I used to apply nanosecond laser (NdYAG, 1064nm, 7ns) to generate plasma, now I read some paper of femtosecon LIBS, and I a little puzzled. What is the essential difference between femtosecond laser induced breakdown spectroscopy(LIBS) or plasma and nanosecond LIBS ?
Whose line is stronger? Which one is more suitable for quantitative analysis?
Intensity of LIBS will be more in the case of nano second laser. However background emission will also be more.In the case of Femto second laser both will be less. Nano second laser is suitable for quantitative analysis. However femto second laser can be used for some specific purposes. Mostly for elemental analysis nano second laser is being used.
Virendra Nath Rai
Thank you very much first.
Why intensity of ns-LIBS will be more? What does the fs-LIBS can do?
The laser-material interaction mechanism is different between ns-LIBS and fs-LIBS. In ns-LIBS, the interaction is based on “photodisruption”, in which strong shockwave is produced together with the plasma. In fs-LIBS, the interaction is based on the so-called “plasma-medicated ablation” (Please do not get confused based on the names, in both cases, plasma is generated due to a breakdown). The main difference is that the higher impact of mechanical effects in photodisruption (ns-LIBS). The bremsstrahlung background is less in fs-LIBS, and it also offers a better spatial resolution (because of nonlinear absorption). However, the generated plasma in fs-LIBS is less strong (low intensity or let say less illuminant) and also smaller in size (harder to catch it by fiber-optic). This is due to the usage of less energy to create plasma in fs-LIBS, as compared to ns-LIBS.
In the case of Nano second laser, interaction time is more that increases the thermal diffusion length in the material that is less in the case of Femto second laser. This produces more material ablation in the case of nanosecond laser than the femto second laser ablation. This makes the plasma emission more intense in ns-LIBS than fs-LIBS. More melting of material in ns- LIBS makes it in efficient for depth profiling. In fs-LIBS ablation mechanism is different and fast that makes very sharp hole in material. Thermal diffusion is also very less that makes it very much suitable for depth profiling. However, ns-LIBS is much suitable for elemental analysis. Another most important application of fs-LIBS is known as FIBS (Filamentation induced breakdown spectroscopy). FIBS can be able to provide elemental analysis from a sample located at more than ~ 90 meters away. This distance is many times more than the distance reported for Stand off LIBS.
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