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WEBINAR: Basic Principles of Laser-Induced Breakdown Spectroscopy (LIBS) - Q & A below

How is the sensitivity of LIBS dependent on the distance from the sample?

I assume you mean “lens-to-sample distance”. That will change the irradiance on sample (leading to a change in sampled mass). In addition to the distance, the position of the focus, either above or below the surface of the sample, is another parameter. Usually, the choice is to position the focus below the surface to avoid any excitation of the background gas above the surface. Several studies have shown a better stability of the signal when focused “inside the sample”.

Are there "matrix" effects if there are mixed materials in the same sample? for example, polymers and inorganic particles?

Yes. The optical properties will be different, and as a consequence the ablation and the emission. If your samples are known, it is easy to establish calibration curves for your elements of interest in a specific polymer matrix.

Do I pelletize a pulverized material before I used LIBS?

You can use LIBS on powders. It depends on your needs, you can pelletize such powder to increase the amount of material analyzed in one single laser shot.

Molecules vaporized by the laser get into the plasma and will emit light in all directions. How sensitive can be the detection at distances (like 100m or more) ?

Intensity I detected at a distance R is always ruled by the relation “I(R)=A/R2” where A is the area of the collector. Single-shot spectra of plasmas have been detected at several hundreds of meters. The sensitivity is increased if you optimize the detection timing and the optical coupling to the spectrometer.

One of the major advantages at normal conditions could be direct solid sampling. How good is the quantitative elemental analysis on LIBS compared to e.g., LA-ICP-MS?

You are right when you say that a major advantage is the direct solid sampling offered by LIBS. The comparison with LA-based methods (such as LA-ICP-MS or LA-ICP-OES) is often difficult because the ablation of followed in general by an ICP-based method. The ICP techniques are way more sensitive than LIBS because the plasma is well controlled and stable, in opposition to the LIBS plasma created during the sampling and only a transient event.

Can laser pulse (fs) shaping be employed to better direct LIBS chemistries for improved selectivity?

The use of pulse shaping has been explored for improving the emission of some elements in gases. This approach is promising, with the development of compact femtosecond lasers and should see more interest in the near future. Addressing the chemical bonds for ablation of polymers has also been explored and shows changes in the emission, but no analytical work has been done.

What about advantages of LIBS applications in archeology?

LIBS has been used for archeology but rather in laboratories than in the field. Then the advantages of LIBS can find a full application: no preparation, muti-element emission, elemental fingerprinting for databases.

What are the laser ablation thresholds for tungsten and tungsten trioxide?

You can find the information associated with your type of laser pulse (duration, spectrum) in publications. Some models can be evaluated. One reference is “Laser ablation threshold determination by photoelectric emission” by Beleznai et al. (Applied Physics A 69 S113)

Are the spectral interferences seen in ICP analysis typical of LIBS?

Every spectral interference seen in a plasma technique could be seen in LIBS.

Are there applications w/polymer and advanced composite materials?

Yes. I don't know all of them but a search in Web of Science or Google Scholar will provide you some publications on these applications.

What do you think about using LIBS for pathogens identification?

This is an area of interest for me since my PhD was on this subject. I believe LIBS can provide technological responses for the detection of pathogens. The analysis of the inorganic content has shown the way LIBS can be applied for pathogen identification. Furthermore, the need for data analysis of the rich spectrum is a crucial aspect in this application.

Is there a standard spot-size that is used for analysis?

This question raises one of the needs for LIBS at the moment: a standardization of the experimental parameters. Usually, publications talk about spot sizes of 100 μm diameter. But other applications can go towards the micron and some to the millimeter.

What is your opinion of using LIBS for detection of energetic materials?

LIBS for detection of energetic materials works. Several groups show that detection AND identification of the materials is possible.

Is an echelle spectrograph that was present in your slides essential or can Czerny Turner spectrographs be used?

The main question is: what is your need? Do you need a complete picture of the UV-Vis-NIR spectrum in a single laser shot or do you just want to analyze one or two elements. The echelle spectrometer is very interesting for the “exploratory” step of the analysis. Then , Czerny-Turner spectrometers are better suited for resolution and throughput in a quantitative step of the analysis.

If you had one magic bullet to produce an "ideal" component, which component would that be? It sounds like sensitivity, meaning better detectors.

You point it out yourself. I think more compact detectors adapted to LIBS (microsecond gates with low noise and nanosecond jitter) still need to be developed to apply LIBS in the field where iCCD cameras are not an option.

Comment on the shot to shot reproducibility of LIBS emissions. Is it appropriate to characterize LIB processes as stochastic?

LIBS is not stochastic. Plasma physics and chemistry are modeled and understood in general. The main problem is to handle inhomogeneities of the sample and laser stability.