Last Day of the Program
Dinner with the group: Left to Right: Steve, Michelle, Hilary, Lee, Sean, Johanna, Patrick, Robyn, and Thomas.
Y0.6Eu0.4VO4 Nanoparticle Photoreduction Parameters in Solvents of Varying Polarity and Proticity
The Eu3+ ions in Y0.6Eu0.4VO4 nanoparticles can be reduced to Eu2+ by means of laser illumination. The Europium in the nanoparticles can be oxidized back to its initial state by means of a chemical reaction with an oxidant such as hydrogen peroxide. The fact that Eu3+ has a sharp absorption peak at 466 nm and a sharp emission peak at 617 nm and that Eu2+ lacks both of these peaks makes these nanoparticles ideal hydrogen peroxide probes in cells. The goals of this project were to elucidate the mechanism behind the photoreduction of Europium in the nanoparticles by examining the photobleaching parameters for the decay in luminescence of the nanoparticles in different solvents and to study the endothelin stimulated production of hydrogen peroxide in cells. Results from the decay parameters in different solvents suggest that polar solvents are required in order to obtain appreciable photobleaching. The characteristic times and percentage photobleaching were greatest in the DMSO and ethanol solvents and smallest in the heptane solvent. The parameters for the phosphate buffer were slightly smaller than those of DMSO and ethanol. Results were not obtained for the study of endothelin stimulated production of hydrogen peroxide in cells. Two experiments were attempted to this end. In the first the signal to noise ratio was too low so the photobleaching parameters of the nanoparticles couldn’t be determined. In the second the pinocytosis process used to load the nanoparticles into the cells failed and so no photobleaching or luminescence was observed.
I enjoyed my project this summer. I spent the first two and a half weeks studying papers, learning procedures and familiarizing myself with the lab equipment. After that I spent most of my remaining time cultivating cell cultures for experiments, loading them with nanoparticles and doing photobleaching and recovery experiments on them, as well as doing photobleaching and recovery experiments on the nanoparticles placed directly on the cover slips immersed in different solvents. During the last week and a half I prepared a final report and a PowerPoint presentation regarding the experiments that I attempted and the results I obtained. My supervisors were very supportive and not only showed me how to use all of the equipment and how to analyze the data but also helped give direction to my research. The rest of the LOB researchers were helpful as well. Two of the biologists showed me how to cultivate and prepare the cells, and one of them helped with my data analysis early on since he has done studies regarding the photobleaching and recovery parameters of the nanoparticles as well. Overall I am very pleased with how this summer went and am glad that I had the opportunity to participate in such interesting research.
The motivation for my project was to characterize the density profile of gas jets for use in laser wakefield acceleration experiments. We used a helium neon laser to build a Mach-Zhender interferometer and used tomographical techniques to reconstruct the density profile. A variety of nozzles were used, including sonic nozzles, supersonic nozzles, and supersonic nozzles with blades on top to alter the flow. As both high density and a steep density profile gradient are of interest in laser wakefield acceleration experiments, we looked for these features specifically. The supersonic jet has a steep gradient already, but the introduction of a blade creates a shock, across which the density sharply increases. By the end of my time there, we were able to observe the shock and found that the addition of blades increases the density gradient, but the current prototypes have limitations.
As a side project, I looked into ways to increase the accuracy of the tomographical reconstruction techniques with a severely reduced number of views. My idea was to modify the iterated error redistribution technique by assuming a general profile shape. I created several density profiles, including with and without the shock. I took the projections of these profiles and used them in the modified reconstruction program to test the accuracy of the calculated profiles. The conclusions of this project were that, while the quality of the reconstructed profiles may be increased with this assumption, actual results may be invalidated due to the assumption of the profile shape being only partially justified.
For the summer of 2010 I conducted research on a project entitled “Cleaning Artifacts with Femtosecond Lasers” under the supervision of Dr. Gérard Mourou and his post-doctorate student J Bianca Jackson. The objective of the project was to study the cleaning effects of irradiation with a Ti:Sapphire with pulse duration of approximately 20 fs incident upon artifacts of cultural significance, specifically coins. We intended to study the cleaning as a function of incident fluence (energy/area) and as a function of the number of incident laser pulses. The project was complicated by the necessity of utilizing lab space and equipment belonging to other groups. For approximately the first month of my internship, my duties consisted of assembling a laboratory system with which to conduct the aforementioned experiments, and when the above was not possible due to lack of equipment, reading scholarly articles related to laser ablation and ablation as an instrument for the cleaning and preservation of artifacts of cultural significance. The second month consisted of performing the experiments and utilizing SEM facilities at the C2RMF at the Louvre to carefully examine the samples pre and post ablation. We found that a laser fluence of ~150 J/cm^2 at 50 to 100 pulses per spot successfully locally cleaned one of our specimens, an American World War II era nickel, while said fluence inflicted no observable change on a second sample, an 18th century Japanese coin. We also found that the fluences utilized (~10 J/cm^2) in the attempted cleaning of our third sample, a 3rd century A.D. Roman coin, were far too high and resulted not only in the removal of the corrosion products, but also in the damaging of the coin for more than 10 pulses/spot. It is unlikely that these results will be published. Although the work is similar in content to articles written by others in the field of laser cleaning and restoration such as Fotakis and Serafetinides, the volume of work done is not sufficient to warrant a publication. Another two weeks of laboratory time with a functioning system would have greatly increased the likelihood of publication.
I spent my Summer working under mentor J Bianca Jackson PhD, at ILE, processing and analyzing Terahertz Time Domain Transmission Data of pigment media. The goal was to create MATLAB and LabVIEW programs that enable easy extraction of spectrum data like real refractive index and absorption. It took a lot of reading of important THz papers, fiddling around with the software, and question asking to understand what I was doing and the best way to go about it. Throughout our projects we kept blogs about the technical aspects of our work and also about our day-to-day experiences. This summer I was introduced to the use of THz for the conservation and study of art and our cultural heritage, which to put it simply, was awesome. We made visits to the Centre de recherche et de restauration des musées de France (C2RMF) located in the Louvre where they use what seems to be a myriad of scientific techniques for the purposes mentioned above. Of course the summer was a wonderful learning experience as REUs are; but, participating in an iREU gave me the chance to travel to a great city. We explored so many places, spoke French, ate amazing food, met a lot of interesting characters, and were introduced to the Parisian way of life. Art and science are very romantic concepts especially in Paris.
I worked in the Laboratoire pour l’Utilisation des Lasers Intenses (LULI) on project ELFIE (Équipement des Laser Forte Intensité et Energie. LULI is a facility that maintains two high field lasers (LULI 2000 and ELFIE) used mainly for plasma physics research. Project ELFIE was initiated to upgrade LULI’s 100 TW facility to make available an even stronger laser in a renovated area with double the output energy and a short-pulse, high energy OPCPA (optical parametric chirped pulse amplification) beam line. I assisted with the construction, testing, and alignment of ELFIE.
My tasks included:
Assembling amplification room laser casings
Installing OPCPA beam line mirrors
Aligning beam entry into amplification room
Aligned rod amplifiers for maximum beam amplification
All these tasks helped to make available a highly configurable laser which will eventually be capable of providing four beams (two 30 J / 300 fs, one 5 J/ 50 fs, and one 60 J/500 ps).
While in Paris, I was assigned to work under Dr. Guilhem Gallot at the Laboratoire d’Optique et Biosciences at École Polytechnique. I worked almost exclusively with his Ph.D student, Antoine Wojdyla, on developing a system to image by absorption of evanescent waves in the terahertz domain. We produced the evanescent waves by total internal reflection of a pulsed terahertz beam through silicon against a drop of water (which will eventually be replaced by some biological sample once the system is optimized). We tried two different setup configurations and designed a third (which we need to order a piece for). Most of our time in lab was spent aligning and tuning these setups which was particularly difficult given the invisibility of the beam (what we could align with an IR beam was limited since it doesn’t propagate through silicon) and the large number of degrees of freedom in our setups. On the second to last day of my stay though, we managed to get a great image! Our lab expects to begin imaging biological samples with this technique and publish the results within the next few months.
The goal of my project was to measure and characterize the optical losses from ferroelectric thin film waveguides grown by the Manolia group at L’Institut d’Optique Graduate School. The group studies non-linear optical materials and is interested in testing their thin film waveguides. The waveguides are Strontium Barium Niobate films grown via epitaxy on Magnesium Oxide or Silica substrates. For my projects, I used a standard Helium-Neon laser to measure the optical losses. The waveguides were positioned on a moveable x-y-z translation stage hooked up to a piezoelectric crystal system so that we could fine-tune the position of the waveguides. The laser light was directed toward the waveguide using three mirrors before it was focused through a microscope objective onto the side of the waveguide. Light exiting the waveguide passed through another microscope objective before being imaged onto a screen. Two camera systems were also used to monitor the light. One was positioned above the waveguide to examine light scattered from the top, and another camera often replaced the screen so that we could image light exiting the side. The images were then analyzed and fit with exponential functions to determine the loss coefficients for the waveguides. A majority of the time was spent trying to determine whether or not light was being coupled into the waveguide and, when we were guiding light, reproducing the results for all of the waveguides. At the culmination of the program, losses for one waveguide had been measured, but more trials needed to be completed in order to get sufficient statistics.
This summer, I worked with the XUV Optics team at Institut d’Optique on a theoretical project determining the influence of spatio-temporal wavefront perturbations on attosecond pulse duration. Attosecond pulses are in the XUV spectral range, and are thus very difficult to develop optical components for. Mirrors used to reflect attosecond pulses are multilayer mirrors, with typical configurations being grazing-incidence toroidal mirrors, or elliptical and parabolic mirrors at near-normal incidence. Such optics are optimized to be used at certain incidence angles in precise configurations, and any small alterations from these configurations can result in significant pulse aberrations. Much work in this field has already been focused on eliminating higher-order terms in the spectral phase (like the Group-Delay-Dispersion or “Chirp” inherent to attosecond pulses), however, the spatial phase has been largely neglected.
I first developed a simple theoretical model to predict how the pulse duration evolves with spatio-temporal wavefront perturbations, and then found a powerful method to measure perturbations’ effects using the techniques that experimentalists already have available for measuring attosecond pulse trains. The validity of these results was tested with numerical simulations, through a ray-tracing software previously developed by my group that is also capable of simulating the measurement of an attosecond pulse. This resulted in the development of a criterion that ensures a pulse stretch due to aberrations of less than 20%. I am currently working on a paper with my group, and we are aiming for the results to be published in early October.
My day-to-day work in the group came in three main phases. For the first week, I familiarized myself with the world of attosecond pulses: I read papers, went through presentations, and asked lots of questions to the Ph.D. student that I mainly worked with. During this time, I also familiarized myself with the other directions taken by members of my group – who mainly worked on optimizing and creating the multilayer mirrors used for the XUV spectral range. Their optical components are used in several large-scale experiments, including the Solar Helium Observatory (SOHO) satellite. In the second phase, I worked with Charles, a Ph.D. student, on developing the mathematical models described above. This was both very frustrating and very rewarding work; I enjoyed calling on all of the mathematics I had ever learned to lead me forward and figuring out where to make appropriate approximations. I learned how to be attentive to detail and be very rigorous about any assumptions that were being made. The last phase of my work involved running the numerical simulations. Because one such simulation would take nearly an entire day to run, I was able to begin work on the paper that we will publish soon.
Aside from the valuable mathematical skills that I gained, I also gave two presentations to my group and kept a document updated with a summary of what we had done so far. These things helped me develop my communication skills, and having to be able to explain my work to others also helped me spot any gaps in my understanding. This summer was an invaluable experience; in addition to learning about the world of XUV pulses and improving my French, it has helped me define my direction in graduate school.