In 2005, our group first reported a two-pulse multi-element analysis technique that was both sensitive and minimally destructive. The first laser pulse ablated a thin layer of the sample over a hundred m spot; the second laser pulse at 193 nm induced multi-analytes in the desorbed plume to fluoresce. Since then, this technique of laser-excited atomic fluorescence (LEAF) of ablated plumes, or PLEAF for short, had been applied to the analysis of aqueous lead colloids and metals. Sub ng/g and tens of atto-mole detection limits were demonstrated. The non-selective photoexcitation in PLEAF was believed to be due to smeared energy levels of species in dense plumes. Smearing was especially severe for highly excited states such as those reached by 193 nm excitation. As the plumes subsequently expanded, the electronic structure of the plume species evolved adiabatically from a dense gas to that of an isolated atom with the electrons still in the excited states. Signature fluorescence from multi-analytes was therefore possible. The suggested mechanism implied that ArF laser-induced PLEAF should be applicable to any sample matrix and any analyte as long as the species were imbedded in dense plumes and whose excited states could be reached by 193 nm photoexcitation. We therefore investigated the universality of PLEAF in this study by extending the analysis to ceramics, polymers, and their composites. We showed that these matrices could be successfully sampled and emissions from practically all analyte elements were observed. The detection sensitivity was orders of magnitude better than alternative laser spectrochemical probes such as laser-induced breakdown spectroscopy (LIBS). Under minimally destructive conditions, emissions from Al, Ca, Co, Cr, Cu, Fe, In, Mg, Mn, Na, Pb, Sn, and Si were observed. We also applied the technique to four practical problems: The analysis of dried paint for trace lead when g/g detection limits were achieved; the analysis of valuable potteries when two look-alike specimens were differentiated based on practically non-destructive single-shot analysis; the elemental analysis of ink when lines written with different pens could be discriminated yet without discernable sample destruction even under the microscope; and the analysis of electrode-plastic interfaces when the detection sensitivity was comparable to SIMS. In some of these applications, we found that the fluorescence intensity varied with the fluence and the timing of the ArF laser pulse in ways suggestive of particulates in the plume. Because nearly all analyte elements were excited in PLEAF, multi-analyte spectra were generated even in single-shot analysis. We showed that the rich spectral information contents could be fully exploited by chemometric techniques such as principal component analysis, SIMCA and K-means clustering. In sum, the combination of PLEAF and chemometrics paved way for ultra-sensitive and minimally destructive multi-element analysis of complex samples. The analysis was all-optical and therefore could be done in air with no restriction on sample size. No sample preparation was needed. The analysis was fast, with a turn-around time of minutes. At the end, the sample was not visibly damaged even when examined under the microscope. If the ablation could be congruent, 3-dimensional chemical profiling at tens to hundreds of m lateral resolution and tens of nm depth resolution would be possible.

No description available.

No description available.

When an optically rough surface is illuminated by laser, a grainy pattern is produced at a distance away from the surface, which is known as laser speckle pattern. This pattern is random in intensity with its grains separated by an average amount controlled by the intermediate optical system or the diameter of the illuminated area of the surface in absence of an optical system. It has been shown that the grain spacing of such pattern may be correlated to yield a singly-peaked power spectral density of an intensity ensemble which is found by spatial ensemble averages. This correlation holds only if the sampling is done in a plane referred to as the constant plane. On an average basis such a characteristic peak persists with an in-plane rigid-body motion of the test object and within a uniformly rough area of the surface. The behavior of such peak with an induced in-plane strain is shown to be non-linear and of second order for the test range, when frequency values of such peak is plotted versus strain. Further, the slope of such curve changes sign when a strain of opposite sign is sensed. Finally, the best responses were obtained when no intermediate optical system was employed in the observation field.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Laser and Fourier transform spectroscopy were used to study a variety of gas phase molecules. A series of calcium and strontium monoalkoxides, CaOR and SrOR [R=H, CH₃, CH₂CH₃, CH(CH₃)₂, CH₂CH₂CH₃, CH₂(CH₂)₂CH₃, CH₂(CH₃)CH₂CH₃ and C(CH₃)₃] was studied by laser induced fluorescence and laser excitation techniques. The A - X and B - X electronic transitions were recorded. Calcium and strontium monocyclopentadienide, CaCp and SrCp, were produced in a Broida oven and the spectra were recorded at low resolution by laser techniques. The geometry of these molecules is like an "open-faced sandwich", with C₅ᵥ symmetry. The A²Π - X²Σ⁺ and B²Σ⁺ - X²Σ⁺ transitions of calcium and strontium monoisocyanate, CaNCO and SrNCO, were recorded for the first time. The spectra are interpreted as arising from a molecule with linear, ionic Sr⁺ - ⁻NCO structure. The 0-0 band of the A - X transition of SrNCO was recorded at high resolution and rotationally analyzed. The use of a 0.64 m monochromator, acting as a narrow bandpass filter, was necessary for recording the spectra and enabled the correct assignment of the rotational lines. By comparing the molecular constants of SrNCO with related molecules, the NCO⁻ ligand was found to be nitrogen bonding to the strontium atom. The Sr-N bond length was estimated to be 2.26 A in the ground state. The rotational analysis of the 0-0 band of the A²E₁/₂ - X²A₁ transition of the SrOCH₃ free radical has been carried out by laser excitation spectroscopy. The SrOCH₃ molecule was found to have C₃ᵥ symmetry with a Sr-O bond length of 2.12 A. There was no evidence of a Jahn-Teller effect in the A²E state. This work is the first high-resolution analysis of a metal alkoxide molecule. The rotationally cool (30 K) spectrum of the 0-0 vibrational band of the A²Δ - X²Π electronic transition for the diatomic free radical CCl was recorded using a Fourier transform spectrometer. The first rotational lines of the six strongest branches were observed, and transitions in three other branches were also detected. The CCl radical was produced in a corona-excited supersonic expansion source.

Two spectral regions of gain exist for a weak probe beam propagating through a medium of two-level-atoms pumped by a strong near-resonance field. Experimentally a cw ring-dye laser is used to explore this gain at the Na D₂ resonance in a vapor. Plane-wave calculations of probe-gain spectra which include the Doppler broadening inherent in a vapor agree well with experimental spectra obtained with a Fabry-Perot interferometer. Such two-beam-coupling gain might have applications as optical pre- or power amplifiers. The gain is also the primary step in four-wave-mixing. Mixing of the pump and sideband which experiences gain produces the medium polarization from which the fourth-wave arises. For phase-matched propagation the fourth-wave, which is at a frequency that experiences little or negative probe-gain (i.e., absorption), grows at nearly the same rate as the primary sideband. Together the two sidebands extract far more than twice as much energy from the pump than does the primary sideband acting alone. Experimentally four-wave-mixing which arises from noise at the gain-sideband-frequency is sometimes accompanied by conical emission at the fourth-wave sideband. Since this sideband is also seen on axis the explanation cannot be simply phase-matching. Simulations which include the full transverse nature of the experiment are currently running on a CRAY supercomputer. These simulations indicate that the radial variation of the medium index of refraction is responsible for conical emission.

No description available.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Biology. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.

Nuclear and laser spectroscopy measurements have been conducted at the Ion Guide Isotope Separator On-Line, IGISOL-IV, JYFL laboratory, Jyvaskyla. Nuclear moments have been extracted for two ground and two isomeric states of neutron deficient yttrium, 85g,mY and 86g,mY. The mean square charge radii and moments have been extracted for all states, providing, for the first time, estimates of static and dynamic quadrupole deformations in these shape transitioning nuclei. A second laser spectroscopy experiment yielded the frequency shifts between all stable isotopes of ionic ytterbium in exotic (high-lying metastable) resonance lines. Atomic field and mass shift parameters in these (high purity) transitions have been evaluated. A discussion of the impact these parameters may have on the chemical homologue, nobelium, is presented. New measurements of charge-state dependent IGISOL fission production yields (of strontium, yttrium and zirconium) are reported in this thesis. For the first time, charge state dependent effects in relative isomeric to ground state production have been detected. Possible explanations for, and exploitation of, this unexpected phenomenon is presented. A new data acquisition (DAQ) system has been built at The University of Manchester. It has been designed to fully replace the current setup used for laser spectroscopy at the JYFL laboratory. The new hardware has been extensively tested off-line and is ready to be installed at the laser-IGISOL. To work in conjunction with the new DAQ, two graphical user interfaces (GUIs) have been created, to display and sort data online, and permit efficient data extraction. Both have been shown to perform at the level required for experimental on-line use. An updated report on the status of an electrostatic ConeTrap is presented. Improved (more realistic) simulations are now seen to be capable of reproducing experimentally observed results. Further computational effort on the ion optics has shown that improved containment and transport efficiency can be readily achieved. A new trap, featuring a larger rear electrode, promises a greatly increased ion survival. The next commissioning phase will see the construction and installation of this upgraded ConeTrap.