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A Charles Townes Legacy

A Charles Townes Legacy

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A Charles Townes Legacy

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  1. A Charles Townes Legacy Elsa Garmire Sydney E. Junkins Professor of Engineering Sciences Thayer School of Engineering Dartmouth College Townes’ PhD student (1962-1965)

  2. Dartmouth College An Ivy League School in New England Maine Dartmouth Boston

  3. Dartmouth College 4000 undergraduates (# men = # women) Graduate school in the sciences Medical school (1797 – fourth oldest) Tuck Business School (1900 – the first) Thayer School of Engineering – (1867) the oldest engineering graduate school

  4. Thayer School of Engineering • No separate departments • Synergy across expertise from different engineering disciplines • Teamwork and entrepreneurship are encouraged • Opportunity to take courses with Tuck Business School professors • Opportunity for collaborative research with Dartmouth Medical School • Opportunity for collaborative research with the Science Departments • Graduate Enrollment: 47 PhD students 20 MS students (with research thesis) 60 Masters in Engineering Management (with industrial project) • Undergraduate Enrollment: 112 juniors and seniors • 44 Bachelor in Engineering students (5th year for ABET credit)

  5. Thayer School Impact Areas • Engineering in Medicine Addresses today's technology-driven healthcare system. Advances depend in the technical side of patient care. Collaboration between Dartmouth engineers, medical researchers, and clinicians speeds testing and implementation of technological advances. • Energy Technologies Crucial to the future stability of human society. Research includes a range of projects—from biomass processing to power electronics optimization. Investigators synthesize ideas and expertise from biochemical and chemical, electrical, and materials engineering as well as physics, chemistry, and microbiology. • Complex Systems Systems permeate technology in the 21st century. The goal is to analyze and design complex systems so that their behavior can be predicted and controlled. Dartmouth engineers are working together to meet the challenges of large, complex engineered systems such as computer networks, social networks, smart robots, living cells, energy infrastructure, and the near-Earth space environment. Source:

  6. Optics and Lasers at Thayer • Instrumentation A new type of non-contact optical sensor of vibration and other motion detection. New designs for free space optical communications, both for transmission through the atmosphere and through water. Active and passive waveguides for optical signal processing, telecommunications, optical data storage, and other applications. Fiber optics devices such as tunable filters and fiber lasers. (Faculty contact: Garmire) • Femtosecond pulses being transmitted through water sustain much less loss than longer pulses, particularly at long distances. Femto-second pulses are used to create terahertz radiation, whose transmission through a variety of media is being investigated. (Faculty contacts: Osterberg, Garmire) • Nonlinear optical studies investigate second- and third-order nonlinear effects in optical glass fibers, thin films, and semiconductor structures. A novel project is ultrafast pulse shaping of wavelets for high bandwidth fiber-optic free-space systems. Nonlinear devices are being investigated for high-speed image processing and for time-to-wavelength conversion for communication systems. (Faculty contact: Garmire, Osterberg) Source:

  7. Other optics at Thayer Magneto-optics: production and studies of magnetic vortex states in ring structures, and the coupling between them. Thin dielectric films enhance the magneto-optic Kerr effect signal. Interactions of proximal rings and symmetry effects. (Faculty contact: Gibson) Nanophotonics: interaction of light with sub-micron structures and nano-textured materials. Molecular Imprint Polymers (MIPS) with surface plasmon resonance and capacitive measurements for chemical sensing. Applications include the detection of pollutants, chemical residues and biological compounds indicative of early-stage cancer. ZnO nanopillars for photonic bandgap engineered devices. (Faculty contact: Gibson) Microelectromechanical Systems (MEMS) -- includes modeling, fabrication, and testing of the following: • untethered mobile micro-robots, and interactions between small swarms of micro-robots; • stress engineering of out-of-plane electromechanical structures such as microturbines; • integrated micro-inductors for power electronics; • high sensitivity optical sensors; • binary optical devices. MEMS device fabrication takes place in Thayer School's microengineering lab, a Class 100 clean room facility. (Faculty contact: Levey)

  8. Biomedical Imaging Research at Thayer Fluorescence imaging to track molecular signals and tags in tissue, especially cancer tumors in vivo and vascular diseases. Also coupled to magnetic resonance imaging and computed tomography imaging. Evaluating their response to therapy. (Faculty contact: Pogue) Dynamic multimodal imaging (DMI), a framework for reconstructing images of neural and vascular dynamics in the human brain. DMI combines concurrently recorded data from multiple imaging modalities such as electroencephalography, near-infrared spectroscopy, and functional magnetic resonance imaging. (Faculty contact: Diamond) Image-guided neurosurgery gives the surgeon the ability to track instruments in reference to subsurface anatomical structures. Using clinical brain displacement data, a computational technique is being developed to model the brain deformation that typically occurs during neurosurgery. The resulting deformation predictions are then used to update the patient's preoperative magnetic resonance images seen by the surgeon during the procedure. (Faculty contact: Paulsen) Near-infrared imaging (NIR) to quantify blood and water concentrations in tissue, as well as structural and functional parameters. NIR spectroscopy can be combined into standard imaging systems to provide additional information for breast cancer detection and diagnosis. Work is ongoing to improve techniques for better image reconstruction, display and integration with magnetic resonance imaging (MRI) and computed tomography (CT) imaging. (Faculty contacts: Pogue, Paulsen, Jiang) Non-linear image reconstruction techniques: Excitation-induced measurements from each instrument are compared with calculations to compute images. As images are updated in a non-linear iterative process, important features become more apparent. The computational core of the breast imaging project works synergistically to improve our fundamental understanding of these mathematical systems to improve overall image quality and resolution. These processes have been developed for both 2D and 3D geometries in each modality and are being expanded to exploit emerging parallel computing capabilities. (Faculty contacts: Paulsen, Meaney)

  9. Other lasers and optics biomedical research Photodynamic therapy for cancer, age-related blindness, pre-malignant transformation or psoriasis. Administration of a photosensitizing agent, together with the application of moderate intensity light activates the molecules to produce local doses of singlet oxygen. Developing dosimetry instrumentation and software, fluorescence tomography imaging to sense drug localization, and assaying treatment effects in experimental cancers. (Faculty contacts: Pogue, Hoopes) Therapy monitoring using imaging modalities. These include: • near-infrared imaging of brain tissue; • near-infrared spectroscopy for diagnosing peripheral vascular disease; • electrical impedance spectroscopy for radiation therapy monitoring; • magnetic resonance elastography for detecting brain or prostate lesions; to follow the progression of diabetic damage in the foot; • microwave imaging spectroscopy for hyperthermia therapy monitoring, brain imaging, and detection of early-stage osteoporosis. (Faculty contacts: Paulsen, Meaney) Clinical optical-electric probes are being developed for noninvasive simultaneous measurement of blood oxygenation and electrical potential changes associated with brain activity. (Faculty contact: Diamond) Label free genome sequencing to "read" the sequence in a single DNA molecule in a massively-parallel fashion. The technology combines concepts of single nucleotide addition sequencing, near field optics, single molecule force spectroscopy, and microfluidics. (Faculty contact: Shubitidze)

  10. A Townes Legacy Lasers that are everywhere eg. the laser pointer

  11. Laser Printer Laser diode

  12. CD/DVD Players Laser diode Lens CD

  13. The Internet Optical Fiber Multiple Optical Fibers Laser Diode Laser light is focused into a single fiber

  14. Product ScannersSupermarkets Laser scans across bar code. Reflected light, modulated by the bar code, is detected, and data is entered in a computer. Photo-Detector Hand scanner

  15. Hologram for Security Credit Card, ID Cards, Advertising November, 1985

  16. LASIK procedure Laser Light Laser re-shapes cornea after flap (conjunctiva) is lifted

  17. History:From Quantum Electronics to Laser • Combine physics of “quantum” with electrical engineering of “electronics” • Developed after WWII • Microwave devices, originating from radar • Charles Townes: designed/built radars then studied microwave spectroscopy

  18. Stimulated Emission: the source of gain Einstein, 1916 Absorption Spontaneous emission excited state photon ground state More light leaves than came in Stimulated emission

  19. Charles Townes and the Maser(with post-doc Jim Gordon) about 1953 Townes Gordon Maser Maser requires gain and feedback Microwave Amplification by Stimulated Emission of Radiation Gain requires Stimulated emission Result: Oscillation

  20. Oscillation from gain and feedbackExample: sound systems Result: a shriek!!

  21. The Laser Idea (1958) Charles Townes and Art Schawlow Atoms as gain medium gain Mirrors for feedback Townes Schawlow Argon Laser Beam ~ 1963

  22. The First Ruby Laser: 1960Ted Maiman at Hughes Aircraft Flash Lamp Ruby Gain: ruby rod excited by light from a helical flash lamp Mirrors: silver films on the end of the ruby rod

  23. The First Gas Laser – Helium/Neon(Inventors: Javan, Bennett and Herriott) 1961 Gain: helium-neon gas discharge Mirrors: Special high-reflectivity multi-layer films

  24. What do today’s lasers look like?They can be small … Laser diodes are tiny chips of semiconductor A commercial package Laser_diode_chip.jpg/300px-Laser_diode_chip.jpg The laser diode chip Used in CD players, laser printers, and fiber optic systems

  25. They can be large: National Ignition Facility The world’s largest laser, being built now A person View of Laser Bay 1 from the transport spatial filter, containing 96 laser beams. In all, 192 beams of beampath are complete: 1.8 Million Joules of light. To ignite nuclear fusion Lawrence Livermore National Laboratories

  26. Capabilities of Lasersgain + feedback = stimulated emission Coherent (All photons behave in an identical manner) directional focus to small point interfere Ultra-stable single frequency or color (1 part in 1015) Ultra-high speed communications 1012 bps Ultra-longdistance communications (to the moon) Ultra-short pulses 3 attoseconds 10-15 sec Ultra-high power (for 10-12 s) >1018 W Ultra-small size 10-12 cm3

  27. Coherence All stimulated emission photons are identical, like soldiers Spontaneous emission photons are random U.S. Soldiers, World War II Time’s Square New Year’s Eve speckle

  28. Directional: Laser beams reach the moon and back Time delay of pulses gives distance Lasers beams travel in straight lines

  29. Focus to a small point: Lasers drill holes smaller than human hair Hole Size ~50 µm Hole size ~ 2 µm Human Hair Sizes to scale Optical Fiber

  30. Interference

  31. Miniature Commercial Interferometers Reflective surface Measurement of distance, motion, non-destructive testing Non-contact measurement

  32. Ultrastable: LIGO Interferometerfor measuring gravity waves near Baton-Rouge Louisana – two arms, each 2.5 mi long

  33. Monochromatic: Ring Laser Gyro Sagnac Effect One gyro Honeywell’s 3-gyro system Clockwise vs. Counterclockwise Frequency Difference determines rotation

  34. Interference: Holograms

  35. Research at MIT: 1962-1966 Townes moved to MIT in the fall, 1961 Existing lasers: Ruby laser (pulsed, high power), HeNe (continuous, monochromatic, invisible) Fundamental research: Michelson-Morley experiment with HeNe (looking for aether). Nonlinear Optics with the ruby laser

  36. Lasers enabled Nonlinear Optics >Second Harmonic Generation< Laser beam enters a crystal of ADP as red light and emerges as blue Electron orbitals distort nonlinearly -- non-linear polarization

  37. 2w0 w0

  38. w1 + w2 2w1 2w2

  39. Light Pulse Electrical Signal w0 - w0

  40. 7670 A 6943 A SRS Laser wL - W wL Representation of the spectrum Energy difference between photons is given up to molecular vibrations W

  41. MIT Laser Laboratory, 1962-65 Stimulated Raman Scattering

  42. My PhD research: Nonlinear Optics Stimulated Raman Scattering Laser  Stokes + molecular vibration A nonlinear process that introduces new wavelengths by involving molecular vibrations Stokes beam wL + W wL - W Anti-Stokes Stokes Laser beam Two Laser Photons wL wL Molecular vibration + Laser  anti-Stokes Anti-Stokes radiates in rings driven by Stokes in corresp. ring

  43. First explanation of multi-photon processes in Stimulated Raman Scattering. First explanation of anti-Stokes and several orders of Stokes First explanation of angular emission of anti-Stokes

  44. Proof of coherent molecular vibration theory:Chiao, Stoicheff and Townes: SRS in calcite

  45. My Experimental SRS Data in Liquids Most of my results “Stokes” “Anti-Stokes” Agrees with theory Ultimately explained by the presence of self-trapping

  46. Townes’ New Idea:Stimulated Brillouin Scattering Experiments in quartz with Chiao and Stoicheff (PRL May 1964)

  47. My Data on Stimulated Brillouin ScatteringAppl Phys. Lett. August, 1964 experiments in liquids Q-switch SBS mirror gain Fabry-Perot Interferogram SBS Several orders observed Laser

  48. Nonlinear Refractive Index Enables Light to Form its Own Waveguide Spatial Soliton Threshold Power is Required.

  49. Self-trapping of Optical Beams Laser Increasing Laser Power Self- trapping No Pinhole Garmire, et. al. PRL, 1966

  50. How they looked then (1966) Charles Townes Frances Townes