WHAT IT IS
The femtosecond (fs) laser ablation system is an ultrafast solid-state laser source used in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). It delivers pulses on the order of 10⁻¹⁵ seconds, which are so short that energy is deposited into the sample before significant heat can diffuse. This “athermal” ablation minimizes melting and fractionation, producing aerosols that closely reflect the stoichiometry of the target material. Femtosecond lasers are used for the highest-precision applications, including isotope geochemistry, microelectronics, materials science, and bioimaging.
HOW IT WORKS
Laser Generation - Femtosecond lasers are typically based on titanium:sapphire or fiber-laser technology, producing fundamental near-IR output (~800–1030 nm). Frequency conversion optics generate UV or visible wavelengths suitable for ablation.
Pulse Delivery - The beam is guided and focused into the ablation chamber with adjustable optics. Spot sizes from <1 µm to tens of µm enable ultra-high spatial resolution.
Sample Interaction - Because pulses are extremely short, ablation occurs through rapid ionization and material ejection before heat conduction can occur. This prevents melting and reduces thermal effects compared with nanosecond lasers.
Aerosol Transport - The resulting fine aerosol is carried by helium or argon into the ICP. Particle size is small and uniform, supporting efficient transport and ionization.
Detection - Ions produced in the plasma are analyzed by ICP-MS, giving highly accurate elemental and isotopic information with minimal fractionation bias.
ADVANTAGES
Minimal Fractionation: Near-stoichiometric transfer from solid to aerosol, reducing matrix effects.
High Resolution: Sub-micrometer spot sizes allow micro-analysis and imaging at cellular or mineral-grain scale.
Clean Ablation: Negligible melting or redeposition around craters.
Versatility: Applicable to delicate materials (biological tissues, thin films) and resistant solids alike.
Improved Quantification: Reduced need for matrix-matched standards compared with nanosecond lasers.
CHALLENGES AND LIMITATIONS
High Cost: Femtosecond laser systems are significantly more expensive than Nd:YAG or excimer lasers.
Complexity: Require sophisticated optics, alignment, and control software.
Maintenance: Sensitive to environmental stability; components demand regular service.
Lower Throughput: Very fine ablation rates may limit bulk sampling speed.
Adoption Barrier: Not yet as widespread as 193 nm excimer systems, though usage is growing in advanced laboratories.