laser propagation and ion beam distribution, obtained with General Particle Tracer code.