Reuben Dahan

Plastic hollow fibers as a selective infrared radiation transmitting medium

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.

Characterization of chemically formed silver iodide layers for hollow infrared guides

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 β and γ AgI phases. The substrate of the silver layer (teflon or glass) has no influence on the β and γ distribution. The fastest achieved is a γ form which is converted during the forming process partially into β isomer. The γ isomer is the most suitable form for IR light guiding.

Transparent indium tin oxide films prepared by ion-assisted deposition with a single-layer overcoat

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 15B/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 (lAD) 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.

Laser induced chemical vapor deposition of optical thin films on curved surfaces

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 SiH 4 /NH 3 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 SiH 4 /N 2 O. Using this gas mixture the film composition depended strongly upon the SiH 4 /N 2 O 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 SiH 4 /N 2 O 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.

Scattering and beam profile measurements of plastic, silica, and metal radiation waveguides

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, l52.94 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.

Influence of heating on performances of flexible hollow waveguides for the mid-infrared

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.

Nondestructive method for attenuation measurements in optical hollow waveguides.

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 waveguides guiding layers.

Scattering of IR and visible radiation from hollow waveguides

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.

Diamond-like carbon thin films as antireflective and protective coatings of GaAs elements and devices

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 < ? < 16.5 ?m 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.

New performances and applications of fused silica and plastic waveguides

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.