Short pulse irradiation

Short pulse irradiation of Mg alloys using XeCl excimer laser produced a wavy structure on the surface and the development of about 3-6 i.m thick amorphous layers on the surface. The corrosion resistance was reported to be enhanced (Schippman et al., 1999). Control of laser scanning speed plays... 

Schippman D, Weisheit A, Mordike BL, (1999), Short pulse irradiation of magnesium based alloys to improve surface properties . Surface Engineering, 15, 23-26. 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

Final resolution of these problems, particularly the complications from multiple matrix sites, came from investigations using spectroscopic methods with higher time resolution, viz. laser flash photolysis. Short laser pulse irradiation of diazofluorene (36) in cold organic glasses produced the corresponding fluorenylidene (37), which could be detected by UV/VIS spectroscopy. Now, in contrast to the results from EPR spectroscopy, single exponential decays of the carbene could be observed in matrices... 

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra... 

As with gamma radiation. X-rays in the steady-state mode have not produced any initiations in any of the expls irradiated. Effects are being directed towards intense, pulsed irradiations in order to simulate nuclear weapons effects. The prospect of higher dose rates in short time frames should produce results not common, to the steady-state irradiation... 

For the techniques using very short, high irradiance laser pulses, a more or less smooth transition to pyrolysis of the sample is observed with increasing irradiance. It appears that at least for the LAMMA technique this transition does not always occur at identical irradiances for positive and negative ions. This will be discussed in more detail later in this paper. 

A relatively sharp absorption in the UV region due to alkyl radicals is observed in electron-pulse irradiated alkanes [93]. It has an absorption maximum at 240 nm in n-dodecane and cyclohexane. (Mehnart et al. did not see this absorption maximum but found another short-lived absorption band peaking at 270 nm in n-hexane, n-heptane, and n-hexadecane containing 10 mmol dm-3 CC14. This absorption band was assigned to olefin monomer radical-cation... 

The sample is irradiated with a short pulse of radiofrequency energy. This disturbs the equilibrium balance between the two energy levels some nuclei absorb the energy and are promoted to a higher energy level... 

Advantages Short reaction time, beam focusing, pulse irradiation Homogeneously cross-linked samples, no restrictions regarding dimension... 

We cannot say what the relative mix of photochemical and thermal effects is as yet. The literature suggests that significant photochemical reactions should occur due to 248nm irradiation of acridine (25,26), but these are not the massive bond-breaking type that characterize 193nm photoablation(16). The fluorescence yield of acridine in PMMA is known to be about 0.2 (26) so considerable heat is produced by the absorption of short pulses in the 100 mJ/cm2 range an estimate based on an approximate heat capacity formula (27) is about 300 0. The excited state properties of acridine in PMMA show a pronounced temperature dependence (26). It seems likely that the bleaching arises from a combination of photochemical destruction of the acridine chromophore and polymer ablation. 

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