T. Baldacchini, J. E. Carey, M. Zhou, and E. Mazur. 2006. “Superhydrophobic surfaces prepared by microstructuring of silicon using a femtosecond laser.” Langmuir, 22, Pp. 4917–4919. Publisher's VersionAbstract
Superhydrophobic surfaces exhibit contact angles with water that are larger than 150 and negligible difference in contact angle between the advancing and receding contact angles, the so-called contact angle hysteresis. In this paper, we present a novel and simple structuring process that uses intense femtosecond- laser pulses to create microstructured superhydrophobic surfaces with remarkable wetting characteristics.
B. R. Tull, J. E. Carey, E. Mazur, J. McDonald, and S. M. Yalisove. 2006. “Surface morphologies of silicon surfaces after femtosecond laser irradiation.” Mat. Res. Soc. Bull., 31, Pp. 626–633. Publisher's VersionAbstract
In this article, we present summaries of the evolution of surface morphology resulting from the irradiation of single-crystal silicon with femtosecond laser pulses. In the first section, we discuss the development of micrometer-sized cones on a silicon surface irradiated with hundreds of femtosecond laser pulses in the presence of sulfur hexafluoride and other gases. We propose a general formation mechanism for the surface spikes. In the second section, we discuss the formation of blisters or bubbles at the interface between a thermal silicon oxide and a silicon surface after irradiation with one or more femtosecond laser pulses. We discuss the physical mechanism for blister formation and its potential use as channels in microfluidic devices.
C. R. Mendonca, P. Tayalia, T. Baldacchini, and E. Mazur. 2006. “Three-dimensional microfabrication for photonics and biomedical applications.” In . Macro 2006 - 41st International Symposium on Macromolecules Proceedings. Publisher's VersionAbstract
We use two-photon absorption polymerization to fabricate microstructures containing compounds with interesting properties for optical and biomedical applications. Our investigations open the door to new applications in data storage, waveguides manufacturing, organic LEDs, optical circuitry and scaffold for bio-applications.
M. Kandyla. 2006. “Ultrafast dynamics of the laser-induced solid-to-liquid phase transition in aluminum”. Publisher's VersionAbstract
This dissertation reports the ultrafast dynamics of aluminum during the solid-toliquid phase transition of melting after excitation by an intense femtosecond laser pulse. Photoexcitation with intense femtosecond laser pulses is known to create a novel melting mechanism called non-thermal melting. This mechanism has been observed repeatedly in semiconductors, but not yet in metals. We investigate the melting mechanism of aluminum by monitoring the reflectivity response following excitation by an intense laser pulse. We employ an optical pumpprobe technique designed to measure broadband reflectivity across the visible spectrum with femtosecond time resolution. A non-thermal melting mechanism was proposed for aluminum by optical experiments that demonstrated transition of the optical properties from solid to liquid values within 500 fs after phototexcitation. This result was later challenged by electron diffraction experiments, which showed that the lattice loses long range order within 3.5 ps during photoinduced melting. This time scale implies conventional thermal melting. We find that the broadband optical properties during the solid-to-liquid phase transition in aluminum agree with the results obtained by the electron diffraction experiments. The transition of the broadband reflectivity from solid to liquid values is complete within 1.5 2 ps in our experiments, which is compatible with thermal melting. We dont observe time scales on the order of 500 fs. All the experimental evidence in this dissertation lead to the conclusion that the laser-induced, solid-to-liquid phase transition in aluminum is a thermal process.
S. Kumar, I. Zaharieva Maxwell, A. Heisterkamp, T. R. Polte, T. Lele, M. Salanga, E. Mazur, and D. E. Ingber. 2006. “Viscoelastic retraction of single living stress fibers and its impact on cell shape, cytoskeletal organization, and extracellular matrix mechanics.” Biophys. J., 90, Pp. 3762–3773. Publisher's VersionAbstract
Cells change their form and function by assembling actin stress fibers at their base and exerting traction forces on their extracellular matrix (ECM) adhesions. Individual stress fibers are thought to be actively tensed by the action of actomyosin motors and to function as elastic cables that structurally reinforce the basal portion of the cytoskeleton; however, these principles have not been directly tested in living cells, and their significance for overall cell shape control is poorly understood. Here we combine a laser nanoscissor, traction force microscopy, and fluorescence photobleaching methods to confirm that stress fibers in living cells behave as viscoelastic cables that are tensed through the action of actomyosin motors, to quantify their retraction kinetics in situ, and to explore their contribution to overall mechanical stability of the cell and interconnected ECM. These studies reveal that viscoelastic recoil of individual stress fibers after laser severing is partially slowed by inhibition of Rho-associated kinase and virtually abolished by direct inhibition of myosin light chain kinase. Importantly, cells cultured on stiff ECM substrates can tolerate disruption of multiple stress fibers with negligible overall change in cell shape, whereas disruption of a single stress fiber in cells anchored to compliant ECM substrates compromises the entire cellular force balance, induces cytoskeletal rearrangements, and produces ECM retraction many microns away from the site of incision; this results in large-scale changes of cell shape (> 5% elongation). In addition to revealing fundamental insight into the mechanical properties and cell shape contributions of individual stress fibers and confirming that the ECM is effectively a physical extension of the cell and cytoskeleton, the technologies described here offer a novel approach to spatially map the cytoskeletal mechanics of living cells on the nanoscale.
M. Vogt and E. Mazur. 2005. “The Interactive Learning Toolkit.” Phys. Teach., 43, Pp. 398–398. Publisher's VersionAbstract
Peer Instruction (PI) and Just-in-Time-Teaching (JITT) have been adopted widely in introductory science teaching because they have shown to increase both conceptual understanding of the material and problem solving skills. One of the main implementation hurdles, however, is the effort that goes into the preparation of questions and the management of student responses. To overcome this hurdle we have developed a number of Web-based resources.
N. Shen, D. Datta, C. B. Schaffer, P. LeDuc, D. E. Ingber, and E. Mazur. 2005. “Ablation of cytoskeletal filaments and mitochondria in cells using a femtosecond laser nanoscissor.” Mechanics and Chemistry of Biosystems, 2, Pp. 17–26. Publisher's VersionAbstract
Analysis of cell regulation requires methods for perturbing molecular processes within living cells with spatial discrimination on the nanometer- scale. We present a technique for ablating molecular structures in living cells using low-repetition rate, low-energy femtosecond laser pulses. By tightly focusing these pulses beneath the cell membrane, we ablate cellular material inside the cell through nonlinear processes. We selectively removed sub- micrometer regions of the cytoskeleton and individual mitochondria without altering neighboring structures or compromising cell viability. This nanoscissor technique enables non-invasive manipulation of the structural machinery of living cells with several-hundred-nanometer resolution. Using this approach, we unequivocally demonstrate that mitochondria are structurally independent functional units, and do not form a continuous network as suggested by some past studies. Keywords: Nanoscissor; nanosurgery; femtosecond laser; photodisruption; cytoskeleton; mitochondria
L. Tong, J. Lou, R. R. Gattass, S. He, X. Chen, L. Liu, and E. Mazur. 2005. “Assembly of silica nanowires on silica aerogels for microphotonic devices.” Nano Lett., 5, Pp. 259–262. Publisher's VersionAbstract
We report on the assembly of low-loss silica nanowires into functional microphotonics devices on a low-index non-dissipative silica aerogel substrate. Using this all-silica technique, we fabricated linear waveguides, waveguide bends and branch couplers. The devices are significantly smaller than existing comparable devices and have low optical loss, indicating that the all-silica technique presented here has great potential for future applications in optical communication, optical sensing, and high-density optical integration.
C. A. D. Roeser and E. Mazur. 2005. “Light-matter interactions on the femtosecond time scale.” In Frontiers of Optical Spectroscopy: Investigating Extreme Physical Conditions with Advanced Optical Techniques, edited by B. Di Bartolo and O. Forte, Pp. 29–54. Kluwer Academic Publishers. Publisher's VersionAbstract
The subject of electromagnetism in the presence of matter is both extensively studied and rich in diverse phenomena. It spans such topics as the quantization of the electromagnetic field to the semiclassical treatment of lightmatter interactions to the derivation of the Fresnel reflectivity formulas. Interest in femtosecond optics is rooted in nonlinear optical phenomena and in the complex electron and lattice dynamics that occur in a material following intense ultrashort-pulse irradiation. The experiments we discuss are concerned mainly with the latter and lie at the crossroad of femtosecond optics and materials science, so-called ultrafast materials science.
L. Tong, J. Lou, and E. Mazur. 2005. “Modeling of subwavelength-diameter optical wire waveguides for optical sensing applications.” In . Advanced Sensor Systems and Applications II. Publisher's VersionAbstract
Low-loss optical wave guiding along a subwavelength-diameter silica wire leaves a large amount of the guided field outside the solid core as evanescent wave and at the same time maintains the coherence of the light, making it possible to develop sensitive and miniaturized optical sensors for physical, chemical and biological applications. Here we introduce, for the first time to our knowledge, a scheme to develop optical sensors based on evanescent-wave- guiding properties of subwavelength-diameter wires. Optical wave guiding properties of these wires that are pertinent to a waveguide sensor, such as single-mode condition, evanescent field, Poynting vector and optical loss are investigated. By measuring the phase shift of the guided light, we propose a Mach-Zehnder-type sensor assembled with two silica wires. The sensitivity and size of the sensor are also estimated, which shows that, subwavelength- diameter silica wires are promising for developing optical sensors with high sensitivity and small size.
I. Zaharieva Maxwell, S. H. Chung, and E. Mazur. 2005. “Nanoprocessing of subcellular targets using femtosecond laser pulses.” Med. Laser Appl., 20, Pp. 193–200. Publisher's VersionAbstract
In this paper we review the work done in our laboratory on femtosecond laser dissection within single cells and living organisms. Precise dissection of biological material with ultrashort laser pulses requires a clear understanding of the pulse-energy dependence of the onset and extent of plasma-mediated ablation (i.e., the removal of material). We carried out a systematic study of the energy dependence of the plasma-mediated ablation of fluorescently-labeled subcellular structures in the cytoskeleton and in nuclei of fixed endothelial cells using femtosecond, near- infrared laser pulses focused through a high- numerical aperture objective lens (1.4 NA). We performed laser nanosurgery in live cells, where we ablated a single mitochondrion and severed cytoskeletal filaments without compromising the cell membrane or the cells viability. We also cut dendrites in living C. elegans without affecting the neighboring neurons. This nanoprocessing technique enables non-invasive manipulation of the structural machinery of cells and tissues down to several-hundred- nanometer resolution.
A. Heisterkamp, I. Zaharieva Maxwell, S. Kumar, J. M. Underwood, J. A. Nickerson, D. E. Ingber, and E. Mazur. 2005. “Nanosurgery in live cells using ultrashort laser pulses.” In . SPIE Photonics West. Publisher's VersionAbstract
We selectively disrupted the cytoskeletal network of fixed and live bovine capillary endothelial cell using ultrashort laser pulses. We image the microtubules in the cytoskeleton of the cultured cells using green fluorescent protein. The cells are placed on a custom-built inverted fluorescence microscope setup, using a 1.4 NA oil-immersion objective to both image the cell and focus the laser radiation into the cell samples. The laser delivers 100-fs laser pulses centered at 800 nm at a repetition rate of 1 kHz; the typical energy delivered at the sample is 15nJ. The fluorescent image of the cell is captured with a CCD-camera at one frame per second. To determine the spatial discrimination of the laser cutting we ablated microtubules and actin fibers in fixed cells. At pulse energies below 2 nJ we obtain an ablation size of 200 nm. This low pulse energy and high spatial discrimination enable the application of this technique to live cells. We severed a single microtubule inside the live cells without affecting the cells viability. The targeted microtubule snaps and depolymerizes after the cutting. This nanosurgery technique will further the understanding and modeling of stress and compression in the cytoskeletal network of live cells.
G. Thomas Svacha, E. Mazur, and L. Tong. 2005. “Nanowiring Light.” In . Optical Fiber Communication Conference 2005. Publisher's VersionAbstract
Recent advances in the fabrication and manipulation of sub-wavelength optical fibers provide new methods for building chemical and biological sensors, generating supercontinuum light by nonlinear pulse propagation, and constructing microphotonic components and devices.
M. Kamata, M. Obara, R. R. Gattass, L. R. Cerami, and E. Mazur. 2005. “Optical vibration sensor fabricated by femtosecond laser micromachining.” Appl. Phys. Lett., 87, Pp. 051106-1–051106-3. Publisher's VersionAbstract
We fabricated an optical vibration sensor using a high-repetition rate femtosecond laser oscillator. The sensor consists of a single straight waveguide written across a series of three pieces of glass. The central piece is mounted on a suspended beam to make it sensitive to mechanical vibration, acceleration, or external forces. Displacement of the central piece is detected by measuring the change in optical transmission through the waveguide. The resulting sensor is small, simple, and requires no alignment. The sensor has a linear response over the frequency range 20 Hz 2 kHz, can detect accelerations as small as 0.01 m/s2, and is nearly temperature independent.
R. R. Gattass, L. R. Cerami, and E. Mazur. 2005. “Optical waveguide fabrication for integrated photonic devices.” In . Nano photonics and functional device technology. Publisher's VersionAbstract
The dynamic nature of future optical networks requires high levels of integration, fast response times, and adaptability of the optical components. Laser micromachining circumvents the limitations of planar integration, allowing both three-dimensional integration and dense packaging of optical devices without alignment requirements. Femtosecond micromachining enables the analog of circuit printing by wiring light between photonic devices in addition to printing the actual photonic device into a single or multiple substrates. Femtosecond laser oscillator-only micromachining has several advantages over amplified femtosecond laser micromachining: easy control over the size of the structures without changing focusing, polarization-independent structures, lower initial investment cost and higher-speed manufacturing. In this paper we review recent results obtained in the field of femtosecond micromachining. Keywords: Femtosecond, micromachining, nonlinear absorption.
A. Heisterkamp, I. Zaharieva Maxwell, E. Mazur, J. M. Underwood, J. A. Nickerson, S. Kumar, and D. E. Ingber. 2005. “Pulse energy dependence of subcellular dissection by femtosecond laser pulses.” Opt. Express, 13, Pp. 3690–3696. Publisher's VersionAbstract
Precise dissection of cells with ultrashort laser pulses requires a clear understanding of how the onset and extent of ablation (i.e., the removal of material) depends on pulse energy. We carried out a systematic study of the energy dependence of the plasma-mediated ablation of fluorescently-labeled subcellular structures in the cytoskeleton and nuclei of fixed endothelial cells using femtosecond, near-infrared laser pulses focused through a high- numerical aperture objective lens (1.4 NA). We find that the energy threshold for photobleaching lies between 0.9 and 1.7 nJ. By comparing the changes in fluorescence with the actual material loss determined by electron microscopy, we find that the threshold for true material ablation is about 20% higher than the photobleaching threshold. This information makes it possible to use the fluorescence to determine the onset of true material ablation without resorting to electron microscopy. We confirm the precision of this technique by severing a single microtubule without disrupting the neighboring microtubules, less than 1 m away.
E. Mazur. 2005. “Qualitative versus quantitative reasoning: Are we teaching the right thing?” In Motivating Science: Science communication from a philosophical, educational and cultural perspective, edited by Nigel Sanitt, Pp. 139–141. The Panteneto Press. Publisher's VersionAbstract
This paper is a reprinting of an article that first appeared in Optics and Photonics News in 1992. The article deals with the eye-opening experience that made me completely change my approach to teaching.
M. A. Sheehy, L. Winston, J. E. Carey, C. M. Friend, and E. Mazur. 2005. “Role of the background gas in the morphology and optical properties of laser-microstructured silicon.” Chem. Mater., 17, Pp. 3582–3586. Publisher's VersionAbstract
We irradiate silicon with a train of femtosecond pulses in the presence of SF6, H2S, H2, SiH4, and a mixture of Ar and SF6 in order to analyze the role of the background gas in determining the morphology and the optical properties of the resultant surfaces. We discuss factors that affect the surface morphology created during irradiation and show that the presence of sulfur in these gases is important in creating sharp microstructures. We also show that the presence of sulfur is necessary to create the near-unity absorptance for both above-band and below-band gap radiation (0.25 2.5 micrometer) by silicon; only samples with sulfur concentrations higher than 0.6% absorb 95% for above-band gap radiation and have a flat, featureless absorptance of 90% for below-band gap radiation. KEYWORDS silicon, infrared absorptance, laser materials processing, microstructures, sulfur doping, femtosecond laser irradiation, RBS, elemental semiconductors
L. Tong, J. Lou, Z. Ye, G. Thomas Svacha, and E. Mazur. 2005. “Self-modulated taper drawing of silica nanowires.” Nanotechnology, 16, Pp. 1445–1448. Publisher's VersionAbstract
We report a self-modulated taper-drawing process for fabricating silica nanowires with diameters down to 20 nm. Long amorphous silica nanowires obtained with this top-down approach present extraordinary uniformities that have not been achieved by any other means. The measured sidewall roughness of the wires goes down to the intrinsic value of 0.2 nm, along with a diameter uniformity better than 0.1%. The wires also show high strength and pliability for patterning under optical microscopes. The ability to prepare and manipulate highly uniform silica nanowires map open up new opportunities for studying and using low-dimensional silica material on a nanometer scale.
L. Tong and E. Mazur. 2005. “Subwavelength-diameter silica wires for microscale optical components.” In . SPIE Photonics West 2005. Publisher's VersionAbstract
Subwavelength-diameter silica wires fabricated using a taper-drawing approach exhibit excellent diameter uniformity and atomic-level smoothness, making them suitable for low-loss optical wave guiding from the UV to the near-infrared. Such air-clad silica wires can be used as single-mode waveguides; depending on wavelength and wire diameter, they either tightly confine the optical fields or leave a certain amount of guided energy outside the wire in the form of evanescent waves. Using these wire waveguides as building blocks we assembled microscale optical components such as linear waveguides, waveguide bends and branch couplers on a low-index, non- dissipative silica aerogel substrate. These components are much smaller than comparable existing devices and have low optical loss, indicating that the wire-assembly technique presented here has great potential for developing microphotonics devices for future applications in a variety of fields such as optical communication, optical sensing and high-density optical integration. Keywords: Subwavelength, silica, nanowire, microphotonics, nanophotonics, optical components