Bulletin of the American Physical Society
Fall 2009 Meeting of the Four Corners Section of the APS
Volume 54, Number 14
Friday–Saturday, October 23–24, 2009; Golden, Colorado
Session B3: Symposium on Advanced Optical Measurements I: Attosecond Physics |
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Chair: Emily Gibson, University of Colorado Denver Room: Green Center Metals Hall |
Friday, October 23, 2009 2:10PM - 2:34PM |
B3.00001: Real-time observation of attosecond and femtosecond quantum dynamics using ultrafast lasers Invited Speaker: Recent innovations in ultrafast laser technology have led to generation of intense near-infrared (NIR) laser pulses in the few-cycle regime, which implies light pulses as short as 5-10 fs. These pulses offer an exciting opportunity to perform real-time measurements of the fast quantum dynamics occurring in gaseous and condensed phase matter. Experiments using such techniques can time-resolve the electronic, nuclear and correlated motions inside atoms, molecules and solids. In particular, the interaction of intense ultrafast laser pulses with noble gases can be used to generate coherent extreme ultraviolet (XUV) pulses with temporal duration as short as 100 attoseconds. As a comparison, the Bohr timescale of electron in a Hydrogen atom is $\sim$ 150 attoseconds. Thus, a pump-probe scheme consisting of attosecond XUV pulses and intense femtosecond NIR laser pulses has opened up the doors for excitation and control of extremely fast electronic processes. I will describe some of our work which uses these techniques to probe inner-shell ionized and highly-excited electron dynamics in atoms and molecules. [Preview Abstract] |
Friday, October 23, 2009 2:34PM - 2:46PM |
B3.00002: High repetition rate HHG for VUV frequency combs Dylan Yost, Jun Ye By coupling a low-phase-noise, short-pulse laser to a femtosecond enhancement cavity, it is possible to obtain a large enhancement of the pulse energy and subsequently drive the high harmonic process at very high repetition rates ($\sim$100 MHz repetition rates). The generated radiation has could potentially be used for a multitude of experiments requiring VUV radiation with exceptional temporal coherence. An open question is whether a high level of phase coherence can be maintained through the HHG process. In response, we have recently conducted experimental studies of the quantum paths which contribute to a given below-threshold harmonic order. In addition to answering fundamental questions pertaining to the high harmonic process, these studies will allow one to understand amplitude to phase noise conversion in HHG more precisely. Finally, to show that temporal coherence can be maintained in practice, we utilize a self-homodyne measurement and find that the coherence time is greater than $\sim$10 ns by measuring the pulse-to-pulse coherence within the harmonic pulse train. [Preview Abstract] |
Friday, October 23, 2009 2:46PM - 2:58PM |
B3.00003: Characterization and Application of Attosecond Pulse Trains Niranjan Shivaram, Lei Xu, Adam Roberts, Arvinder Sandhu Femtosecond high intensity ($>$10$^{14}$ Wcm$^{-2})$ laser pulses can be focused onto a suitable gas to produce extreme ultraviolet (XUV) emission by the process high harmonic generation (HHG). In this process, the driving laser field pulls the electron out from an atom and when the laser electric field changes direction, the electron can be driven back to recollide with the parent ion core resulting in XUV emission. Since the recollision occurs once every half laser cycle, the emission consists of bursts which are a few hundred attoseconds in duration and separated by $\sim $1fs. In this talk I will provide a brief overview of attosecond pulse train generation and characterization. I will describe a two-pulse (one high harmonic pulse and one fundamental pulse) pump-probe measurement technique to extract information (particularly the phase) about the high harmonic pulse. A velocity map imaging detector is employed to image the photo-electrons produced in this process. This setup can also be used to study electron dynamics in atoms and molecules on a sub-femtosecond time scale. I will describe our work in progress using He and Ar atoms and our future plans. [Preview Abstract] |
Friday, October 23, 2009 2:58PM - 3:10PM |
B3.00004: High-Frequency Surface Acoustic Wave Propagation in Nanostructures Characterized by Coherent Extreme Ultraviolet Beams Mark Siemens, Qing Li, Keith Nelson, Ronggui Yang, Erik Anderson, Margaret Murnane, Henry Kapteyn We study ultrahigh frequency surface acoustic wave propagation in nickel-on-sapphire nanostructures. We make use of high-order harmonic generation to obtain ultrafast, coherent, beams in the extreme ultraviolet (EUV) region of the spectrum. The short wavelengths $\sim $30 nm allow us to measure propagation dynamics of surface acoustic waves to frequencies of nearly 50 GHz, corresponding to wavelengths as short as 125 nm. We repeat the measurement on a sequence of nanostructured samples to quantify dispersion of surface acoustic waves in a nanostructure series for the first time [1]. These measurements are critical for accurate characterization of interfaces beneath very thin films using this technique. [1] M. E. Siemens, et al. Applied Physics Letters, 94(9):093103, 2009. [Preview Abstract] |
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