Matthieu Baudelet

Femtosecond time-resolved laser-induced breakdown spectroscopy for detection and identification of bacteria: A comparison to the nanosecond regime

Bacterial samples (Escherichia coli and Bacillus subtilis) have been analyzed by laser-induced breakdown spectroscopy (LIBS) using femtosecond pulses. We compare the obtained spectra with those resulting from the classical nanosecond LIBS. Specific features of femtosecond LIBS have been demonstrated, very attractive for analyzing biological sample: (i) a lower plasma temperature leading to negligible nitrogen and oxygen emissions from excited ambient air and a better contrast in detection of trace mineral species; and (ii) a specific ablation regime that favors intramolecular bonds emission with respect to atomic emission. A precise kinetic study of molecular band head intensities allows distinguishing the contribution of native CN bonds released by the sample from that due to carbon recombination with atmospheric nitrogen. Furthermore a sensitive detection of trace mineral elements provide specific spectral signature of different bacteria. An example is given for the Gram test provided by different magne...

Elemental analysis by microwave-assisted laser-induced breakdown spectroscopy: Evaluation on ceramics

A new Laser-Induced Breakdown Spectroscopy (LIBS) enhancement method utilizing interaction between microwave radiation and laser-induced plasma has been evaluated. Experimental parameters such as laser pulse irradiance, microwave duration, and surrounding gas were studied and optimized for the microwave effect through a series of experiments on a piece of alumina ceramic sample. Up to 33 times enhancement on different spectral lines was achieved. Enhancement of the line intensity was found to be at a maximum when the laser ablation was induced at low irradiance on a large area in normal atmosphere. The enhancement was element-dependent and stronger for transitions with low excitation energy. The microwave enhancement in argon atmosphere was not as effective as in air, and the reasons are discussed.

Laser-induced breakdown spectroscopy of copper with a 2 μm thulium fiber laser

We report the first implementation of a 2 microm thulium fiber laser in a Laser-Induced Breakdown Spectroscopy system. Emission from plasma on copper samples was analyzed from 200 to 900 nm. The low ablation fluence (<100 J.cm(-2)) and 200 ns pulse duration lead to a plasma with neither continuum emission, nor air emission in the near-infrared region.

Nd:YAG-CO 2 double-pulse laser induced breakdown spectroscopy of organic films

Laser-induced breakdown spectroscopy (LIBS) using double-pulse irradiation with Nd:YAG and CO(2) lasers was applied to the analysis of a polystyrene film on a silicon substrate. An enhanced emission signal, compared to single-pulse LIBS using a Nd:YAG laser, was observed from atomic carbon, as well as enhanced molecular emission from C(2) and CN. This double-pulse technique was further applied to 2,4,6-trinitrotoluene residues, and enhanced LIBS signals for both atomic carbon and molecular CN emission were observed; however, no molecular C(2) emission was detected.

Transition from linear- to nonlinear-focusing regime in filamentation

Laser filamentation in gases is often carried out in the laboratory with focusing optics to better stabilize the filament, whereas real-world applications of filaments frequently involve collimated or near-collimated beams. It is well documented that geometrical focusing can alter the properties of laser filaments and, consequently, a transition between a collimated and a strongly focused filament is expected. Nevertheless, this transition point has not been identified. Here, we propose an analytical method to determine the transition, and show that it corresponds to an actual shift in the balance of physical mechanisms governing filamentation. In high-NA conditions, filamentation is primarily governed by geometrical focusing and plasma effects, while the Kerr nonlinearity plays a more significant role as NA decreases. We find the transition between the two regimes to be relatively insensitive to the intrinsic laser parameters, and our analysis agrees well with a wide range of parameters found in published literature.

The first years of laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been developed since the invention of the laser in 1960. The push from analytical companies from the beginning started a huge scientific adventure combining analytical science, plasma physics engineering and commercialization that still is in place fifty years later. This historical review of the first five years of laser‐based micro‐spectrochemical analysis introduces the first measurements and systems for laser micro-analysis and its evolution to conventional LIBS.

Stand-off filament-induced ablation of gallium arsenide

Using femtosecond filaments for the ablation of GaAs in air, we have observed that the diameter and volume of the resulting ablation craters remained almost constant with propagation distance. This constant mass removal along the propagation of a filament in both focused and non-focused configurations is valuable for applications such as material processing and stand-off laser-ablation based spectroscopy.

High-energy Q-switched Tm3+-doped polarization maintaining silica fiber laser

We report the performance of an actively Q-switched Tm fiber laser system. The laser was stabilized to sub-nanometer spectral width using each of two feedback elements: a blazed reflection grating and a volume Bragg grating. Maximum pulse energy using the reflection grating was 325 μJ pulses at 1992 nm (< 200 pm width) with a 125 ns duration at a 20 kHz repetition rate. Maximum pulse energy using the volume Bragg grating was 225 μJ pulses at 2052 nm (<200 pm width) with a 200 ns duration also at 20 kHz. We also report the lasers performance as an ablation source for LIBS experiments on copper.

Atmosphere issues in detection of explosives and organic residues

This study makes a comparison of LIBS emission from molecular species in plasmas produced from organic residues on a non-metallic substrate by both a 5 ns Nd:YAG laser (1064 nm) and a 40 fs Ti:Sapphire laser (800 nm) in air and argon atmospheres. The organic samples analyzed had varying amounts of carbon, nitrogen, hydrogen, and oxygen in their molecular structure. The characterization was based on the atomic carbon, hydrogen, nitrogen, and oxygen lines as well as the diatomic species CN (B2Σ+ - X2Σ+) and the C2 (d3Πg - a3Πu). Principal Component Analysis (PCA) was used to identify similarities of the organic analyte via the emission spectra. The corresponding Receiver Operating Characteristics (ROC) curves show the limitations of the PCA model for the nanosecond regime in air.

Molecular signal as a signature for detection of energetic materials in filament-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) by self-channeled femtosecond pulses is characterized for detection of energetic materials. Different polymers are spin coated on silicon wafers to provide a thin organic layer with controllable thickness ranging from 500 nm to 1 μm. Spectral analysis of atomic and molecular carbon emission shows CN molecular signal from samples that do not contain nitrogen. This can be explained by possible molecular recombination between native atomic carbon and atmospheric nitrogen. As a consequence, caution must be exercised when using spectral signatures based on CN emission for explosive detection by filament-induced LIBS.