Current Research Projects:

General Research Theme: High-speed optical-fiber communications and the unrelenting demand for Internet "bandwidth" are revolutionizing today's communication industry as played out by the increasing emphasis on photonics versus electronics technologies. This powerful transition is spurring industry to miniaturize and integrate optical components into highly functional optical circuits much like the planarization and integration of electronic components on silicon or germanium wafers four decades earlier. New processing and packaging technologies are now required that can precisely shape and assemble transparent optical components to sub-wavelength accuracy. Laser microfabrication technology is playing a role here, although only for light sources that interact strongly with transparent materials. We are exploiting two extremes in laser technology that provide strong interactions in wide-bandgap optical materials:   the deep-ultraviolet F2 laser (157 nm) and ultrafast lasers. These lasers drive fundamentally different interactions that offer distinct advantages for a variety of photonic applications through surface microsculpting or trimming of refractive index. The precise laser and optical-tool systems are defining new processes for shaping photonic components such as optical fiber devices, optical planar circuits, 3-photonic devices, and photonic bandgaps. Novel photonic designs are being explored and we are showcasing this technology to our industrial partners in the rapidly growing photonics industry in Canada and around the world.

                      Research Contributions:

Laser material processing at two contrasting forefronts—extremely short wavelength lasers and ultrafast lasers—have been studied and applied to emerging new fields in photonics, biophotonic devices, electronics, and micro-electro-mechanical structures (MEMs).

Vacuum-Ultraviolet Laser Processing of Materials - F2 Laser:   Our laboratory has pioneered the development of several novel materials processing applications centred on the 157-nm fluorine laser. The work was born out of collaboration with Lumonics, Canada in the early 1990’s, in which we developed a high-energy vacuum-ultraviolet (VUV) laser. Our group showed that the short-wavelength light furnishes smooth surfaces, supports nano-scale surface structuring (~100 nm), and offers precise etch-depth control (<25 nm), for microfabrication applications of novel electronic, biomedical and photonic components. The unique processing facility also cultivates many opportunities for scientific collaborations around the world. We worked with G. Mourou and X. Liu (Center for Ultrafast Optical Sciences, University of Michigan) to extend our VUV technique of profiling rib waveguides to ultrafast lasers, and are continuing this work with Prof. Marjoribanks, Miller, and Nantel at the University of Toronto. We are currently working with G. Marowsky and J. Ihlemann of Laser Laboratorium, Goettingen (Germany) to micropattern dielectric masks and binary optical components. F2-laser poling is also being studied here with S. Fleming and T. Xu of the Optical Fibre Technology Centre in Australia. Our research work has been influential in stimulating related research in Japan and Germany, home to world leaders in laser materials processing research and manufacturing. Our silica work inspired Prof. Jitsuno of the Institute of Laser Engineering to apply F2 lasers to directly shape large lenses for aberration correction. Lambda Physik was encoraged to establish a F2 laser micromachining facility in Florida. International research groups and industry scientists frequently tour our laboratory: our group hosted three long-term visitors funded by Japan: Prof. K. Kurosawa (Miyazaki University), H. Higaki (Kyoto U.), and H. Yamakoshi (Mitsubishi Heavy Industries), several short-term visitors, and numerous industry-group tours. Our laser processing developments, especially in photonics microfabrication, has attracted widespread industrial interest, cooperation, and research support. Lambda Physik and partner MicroLas provided strong support towards commercial exploitation of F2-laser technology for processing photonic materials. We have begun prototype work with several companies (JDS Uniphase, Scintrex, Raytheon - Elcan Optical Technologies, Photonics Integrated Research). This success convinced the Canadian Foundation for Innovation to strengthen our F2- laser processing program with $ 1.6M (combined total) over 3 years. Industrial interactions are strong and very active (Section 4)—near term commercialization is anticipated, possibly through a start-up company.

	F2 Laser Characterization: Our measurement of a surprisingly narrow linewidth (5 pm) suggested several possible coherent VUV applications such as the fabrication of 0.11-mm period surface-relief gratings and stimulated our subsequent work on writing photonic structures (Bragg gratings) in glass. This narrow linewidth is of current importance to semiconductor lithography now that Sematech (www.sematech.org) has placed the F2 laser on the roadmap.
	Glass Photosensitivity at 157-nm Wavelength: The potential impact of our current photosensitivity studies is exceptionally promising. We are pioneering basic science studies at this record short wavelength and are attracting industrial interest because of the rapid refractive index changes driven by this radiation. The shorter wavelength extends practical index writing to ‘pure’ fused silica, a material which does not respond materially at longer wavelengths.
	Intense Ps-Laser Interaction with Nanostructured Surfaces: A three-way collaboration was stimulated with Prof. M. Moskovits (Chemistry) and Marjoribanks (Physics) to investigate the soft x-ray conversion efficiency of a new type of structured surface—a ‘nanowire’ target. The velvet-like “black” structure is fundamentally interesting for studying plasma closure on 1-ps time scales and the dependence of absorption on laser polarization. Of practical importance is the order-of-magnitude increase in the soft x-ray yield for efficient photopumping of EUV lasers.
	Deep-Ultraviolet Vs. Ultrafast Laser Processing: A 12-year collaboration with Prof. R. Marjoribanks (Physics, University of Toronto) provided an exciting base of studies in laser-matter interaction physics, and in comparing deep-ultraviolet laser processing with ultrafast lasers. We discovered that pondermotive effects provide a 10-fold enhancement of 1-ps laser etch rate. We defined ultrafast-laser processing windows for micromachining transparent glasses and metal foils, and provided head-to-head comparison with F2-laser results. This latter work was influential in taming overzealous claims amongst ultrafast laser research groups on the merits of such lasers, and many other groups now follow a similar comparison style. A collaboration with Dr. P. Corkum (National Research Council, Canada) is pointing to interesting contrasts of deep-ultraviolet and ultrafast lasers in writing refractive-index structures in glasses – the photosensitivity response was surprisingly similar for different underlying interactions of single photon vs. multi-photon absorption. Our group is extending this waveguiding writing effort to the patterning of three-dimensional photonic structures. Joint modeling efforts with Prof. J. Sipe (Physics, University of Toronto) promise to create new photonic component designs that serve the heart of today’s rapidly expanding optical communication networks.
	Burst-Ultrafast Laser MicroFabrication With Prof. Marjoribanks, we discovered a new mode of laser interaction that combines the attributes of ultrafast laser processing with the smoothing benefit of a thermal process. Rapid bursts (133 MHz) of 1-ps pulses provided ‘crack-free’ micromachining of glasses – overcoming a real limitation with conventional ultrafast laser systems. A patent application is in progress. Our work motivated Prof. Mazur’s group (Harvard University) to rebuild their ultrafast laser oscillator and extend burst-processing to optical waveguide writing. Work with Dr. P. Corkum suggests a 3-fold photosensitivity enhancement due to a burst-driven thermal process. Our current research is expanding the scope of these studies to broader range of materials; rapid formation of photonic circuits is an especially promising research area.
	Laser-Induced Breakdown Spectroscopy (LIBS): Our group is exploring with Alcan International, novel laser approaches that can provide accurate assays of aluminum for sorting scrap metal in automobile recycling plans. The technique of laser-induced optical emission spectroscopy (OES) is being studied with various laser approaches - infrared and ultraviolet wavelength sources, shaped pulses, and bursts of ultrafast light - to optimize the precision and the speed of the diagnostic process. A viable laser-based automobile recycling system is required within the next 3 to 5 years to reduce to recovery cost of high-grade aluminum alloys from automobiles. This effort will encourage more use of light-weight metal in automobiles and help reduce fuel consumption.
	Laser Processing Facilities: The above work has stimulated numerous collaborations with new and existing colleagues at the University of Toronto, that has over the years built a critical mass of research activity in laser processing. Laser processing is now one key theme area in the provincial centre of excellence, Photonics Research Ontario. Collective efforts have brought much increased research funding, established state-of-the-art research facilities, and developed a broad range of expertise from laser physics to material diagnostics to support advanced laser-processing research and training at the University of Toronto.