Bulletin of the American Physical Society
77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010; Baton Rouge, Louisiana
Session HB: 50 Years of Solving Problems in Science, Technology, and Medicine with Lasers |
Hide Abstracts |
Chair: John Thomas, Duke University Room: Nicholson Hall 109 |
Friday, October 22, 2010 1:30PM - 2:00PM |
HB.00001: Simple Devices for Measuring Complex Laser Pulses Invited Speaker: Shortly after the development of the first lasers, researchers learned a valuable lesson: lasers were not very useful if their beam spatial quality was poor. Fortunately cameras could measure the beam quality, which then rapidly improved. Just as lasers must be smooth and stable in space, they must also be so in time. Fortunately, electronic detectors and oscilloscopes could measure the laser intensity vs. time. Until, that is, researchers began to generate pulses nanoseconds and even picoseconds long, too fast for these devices. It was not until pulses reached fs lengths that complete intensity-and-phase measurements became possible. Frequency-Resolved Optical Gating (FROG) nicely solved the problem, yielding the pulse intensity and phase vs. time for arbitrary fs pulses. Additional simple techniques can measure fs pulses' complete intensity and phase vs. time and space. Indeed, fs light pulses are now arguably the best characterized type of light, and they are the basis of ultrastable metrology. But what about ns pulses? In the process of opening up new regimes of science, the measurement of much longer---and far more common---intermediate length pulses was forgotten. As a result, ns pulses from Q-switched solid-state lasers, pulsed diode lasers, and high-power fiber lasers and amplifiers are often far from ideal in time and no one knows precisely what their distortions look like. Yes, electronic detectors and oscilloscopes have become faster, but such exotic devices are expensive and fragile and only yield the intensity and not the phase. Measuring ns pulses has proved much more difficult than measuring fs and ps ones. Happily, we have recently demonstrated a novel FROG for measuring ns pulses. The main challenge was generating a ns delay range on a single shot, a problem we solved in a novel manner: by tilting the input pulse by 89.9 degrees. This novel device completes the many-decades-old task of developing simple techniques for measuring essentially all laser pulses. [Preview Abstract] |
Friday, October 22, 2010 2:00PM - 2:30PM |
HB.00002: Multiphoton and photothermal imaging of molecular events in cancer Invited Speaker: Optical techniques are attractive for monitoring disease processes in living tissues because they are relatively cheap, non-invasive and provide a wealth of functional information. Multiphoton microscopy (MPM) and Optical Coherence Tomography (OCT) are two types of three-dimensional optical imaging modalities that have demonstrated great utility in pre-clinical models of disease. These techniques are particularly useful for identifying metabolic and molecular biomarkers in cancer. These biomarkers can be used to identify the mechanisms of tumor growth, and to predict the response of a particular tumor to treatment. Specifically, MPM of the co-enzymes NADH and FAD was used to quantify metabolic changes associated with developing cancers in vivo. This imaging technique exploits intrinsic sources of tissue contrast and thus does not require contrast agents. Ongoing work combines this metabolic imaging technique with vascular imaging to provide a comprehensive picture of oxygen supply and demand with tumor therapy. Molecular signaling represents a third critical component in tumor physiology. To this end we have recently developed photothermal OCT, which combines coherent detection with laser-heated gold nanoparticles to achieve high-resolution molecular contrast at deeper depths than MPM. This multi-functional imaging platform will provide unprecedented insight into oxygen supply and demand, and molecular signaling in response to tumor growth and targeted cancer therapies in pre-clinical models. [Preview Abstract] |
Friday, October 22, 2010 2:30PM - 3:00PM |
HB.00003: Nonlinear Microscopy with Shaped Laser Pulses - Shedding New Light on Tissue Invited Speaker: The advent of ultrafast pulsed lasers substantially advanced studies of nonlinear optical effects by providing high peak intensities at low average power. When applied to microscopy in highly scattering tissue, the localized nature of the nonlinear interaction leads to high spatial resolution, optical sectioning, and larger possible imaging depth than linear methods. However, nonlinear contrast (other than fluorescence) is generally difficult to measure because it is overwhelmed by the large background of detected illumination light. This background can be suppressed by using femtosecond pulse shaping to encode nonlinear interactions in background-free regions of the frequency spectrum. We will discuss two techniques aimed at measuring nonlinear absorptive and nonlinear dispersive contrast, respectively. Nonlinear absorption offers a dramatically expanded range of molecular contrast, because not all markers that absorb photons fluoresce. We will describe a technique that utilizes shaped pulse trains of multiple colors, where an amplitude modulation of the pump beam is transferred onto the probe beam of a different wavelength, thereby generating a new frequency in the probe beam. Using this technique we have been able to detect non-fluorescent metabolic markers in tissue (e.g. the imaging of different types of melanin in pigmented lesions and the mapping of oxygenation in blood vessels). We also have developed a technique that is able to measure nonlinear phase contrast (e.g. self-phase modulation) in tissue with very moderate laser power. The key concept of this technique is the fact that nonlinear processes can create new frequency components within the pulse spectrum. We can efficiently detect these spectral changes by appropriately pre-shaping the spectrum such that the changes show against a small background. Using these pulse shaping techniques we have been able to detect nonlinear optical signatures of neuronal activity in live neurons. [Preview Abstract] |
Friday, October 22, 2010 3:00PM - 3:30PM |
HB.00004: Bowls made of Laser Light to Corral Ultracold Atoms Invited Speaker: Using stable lasers, it is now possible to create nearly perfect bowls made of pure light, which are smaller than a piece of lint and store atoms for several minutes in an ultrahigh vacuum environment. These almost frictionless bowls are ideal for cooling atoms by evaporation, the same way that alcohol cools the skin. In just a few seconds, atoms trapped in the bowl are cooled to temperatures of ten of billionths of a degree above absolute zero, where the de Broglie wavelength is several microns. These ultracold atoms occupy the quantum energy levels of the bowl, producing a giant quantum system that can be directly observed using laser flash photography. I will describe our laser trapping methods and show how they can be use to study a unique quantum gas of spin-up and spin-down $^{6}$Li atoms, which are fermions that obey the Pauli exclusion principle. I will describe how this ultracold atomic gas now tests predictions in nearly all fields of physics, from high temperature superconductors to neutron stars, the quark-gluon plasma of the Big Bang, and even string theory. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700