Attosecond Pulse Laser

Making a pulse of light that disappears a few hundred billionths of a billionth of a second after its creation. An attosecond laser could function as a high speed camera
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Atomic Interferometer

Pass light through a pair of slits in a barrier , and an array of bright and dark lines appear on a distant screen as light waves from two sources interfere with each other. Noel and Stroud, have replaced the barrier with a single potassium atom. For the two light source use 1 of the atom's electrons, shaped by laser pulses into a pair of distinct wave packets. Such experiments display physicists ability to resurrect some of the certainties of classical physics from the hazy quantum world of the atom. An atom's electron ordinarily can't be pinned down precisely enough to make an interferometer, because it spreads out through space in a haze of probability. But by bumping the outermost electron of an atom with a laser of the right frequency, physicists can boost part of the electron's quantum wave into a well defined shell of charge that behaves like a planet following a classic elliptical orbit. Just as the planet's orbital radius varies, this Rydberg packet, oscillates in and out in a breathing motion. Unlike a planet the packet has a phase corresponding to the phase of the laser pulse that created it. By bombarding potassium atoms w/ a pair of laser pulses, Noel and Stroud excite a single electron in two different radial positions - the equivalent of an interferometer's two slits. all that remains is to bring the two wave packets together and watch them interfere. Fortunately the "orbits" of the Rydberg packets spread out they age, eventually overlapping. Where they overlap , they interfere and either cancel or reinforce each other, depending on the relative phase of thes two laser pulses that created them. A third probe pulse reveals the results and shows that the textbook rules of wave interference hold sway even in the real of the atom. flash, allowing scientists to get their first-even looks at fleeting phenomena like electrons whirling about a single atom. Allow snapshots of atoms being ionized or electron bonds forming as they happen. To get attosecond laser requires multitude of light rfrequencies to be synchronized in a manner and at a speed never before attmpted. (1) An attosecond pulse must be composed of many different and high frequencies of light. If too few frequencies are involved, or if their frequencies are too low, the pulse will last too long. (2) Even though waves have different frequencies, they must be coherent. Their peaks and troughs must all align periodically. - like trying to swing pendulums of a dozen grandfather clocks are different rates , yet make them all hit the right extreme of their arc one a minute. (3) A Pulse must be strong, w/ enough photons to illuminate its subatomic subjects. (4) The attosecond flashed must be separated by at least 1 millionth of a second in order to work with the "low-speed" electronics that will record the results. Challenges : (1) Quantum mechanics, trade-off between duration of light pulse and range of frequencies that make it up. As one shrinks the other grows. As light pulse is squeezed into a shorter time period, the range of frequencies in the pulse becomes broader. Because lasers pump out light at one or a few closely related frequencies, using one to create a quick broad spectrum pulse can be difficult. Use a pulse from a titanium sapphire laser to ionize a gas of xenon or argon atoms. The pulse generates an oscillating electric field which drives freed electrons in the gas away from their parent atoms. Then reverses course and drives them back at near light speed. Some of these collide w/ parent,s and the energy of the collision is released as a short-wavelength photon. Only the harmonics survive. (2) Coherence - as they travel, regular relationsihp among harmonic wave peaks/troughs align at regular intervals. Without this, waves would cancel each other out. (3) Strong pulse - harmonic generation is inefficient process. transforming only a tiny fraction of laser's original photons into harmonic photons. 94) Producing intermittent pulses - the low-speed electronics will record an electron's position. These detectors act like a camera shutter. If 2 or more attosecond flashes go off while the shutter is open the electron will illuminate will be seen at several positions not just one, and will look like a blur. Pump-probe : detect electrons in an atom. Divide short pulses into two beams and delay one beam slightly by routing it through an extra series of mirros. Energy from the first beam, the pump, triggers a reaction, such as splitting a molecule into it s component atoms. The probe is then routed in just behind the pump beam to illuminate the atoms as they fly apart. S +

Circuit simulation of Genetic Networks

Genetic networks with tens to hundreds of genes are difficult to analyze with currently available techniques. Because of the many parallels in the function of these biochemically based genetic circuits and electrical circuits, a hybrid modeling approach is proposed that integrates conventional biochemical kinetic modeling within the framework of a circuit simulation. The circuit diagram of the bacteriophage lambda lysislysogeny decision circuit represents connectivity in signal paths of the biochemical components. A key feature of the lambda genetic circuit is that operons function as active integrated logic components and introduce signal time delays essential for the in vivo behavior of phage lambda. S +

Submicrometer Feature Fabrication on curved substrates by microcontact printing

Microcontact printing has been used to produce patterned self-assembled monolayers (SAMs) with submicrometer features on curved substrates with radii or curvature as small as 25micrometers. Wet-chemical etching that uses the patterned SAMs as resists transfers the patterns formed by microcontact printing into gold. At present, there is no comparable method for microfabrication on curved surfaces. S +

2D Imaging of potential waves in Electrochemical systems w/ surface plasmon microscopy

The potential dependence of resonance conditions for the excitation of surface plasmons was exploited to obtain 2D images of potential distribution of an electrode w/ high temporal resolution. This method allows the study of spatiotemporal patterns in electrochemical systems. Potential waves traveling across the electrode with a speed on the order of meters per second were observed in the bistable regime of an oscillatory electrochemical reaction. This velocity is close to that of excitation waves in nerve fibers and is far greater than the velocity of reaction-diffusion waves observed in other chemical system. S +

Molecular diffuse interstellar band carriers in red rectangle

High-resolution optical spectroscopic observations of unidentified emission bands from the unusual biconical nebula known as the Red rectangle are reported. The peak wave-lengths and the widths of prominent bands near 5799,5853 and 6616 angstroms decrease with increasing offset from the central A0-type star HD44179 and, in the limit of large distance from the star, are shown to converge to the known values for some of the narrower diffuse interstellar absorption bands at 5797,5850 and 6614 angstroms. The same carriers give rise to both Red Rectangle emission and corresponding diffuse interstellar absorption bands, and these particular bands arise from electronic transitions in gas-phase molecules