The chapter discusses the fundamental principles and applications of femtosecond (fs) laser ablation, with a strong emphasis on its differences from conventional nanosecond (ns) laser ablation. Its main focus is on the interaction between ultrashort laser pulses and materials, the mechanisms of ablation, the evolution of plasma plumes, and the growing importance of fs lasers in analytical techniques such as LIBS and LA-ICP-MS.

One of the chapter’s key points is that fs laser pulses behave very differently from ns pulses because their duration is shorter than the times required for electron-ion energy transfer and heat conduction. As a result, in fs ablation, energy is deposited before significant heating or material expansion can occur. This leads to reduced thermal damage, a much smaller heat-affected zone, cleaner crater formation, and higher spatial precision compared with ns ablation. In contrast, ns ablation is accompanied by melting, vaporization, plasma shielding, and stronger thermal effects during the pulse itself.

The chapter also explains the laser system used to generate femtosecond pulses, particularly chirped pulse amplification (CPA). CPA enables the production of extremely short pulses with very high peak power while preventing damage to the optical system. It also points out that fs laser systems require careful control of factors such as pre-pulses, pulse chirp, dispersion, and filamentation, since these can strongly influence laser-material interaction and measurement accuracy.

Regarding the ablation mechanism, the chapter describes two major processes involved in fs ablation: Coulomb explosion and thermal vaporization. Near the ablation threshold, Coulomb explosion can remove only a few nanometers of material and leave a smoother surface. At higher laser intensities, thermal vaporization becomes the dominant process and removes a larger amount of material. The chapter further explains that the ablation threshold in fs lasers does not follow the same pulse-width scaling observed in ns lasers, because photon absorption depth becomes more significant than heat diffusion depth.

Another important topic is the comparison of plasma behavior in ns and fs laser-produced plasmas. Ns plumes tend to expand in a more spherical manner, whereas fs plumes are more forward-directed and cylindrical. In addition, fs plasmas generally exhibit lower continuum emission, less line broadening, lower electron density, and a shorter emission lifetime, all of which can improve spectral clarity. These characteristics are particularly beneficial in analytical applications because they can enhance the signal-to-background ratio, reduce elemental fractionation, and improve precision, especially in LA-ICP-MS.

In conclusion, the chapter argues that femtosecond laser ablation offers several significant advantages over nanosecond ablation, including higher precision, reduced thermal damage, cleaner material removal, and improved analytical performance.