In this paper we show results of Nd:YAG laser-induced bubbles formed in a one millimeter thick agar gel slab. The nine nanosecond duration pulse with a wave length of 532 nm was tightly focused inside the bulk of the gel sample. We present for the first time a pump-probe laser-flash shadowgraphy system that uses two electronically delayed Nd:YAG lasers to image the the bubble formation and shock wave fronts with nanosecond temporal resolution and up to nine seconds of temporal range. The shock waves generated by the laser are shown to begin at an earlier times within the laser pulse as the pulse energy increases. The shock wave velocity is used to infer a shocked to unshocked material pressure difference of up to 500 MPa. The bubble created settles to a quasi-stable size that has a linear relation to the maximum bubble size. The energy stored in the bubble is shown to increase nonlinearly with applied laser energy, and corresponds in form to the energy transmission in the agar gel. We show that the interaction is highly nonlinear, and most likely is plasma-mediated.

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We present a study of the spectral properties of photon pairs generated through the process of spontaneous four wave mixing (SFWM) in single mode fiber. Our analysis assumes narrowband pumps, which are allowed to be frequency-degenerate or non-degenerate. Based on this analysis, we derive conditions on the pump frequencies and on the fiber dispersion parameters which guarantee the generation of ultra-broadband photon pairs. Such photon pairs are characterized by: i) a very large degree of entanglement, and ii) a very high degree of temporal synchronization between the signal and idler photons. Through a numerical exercise, we find that the use of photonic crystal fiber (PCF) facilitates the fulfilment of the conditions for ultra-broadband photon pair generation; in particular, the spectral region in which emission occurs can be adjusted to particular needs through an appropriate choice of the PCF parameters. In addition, we present a novel quantum interference effect, resulting from indistinguishable pathways to the same outcome, which can occur when pumping a SFWM source with multiple spectral lines.

This report presents a study of shock wave and cavitation bubble dynamics induced by nanosecond laser pulses in pressurized water. Three methods were used to obtain data from the irradiated sample: (1) pump-probe laser flash shadowgraphy, (2) pressure wave sensing by means of a fiber optic interferometer hydrophone, and (3) a novel technique based on the modulation of spatial transmittance by the cavitation bubble. The medium used in these experiments was distilled water in a chamber under different pressure conditions which included values found in human intraocular liquid. It could be shown that while external pressure does not affect either the shock wave propagation or the initial bubble growth rate, it does affect the first collapse time of the bubble and its maximum diameter.Keywords: bubble; shock wave; microsurgery; pressure; intraocular.Zusammenfassung : Die vorliegende Arbeit untersucht die Dynamik von Schockwellen und Kavitationsblasen, die mittels Nanosekunden-Laserpulsen in unter Druck gesetztem Wasser erzeugt wurden. Dabei wurden drei unterschiedliche Methoden verwendet: (1) Laserflash-Verfahren, (2) Druckwellenmessung mittels faseroptischem Interferometer und (3) eine neuartige Technik basierend auf der Modulation der r ä umlichen Transmission durch die Kavitationsblase. Die Untersuchungen wurden an destilliertem Wasser unter unterschiedlichen Dr ü cken -u.a. auch physiologische Werte, wie sie intraokular vorkommen -vorgenommen, die mittels einer speziellen Druckkammer erzeugt wurden. Es konnte gezeigt werden, dass weder die Ausbreitung der Schockwelle noch das anf ä ngliche Blasenwachstum durch den ä u ß eren Druck beeinflusst wird, die Kollapszeit der Blase und ihr maximaler Durchmesser jedoch sehr wohl.Schl ü sselw ö rter: Blase; Schockwelle; Mikrochirurgie; Druck; intraokular.

This article presents the analysis of the laser-produced-plasma (LPP) formed by the focusing of a 9 ns laser pulse, λ=532 nm, with a NA=0.6 aspherical lens using energies between 100–1500 μJ, into distilled water with varying solutions of table salt. Observations of the filamentation plasma were made, which are explained by self-focusing of the laser pulse by the LPP through ponderomotive cavitation of the electron plasma in the center of the beam. The filamentation of the beam through a low density plasma wave guide explains why the transmission of the pump laser through the interaction region was notably higher on previous experiments that we performed [R. Evans et al., Opt. Express 16, 7481 (2008)], than a very similar set of experiments performed by Noack and Vogel [IEEE J. Quantum Electron. 35, 1156 (1999)].