Basic science studies in photosensitivity response and heat accumulation effects in various glasses and crystals are opening practical new directions in making optical circuits and new types of 3-D optical devices. Material interaction studies with extreme short wavelength F2 laser radiation are giving way to ultrashort pulse laser interactions for improving the control of refractive index profile and for reducing optical scattering loss in laser fabricated devices. The short pulse lasers interactions strongly confined by nonlinear absorption a to small focal volume (see figure), facilitating the direct-writing of optical waveguides, gratings, interferometers, and other phase-contrast optics that we are broadly exploring in glasses, crystals, photoresist, polymers, and active laser media.

The flickering light produced during laser processing is both a curse and an opportunity. Such undulating light emissions are associated with poorly formed seams in laser welding, misalignment of the samples, non-uniform walls in microhole or microchannel machining, and formation of scattering defects in optical circuits.

A new research tool is being developed that captures the lights emissions created by ultrashort pulse lasers - the fastest man-made event - and harvests the rich spectroscopic signature of the underlying laser-interaction physics, evolving erratically as the laser cuts through the work sample. We are integrating to our ‘burst’ femtosecond laser processing facility a multi-photon (2-photon) microscope similar to commercial systems now revolutionizing biological research and clinical medicine with vivid three-dimensional (3-D) images of living cells and the inner workings of genes and proteins. This novel combination of laser modification and laser probing enables time- and spectrally resolved fluorescence microscopy for real-time probing and analysis of laser interactions volumes that undergo extreme physical transformations at sun-like temperatures. By monitoring devices as they take shape under such lasers, we hope to improve the fabrication precision, alignment, and flexibility of ultrafast laser processes and develop new approaches in “Intelligent Laser Processing”. This path promises to open new frontiers in nano-science by fabricating nano-optic systems to guide light at dimensions below conventional diffraction limits or precisely probe electron wavefunctions in protein molecules with high optical resolution.

Laser Nanofabrication lights up Biophotonic Chips

Photons are central to many of the forefront trends in science and technology today, serving as a powerful nanofabrication tool, or a delicate laser tweezer to manipulate nanoparticles, or an insightful spectroscopic probe for unraveling the structure of large protein molecules. Our research program touches many science fronts that include nano-optics, ultrafast laser science, photonic devices, laser material processing, nanofabrication, and biophotonics, from which is emerging a powerful opportunity for creating advanced lab-on-chip devices for sensing, analysis, and biological applications.

Our program is creating this future microlab by laser imprinting and integrating micro- and nano-tools onto a small chip. We are motivated by the five-decade explosive upsurge of the microelectronics industry, which began once bulky vacuum tubes could be replaced with compact silicon transistors, and enable high device integration on a low-cost planar platform. The emphasis is on harnessing light at this new biochip level to serve a multitude of new biophotonic possibilities in scientific research, drug discovery, home security, and clinical diagnostics. Our approach is to apply laser microfabrication technology that can replace today’s large-frame lab instrumentation - microscopes, spectrometers, test tubes, and beakers – with new compact, highly integrated, and multi-function systems on a chip.

Our program is part of a large cross-country research network that is developing the science and building the next generation tools for creating advanced biophotonic ‘circuits’ on a chip.

Two approaches in creating 3D photonic bandgap and other nano-optic devices:

• Direct writing with femtosecond lasers provides high flexibility to shape 1-D, 2-D or 3-D periodic templates in photoresist, together with various microfluidic, reservoir, mixing channels (see photo below).


• A novel phase mask approach developed by our group provides rapid writing of 3-D photonic bandgap structures in thick resist with a cw Ar-ion laser (top photo). The approach is more stable than traditional beam interference methods, and promises high volume and low cost manufacturing of photonic crystals (middle photo) made practically useful with optical engineering of ‘defects’ in the phase mask.