Nanosecond laser pulses

Garcia-Araez N, Climent V, Feliu JM. 2008. Evidence of water reorientation on model electrocatalytic surfaces from nanosecond-laser-pulsed experiments. J Am Chem Soc 130 3824-3833. 

This paper presents an overview of the current research issues and commercialization efforts related to laser ablation for chemical analysis, discusses several fundamental studies of laser ablation using time-resolved shadowgraph and spectroscopic imaging, and describes recent data using nanosecond laser pulsed ablation sampling for ICP-MS and LIBS. Efforts towards commercialization of field based LIBS systems also will be described. 

Fig. 8.2 Principle of the MALDI process. Initially, analyte and matrix are co-crystal I ized. After evaporation of the solvent, a nanosecond laser pulse is directed onto the crystalline surface, and both matrix and analyte molecules are desorbed. A complex reaction cascade leads to the formation of charged analyte molecules that reach the mass spectrometer without significant fragmentation.

The nanosecond studies that have been performed on similar systens [48-51,104] are apparendy at odds with the previously mentioned femtosecond study. However, 532-nm nanosecond laser pulses have different characteristics compared to a 388-nm femtosecond pulse and this may explain the discrepancies. Again, different substiments can also affect the outcome, and certainly the 6,8-dinitro-BIPS system is not a standard to gauge all other spiropyran systems. In fact, no typical molecule or molecular system exists which can be used as an example for describing the behavior of all other nominally similar systems. 

One common use of SHG is to convert the output of a fixed-frequency laser into a different spectral region. For example, the Nd-YAG laser operates in the near IR at a wavelength of 1,064 nm, while SHG is routinely used to convert the wavelength of the radiation to 532 nm. For x processes, the conversion efficiency can be up to 30% for phase-matched case with a nanosecond laser pulse. 

Figure 8. Scheme of the experimental setup of the CIS experiment. Two Fourier-transform-limited nanosecond laser pulses with different frequencies are interacting with cold molecules or van der Waals complexes in a skimmed supersonic molecular beam. 

Our experiments with tryptophan (Trp) and a tryptophan-containing tripeptide revealed some specific features that are especially evident from comparison between the mass spectra resulting from irradiation with femtosecond and nanosecond laser pulses in the UV (308 nm) and visible (620 nm) regions of the spectrum. The degree of fragmentation depends on both... 

A series of solution-processible and tractable polymetallaynes of Pt and their mixed-metal analogues were demonstrated to be excellent OPL materials to nanosecond laser pulses at 532 nm, with optimized optical transparency/ nonlinearity trade-offs. The optical-limiting behavior of selected platinum(II) polyynes was investigated by the Z-scan technique. Polyynes 19, 21, 22, 27, 29,... 

The experiments described above used nanosecond laser pulses, which are much longer than the rotational period of the molecules. At the termination of the pulse, the pendular state that is formed relaxes adiabatically to a free-rotor eigenstate. If instead picosecond laser pulses are used, a rotational wave packet is formed by successive absorption and re-emission of photons during the laser pulse. Such wave packets are expected to display periodic recurrences of the alignment after the end of the pulse. 

Another micro-destructive technique is laser-induced breakdown spectroscopy (LIBS) which is used to analyse the paint layers. Nanosecond laser pulses vaporise a small amount of material from the surface of the painting and the amounts so lost are only 50 billionths of a gram and too small to be seen with the naked eye. The vapour passes between two high-voltage electrodes which excite the atoms and these then emit a pattern of light energy bands which identify the elements. LIBS together with Raman spectroscopy has been used to examine Russian icons which are multilayered. 

The rotational relaxation time informs on problems like the sequental flexibility of antibodies, of DNA, of myosin, of membrane proteins or the rotational diffusion of transfer-RNA 47). For example transfer-RNA (ribonucleic acid) which was labelled with the dye ethidium bromide was investigated using nanosecond laser pulses 25,60). 

Laser ionization mass spectrometry of explosives and chemical warfare simulants has been studied using nanosecond laser pulses. Primary ions observed in many of these studies were NO and PO, which are not unique signatures of the parent molecules. It is now widely accepted that after absorption of the first photon, the parent molecule dissociates on a time scale of about 100 femtoseconds (fs). We can attempt to compensate for this rapid dissociation by using ultrafast laser pulses of a corresponding time duration." Here we compare the nanosecond, ultrafast, and SPI approaches. 

C. Mullen, D. Huestis, M. Coggiola and H. Oser, Laser Photon Ionization of Triacetone Triperoxide (TATP) hy Femtosecond and Nanosecond Laser Pulses, Int. J. Mass Spec. 252, 69-72 (2006). 

Let us now examine the case of a nonlinear scattering process. Ispasoiu et al. deduced from considerations regarding the excited-state lifetime that the optical limiting observed using nanosecond laser pulses at X = 532 nm in their silver-dendrimer nanocomposite aqueous solution was due to absorption-induced nonlinear scattering [142]. They suggested that the scattering centres were micro-bubbles... 

The incident probe pulse was the 532 nm second harmonic beam from a Coherent Infinity Nd YAG laser. The 3 nanosecond laser pulse was oriented 60 degrees from the water surface normal direction. The 6 millimetre diameter laser beam was not focussed, and the beam energy was 85 mJ per pulse. The imaging detection system described in Part 1 was used in this experiment it consisted of a dichroic image splitter, quartz Nikon camera lens, and a pulsed gated, intensified CCD camera (Roper Scientific formerly Princeton Instruments). 

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