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 Optical coherence tomography (2)
 Nonlinear optics (2)
 Plasmas (2)
 Thin films (2)
 Photon density waves (2)

 Frequencydomain photon migration (2)
 Angular scattering (1)
 Harmonic generation (1)
 Indeterminancy (1)
 Boundary conditions (1)
 Coherence and statistical optics (1)
 Interferometry (1)
 FranzKeldysh effect (1)
 Depletion field (1)
 Index profile (1)
 Laser Cooling (1)
 Acoustooptical effects (1)
 Ellipticity (1)
 Brillouin effect (1)
 Channel correlation (1)
 Elemental semiconductors (1)
 Imaging systems (1)
 Emission spectra (1)
 Kshell emission spectrum (1)
 Copper (1)
 Code V (1)
 Infrared spectra (1)
 Indium phosphides (1)
 Frequencydomain Photon Migration (1)
 Frequencydomain techniques (1)
Articles 1  23 of 23
FullText Articles in Physics
How Much Can Guided Modes Enhance Absorption In Thin Solar Cells?, Peter N. Saeta, Vivian E. Ferry, Domenico Pacifici, Jeremy N. Munday, Harry A. Atwater
How Much Can Guided Modes Enhance Absorption In Thin Solar Cells?, Peter N. Saeta, Vivian E. Ferry, Domenico Pacifici, Jeremy N. Munday, Harry A. Atwater
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Absorption enhancement in thin metalbacked solar cells caused by dipole scatterers embedded in the absorbing layer is studied using a semianalytical approach. The method accounts for changes in the radiation rate produced by layers above and below the dipole, and treats incoherently the subsequent scattering of light in guided modes from other dipoles. We find large absorption enhancements for strongly coupled dipoles, exceeding the ergodic limit in some configurations involving lossless dipoles. An antireflectioncoated 100nm layer of aSi:H on Ag absorbs up to 87% of incident abovegap light. Thin layers of both strong and weak absorbers show similar strongly ...
Designs And Optical Tests Of Thermal Links For An Optical Refrigerator, John Parker, David Mar, Steven Von Der Porten, John Hankinson, Kevin Byram, Chris Lee, Kai Mayeda, Richard C. Haskell, Qimin Yang, Scott R. Greenfield, Richard I. Epstein
Designs And Optical Tests Of Thermal Links For An Optical Refrigerator, John Parker, David Mar, Steven Von Der Porten, John Hankinson, Kevin Byram, Chris Lee, Kai Mayeda, Richard C. Haskell, Qimin Yang, Scott R. Greenfield, Richard I. Epstein
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Dielectric mirror leakage at large angles of incidence limits the effectiveness of solid state optical refrigerators due to reheating caused by photon absorption in an attached load. In this paper, we present several thermally conductive link solutions to greatly reduce the net photon absorption. The Los Alamos Solid State Optical Refrigerator (LASSOR) has demonstrated cooling of a Yb/sup 3+/ doped ZBLANP glass to 208 K. We have designed optically isolating thermal link geometries capable of extending cooling to a typical heat load with minimal absorptive reheating, and we have tested the optical performance of these designs. A surrogate source ...
Role Of Beat Noise In Limiting The Sensitivity Of Optical Coherence Tomography, Richard C. Haskell, David Liao, Adam E. Pivonka, Tera L. Bell, Brendan R. Haberle, Barbara M. Hoeling, Daniel C. Petersen
Role Of Beat Noise In Limiting The Sensitivity Of Optical Coherence Tomography, Richard C. Haskell, David Liao, Adam E. Pivonka, Tera L. Bell, Brendan R. Haberle, Barbara M. Hoeling, Daniel C. Petersen
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The sensitivity and dynamic range of optical coherence tomography (OCT) are calculated for instruments utilizing two common interferometer configurations and detection schemes. Previous researchers recognized that the performance of dualbalanced OCT instruments is severely limited by beat noise, which is generated by incoherent light backscattered from the sample. However, beat noise has been ignored in previous calculations of Michelson OCT performance. Our measurements of instrument noise confirm the presence of beat noise even in a simple Michelson interferometer configuration with a single photodetector. Including this noise, we calculate the dynamic range as a function of OCT light source power, and ...
Harmonic Generation In Thin Films And Multilayers, William S. Kolthammer '04, Dustin Barnard '03, Nicole Carson, Aaron D. Edens '00, Nathan A. Miller '01, Peter N. Saeta
Harmonic Generation In Thin Films And Multilayers, William S. Kolthammer '04, Dustin Barnard '03, Nicole Carson, Aaron D. Edens '00, Nathan A. Miller '01, Peter N. Saeta
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A general method for computing harmonic generation in reflection and transmission from planar nonmagnetic multilayer structures is described. The method assumes plane waves and treats harmonic generation in the parametric approximation. The method is applied in studying the second and thirdharmonic generation properties of thin crystal silicon layers surrounded by thermal oxide. Most independent components of the nonlinear susceptibility tensor have unique signatures with silicon layer thickness d, allowing their strength to be determined in principle by measuring harmonic generation as a function of d. Surface and bulk contributions to thirdharmonic generation are cleanly distinguished, with the bulk signal dominating ...
XRay Generation From Metal Targets Coated With WavelengthScale Spheres, D. R. Symes, H. A. Sumeruk, I. V. Churina, Thomas D. Donnelly, J. Landry, T. Ditmire
XRay Generation From Metal Targets Coated With WavelengthScale Spheres, D. R. Symes, H. A. Sumeruk, I. V. Churina, Thomas D. Donnelly, J. Landry, T. Ditmire
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Xray yield measurements from targets coated with wavelengthscale spheres are compared with measurements from polished targets. Evidence for a hotter resonant electron temperature due to field enhancements from Mie resonances in the spheres is investigated.
Femtosecond Spectrotemporal MagnetoOptics, J.Y. Bigot, L. Guidoni, E. Beaurepaire, Peter N. Saeta
Femtosecond Spectrotemporal MagnetoOptics, J.Y. Bigot, L. Guidoni, E. Beaurepaire, Peter N. Saeta
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A new method to measure and analyze the time and spectrally resolved polarimetric response of magnetic materials is presented. It allows us to study the ultrafast magnetization dynamics of a CoPt_{3} ferromagnetic film. The analysis of the pumpinduced rotation and ellipticity detected by a broad spectrum probe beam shows that magnetooptical signals predominantly reflect the spin dynamics in ferromagnets.
Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly
Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly
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By numerically solving the nonlinear field equations, we simulate secondharmonic generation by laser pulses within a nonlinear medium without making the usual slowlyvaryingamplitude approximation, an approximation which may fail when laser pulses of moderate intensity or ultrashort duration are used to drive a nonlinear process. Under these conditions we show that a backwardtraveling, secondharmonic wave is created, and that the magnitude of this wave is indicative of the breakdown of the slowlyvaryingamplitude approximation. Conditions necessary for experimental detection of this wave are discussed.
Distinguishing Surface And Bulk Contributions To ThirdHarmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01
Distinguishing Surface And Bulk Contributions To ThirdHarmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01
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We report measurements of thirdharmonic generation from ultrathin crystalline silicon layers of gradually varying thickness. Both the angular and thickness dependence of the thirdharmonic light generated in transmission at normal incidence are consistent with negligible surface contribution to thirdharmonic generation in silicon, even under tight focusing. This work illustrates a method for distinguishing surface and bulk contributions to harmonic generation.
An Optical Coherence Microscope For 3Dimensional Imaging In Developmental Biology, Barbara M. Hoeling, Andrew D. Fernandez, Richard C. Haskell, Eric Huang, Whittier R. Myers, Daniel C. Petersen, Sharon E. Ungersma, Ruye Wang, Mary E. Williams, Scott E. Fraser
An Optical Coherence Microscope For 3Dimensional Imaging In Developmental Biology, Barbara M. Hoeling, Andrew D. Fernandez, Richard C. Haskell, Eric Huang, Whittier R. Myers, Daniel C. Petersen, Sharon E. Ungersma, Ruye Wang, Mary E. Williams, Scott E. Fraser
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An optical coherence microscope (OCM) has been designed and constructed to acquire 3dimensional images of highly scattering biological tissue. Volumerendering software is used to enhance 3D visualization of the data sets. Lateral resolution of the OCM is 5 mm (FWHM), and the depth resolution is 10 mm (FWHM) in tissue. The design tradeoffs for a 3D OCM are discussed, and the fundamental photon noise limitation is measured and compared with theory. A rotating 3D image of a frog embryo is presented to illustrate the capabilities of the instrument.
Probing Nonequilibrium Electron Distributions In Gold By Use Of Second Harmonic Generation, K. L. Moore '99, Thomas D. Donnelly
Probing Nonequilibrium Electron Distributions In Gold By Use Of Second Harmonic Generation, K. L. Moore '99, Thomas D. Donnelly
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Secondharmonic radiation is generated at a gold surface by use of a laser pulse that is varied in duration from 14 to 29 fs and in intensity from 10^{9} to 10^{11}W/cm^{2} . At laser intensities below 10^{10}W/cm^{2} , the secondharmonic signal has the expected quadratic dependence on pumplaser intensity; however, at higher intensities, the dependence is supraquadratic. This difference arises because the leading edge of the laser pulse interacts significantly with the gold electrons to create a nonequilibrium, photoexcited distribution. The secondharmonic generation process occurs before electron–electron or electron–phonon collisions can ...
Ultrafast Phenomena: A Laboratory Experiment For Undergraduates, Thomas D. Donnelly, Carl Grossman
Ultrafast Phenomena: A Laboratory Experiment For Undergraduates, Thomas D. Donnelly, Carl Grossman
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We present a set of experiments that introduce students to ultrafast science. We discuss the relationship between the description of an ultrashort laser pulse in the frequency domain and the time domain. Using experimental results we demonstrate that this relationship is constrained by the lower limit of the Heisenberg uncertainty principle. Students carrying out the experiments will become familiar with ultrafast techniques, such as autocorrelation and laser cavity design, as well as various other concepts such as dispersion, Fourier transformation, interference, and nonlinear optics.
Experimental And Theoretical Investigation Of Recombination Pumped XRay Lasers Driven By HighIntensity, Short Pulse Lasers, Thomas D. Donnelly, L. Da Silva, R. W. Lee, S. Mrowka, M. Hofer, R. W. Falcone
Experimental And Theoretical Investigation Of Recombination Pumped XRay Lasers Driven By HighIntensity, Short Pulse Lasers, Thomas D. Donnelly, L. Da Silva, R. W. Lee, S. Mrowka, M. Hofer, R. W. Falcone
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We have experimentally investigated a recombinationpumped softxray laser on a Lymanα transition (135 Å) of hydrogenlike lithium. Furthermore, we have modeled the dynamics of this system, including the effects of the multipeaked electron distribution function that is obtained from the sequential, opticalfield ionization of an atom. We compare the predictions of our model and our experimental results.
Optical Measurements Of The Core Radius Of HighΔ Fibers With 1Nm Resolution, Peter N. Saeta
Optical Measurements Of The Core Radius Of HighΔ Fibers With 1Nm Resolution, Peter N. Saeta
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An optical technique for measuring the core radius of highΔ optical fibers is described. Variations in the core radius of stepindex fibers can be measured down to a scale of 1 nm.
Portable, HighBandwidth FrequencyDomain Photon Migration Instrument For Tissue Spectroscopy, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg
Portable, HighBandwidth FrequencyDomain Photon Migration Instrument For Tissue Spectroscopy, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg
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We describe a novel frequencydomain photon migration instrument employing direct diode laser modulation and avalanche photodiode detection, which is capable of noninvasively determinating the optical properties of biological tissues in near real time. An infinite medium diffusion model was used to extract absorption and transport scattering coefficients from 300kHz to 800MHz photondensity wave phase data. Optical properties measured in tissuesimulating solutions at 670 nm agreed to within 10% of those expected.
LowFrequency Line Shapes In Guided AcousticWave Brillouin Scattering, Benjamin I. Greene, Peter N. Saeta
LowFrequency Line Shapes In Guided AcousticWave Brillouin Scattering, Benjamin I. Greene, Peter N. Saeta
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Guided acoustic‐wave Brillouin scattering (GAWBS) measurements were performed on 20‐cm lengths of optical fibers with particular attention focused on the lowest lying resonance. In 125‐μm‐diam silica fibers, this resonance was observed to occur at ~22 MHz and have a line shape which varied erratically from sample to sample. Significant line shape fluctuations were evident even between sequential samples from the same fiber spool. We speculate that the observed effects are attributable to 0.010.1 μm distributed geometric deviations from a perfect cylinder.
Boundary Conditions For The Diffusion Equation In Radiative Transfer, Richard C. Haskell, Lars O. Svaasand, TsongTseh Tsay, TiChen Feng, Matthew S. Mcadams, Bruce J. Tromberg
Boundary Conditions For The Diffusion Equation In Radiative Transfer, Richard C. Haskell, Lars O. Svaasand, TsongTseh Tsay, TiChen Feng, Matthew S. Mcadams, Bruce J. Tromberg
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Using the method of images, we examine the three boundary conditions commonly applied to the surface of a semiinfinite turbid medium. We find that the imagecharge configurations of the partialcurrent and extrapolatedboundary conditions have the same dipole and quadrupole moments and that the two corresponding solutions to the diffusion equation are approximately equal. In the application of diffusion theory to frequencydomain photonmigration (FDPM) data, these two approaches yield values for the scattering and absorption coefficients that are equal to within 3%. Moreover, the two boundary conditions can be combined to yield a remarkably simple, accurate, and computationally fast method for ...
XRays From Microstructured Targets Heated By Femtosecond Lasers, S. P. Gordon, Thomas D. Donnelly, A. Sullivan, H. Hamster, R. W. Falcone
XRays From Microstructured Targets Heated By Femtosecond Lasers, S. P. Gordon, Thomas D. Donnelly, A. Sullivan, H. Hamster, R. W. Falcone
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We have demonstrated efficient conversion of ultrashortpulse laser energy to x rays with energies above 1 keV, using laserproduced plasmas generated on a variety of microstructured surfaces. Lithographically produced grating targets generated 0.1 mJ of kiloelectronvolt x rays, and porous gold and aluminum targets emitted 1 mJ. This represents an improvement of a factor of 100 over flat targets. The Kshell emission spectrum of porous aluminum was composed primarily of heliumlike spectral lines.
Optical Properties Of Human Uterus At 630 Nm, Steen J. Madsen, Bruce J. Tromberg, Yona Tadir, Pius Wyss, Lars O. Svaasand, Richard C. Haskell
Optical Properties Of Human Uterus At 630 Nm, Steen J. Madsen, Bruce J. Tromberg, Yona Tadir, Pius Wyss, Lars O. Svaasand, Richard C. Haskell
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The optical properties of normal and fibriotic human uteri were determined using frequencydomain and steadystate techniques .
FrequencyDomain Photon Migration In Turbid Media, Bruce J. Tromberg, Steen J. Madsen, Curtis Chapman, Lars O. Svaasand, Richard C. Haskell
FrequencyDomain Photon Migration In Turbid Media, Bruce J. Tromberg, Steen J. Madsen, Curtis Chapman, Lars O. Svaasand, Richard C. Haskell
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An analytical model is presented for the propagation of diffuse photon density waves in turbid media. The frequency and wavelengthdependence of photon density waves are measured using Frequencydomain Photon Migration (FDPM). Media optical properties, including absorption, transport, and fluorescence relaxation times are calculated from experimental results.
Short Terahertz Pulses From Semiconductor Surfaces: The Importance Of Bulk Difference‐Frequency Mixing, Peter N. Saeta, Benjamin I. Greene, Shun Lien Chuang
Short Terahertz Pulses From Semiconductor Surfaces: The Importance Of Bulk Difference‐Frequency Mixing, Peter N. Saeta, Benjamin I. Greene, Shun Lien Chuang
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The crystallographic orientation dependence of the far‐infrared (FIR) light generated at the (001) surface of a zincblende semiconductor is shown to derive principally from bulk difference‐frequency mixing. A strong modulation is observed for 1‐GW/cm^{2} pulses on InP, which demonstrates that the radiated FIR wave produced by bulk optical rectification is comparable to that generated by the transport of photoinjected carriers. Using the bulk rectification light as a clock, we show that more than 95% of the light produced from an InP (111) crystal by 100‐fs, 100‐μJ pulses is generated in a time shorter ...
Properties Of Photon Density Waves In MultipleScattering Media, Bruce J. Tromberg, Lars O. Svaasand, TsongTseh Tsay, Richard C. Haskell
Properties Of Photon Density Waves In MultipleScattering Media, Bruce J. Tromberg, Lars O. Svaasand, TsongTseh Tsay, Richard C. Haskell
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Amplitudemodulated light launched into multiplescattering media, e.g., tissue, results in the propagation of density waves of diffuse photons. Photon density wave characteristics in turn depend on modulation frequency (ω) and media optical properties. The damped spherical wave solutions to the homogeneous form of the diffusion equation suggest two distinct regimes of behavior: (1) a highfrequency dispersion regime where density wave phase velocity V_{p} has a ω dependence and (2) a lowfrequency domain where V_{p} is frequency independent. Optical properties are determined for various tissue phantoms by fitting the recorded phase (Φ) and modulation (m) response to simple ...
Optical Rectification At Semiconductor Surfaces, Shun Lien Chuang, Stefan SchmittRink, Benjamin I. Greene, Peter N. Saeta, Anthony F. J. Levi
Optical Rectification At Semiconductor Surfaces, Shun Lien Chuang, Stefan SchmittRink, Benjamin I. Greene, Peter N. Saeta, Anthony F. J. Levi
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We show that farinfrared radiation can be generated in the depletion field near semiconductor surfaces via the inverse FranzKeldysh effect or electricfieldinduced optical rectification. This mechanism is conceptually different from those previously proposed and accounts for many recent experimental observations.
Problems Of Channel Correlation And Statistical Bias In PhotonCorrelation Spectroscopy, Richard C. Haskell, Gary L. Pisciotta
Problems Of Channel Correlation And Statistical Bias In PhotonCorrelation Spectroscopy, Richard C. Haskell, Gary L. Pisciotta
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Correlation between channels of the normalized photocountrate correlation function g^{(2)}(τ) becomes significant at high count rates and leads to a number of dataanalysis problems. We derive an expression for channel correlation that is valid for a detector area of arbitrary extent and compare the theoretical predictions with measured values. A dataanalysis procedure is demonstrated that employs the theoretical expression for channel correlation and provides a rigorous test of an assumed fitting function. The procedure facilitates the use of the cumulant method in determining the polydispersity of scatterers. An expression for the statistical bias of g^{(2)}(τ) is ...