An Introduction to Laser Spectroscopy

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Apply effective organizational and presentational skills. Apply effective lab skills and techniques. Correct use of data of results to draw appropriate conclusions. Demonstrate general but incomplete command of knowledge and skills required for attaining most of the course learning outcomes.

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Show evidence of some analytical and critical abilities and logical thinking, and ability to apply knowledge to most familiar situations. Apply moderately effective organizational and presentational skills.

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Apply moderately effective lab skills and techniques. Mostly correct but some erroneous use of data and results to draw appropriate conclusions.

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Demonstrate partial but limited command of knowledge and skills required for attaining some of the course learning outcomes. Show evidence of some coherent and logical thinking, but with limited analytical and critical abilities.

Show limited ability to apply knowledge to solve problems. Apply limited or barely effective organizational and presentational skills. Apply partially effective lab skills and techniques.

The Nd:YAG laser generates energy in the near infrared region of the electromagnetic spectrum , with a wavelength of nm. Other lasers have been used for LIBS, mainly the Excimer Exc ited d imer type that generates energy in the visible and ultraviolet regions. The spectrometer consists of either a monochromator scanning or a polychromator non-scanning and a photomultiplier or CCD detector respectively.

The most common monochromator is the Czerny—Turner type whilst the most common polychromator is the Echelle type. However, even the Czerny-Turner type can be and is often used to disperse the radiation onto a CCD effectively making it a polychromator. The polychromator spectrometer is the type most commonly used in LIBS as it allows simultaneous acquisition of the entire wavelength range of interest. The spectrometer collects electromagnetic radiation over the widest wavelength range possible, maximising the number of emission lines detected for each particular element.

All elements have emission lines within this wavelength range. The energy resolution of the spectrometer can also affect the quality of the LIBS measurement, since high resolution systems can separate spectral emission lines in close juxtaposition , reducing interference and increasing selectivity.

This feature is particularly important in specimens which have a complex matrix , containing a large number of different elements. Accompanying the spectrometer and detector is a delay generator which accurately gates the detector's response time, allowing temporal resolution of the spectrum. Because such a small amount of material is consumed during the LIBS process the technique is considered essentially non-destructive or minimally-destructive, and with an average power density of less than one watt radiated onto the specimen there is almost no specimen heating surrounding the ablation site.

Due to the nature of this technique sample preparation is typically minimised to homogenisation or is often unnecessary where heterogeneity is to be investigated or where a specimen is known to be sufficiently homogeneous , this reduces the possibility of contamination during chemical preparation steps. One of the major advantages of the LIBS technique is its ability to depth profile a specimen by repeatedly discharging the laser in the same position, effectively going deeper into the specimen with each shot.

Laser-induced breakdown spectroscopy

This can also be applied to the removal of surface contamination, where the laser is discharged a number of times prior to the analysing shot. LIBS is also a very rapid technique giving results within seconds, making it particularly useful for high volume analyses or on-line industrial monitoring. LIBS is an entirely optical technique, therefore it requires only optical access to the specimen.

This is of major significance as fiber optics can be employed for remote analyses. And being an optical technique it is non-invasive, non-contact and can even be used as a stand-off analytical technique when coupled to appropriate telescopic apparatus. These attributes have significance for use in areas from hazardous environments to space exploration.

Additionally LIBS systems can easily be coupled to an optical microscope for micro-sampling adding a new dimension of analytical flexibility. With specialised optics or a mechanically positioned specimen stage the laser can be scanned over the surface of the specimen allowing spatially resolved chemical analysis and the creation of 'elemental maps'. This is very significant as chemical imaging is becoming more important in all branches of science and technology. Portable LIBS systems are more sensitive, faster and can detect a wider range of elements particularly the light elements than competing techniques such as portable x-ray fluorescence.

And LIBS does not use ionizing radiation to excite the sample, which is both penetrating and potentially carcinogenic. LIBS, like all other analytical techniques is not without limitations.

Introduction to Laser Spectroscopy

It is subject to variation in the laser spark and resultant plasma which often limits reproducibility. The detection limits for LIBS vary from one element to the next depending on the specimen type and the experimental apparatus used. From —, the U. Designed for material analysis, the spectrometer allowed the LIBS system to be sensitive to chemical elements in low concentration. In the s, interest developed in LIBS that focused on the miniaturization of the components and the development of compact, low-power, portable systems.

Recent developments in LIBS have seen the introduction of double-pulsed laser systems. In perpendicular configuration the laser fires twice on the same spot on the specimen with a pulse separation in the order of one to a couple of tens of microseconds. Depending on pulse separation, the second pulse is more or less absorbed by the plasma plume caused by the previous pulse, resulting in a reheating of the laser plasma leading to signal enhancement.

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In orthogonal configuration a laser pulse is fired parallel to the sample surface either before or after the perpendicular pulse hits the specimen. The laser plasma ignited in the surrounding medium above the surface by a first pulse causes by its shock wave an area of reduced pressure above the specimen into which the actual plasma from the sample can expand. This has similar positive effects on sensitivity like LIBS performed at reduced pressures.

If the orthogonal laser pulse is delayed with respect to the perpendicular one, the effects are similar as in the perpendicular configuration. Timing electronics such as digital delay generators can precisely control the timing of both pulses. It also significantly reduces the matrix effects. Double-pulsed systems have proven useful in conducting analysis in liquids, as the initial laser pulse forms a cavity bubble in which the second pulse acts on the evaporated material.

LIBS is one of several analytical techniques that can be deployed in the field as opposed to pure laboratory techniques e. As of [update] , recent research on LIBS focuses on compact and man- portable systems. Some industrial applications of LIBS include the detection of material mix-ups, [11] analysis of inclusions in steel, analysis of slags in secondary metallurgy, [12] analysis of combustion processes, [13] and high-speed identification of scrap pieces for material-specific recycling tasks.

Armed with data analysis techniques, this technique is being extended to pharmaceutical samples. Following multiphoton or tunnel ionization the electron is being accelerated by inverse Bremsstrahlung and can collide with the nearby molecules and generate new electrons through collisions. Journal of Raman Spectroscopy Volume 35, Issue 1. Long Search for more papers by this author. Tools Request permission Export citation Add to favorites Track citation.

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Introduction to Laser Spectroscopy Pdf
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy
An Introduction to Laser Spectroscopy An Introduction to Laser Spectroscopy

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