Reuben Dahan

Tel Aviv University, Tell Afif, Tel Aviv, Israel

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Publications (23)22.79 Total impact

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    ABSTRACT: Diamond-like carbon (DLC) films were deposited directly on GaAs substrates by a capacitively coupled 13.56 MHz glow discharge in a CH4 plasma. The deposition process for antireflective DLC coating deposition on GaAs was optimized. DLC films of different thicknesses were deposited to investigate IR spectral characteristics. DLC films on GaAs increased microhardness from 500 kg/mm2 for the uncoated substrate to 1200 kg/mm2. The spectral transmittance of the bare and coated substrates in the 2.5 < (lambda) < 16.5 micrometers region was measured. DLC layer thickness affects the optical transmittance of the coated substrate. The peak transmittance with DLC coatings on both sides of the substrate reaches 95%, with about 1% absorption and 4% reflection.
    No preview · Article · Apr 2000 · Optical Engineering
  • Mordechai Gilo · Reuben Dahan · Nathan I. Croitoru
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    ABSTRACT: Transparent indium tin oxide (ITO) films have many applications as electrodes in Liquid Crystal displays and EMI/RFI shielding. We have compared two processes for obtaining ITO thin films with low resistivity (below 15 (Omega) /sq) and high transmittance (above 90%) in the visible region. The first process was deposition using electron beam gun evaporation. The second process was using Ion Assisted Deposition (IAD) of low energy oxygen ions from an end-Hall ion source. In both cases the conductive layer was overcoated with 50 - 250 nm thickness of a MgF2 layer to enhance the transmittance. When ITO produced by IAD was overcoated with a MgF2 layer, the surface was found to be conductive. The surface was analyzed using the Auger Electron and Second Ion Mass Spectroscopy methods. Traces of indium were found on the MgF2 layer. We speculate that indium that diffused through the overcoat layer gives assistance to the conductivity and enables the measurement of the resistivity from the top surface of the coating. This effect occurred only when the ITO was deposited using IAD. This is an advantage in manufacturing of optical conductive windows. Otherwise there is a need to leave exposed areas of ITO for conductive contacts. The diffusion process was not observed with oxide layers. Atomic Force Microscopy scans show that the IAD process decreased the average roughness of the surface.
    No preview · Article · Jun 1999 · Optical Engineering
  • J Dror · A Inberg · R Dahan · A Elboim · N Croitoru
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    ABSTRACT: Two types (plastic and fused silica) of waveguides suitable for transmitting and Er-YAG laser radiation were prepared and characterized. The temperature of several points on the external surface of the waveguides was measured. Optical parameters (transmission, focusing, misalignment) of the two types of waveguides were measured and compared. The importance of heating (due to losses) on the long time delivery performance is also shown.
    No preview · Article · Dec 1998 · Journal of Physics D Applied Physics
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    ABSTRACT: Laser induced chemical vapor deposition (LCVD) of silicon nitride and silicon dioxide single and double layers has been investigated using excimer laser operating at a wavelength of 193 nm. Single layers of silicon nitride were formed from SiH4/NH3 gas mixture with Si/N atomic ratio of 0.6–0.7. The layers that contained a small amount of hydrogen had a refractive index and extinction coefficient of n=2, k=0015 at 600 nm. Deposition of silicon dioxide was investigated using SiH4/N2O. Using this gas mixture the film composition depended strongly upon the SiH4/N2O ratio. At high ratio the film formed was silicon oxynitride, which contained both SiN and SiO bonds. The film also contained small a amount of SiH bonds. Decreasing the SiH4/N2O ratio led to the formation of pure silicon dioxide with a refractive index of 1.45. A two layer coating of silicon nitride and silicon dioxide resulted in the formation of an antireflection coating with a reflectivity of about 0.5% at 750 nm.
    No preview · Article · Nov 1998 · Thin Solid Films
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    ABSTRACT: Working characteristics of silicon radiation detectors have been observed to change, when irradiated at very large neutron fluences (Φ>1012 n/cm2), due to generation of defect levels and capture of majority carriers on these levels. Direct study and confirmation of these phenomena were made by measuring the Hall effect constant RH and Resistivity, of the silicon material as a function of neutron irradiation of up to about 9x1015 n/cm2. It was found that, for fluences of about Φ≥5.95x1014 n/cm2, the sign of the Hall constant RH changes from negative to positive. Taking into account that, for Φ≥1.19x1014 n/cm2, the value of ϱ is independent on fluence, we assumed that the damage, craused at those neutron fluences, was high enough to create disordered silicon crystal structures. This disordered silicon may contribute to the positive sign of RH and make the ϱ of this material insensitive to further neutron irradiation. This can be explained by assuming that, for Φ>1.19x1014 n/cm2, the created disordered silicon material has an equivalent resistance in series with the single crystal Si resistance. The contribution to ϱ of the disordered silicon is large enough to have a strong influence on the silicon characteristics. The new defect structure was seen under a microscope on etched samples, irradiated at Φ>1013 n/cm2.
    No preview · Article · Feb 1998 · Nuclear Physics B - Proceedings Supplements
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    ABSTRACT: Working characteristics of silicon radiation detectors have been observed to change, when irradiated at very large neutron fluences (Φ > 1012n/cm2), due to the generation of defect levels and capture of majority carriers on these levels. Direct study and confirmation of these phenomena were made by measuring the Hall effect constant RH and resistivity of the silicon material as a function of neutron irradiation of up to about 9 × 1015 n/cm2. It was found that, for fluences of Φ ≥ 5.95 × 1014n/cm2, the sign of the Hall constant RH changes from negative to positive. Taking into account that, for Φ ≥ 1.19 × 1014n/cm2, the value of resistivity ϱ is independent of the fluence, we assumed that the damage caused by those neutron fluences was high enough to create disordered silicon crystal structures. This disordered silicon may contribute to the positive sign of RH and make the ϱ of this material insensitive to further neutron irradiation. This can be explained by assuming that, for Φ > 1.19 × 1014n/cm2, the created disordered silicon material has an equivalent resistance in series with the single crystal Si resistance. The contribution to ϱ of the disordered silicon is large enough to have a strong influence on the silicon characteristics. The new defect structure was seen under a microscope on etched samples, irradiated at Φ > 1013n/cm2.
    No preview · Article · May 1997 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
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    ABSTRACT: Hollow waveguides (WG) made of plastic, silica, and metals have been developed for mid-IR spectrum transmission and are already being used, mainly in medical applications, in laser surgery and treatments. Characterization of these fibers is one of the important steps that enables further understanding of newly developed methods of preparation or applications. Scattering and beam profile measurements are discussed which have provided new data that may be used for future improvement or applications of these types of waveguides. Data on the roughness of the tube walls of WGs were obtained from backscattering measurements before and after deposition of the guiding layers. This is important for developing WGs for the shorter wavelengths in the mid-IR range (e.g., Er:YAG lasers, λ = 2.94 nm). Measurements under various bending radii have made it possible to calculate the contribution of scattering as well as absorption and changes in modes of propagation. Beam profile measurements have supplied data on the contribution of coupling to the mode of propagation, and the dependence of delivered energy to a target at a distance on the coupled value of energy. The conditions under which a whisper gallery mode of propagation appears as a function of the radius of bending and the angle of incidence to the normal of the inner wall, were found.
    No preview · Article · Apr 1997 · Journal of Biomedical Optics
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    ABSTRACT: Scattering of visible and mid-IR radiation transmitted through hollow flexible waveguides was measured employing two methods: total integrated scattered (TIS) and back scattered (BS) radiation. The root mean square ((sigma) ) of roughness was evaluated employing these two methods. This has also enabled evaluation not only of the (sigma) but also the location of important centers of scattering of the metal and dielectric deposited layers on the internal wall of waveguide tubes. Measurements of beam profile were performed using perspex cubes, in which the formed crater image has given information of the mode propagation into the waveguides as a function of distance from: (a) the coupling to the laser, (b) radius of bending, (c) ID of hollow tubes, and (d) coupled energy of laser in waveguide. It was shown that for given radii of bending whisper gallery mode of propagation appears.
    No preview · Article · Apr 1996 · Proceedings of SPIE - The International Society for Optical Engineering
  • Moshe Ben-David · R. Dahan · J. Dror · N. Croitoru

    No preview · Conference Paper · Jan 1996
  • R Dahan · J Dror · A Inberg · N Croitoru
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    ABSTRACT: A new method for characterizing hollow waveguides has been developed in which the laser radiation is coupled into the waveguide hollow bore through an optical fiber. By moving the distal end of the fiber along the waveguide we achieved scanning of the incident radiation in the waveguide at various points on the internal walls. This method can be employed for measuring attenuation without cutback or for detecting point defects on the waveguide's guiding layers.
    No preview · Article · Jul 1995 · Optics Letters
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    ABSTRACT: Surface roughness of sections of hollow waveguides is examined by measuring the backscattering reflection and using the total integral scattering (TIS) method. The iodination of silver was found as the main factor affecting the surface roughness. The AgI layer thickness also affects an interference phenomena as a function of wavelength.
    No preview · Article · Jun 1995 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Plastic and fused silica waveguides suitable for transmitting CO2 and Er-YAG laser radiation were prepared and characterized. The temperature of several points on the waveguide was measured. Optical parameters (transmission, focussing, misalignment) of the two types of waveguides were determined and compared.
    No preview · Article · May 1995 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: The scattering phenomenon of infrared and visible radiation from hollow waveguides, made of teflon or fused silica, having Ag and AgI guiding layers, was measured by two methods; Total Integrated Scattered and Backscattering. The root means square roughness was evaluated by both methods. It was found that the roughness of the silver layer is influenced by the substrate. The AgI is the main contributor to roughness and this is a function of its preparation method.
    No preview · Article · May 1995 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: The direct or waveguide transmitted beam shape of carbon dioxide laser was recorded by irradiating perspex blocks. The influence of waveguides materials, geometry, defects and roughness on the crater produced in the blocks was observed. Fused silica transmitted beams are narrower and sharper than the plastic transmitted beams, and the energy distribution can be clearly observed. The main effect on the beam shape comes from the wall roughness. The moving tip method was applied for non-destructive attenuation measurements.
    No preview · Article · Jan 1995 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: The influence of substrate material and deposition method on the surface roughness of section of hollow waveguides was examined by measuring the backscattering reflection. The iodination of silver was found as the main contributor to the surface roughness. The AgI laser thickness also affects an interference pattern.
    No preview · Article · Dec 1994 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Scattering measurements were performed on samples of waveguides used for CO2 laser energy transmission for medical purposes. The scattering results are a sensitive tool which indicate the relative transmission of laser energy through the waveguide.
    No preview · Article · Jul 1994 · Proceedings of SPIE - The International Society for Optical Engineering
  • M. Alaluf · J. Dror · R. Dahan · N. Croitoru
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    ABSTRACT: Plastic hollow waveguides (used as fibers) for infrared (IR) transmission were made from plastic tubes covered, on the internal wall, with a metal layer (Ag) and growing a dielectric thin (AgI) overlayer by direct iodination on it. The existence of several absorption lines at given wavelengths in the middle infrared (mid‐IR) region is predicted theoretically and measured experimentally. From the wavelengths of absorption lines the thickness of the AgI film has been computed. The average thickness of the AgI in the hollow waveguide increased with the iodination time and with the concentration of the iodine solution. The crystal size of the AgI was increased with the increase of the AgI thickness. By controlling the iodination process it was possible to make waveguides which can be employed as filters for various wavelengths of the transmitted mid‐IR radiation.
    No preview · Article · Dec 1992 · Journal of Applied Physics
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    ABSTRACT: Experimental parameters, as well as chemical and morphological parameters, were investigated with the purpose of improving the performance of the previous type plastic hollow fibers. The dielectric layer was identified as (beta) and (gamma) AgI. The dielectric layer thickness (t) was measured and was found to be dependent on the iodination time (T) according to the relation t equals T0.37. The thickness of the dielectric layer influenced the transmission through the hollow fiber by shifting absorption maxima and reducing the smoothness of AgI layer. The best focal lens of the coupling lens (ZnSe) was found to be 200 mm, and the colinearity angle between the beam and the fiber could deviate +/- 5 degree(s) from O degree(s) angle. The parameters of the new type of fibers were measured and found considerably improved. Employing cooling and pulse power reduced the heating and increased the lifetime of the fiber.
    No preview · Article · Aug 1992 · Proceedings of SPIE - The International Society for Optical Engineering
  • R Dahan · J Dror · N Croitoru
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    ABSTRACT: The process of iodination of a thin layer of Ag deposited by electrodes on the internal well of a tube was investigated. The AgI layer was formed employing several methods, which give a mixture of beta and gamma-AgI phases. The substrate of the silver layer (teflon or glass) has no influence on the beta and gamma-distribution. The fastest achieved is a gamma-form which is converted during the forming process partially into beta-isomer. The gamma-isomer is the most suitable form for IR light guiding.
    No preview · Article · Jun 1992 · Materials Research Bulletin
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    ABSTRACT: Plastic hollow fibers for IR transmission were characterized employing several physical and chemical methods. The dielectric layer was found to be (beta) -AgI or (delta) -AgI on the surface. The amount of iodine decreases gradually at deeper layers. The equivalent depth was determined from coulometric experiments; 0.3 - 1.6 micrometers .
    No preview · Article · Jan 1992 · Proceedings of SPIE - The International Society for Optical Engineering