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ion Designing Glass Structures for Femtosecond Laser Processing

Richard K. Brow, Missouri University of Science and Technology, DMR 1207520Outcome: Researchers at Missouri S&T have developed a new family of durable glasses for femto-second laser writing applications.Impact: These glasses will enable the development of new, reliable optical devices created by spatially-selective f-sec laser processing of optically active glass substrates. Explanation: Recent research has shown that optical wave-guides can be drawn in zinc phosphate (ZP) glass substratesusing a femto-second laser1. Like silica glass, ZP glasses havetetrahedral structural networks, but unlike silica, can retainlarge concentrations of rare earth ions desired for opticallyactive devices. Simple ZP glasses are not chemically stable,but Charmayne Smith, a PhD candidate at Missouri S&T,discovered that zinc alumino-phosphate (ZAP) glasses havethe requisite durability for device applications and could bedesigned with tetrahedral structures that appear to be suitable for f-sec laser processing. The research is led by Prof. Richard Brow, ofthe S&T Materials Science & Engineering Department andinvolves collaborators from UC-Davis, Univ. Lille (Lille,France), and William Jewell College (Liberty, MO).

Charmayne Smith, a PhD candidate at Missouri S&T, with a sample of a ZAP glass 1. L.B. Fletcher, J.J. Witcher, N. Troy, S.T. Reis, R.K. Brow, D.M. Krol, “Direct

femtosecond laser waveguide writing inside zinc phosphate glass,” OpticalExpress, 19 (2011) 7929-7936.

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Zinc phosphate glasses have been shown to be promising candidates for substrates for f-sec laser processing of optical devices. Like silica, these glasses densify when irradiated and so are suitable for writing waveguides. ZP glasses can also be doped with large concentrations of rare earth ions for making active devices like laser amplifiers. Binary ZP glasses, however, rapidly degrade in humid environments and this limits their use. Adding alumina improves corrosion resistance, but changes the way the glass responds to the f-sec laser. We found that the glass composition can be tailored to maximize the numbers of tetrahedral Zn-, Al- and P-anions and that waveguides could then be drawn into these new glasses. A model was developed to relate composition and structure, and NMR spectra, collected by Prof. Lionel Montagne (Univ. Lille) confirmed the predictions of the model.

Glass Chemistry Determines Tetrahedral Structures Richard K. Brow, Missouri University of Science and Technology, DMR 1207520

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49-2-49_3.05 38-7-55_3.04 33-11-56_3.10 0-29-71_3.12

Measured Al coordination numbers in ZAP glasses, from 27Al NMR spectra (inset), agree well with predictions based on a new structural model (Figure courtesy of Charmayne Smith).

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Undergraduate research experiences are integrated into this NSF DMR project. For the 2012/13 academic year, a group of seniors in the MSE program at S&T designed and fabricated a photo-sensitive glass that could be patterned in two colors, using a f-second laser. These pieces are now used in demonstrations related to glass science and technology for pre-college students. The collaboration developed with the MechE program at S&T has been extended to support MSE grad student research on this project.Graduate students at Missouri S&T collaborated with undergraduates in the Physics Department at William Jewell College (Liberty, MO). Electron spin resonance spectra were collected at WJC to study laser-induced defects in ZAP glasses, and students from WJC spent several days in the glass labs at S&T preparing and characterizing glasses.

Research Opportunities for Undergraduate StudentsRichard K. Brow, Missouri University of Science and Technology, DMR 1207520

Undergraduate students from William Jewell College preparing batches in the S&T glass lab (June 2013)

Two-color glass sample created by a f-sec laser- S&T MSE senior design (May 2013)