Laser spark

Gun powders/propcl hints Muzzle blast Recoilless rifle blast Exploding sparks Exploding wires Laser sparks Contained explosions ... 

Other approaches have been taken for on-line analysis of individual aerosol particles as well. Laser spark spectroscopy (33) vaporizes individual particles in the breakdown plasma created by a pulsed laser. Atomic emission spectra can then be used to deduce the elemental composition of the particle that was vaporized. The timing of the laser pulse is critical because the particle must be caught in the focal volume of the pulsed laser, so a second laser is used to detect the particle and trigger the pulsed laser. To date the technique has been applied to large particles, that is, coal particles on the order of 60 to 70 xm in diameter in combustion studies. The use of inductively coupled plasma would eliminate the complex triggering and might allow on-line analysis of smaller particles spectroscopically. 

Raizer Yu. P. Lazernaia iskra i rasprostranenie razriadov [Laser Spark and Propagation of Discharges], Moscow Nauka, 406 p. (1974). 

Raizer, Yu.P. (1974), Laser Spark and Discharge Propagation, Nauka (Science), Moscow. 

There are sample introduction systems that can handle slurries of particles suspended in hquids. Powders can be injected directly into the plasma for analysis. Lasers, sparks, and graphite furnaces (exactly the same as AAS graphite furnaces) are used to generate gaseous samples from sohds for introduction into the plasma. Hydride generation for As and Se and cold-vapor Hg introduction are used for ICP as for AAS these two techniques were discussed in Chapter 6. 

Our spark is undoubtedly rapid enough (2 ys duration) to produce this same effect because we can observe a shock wave due to the spark in our schlieren photographs. In addition, the cone can cause a boundary layer to be formed which adds to the amount of unburned mixture which can flow into the electrode region. Experiments involving electrodeless ignition, such as by a laser spark, would be useful in verifying whether this phenomenon occurs. 

We make no claim to have modeled accurately the ignition process beginning with the formed spark kernel, although that appears to be possible and will be investigated further. We performed these calculations to show that at least one phenomenon, which we know must be present in our experiments, can qualitatively account for the experimental results we have obtained. Viscous boundary layers may also contribute to the relatively slow burning of methane at x=0.0. We plan experiments with electrodeless ignition, such as laser sparks, to further understand this aspect of the ignition process. 

A more suitable approach for on-line analysis is to view atomic emission directly from the small plasma formed above the sample surface when the sample is ablated using the laser. This approach, which is shown schematically in Fig. 20.12 has been applied to analyses of a variety of materials (e.g. [58-74]) and is known under a variety of names such as laser induced plasma spectrometry (LIPS), laser induced breakdown spectrometry (LIBS) and laser spark emission spectrometry (LASS). The laser used is typically a Nd YAG laser operating either at its fundamental, doubled or quadrupled frequency, although excimer and CO2 lasers have also been used. The important parameter of the laser is that it must be capable... 

Laser-induced breakdown spectroscopy (LIBS) is a relatively new atomic emission spectroscopy technique that uses a pulsed laser as the excitation sonrce. LIBS is also referred to as laser spark spectroscopy (LASS) and laser-induced plasma spectroscopy, with the unfortunate acronym of LIPS. The technique was developed in the early 1960s, after the invention of the laser, but the high cost and large size of lasers and spectrometers made this a specialized research tool until the 1990s. The early development of LIBS is covered in the reference by Myers et al. Recent advances... 

Time-gated detectors that allow the optical emission from the laser plasma to be recorded at some time delay after the laser pulse are required to accurately capture the emission spectra. For the first few microseconds after the ignition of the laser spark, the plasma emits a strong white light continuum (also called bremsstrahlung), which decays as the plasma cools the characteristic atomic and ionic emission lines only appear as the plasma cools. A detector delay on the order of several microseconds after the laser pulse is used to eliminate interference from the continuum radiation. The principle is demonstrated in Figure 7.52. 

For example, laser spark emission can be used in discriminating 31 paints with small differences in vehicle composition (essentially all pentaerythritol-o-phthalate alkyd based) [12]. In this application the technique is outstanding as compared to PyGC, PylR, XRD or IR spectroscopy. 

Principles and Characteristics Simultaneous multi-element analysis based on emission from a plasma generated by focussing a powerful laser beam on a sample (solid, liquid, or gas) is known as laser-induced breakdown spectroscopy (LIBS) and under a variety of semantic variations time-resolved LIBS (TRELIBS), laser ablation emission spectroscopy (LAES), laser ablation atomic emission spectrometry (LA-AES), laser ablation optical emission spectrometry (LA-OES), laser plasma emission spectrometry (L-PES), laser-induced plasma spectroscopy (LIPS), laser spark spectroscopy (LSS), and laser-induced emission spectral analysis (LIESA ). Commercial LIBS analysers were already available in the 60/70s the technique now enjoys a renaissance. 

Both liquid samples and solutions of dissolved analyte species are analyzed either by direct introduction into the plasma or by evaporation of tbe solvent and introduction of the residue by direct insertion, thermal vaporization, or laser/spark ablation. Of the two approaches, the direct introduction techniques are by far the simplest and most straightforward. Samples can be reproducibly introduced with a minimum of sample handling. However, significant advantages, for example, enhancement of sensitivity by preconcentration, can be realized using the solvent evaporation approach for some types of samples, except for the analysis of volatile analytes. 

---