We have developed a new method to overcome metastable phase states that prevent microthermometric measurements in fluid inclusions. We use tightly focused femtosecond laser pulses to induce bubble nucleation in one-phase (all liquid) inclusions, nucleation of salt crystals in supersaturated brines, and nucleation of ice and salt hydrates. The threshold laser intensity necessary for phase nucleation was determined to be of the order of 10 TW/cm2. To avoid potential damage to the fluid inclusion, the threshold for producing ablation of quartz visible under the microscope was also determined and found to be about 25 % higher than the threshold for halite nucleation and 100 % higher than that for bubble nucleation. The experimental setup allows us to induce phase nucleation in selected fluid inclusions at different temperatures under microscopic observation. Subsequent microthermometric measurements can be performed in the same setup, making it suitable for routine applications.