RECENT PUBLICATIONS OF CHRISTOPHER C. DAVIS
1. I.I.Smolyaninov, W.A.Atia, S.Pilevar, and C.C.Davis, Ultramicroscopy, 71, 177-182 (1998) "Experimental study of probe-surface interaction in near-field optical microscopy".
Abstract: The physical mechanism of shear-force interaction between a fiber tip and a sample in Near-Field Optical Microscopy has been studied using tunneling current measurements between the tip and a sample. Optical and non-optical (tuning fork) shear-force distance controls have been used. In both cases a tunneling current between the tip and the sample has been detected at the very beginning of shear-force approach curve when the amplitude of tip vibration was just slightly smaller than its initial value. These results indicate that fiber-tips generally mechanically touch samples under shear-force distance feed-back control.
2. S.Pilevar, K.Edinger, W.Atia, I.Smolyaninov, and C.Davis, Applied Physics Letters, 72, 3133-3135 (1998) "Focused ion beam fabrication of fiber probes with well-defined apertures for use in near-field scanning optical microscopy".
Abstract: We present a Focused Ion Beam (FIB) fabrication method for very clean and well defined subwavelength fiber probes with metallic apertures of a desired diameter for use in near-field scanning optical microscopy. Such probes exhibit improved features compared to probes coated with metal by the conventional angled evaporation technique. Examples of FIB fabricated fiber probes are shown and images of a test sample are presented using one of the probes in a near-field microscope.
3. I.I.Smolyaninov and C.C.Davis, Optics Letters, 23, 1346-1347 (1998) "On the nature of apparent "superresolution" in near-field optical microscopy".
Abstract: A "superresolution" phenomenon has been recently reported in images of diffraction gratings obtained with a near-field optical microscope probe positioned at distances on the order of a micrometer from the surface. This experiment was interpreted in terms of evanescent waves observed in the far-field. We show that the effect observed in the experiment is a very well known far-field optical phenomenon called the Talbot effect. The existence of self-imaging Talbot planes for gratings with periods on the order of a few micrometers appears promising for many practical applications.
4. I.I.Smolyaninov, W.Atia, and C.C.Davis, Phys.Rev.B, 59, 2454-2460 (1999) "Near-field optical microscopy of two-dimensional photonic and plasmonic crystals".
Abstract: Near-field optical images of electromagnetic mode structures in two-dimensional photonic and plasmonic crystals are presented. Interference patterns of plasmon Bloch waves in a plasmonic crystal have been observed. Fourier analysis of the photonic crystal images allows the reconstruction of the refractive index spatial distribution in the crystal. A similar procedure performed on images of a plasmonic crystal allows the recovery of parameters of the surface plasmon interaction with the periodic grooves that constitute the plasmonic crystal structure.
5. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, Proc.SPIE, vol. 3666, 626-629 (1999) "Near-field microscopy of second harmonic generation".
Abstract: Near-field scanning optical microscopy (NSOM) allows simultaneous mapping of both the topography and optical properties of a surface with resolution below the diffraction limit. Second harmonic generation (SHG) always occurs at a surface, even for centro-symmetric media, because of symmetry breaking. By combining NSOM and SHG we can study local variations in symmetry breaking, caused for example by ferroelectric and ferromagnetic domains, and can correlate them with surface topography. We report NSOM/SHG measurements made on piezoelectric ceramics, ferromagnetic materials and periodic structures.
6. I.I.Smolyaninov, C.H.Lee, C.C.Davis, and S.Rudin, Journal of Microscopy, 194, 532-536 (1999) "Near-field imaging of surface enhanced second harmonic generation".
Abstract: Surface enhanced second harmonic generation (SHG) from individual topographical defects of an otherwise flat gold film and from metal coated diffraction gratings has been measured using a near-field optical microscope. Experimentally measured second harmonic field distributions have been compared with theoretical calculations.
7. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, Journal of Microscopy, 194, 426-433 (1999) "Near-field second harmonic imaging of lead zirconate titanate piezoceramic".
Abstract: Near-field optical microscopy has been used to image variations in local optical second harmonic generation (SHG) from the surface of lead zirconate titanate (PZT) piezoceramic. Since PZT ceramic is a strongly scattering medium, SHG occurs in the thin layer near the surface of the ceramic. Thus, individual crystalline grains and grain boundaries located near the surface are the main features visible in the images. In general this technique allows us to determine the local poling direction of individual sub-micrometer size crystalline grains of ceramic by near-field second harmonic imaging at different angles of incidence and polarization states of the fundamental excitation light. In some cases "hot spots" of submicrometer sizes showing enhanced SHG have been observed. This enhancement is believed to result from local cavity resonances.
8. A.V.Zayats, I.I.Smolyaninov, and C.C.Davis, Proc.SPIE, vol. 3732, 81-92 (1999) "Near-field microscopy of second-harmonic generation".
Abstract: New experimental technique for near-field second-harmonic imaging of materials is discussed.This technique gives the unique possibility for the investigation of local nonlinear procceses with subwavelength resolution and will be useful for the characterization of materials as well as for fabrication and utilization of optical nonlinear devices at nanometer scale.
9. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, Applied Physics Letters, 74, 1942-1944 (1999) "Near-field second harmonic imaging of lead zirconate titanate piezoceramic".
Abstract: A technique to characterize the local nonlinearity of lead zirconate titanate piezoceramic (PZT) has been developed. Near-field optical microscopy has been used to image variations in local optical second harmonic generation from the PZT surface. Individual crystalline grains and grain boundaries are the main features visible in the images. The technique allows us to determine the local poling direction of individual sub-micrometer size crystalline grains of ceramic by near-field second harmonic imaging at different angles of incidence and polarization states of fundamental excitation light.
10. A.V.Zayats, I.I.Smolyaninov, and C.C.Davis, Optics Communications 169, 93-96 (1999) "Observation of localized plasmonic excitations at thin metal films with near-field second-harmonic microscopy".
Abstract: Specific localized surface plasmons which exist at rough thin metal film are observed using near-field microscopy of second-harmonic generation. This kind of localized excitations can not be visualized and studied by any other techniques as their electromagnetic field is confined close to the surface.
11. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, Phys. Rev. Letters 83, 2429-2432 (1999), "Giant enhancement of surface second harmonic generation in BaTiO3 due to photorefractive surface wave excitation"
Abstract: We report observation of strongly enhanced surface SHG in BaTiO3 due to excitation of a photorefractive surface electromagnetic wave. Surface SH intensity may reach 10-2 of the incident fundamental light intensity. Angular, crystal orientation, and polarization dependencies of this SHG are presented. Possible applications of this effect in nonlinear surface spectroscopy are discussed.
12. I.I. Smolyaninov, and C.C. Davis, Optics Letters 24, 1367-1369 (1999),"Near-field optical study of photorefractive surface waves in BaTiO3".
Abstract: Near-field optical microscopy has been used to study photorefractive surface waves in BaTiO3. The field distribution of the photorefractive surface wave near the crystal-air interface has been measured and compared with theory. Experimental data indicate that a micrometer wide transition layer with dielectric and photorefractive properties different from the properties of the bulk BaTiO3 exists near the interface.
13. Alexander J. Fielding, Klaus Edinger, and Christopher C. Davis, "Experimental observation of mode evolution in single-mode tapered optical fibers," Journal of Lightwave Technology 17, 1649-1656, 1999.
Abstract. Step-index single-mode optical fibers were tapered and then cleaved by ion beam milling to allow direct examination of the mode evolution in the taper with a microscope objective and CCD camera. Observation of He1m modes is reported in tapered fibers cleaved at diameters ranging from 8 to 35 m m. Theoretical scalar mode fields are fit to the experimental data and the mode transitions are explained by considering coupled-mode theory.
14. Elizabeth K. Balcer-Kubiczek, Xiao-Feng Zhang, Lin-Huang Han, George H. Harrison, Christopher C. Davis, Xiao-Juan Zhou, Vladimir Ioffe, Welton A. McCready, John M. Abraham, and Stephen J. Meltzer, "BIGEL analysis of gene expression in HL60 cells exposed to X rays or 60Hz Magnetic fields, "Radiation Research 150, 663-672, 1998
Abstract. We screened a panel of 1,920 randomly selected cDNAs to discover genes that are differentially expressed in HL60 cells exposed to 60Hz magnetic fields (2mT) or X rays (5Gy) compared to unexposed cells. Identification of these clones was accomplished using our two-gel cDNA library screening method (BIGEL). Eighteen cDNAs differentially expressed in X-irradiated compared to control HL60 cells were recovered from a panel of 1,920 clones. Differential expression in experimental compared to control cells was confirmed independently by Northern bloting of paired total RNA sample hybridized to each of 18 clone-specific cDNA probes. DNA sequencing revealed that 16 of the 18 cDNA clones produced matches with the database for genes related to cell growth, protein synthesis, energy metabolism, oxidative stress or apoptosis (including MYC, neuoroleukin, copper zinc-dependent superoxide dismutase, TC4 RA-like protein, peptide elongation factor 1a , BNIP3, GATA3, NF45, cytochrome c oxidase II and triosephosphate isomerase mRNAs). In contrast, BIGEL analysis of the same 1,920 cDNAs reveled no difference greater than 1.5-fold in expression levels in magnetic-field compared to sham-exposed cells. Magnetic-field-exposed and control samples were analyzed further for the presence of mRNA encoding X-ray responsive genes by hybridization of the 18 specific cDNA probes to RNA from exposed and control HL60 cells. Our results suggest that differential gene expression is induced in approximately 1% of a random pool of cDNAs by ionizing radiation but not by 60Hz magnetic fields under the present experimental conditions,
15. Christopher C. Davis, Ian Barber, and Mays L. Swicord, "Food and Drug Administration low-level extremely-low-frequency magnetic field exposure facility, "Bioelectromagnetics 20, 203-215, 1999.
Abstract. We describe the design, construction details, and performance characteristics of an exposure system designed to provide very well controlled extremely-low-frequency magnetic field exposure of in vitro samples. This system uses Helmholtz coils placed inside temperature-controlled m -metal chambers to provide simultaneous ac and dc field exposures at any relative angle with minimal residual background field. The system has both exposed and sham-exposed chambers and is operated under computer control in such a way as to ensure blind exposure of samples.
16. Melody A. Owens, Christopher C. Davis, and Russell R. Dickerson, "A photothermal interferometer for gas-phase ammonia detection, "Anal. Chem.,. 71, 1391-1399, 1999
Abstract. Detection of gas-phase ammonia is particularly challenging because ambient ammonia concentrations may be less than 1ppb (molecules of NH3 per 109 molecules of air), ammonia sticks to many materials commonly used to sample air, and particles containing ammonium may interfere with gas-phase measurements. We have built a new and sensitive photothermal interferometer to detect gas-phase ammonia in situ, under typical atmospheric conditions. Ammonia molecules in sampled air absorb infrared radiation from a CO2 laser at 9.22m m, with consequent collisional heating, expansion,and refractive index change. This change in refractive index is detected as a phase shift in one arm of a homodyne interferometer. Measurements of vibrational and electrical noise in the interferometer correlate to an instrumental lower limit of detection of 6.6ppt ammonia in 1s, The CO2 laser output is modulated at 1.2kHz, and the ac signal from the interferometer is measured with a lock-in amplifier. The detector is zeroed by sampling through a H3PO4-coated denuder tube and is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Signal gain is linear over 5 orders of magnitude. The instrument 2s precision is 31ppt when the signal is integrated for 100s and 250ppt with a 1-s integration time. The windowless sample cell and inlet is fabricated entirely of glass to minimize sample loss and hysteresis. The instrument response time is demonstrated to be about 1s.
17.Christopher C. Davis, Yimin Zhang, Mark L. Plett, Penny Polak-Dingels, Pierre R. Barbier, and David W. Rush, Proceedings of the SPIE Conference "Artificial Turbulence and Wave Propagation," SPIE International Symposium on Optical Science and Instrumentation, 19-24 July, 1998, San Jose.
Abstract. The development of high performance line of-sight optical communication links through the turbulent atmosphere is facilitated by laboratory tests of schemes involving adaptive optics, beam tracking, modulation and coding, aperture averaging, fading statistics, and transmitter/receiver diversity. A water-filled turbulence tube has been implemented to simulate, in some respects, the effects produced on a laser beam when it propagates several kilometers through the air. This tube is being used to investigate on a laboratory scale aperture averaging, fluctuation statistics, optical path difference (OPD), high data rate modulation, and various coding schemes. The liquid-filled tube causes fluctuations on a slower time scale than does the atmosphere. At low turbulence levels it produces log-normal fluctuation statistics, causes tip-tilt errors similar to those previously observed for atmospheric paths, and has already allowed evaluation of aperture averaging and fade statistics. It also allows the testing of various technological schemes to deal with atmospheric turbulence effects without any specific assumptions, such as weak Kolmogorov turbulence, being built into the model.
18. E.A.Vinogradov, C.C.Davis, A.L.Dobryakov, Yu.E.Lozovik, and I.I.Smolyaninov, Laser Physics, In press, "Electron injection dynamics through the Schottky barrier".
Abstract: Ultrafast dynamics of semiconductor microcavity modes in ZnSe/Cr structures was studied by femtosecond pump-supercontinuum probe spectroscopy in wide spectral region 1.6-3.2 eV for different pumping photon energies 2.34 eV, 2.75 eV and 5.5 eV. The ultrafast process ~ 40 fs connecting with the excitation of nonequilibrium electrons of metal (i.e. boundary of the microcavity), which penetrate through the Schottky electron barrier into the semiconductor, was observed. Possible applications of these microcavities as femtosecond broad-band optical switch and as device for effective up-conversing are discussed.
19. Saeed Pilevar, Trevor W. MacDougall, and Christopher C. Davis, "Effects of grating period and mode order on the growth and sensitivity of the resonant peaks of long period gratings," paper submitted to the IEICE Special Issue on Optical Fiber Sensors.
Abstract. A general analytical expression for describing the growth of the resonant peak wavelengths of long period gratings is derived. The theoretical calculations explain the shift of the peak loss wavelengths in the direction of either shorter or longer wavelengths as the induced index change of grating increases. We have calculated and experimentally verified the sensitivity of the resonant peak wavelengths with respect to an overlay index for various grating periods. It is shown that the center wavelength shift of the cladding modes depends strongly on the grating period and the cladding mode order.
1 I.I.Smolyaninov, C.H.Lee, C.C.Davis, and A.V.Zayats, "Near-field optical microscopy of surface second harmonic generation", Bulletin of the American Physical Society, Vol.43, No.1, 481 (1998) Program of the 1998 APS March Meeting.
2. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-field optical second harmonic microscopy", in International Quantum Electronics Conference, Vol.7, 1998 OSA Technical Digest Series (OSA, Washington DC, 1998), p.228.
3. A.V.Zayats, I.I.Smolyaninov, and C.C.Davis, "Near-field Microscopy of Second-harmonic Generation", paper presented at the XVI International Conference on Coherent and Non-Linear Optics, June 1998, Moscow, Russia.
4. E. K. Balcer-Kubiczek, X.-F. Zhang, G. H. Harrison, C. C. Davis, X.-J.Zhou, V. Ioffe, and W. A. McCready, "Expression analysis of 1920 randomly selected transcripts in HL-60 cells exposed to magnetic fields or X rays," paper presented at BEMS 1998, June 7-11, 1998, St. Pete Beach, Florida
5. C.C. Davis, S.M. Motzkin, I. Bikhman, R.Z. Shih, and J. Terlonge, "Dosimetric analysis and baseline studies of in vitro cell exposure to radiofrequency electromagnetic fields," paper presented at BEMS 1998, June 7-11, 1998, St. Pete Beach, Florida
6. G.H. Harrison, X-F. Zhang, E. K. Balcer-Kubiczek, C. C. Davis, X.-J.Zhou, and W. A. McCready, "Expression analysis of 720 randomly selected transcripts in HL-60 cells exposed to 60Hz square wave magnetic fields" paper presented at BEMS 1998, June 7-11, 1998, St. Pete Beach, Florida
7. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-field optical study of second harmonic generation in piezoelectric ceramics", paper presented at the OSA Annual Meeting / ILS-XIV, October 1998, Baltimore, Md, USA
8. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-field microscopy of second harmonic generation", paper presented at International Conference on Fiber Optics and Photonics, December 14-18 1998, Delhi, India.
9. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-field imaging of surface enhanced second harmonic generation", paper presented at the 5th International Conference on Near Field Optics, December 6-10 1998, Shirahama, Japan.
10. I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-field second harmonic imaging of lead zirconate titanate piezoceramic", paper presented at the 5th International Conference on Near Field Optics, December 6-10 1998, Shirahama, Japan.
11. I.I.Smolyaninov, W.Atia, and C.C.Davis, "Near-field microscopy of two-dimensional photonic and plasmonic crystals", paper presented at the 5th International Conference on Near Field Optics, December 6-10 1998, Shirahama, Japan.
12 I.I.Smolyaninov, C.H.Lee, and C.C.Davis, "Near-fieldsecond harmonic imaging of lead zirconate titanate piezoceramic", in Quantum Electronics and Laser Science Conference'99, OSA Technical Digest (OSA, Washington DC, 1999), p.117.
13. S.Pilevar, K.Edinger, W.Atia, I.Smolyaninov, and C.Davis, "Near-field scanning optical microscopy probe fabrication using focused ion beam milling technique", In Conference on Lasers and Electro-Optics'99, OSA Technical Digest (OSA, Washington DC, 1999), pp.68-69.
14. S.M. Motzkin, I. Bikhman, R.Z. Shi, and C.C. Davis, "Are in vitro human trasnformed brain tumor cells affected by exposure to low intensity continuous or pulsed radiofrequency electromagnetic fields?" paper presented at PIERS1999, Taipei, Taiwan, March 22-26, 1999.
15. Alexander J. Fielding and Christopher C. Davis, "2D scalar FDTD analysis of source coupling to a tapered dielectric waveguide, " paper presented at the DoD High Performance Computing Users Group Conference, Monterey, California, June 7-10, 1999.
16. E.A. Vinogradov, A.L. Dobryakov, V.M. Farztdinov, Yu.E. Lozovik,Yu.A. Matveets, I.I. Smolyaninov, and C.C.Davis, "Electron injection dynamics through the Schottky barrier", paper presented at the International Conference on Semiconductor Physics, October 1999, Novosibirsk, Russia.
17. S. Pilevar, I.I. Smolyaninov, K. Cho, and C.C. Davis, "Application of photon scanning tunneling microscopy for probing photoinduced refractive index changes and surface topography in fiber Bragg gratings", paper presented at the 14th UK Quantum Electronics Conference, September 1999, Manchester, UK
18. Christopher C. Davis, "Bio-Optics", invited paper presented at the 14th UK Quantum Electronics Conference, September 1999, Manchester, UK
19. I.I.Smolyaninov, H.Y.Liang, C.H.Lee, C.C.Davis, L.D.Rotter, D.L.Kaiser, "Near-field second harmonic microscopy of thin ferroelectric films",will be presented at the MRS 1999 Fall Meeting, November, 1999, Boston, Ma, USA