P.J. Chandler

Growth of KNbO3 thin films on MgO by pulsed laser deposition

Crystalline and stoichiometric KNbO3 thin films have been grown on (100) oriented MgO substrates by pulsed laser deposition technique. Electron microprobe analysis and Rutherford backscattering spectroscopy of the films show a progressive loss of K with increasing substrate‐target distance. To compensate for this K loss the ceramic KNbO3 targets were enriched with K2CO3 powder, pressed at room temperature, and sintered at 650 °C. For a substrate‐target distance of 6 cm, targets with [K]/[Nb] molar ratio=2.85 yield stoichiometric KNbO3 films. A partial oxygen pressure of 2×10−2 mbar was optimum for growing transparent films. Films grown between 650 and 700 °C show the KNbO3 crystalline phase with its (110) axis preferentially oriented perpendicular to the surface of the substrate. At these temperatures KNbO3 diffusion into the MgO substrate is observed. Films grown from KNbO3 single crystal targets only contain a Mg4Nb2O9 crystalline layer.

Ion-implanted Nd:MgO:LiNbO3 planar waveguide laser

Laser oscillation in an ion-implanted planar Nd:MgO:LiNbO(3) waveguide is demonstrated for the first time to our knowledge. Details of the waveguide structure, spectroscopic properties, photorefractive effects, and laser performance are given. A simple calculation of the absorbed power threshold gives ~8 mW, in fair agreement with the experimental value of ~17 mW.

Mode gaps in the refractive index properties of low-dose ion-implanted LiNbO3 waveguides

Data are presented for the refractive index profiles for low-dose He+ ion-implanted LiNbO3 waveguides. In the nuclear stopping region, the extraordinary index is increased for low ion doses, by contrast with index reduction normally associated with ion-implanted waveguiding structures. The index increase was confirmed by fabricating a buried waveguide for the extraordinary index by use of multi-energy implants. For single-energy implants, data are shown which map the extraordinary index at the surface together with that in the nuclear collision zone, as a function of angle relative to the z axis of light propagation in surface waveguides for X and Y cut LiNbO3. These indices cross over near 45°, which results in a mode gap for which waveguide modes are not supported. A mechanism for this behavior is discussed based on defect-induced lattice relaxation. The phenomenon of a controlled mode gap may have applicability for optoelectronic and nonlinear materials and devices.

Frequency doubling in ion‐implanted KTiOPO4 planar waveguides with 25% conversion efficiency

Second‐harmonic generation (SHG) has been successfully performed in ion‐implanted planar waveguides in KTiOPO4. The waveguides were formed by helium implantation, and SHG was achieved using type 2 zero order mode phase matching at a wavelength of ∼1.07 μm. The results indicate that the high nonlinearity of the material remains in the guiding region after ion implantation. The conversion efficiency in a typical guide is estimated at ∼25% for ∼1 μJ pulsed excitation. At a lower input power level, the harmonic green output from the waveguide is 20 times higher than that from the bulk for the same amount of fundamental power. This clearly demonstrates the advantage of using waveguides in achieving frequency doubling for integrated optical devices.

Ion-implanted Nd:GGG channel waveguide laser

We report what is to our knowledge the first fabrication and laser operation of ion-implanted Nd:GGG channel waveguides. Diode-pumped operation has been achieved with absorbed power thresholds as low as ~2 mW and a slope efficiency of ~30% with respect to absorbed power.

Photorefractive planar waveguides in BaTiO3 fabricated by ion-beam implantation.

For the first time to our knowledge, photorefractive properties have been observed in planar waveguides fabricated by the technique of ion-beam implantation in BaTiO3 single crystals. The implantation was carried out by using 1.5-MeV H+ ions at a dose of 10−16 ions/cm2. For a given input power, a decrease in the effective photorefractive two-beam coupling response time of ≥102 has been observed, owing to a combination of optical confinement within the waveguide and possible modification of charge-transport properties induced through implantation. Experiments carried out on the two-beam coupling gain show that the gain direction has been reversed in the waveguide compared with that of the bulk crystal.

Characterization of ion implanted waveguides in Nd:YAG

Ion implantation into Nd:YAG has been used to produce waveguides which are capable of supporting laser action. The refractive index profiles have been characterized as a function of ion dose and energy, implant temperature, and subsequent thermal annealing. Transmission losses down to 1.2 dB/cm have been obtained in the optimized waveguides. There is a temperature independent index enhancement of ∼0.15% in the electronic stopping (guiding) region. The nuclear collision damage is temperature dependent, and shows an initial index increase (∼0.3% for dose 1 × 1016 ions/cm2), but a subsequent decrease of up to several percent, which forms an optical barrier, as has been observed in many other crystalline materials. The best mode confinement and attenuation is obtained by utilizing the low dose nuclear index enhancement produced by several equally spaced implants (multiple energy) to give a broad well with Δn∼0.25%. Several unusual features of the profiles are reported and discussed.

Ion implanted Nd:YAG waveguide lasers

A detailed description of the use of ion implantation to create optical waveguides in laser crystals is given. Calculated mode profiles and lasing thresholds are shown to be in good agreement with experimental results in a monolithic planar waveguide Nd:YAG laser. The first fabrication and characterization of ion implanted channel waveguides in Nd:YAG is also reported. >

Extra strange modes in ion implanted lithium niobate waveguides

An extra ‘‘strange’’ mode has been observed in the extraordinary index mode spectrum of certain optical waveguides produced by He+ ion implantation in LiNbO3. This behaves differently to the normal modes contained within the main optical well of the waveguide, for example when observed at varying wavelengths or after surface polishing. The mode has been shown to be a real guided‐wave mode, and has been attributed to a subsidiary optical well located beyond the main nuclear damage optical barrier. It is suggested that this well is produced by the radiation‐enhanced diffusion of Li+ towards the nuclear damage barrier, and the mechanism is compared with that responsible for the well on the near side of the barrier which causes the previously reported ‘‘missing’’ modes.

ION beam induced luminescence in fused silica

Abstract A luminescence band at 450 nm (2.7 eV) is observed during ion irradiation of fused silica at energies between 0.7 and 2.0 MeV. The intensity is a function of dose and ion species. In general, the intensity increases to a maximum at which it appears to remain for light ion excitation (H+, He+), but from which it subsequently decays for heavy ions (N+, O+). The energy deposition required to produce this maximum signal is of the same order as that reported for other saturable damage parameters in silica (such as the compaction associated with bond reorientation, and changes in the refractive index).