Optical effects caused by high laser powers in ion-implanted Bi4Ge3O12 waveguides

Abstract

The ‘optical writing’ of permanent channel waveguides in the surface of He⁺ ion-implanted bismuth germanate, Bi₄Ge₃O₁₂, has been studied, using end-coupled argon and Ti:sapphire CW laser beams. Comparisons of the self-focusing effect in waveguides and bulk samples have been made for both Nd³⁺ doped and undoped material. The permanent ‘writing’ effect has been compared with the structural change observed earlier in ion-implanted Bi₄Ge₃O₁₂ waveguides annealed at high temperature.     

Waveguide confinement of cerenkov second-harmonic generation through a graded-index grating coupler: Electromagnetic optimization

Abstract

The feasibility of making a frequency doubler for integrated optics is studied with the electromagnetic theory of gratings and graded-index waveguides as a tool. The device consists of a first waveguide filled with a sol-gel nonlinear material doped or grafted with a nonlinear chromophore whose thickness is chosen to generate a second-harmonic Cerenkov radiation in a dispersive glass substrate. The Cerenkov radiation is coupled into a second waveguide through a graded-index layer produced by ion exchange into glass, lying on top of an ion-etched grating coupler. The aim of the study is to optimize the optogeometrical parameters of the device in order to obtain a resonance line of the second waveguide modes that has an angular width large enough to match the experimental constraints, and which leads to a good enough coupling coefficient. The electromagnetic theory of grating couplers is developed into an S-matrix propagation algorithm form in order to be combined with the electromagnetic analysis of the thick graded-index waveguide with a view to analysing the device.     

Wideband Acousto-optical Bragg Transducer for Integrated Optics

Abstract

The electrical and acousto-optical characteristics of modified chirp surface acoustic wave Bragg transducers for planar optical waveguides in YZ (Y cut, Z propagating) LiNbO₃ are described theoretically and experimentally.     

Reflection of a Beam of Finite Size from a Corrugated Waveguide

Abstract

The paper is concerned with the influence of the finite size of an incident beam upon both the anomalous-reflection spectrum and the shape of the energy distribution in a reflected beam. It is proved experimentally that the use of corrugated waveguides as a laser-resonator selective mirror improves the spatial coherence of radiation.     

Thermal and Band-filling Effects in Prism Coupling to CdSSe-doped Glass Waveguides

Abstract

Prism coupling is employed to investigate the nonlinear properties of CdS_0·9Se_0·1 semiconductor-doped glass slab waveguides. Experiments performed with a nanosecond laser source show distributed-coupling phenomena typical of thermally-driven processes, with compensating effects due to band-filling contributions.     

On the Action of γ Radiation on Solid C60 and C70 Fullerenes: A Comparison with Graphite Irradiation

Abstract

C₆₀ and C₇₀ fullerene have been treated in sealed flasks under Ar with γ radiation using radiation dosages ranging from 10 to 1000 kGy. The treated samples studied by electronic and FT-IR spectroscopy have not shown any evidence about fullerenes decomposition or radiopolymerization. However, through Raman spectroscopy it was possible to observe that γ radiation induces C₆₀ dimerization and trimerization. It has additionally been discovered that γ-treated C₆₀ (oligomerized) can be easily photopolymerized in the solid state by post-irradiation with laser light at 514 nm while this phenomenon has not been observed by using laser light at 782 nm and considerably higher laser power. Previously to this study, C₆₀ photopolymerization was known to occur only by using ultraviolet light.

For comparison also graphite was irradiated with 1000 kGy of γ radiation. Irradiated graphite shows considerably changes in its Raman spectrum, showing the formation of glassy carbon domains, perhaps carbon onions. The l_d bandshift to 1310 cm^?1 could be interpreted in terms of formation of hexagonal diamond.     

Acoustic wave passing through moving rigid screen

Abstract

A rigorous boundary condition for a linear acoustic wave passing through a moving rigid screen is derived from a modified theory of poroelasticity in this paper. The governing equation of the acoustic wave in the air passing through moving rigid screens. The boundary condition is found to be more general than that applied in earlier works done by the first author and his coworkers.

tion is found to be more general than that applied in earlier works done by the first author and his coworkers.     

Fabrication of waveguides in sputtered films of GeAsSe glass via photodarkening with above bandgap light

We have fabricated and characterized waveguides in thin films of Ge₅As₃₄Se₆₁ glass sputtered onto silicon wafer substrates. The 5-μm width waveguides were fabricated by exposure to 514.5 nm light from an Ar³⁺ laser, with a lithographic exposure mask used to provide the lateral patterning for the waveguides. The measured losses of the waveguides ranged from 3.5 to 6.4 dB/cm. From SEM imaging, we concluded that scattering from microcracks at the glass–substrate interface was the dominant source of loss.     

Efficiency of Modal Coupling between Graded-index Optical Waveguides

Abstract

The coupling efficiency between the fundamental modes of two different graded-index waveguides fabricated by ion exchange in the same glass substrate is calculated by numerical and variational methods. Waveguide parameters that allow the designer to achieve the maximum power transfer through the waveguide boundary are determined. A possible application to the design optimization of waveguide lenses is considered.     

Effects of γ Radiation on C60 Fullerene in CCI4 Solution

Abstract

By treating a CCI₄ solution of C₆₀ in a sealed ampoule under argon with γ radiation generated by a ⁶⁰Co source, chlorinated and trichloromethylated C₆₀ oligomers (dimers, trimers) are produced. A total radiation dose of 122 kGy was used.     

Voltage- and current-activated metal–insulator transition in VO2-based electrical switches: a lifetime operation analysis

Abstract

Vanadium dioxide is an intensively studied material that undergoes a temperature-induced metal–insulator phase transition accompanied by a large change in electrical resistivity. Electrical switches based on this material show promising properties in terms of speed and broadband operation. The exploration of the failure behavior and reliability of such devices is very important in view of their integration in practical electronic circuits. We performed systematic lifetime investigations of two-terminal switches based on the electrical activation of the metal–insulator transition in VO₂ thin films. The devices were integrated in coplanar microwave waveguides (CPWs) in series configuration. We detected the evolution of a 10 GHz microwave signal transmitted through the CPW, modulated by the activation of the VO₂ switches in both voltage- and current-controlled modes. We demonstrated enhanced lifetime operation of current-controlled VO₂-based switching (more than 260 million cycles without failure) compared with the voltage-activated mode (breakdown at around 16 million activation cycles). The evolution of the electrical self-oscillations of a VO₂-based switch induced in the current-operated mode is a subtle indicator of the material properties modification and can be used to monitor its behavior under various external stresses in sensor applications.     

Buried interface characterization in optoelectronic materials by interference microscopy

Abstract

In optoelectronic materials development, the analysis of buried interfaces is sometimes necessary in order to achieve the best optical and electrical performance. Interference microscopy has been investigated as a means to characterize interfaces buried under transparent layers. This technique is typically used at the air/material surface but since it is a non-contacting optical far field technique, it can also be used to measure buried interfaces which are innaccessible by near field scanning probes. We have succeeded in measuring the nanometric roughness of interfaces of porous silicon layers on silicon and of up to three successive buried interfaces in rare earth doped fluoride glass planar waveguides having reflectivities as low as 10^?4 using phase stepping microscopy. Errors in the measured roughness values were introduced with increased depth of the interface, due to the distortion of the wavefront passing through the overlying transparent layer. Scanning white light interferometry was also used to measure the depth of the different interfaces in cases where the refractive indices were known to be homogeneous. Further work is required to better understand the origin of errors in the measurements due to the presence of the overlying transparent layers in order to improve the accuracy of the technique.     

Theoretical calculation of the angular distribution of radiation at the output of a flat nanodimensional X-ray waveguide

A model is proposed for theoretical calculations of the angular distribution of radiation intensity at the output of a flat X-ray waveguide representing an air-filled gap between two quartz plates. Good agreement between the theoretical and experimental angular profiles of CuK_α fluorescence intensity is obtained for planar waveguides with the gap widths ranging from 40 to 3000 nm. It is concluded that the Kirchhoff method can be applied to calculations of the spatial distribution of radiation intensity at the X-ray waveguide output.     

Er:YAl3(BO3)4 glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y_1 − xEr_xAl₃(BO₃)₄ multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er^{3+ 4}I_13/2 energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 μs and 200 μs, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl₃(BO₃)₄ compounds are promising for low loss waveguides.     

Study of rectangular waveguides with grooves of irregular shape using the finite element method

Electromagnetic wave propagation through grooved waveguides is studied using the finite element method (FEM). The effect of grooves of irregular shape on TE₁₀, TE₂₀ mode frequencies and passband is studied. The variation in cutoff frequencies for TE₁₀, TE₂₀ mode and passband is observed.     

Surface Plasmon Measurement of the Bonding Potential between an Organic Fluid and a Gold Film

Abstract

The optical excitation of a surface plasmon-polariton (SPP) at a gold/air interface has been used to monitor the thickness of an organic fluid layer condensed on the gold. By passing a current through the gold film its temperature (as monitored directly by its resistance) is elevated above that of the organic fluid reservoir. Measurement of the SPP resonance position as a function of the difference in temperature between the gold film and the fluid reservoir gives a direct determination of the equilibrium film thickness for a known thermal energy. From the degrees of freedom available to the molecules the variation of the bonding potential with distance from the gold surface is established. For methanol and monochlorobenzene the extra contribution to the free energy μ_Au-organic takes the forms of a power law in distance: μ_Au-methanol ∝thickness^?0·53 and μ_{Au-chlorobenzene} ∝thickness^?1·25.     

Theory of excitation of irregular waveguides

A variational method is proposed to study the excitation of waveguides by arbitrarily time-dependent sources, which is suitable for irregular waveguides. Pis’ma Zh. Tekh. Fiz. 24, 60–63 (August 12, 1998)     

He+ ION BOMBARDMENT OF C60 FULLERENE: AN FT-IR AND RAMAN STUDY

ABSTRACT

C₆₀ fullerene films have been bombarded with He⁺ ions at 30?keV at room temperature in vacuum. The structural changes undergone by C₆₀ have been followed by both FT-IR and Raman spectroscopy. Raman spectroscopy was the most useful tool for this scope. It has been clearly discovered that at low radiation dose C₆₀ forms oligomers but at higher radiation doses it is converted into an amorphous carbonaceous matter. The implications of these results on the possible survival of C₆₀ fullerene in the interstellar space have been discussed briefly in connection with the previous results on the effects of various types of electromagnetic radiation over C₆₀.     

Interference Phenomena in Waveguides with Two Corrugated Boundaries

Abstract

Waveguide structures with two corrugated interfaces are considered. It is shown theoretically and experimentally that these structures can form the basis for a highly-efficient unidirectional grating coupler for slab waveguides. The anomalous light reflection from waveguides with two corrugated boundaries is also considered. The possibility of using corrugated waveguides for frequency stabilization of a semiconductor laser is demonstrated.     

Effect of Repeated Application of C60 Combined with UVA Radiation Onto Hairless Mouse Back Skin

Abstract

Repeated application of buckminsterfullerene (C₆₀) toluene solution combined with ultraviolet A (UVA) radiation onto hairless mouse back skin resulted in enhancing formation of erythema as an acute disease but induced no carcinoma on the skin. This result is probably due to insolubility of C₆₀ in the living cells to generate little singlet oxygen ¹O₂ by UVA radiation.