H.N. Rutt

Raman spectra of carbonates of calcite structure

Six new Raman spectra of carbonates of calcite structure (D63d) are presented and compared with the previously reported siderite and calcite spectra. Correction on the assignment of the electronic Raman in siderite was done by this comparative study. In calcite a new line was observed and assigned as an Eg+A1g mode. Some samples were prepared by hydrothermal synthesis and the technique is described.

Single-mode tellurite glass holey fiber with extremely large mode area for infrared nonlinear applications

We report the fabrication of a large mode area tellurite holey fiber from an extruded preform, with a mode area of 3000microm(2). Robust single-mode guidance at 1.55microm was confirmed by both optical measurement and numerical simulation. The propagation loss was measured as 2.9dB/m at 1.55microm. A broad and flat supercontinuum from 0.9 to 2.5microm with 6mW output was obtained with a 9cm length of this fiber.

Fiber Bragg gratings with enhanced thermal stability

Gratings written in tin-doped silica fibers by using a 248 nm excimer laser exhibit extremely high thermal stability. Isothermal measurements up to 1100 K demonstrate significant advantages over conventional fiber gratings. Extrapolations from experimental data indicated that gratings operating at 500 K for ten years will retain more than 99% of the initial strength.

High nonlinearity extruded single-mode holey optical fibers

We report the fabrication of the first microstructured single-mode non-silica glass fiber from an extruded preform. The measured effective nonlinearity (/spl gamma/) is 550 W/sup -1/ km/sup -1/, more than 500 times larger than standard silica fiber.

Characterisation of GaLaS chalcogenide glass thin-film optical waveguides, fabricated by pulsed laser deposition

Abstract The fabrication of stoichiometric thin-film optical waveguides of GaLaS via a pulsed laser deposition technique is reported. Stoichiometric films are grown by ablating GaLaS bulk glass with a KrF excimer laser (λ = 248 nm) at an incident laser flux ⩾ 3.5 J/cm 2 . The composition of the films is determined by energy-dispersive X-ray analysis and the refractive index is measured by a dark-mode prism coupling technique. Photoinduced structural rearrangement of the as-deposited films leads to a blueshift in the visible absorption edge and a permanent refractive index change, Δ n , of −1%. On the basis of these results, grating structures have been written with both blue light, and e-beam addressing, and their suitability for integrated optical structures assessed.

Photosensitivity of lead germanate glass waveguides grown by pulsed laser deposition.

We report very large photoinduced refractive-index changes Dn, of the order of ~10(2), in lead germanate glass waveguides grown by pulsed-laser deposition. The magnitude of Dn was derived from measurements of diffraction efficiency for gratings written by exposure to 244-nm light through a phase mask, whereas the sign of Dn was determined from ellipsometric data. Results are shown for films grown under oxygen pressures ranging from 1 chi 10(-2) to 6 chi 10(-2)mbars (1.33mbars=1 Torr).

Epitaxial growth of high-quality ZnS films on sapphire and silicon by pulsed laser deposition

We report for the first time, epitaxial growth of high-quality ZnS films on sapphire and silicon substrates, using pulsed laser deposition. X-ray diffraction results show that at all growth temperatures from 200°C to 680°C, epitaxial wurtzite (002) ZnS films have been successfully grown on (1012) sapphire and (001) silicon substrates. X-ray diffraction data yield full width at half maximum 2theta values of 0.13° for as-grown samples, compared with 28 values or 0.09° and 0.08° for the bare sapphire and silicon substrates respectively.

Fabrication and characterization of continuous wave direct UV (/spl lambda/=244 nm) written channel waveguides in chalcogenide (Ga:La:S) glass

Gallium lanthanum sulphide (Ga:La:S) optical glass is an interesting material for both fiber and planar technologies, as it offers possibilities for a wide array of devices suitable for use in both nonlinear applications and as IR lasers. Direct laser writing into this glass has yielded low-loss single-mode channel waveguides. Samples were exposed to above-bandgap illumination of focused UV (/spl lambda/=244 nm) light at varying intensities (I/sub UV/=1.5-90 kW/cm/sup 2/) and scan velocities (V/sub SCAN/=0.005-0.067 m/s). The exposed regions were evaluated through atomic force microscopy (AFM), and surface compaction (0.3-3.6 /spl mu/m) was observed. Sample topography was examined using a scanning electron microscope (SEM) with analysis of chemical changes within the exposed regions performed with energy-dispersive X-ray microscopy (EDAX). Waveguide attenuation was measured to be 0.2/spl plusmn/0.1 dB/cm at 1.3 /spl mu/m with a positive change in refractive index (/spl Delta/n=10/sup -3/). The chemical mechanism for these photo-induced changes with resulting photodensification has been correlated with a relative increase in the lanthanum content within the waveguide core.

Soliton-self-frequency-shift effects and pulse compression in an anomalously dispersive high nonlinearity lead silicate holey fiber

We report the fabrication of a single-mode lead silicate glass holey fiber with anomalous dispersion and a record nonlinearity of /spl gamma/=640 W/sup -1/km/sup -1/ at 1550nm. We report what we believe to be the first soliton and pulse compression experiments in this new class of fibers.

Q-switched laser damage of infrared nonlinear materials

Q -switched laser-damage thresholds have been determined for six materials (proustite-Ag 3 AsS 3 , pyrargyrite-Ag 3 SbS 3 , cinnabar-HgS, silver thiogallate-AgGaS 2 , tellurium-Te, and gallium arsenide-GaAs) of interest for nonlinear optics in the medium infrared. Four TEM 00 mode lasers were employed with outputs at wavelengths of 694 nm, 1.06, 2.098, and 10.6 μm. Damage has been found to be confined to the surface of the crystals and occurs for radiation intensities between 3 and 75 MW/cm2. Particular care is needed in the cutting and polishing of tellurium crystals if a high-damage threshold is to be achieved.