Robert J. Gordon

Department of Chemistry

University of Illinois at Chicago

 

 Laser Controlled Chemistry

 

Department of Chemistry m/c 111
University of Illinois at Chicago
845 W Taylor Street
Chicago, IL 60680-7061

Office: 312-996-3280 Cell: 847-594-2383
Fax: 312-996-0431 email: rjgordon@uic.edu


 Teaching Links:

Chem 342
 Research Links:

Energy Transfer in Plasmas

Biomedical Applications
 

 

Publications

Recent Posters

 

Group Research

The focus of our research is on the use of lasers to control the behavior of matter. A primary example is coherent phase control of chemical reactions. By exploiting the quantum mechanical interference between one- and three-photon excitation paths, we are able to control the branching between photodissociation and photoionization of molecules in a molecular beam. Another example is the control of solid materials, using trains of ultrafast laser pulses to produce coherent phonon excitation. Other efforts include ultrafast material processing, application of laser ablation to glaucoma surgery, material analysis by means of laser-induced breakdown spectroscopy (LIBS), and plasma-mediated energy transfer between laser beams.

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Coherent Control

We employ the principle of quantum mechanical interference to control the rates and branching ratios of chemical reactions. In a typical experiment, we excite a molecule with three visible photons of frequency w1 and one ultraviolet photon of frequency w3 = 3 w1. By varying the relative phases of the two light sources, we cause constructive or destructive interference between the excitation paths. A key finding is that it is possible to control the branching ratio of a reaction by simply changing the phases of the laser beams. The phase lag between different products is a new observable that provides information about the continuum properties of a molecule. We also showed that the Gouy phase of the laser beam is a useful control parameter.

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Energy Transfer Between Lasers: The Ghostbuster Effect

We intersect two ultrafact laser beams in air and under the proper focusing we can trassfer most of the energy from one beam to tghe other. This phenomenon is based on plasma mediated Raman scattering.

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Material Processing

Pairs of femtosecond laser pulses are used to ablate metals, semiconductors, and dielectrics. We use plasma emission as a diagnostic to study the melting and ablation of the material. We find that a double pulse produces an order of magnitude uch greater emission than a single pulse of the same total energy, and we attriubute this effect to propagation of the melt front into the material.

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Laser-Induced Breakdown Spectroscopy

Atomic and ionic emssion produced in the laser ablation of metarials provides a sensitive means of standoff elemental analyis. A primary limitaion of the sensitivity and reolution of laser-induced breakdown spectroscopy (LIBS) is a broad continuum background. We have discovered that this background is strongly polarized. For LIBS spectra generated with femtosecond pulses, we have observed greater than 90% polarization for wavelengths shorter than 350 nm, and we have also observed strong polarization with nanosecond LIBS.

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Biomedical Applications

It is well known that glaucoma is associated with elevated pressures of aqueous humor in the eye. A treatment for reducing the intraocular pressue is to create lesions in the trabecular meshwork, so as to increase the aqueous outflow rate. Laser trabelcular ablation with conventional is limited by scarring and inflamation. In our group we have femtosecond laser pulses to create lesions in the trabecular meshwork of intact eyeballs and demonstrated little collateral damage.

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 Revised in November, 2009

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