Generation of tuneable 589nm radiation as a Na guide star source using an optical parametric amplifier

We describe a 5.5W 589nm source based on a passively modelocked Nd:YVO4 laser and a multi-stage Lithium Triborate optical parametric amplifier seeded by a tuneable semiconductor laser. We show this system can produce rapidly tuneable, transform-limited pulses in near diffraction-limited beams at 589nm, useful for Na guide star applications. The attraction of this scheme is that it can be assembled from commercially available hardware and is readily scalable to high average powers

Annealing-induced reduction in nanoscale heterogeneity of thermally evaporated amorphous As2S3 films

The morphology and structural order of thermally deposited and annealed amorphous As2S3 films have been investigated using high resolution transmission electron microscopy. It was found that both the as-deposited and annealed films contained sparsely distributed nanocrystallites of the orpiment As2S3 crystalline phase. However, from selected area electron diffraction both films appeared amorphous. Fluctuation electron microscopy revealed that the as-deposited film contained greater nanoscale inhomogeneity. Low temperature annealing reduced the nanoscale inhomogeneity and resulted in a more homogeneous and energetically favorable network. The reduction in nanoscale inhomogeneity upon low temperature annealing was accompanied by the appearance of a first sharp diffraction peak in the diffraction pattern. This first-sharp diffraction peak has been attributed to chemical ordering of interstitial voids. Our measurements suggest that this chemical short-range ordering is associated with the dissolution of the energetically unfavorable larger correlated structures that contribute to the inhomogeneity of the as-deposited film

Low loss high index contrast nanoimprinted polysiloxane waveguides

Nanoimprint lithography is gaining rapid acceptance in fields as diverse as microelectronics and microfluidics due to its simplicity high resolution and low cost. These properties are critically important for the fabrication of photonic devices, where cost is often the major inhibiting deployment factor for high volume applications. We report here on the use of nanoimprint technology to fabricate low loss broadband high index contrast waveguides in a Polysiloxane polymer system for the first time

Cluster formation through the action of a single picosecond laser pulse

We demonstrate experimentally and describe theoretically the formation of carbon nanoclusters created by single picosecond laser pulses. We show that the average size of a nanocluster is determined exclusively by single laser pulse parameters and is independent of the gas fill (He, Ar, Kr, Xe) and pressure in a range from 20mTorr to 200 Torr. Simple kinetic theory allows estimates to be made of the cluster size, which are in qualitative agreement with the experimental data. We conclude that the role of the buffer gas is to induce a transition between thin solid film formation on the substrate and foam formation by diffusing the clusters through the gas, with no significant effect upon the average cluster size

Picosecond high-repetition-rate pulsed laser ablation of dielectrics: the effect of energy accumulation between pulses

We report experiments on the ablation of arsenic trisulphide and silicon using high-repetition-rate (megahertz) trains of picosecond pulses. In the case of arsenic trisulphide, the average single pulse fluence at ablation threshold is found to be >100 times lower when pulses are delivered as a 76-MHz train compared with the case of a solitary pulse. For silicon, however, the threshold for a 4.1-MHz train equals the value for a solitary pulse. A model of irradiation by high-repetition-rate pulse trains demonstrates that for arsenic trisulphide energy accumulates in the target surface from several hundred successive pulses, lowering the ablation threshold and causing a change from the laser-solid to laser-plasma mode as the surface temperature increases

Laser-induced microexplosion confined in a bulk of silica: formation of nanovoids

We report on the nanovoid formation inside synthetic silica, viosil, by single femtosecond pulses of 30–100nJ energy, 800nm wavelength, and 180fs duration. It is demonstrated that the void is formed as a result of shock and rarefaction waves at pulse power much lower than the threshold of self-focusing. The shock-compressed region around the nanovoid is demonstrated to have higher chemical reactivity. This was used to reveal the extent of the shock-compressed region by wet etching. Application potential of nanostructuring of dielectrics is discussed

High-Q (>750,000) photonic crystal nanocavities fabricated from chalcogenide glass fully embedded in an index-matched cladding

We have fabricated a Ge11.5As24Se64.5 2-D photonic crystal containing a hetero-structure cavity fully embedded in a cladding with index of 1.44. Because of the low index contrast of this structure (≈1.2) we had to use a W0.54 defect waveguide to inhibi

Preacher\u27s Magazine Volume 47 Number 08

The Resource of the Retired, General Superintendent Stowe Does the Name Make a Difference? Editorial How to Stay in the Pastorate and Like It, Milton Harrington Some Thoughts on Pastoral Priorities, G. Lewis Van Dyne A Renewed Emphasis on the Preaching of Holiness, Otho Jennings Too Busy to Be Courteous? An evangelist It Takes More than Tools, Milo L. Arnold Twenty Years of Concern Paid Off! Practical Points Classics of Devotion (II. Imitation of Christ), Ross W. Hayslip What Are We Serving? R. E. Maner A Speaking Relationship, Mrs. R. Edgar Johnson A Letter to the Bereaved, Jesse Turner A Shock That Changed My Ministry, Robert G. Green Memo to Myself, Rene Colaw The Serpent and the Sword, W. E. McCumber DEPARTMENTS Evangelistically Speaking Pastor’s Supplement The Preacher’s Wife Faith in Action Gleanings from the Greek Timely Outlines Idea Sparks Bulletin Barrel Here and There Among Books Calendar Digest Coming Next Month Among Ourselveshttps://digitalcommons.olivet.edu/cotn_pm/1541/thumbnail.jp

Linear optical properties of Ge nanocrystals in silica

The absorption and extinctionspectra of Genanocrystals in silica formed by ion implantation are studied using photothermal deflection and transmission spectroscopies. It is found that scattering makes a significant contribution to the extinction spectrum, damping the spectral features and resulting in a Rayleigh scattering-likeω⁴ dependence. In contrast, the spectra measured by photothermal deflection clearly show features such as the E1/E1+Δ1 transitions. The Tauc gap is extracted to be ∼0.7±0.1 eV

Photonic crystal nanocavities fabricated from chalcogenide glass fully embedded in an index-matched cladding with a high Q-factor (>750,000)

We have designed and fabricated a 2-D photonic crystal hetero-structure cavity in the chalcogenide glass Ge11.5As24Se64.5 that is fully embedded in a cladding with refractive index of 1.44. The low index contrast of this structure (≈1.21) means that high-Q resonances cannot be obtained using standard hetero-structure cavity designs based on W1 waveguides. We show that reducing the waveguide width can substantially improve light confinement, leading to high-Q resonances in a hetero-structure cavity. Numerical simulations indicate intrinsic Qv > 107 are possible with this approach. Experimentally, an optical cavity with a high intrinsic Qv>7.6 x 105 was achieved in a structure with a theoretical Qv = 1.7 x 106.The research was conducted by the Australian Research Council Centre for Excellence for Ultrahigh bandwidth Devices for Optical Systems (project number CE110001018). The device fabrication was partially supported by the facilities of the Australian National Fabrication Facility (ANFF). The calculation was supported by the National Computational Infrastructure (NCI) National Facility