Characterization of Femtosecond Laser Ablation and Deposition

A novel femtosecond micromachining workstation that permits real-time measurement of ablation depth and transient reflectivity is demonstrated. This instrumentation is used to characterize two processes: micromachining of thin metal films, and laser induced forward transfer (LIFT). Spectral interferometry was incorporated in a femtosecond micromachining system to enable real-time visualization of micromachined features as they are written into thin metal films-low energy(pJ) femtosecond oscillator pulses are used to probe the sample as it is cut by high energy (uJ) pulses. Sub-wavelength depths are readily resolved using this technique, making it possible to monitor the integrity of micromachined structures as they are created. This technique can also be employed to characterize interesting processes such as laser induced forward transfer (LIFT) of thin metal films. LIFT essentially involves using a pulsed laser to pattern a structure by deposition as opposed to ablation. Using modest numerical apertures (0.65 or less) we have been able to produce submicron features using this method of femtosecond pulsed laser deposition.