Laser-fabricated glass microlens arrays

We report the fabrication of large, laser-formed refractive microlens arrays on doped borosilicate glass. Tuning the laser heat-source properties was found to give precise control over the melt process and the resulting lenslet geometries. Measurements of focal length, index, and surface shapes show excellent uniformity across these arrays.     

The phase diagram of the system La2(SO4)3Ag2SO4

The phase diagram of the system La₂(SO₄)₃Ag₂SO₄ was studied by DTA, XRD, SEM, and optical methods. One double salt is formed at 67 mole% La₂(SO₄)₃ and this melts incongruently at 876±6°C. A eutectic is formed at 8 mole% La₂(SO₄)₃ and at a temperature of 618±3°C. Suppression of decomposition was effected by the sealed tube method, but some reference is made to experiments conducted with a flowing atmosphere of SO₃, SO₂ and O₂.     

Separation and indirect detection by capillary zone electrophoresis of ppb (w/w) levels of aluminum ions in solutions of multiple cations

Solutions of multiple cations in aqueous solutions at concentrations as low as 200 ppb were analyzed by capillary zone electrophoresis. Aluminum ions were cleanly separated from Li⁺, K⁺, Ca²⁺, Cr³⁺, Zn²⁺, CU²⁺, and other ions less than 6 min after injection of the solution on a 50 cm × 50 μm I.D. uncoated fused-silica capillary column at 15 kV. Indirect detection at 204 nm was carried out using a pH 2.8 background electrolyte containing 5.2 mM ephedrine as a UV-absorbing co-ion and 4.7 mM -hydroxyisobutyric acid as a completing counter ion. Mobilities for Al³⁺ and 14 other complexed cations were determined for this electrolyte.     

Nonwetting of He and dilute He–He mixtures on Cs

For pure ⁴He on Cs a nonwet phase exists below ≈2 K but for dilute ³He–⁴He mixtures the wetting is reentrant. Measurements of the contact angle with dilute mixtures of liquid helium on Cs can be explained in detail in terms of ³He states together with ripplons at the Cs–He mixture interface, but it is impossible to account for the lower wetting temperatures or contact angles with only ³He states or ripplons. We discuss the influence of surface roughness of the Cs on the contribution of interface excitations to the free energy and suggest that the variety of contact angles found with different samples of Cs is due mainly to their degree of roughness.     

The hydroxyl radical reaction rate constant and products of cyclohexanol

The gas phase reaction of the hydroxyl radical (OH) with cyclohexanol (COL) has been studied. The rate coefficient was determined to be (19.0 ± 4.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ (at 297 ± 3 K and 1 atmosphere total pressure) using the relative rate technique with pentanal, decane, and tridecane as the reference compounds. Assuming an average OH concentration of 1 × 10⁶ molecules cm⁻³, an atmospheric lifetime of 15 h is calculated for cyclohexanol. Products of the OH + COL reaction were determined to more clearly define COL's atmospheric degradation mechanism. The observed products and their formation yields were: cyclohexanone (0.55 ± 0.06), hexanedial (0.32 ± 0.15), 3‐hydroxycyclohexanone (0.31 ± 0.14), and 4‐hydroxycyclohexanone (0.08 ± 0.04). Consideration of the potential reaction pathways suggests that each of these products is formed via hydrogen abstraction at a different site on the COL ring. The products and their relative amounts are discussed in light of the predicted yields for each reaction channel. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 108–117, 2001     

Preparation of nanoparticles by continuous-flow microfluidics

We review a variety of micro- and nanoparticle formulations produced with microfluidic methods. A diverse variety of approaches to generate microscale and nanoscale particles has been reported. Here we emphasize the use of microfluidics, specifically microfluidic systems that operate in a continuous flow mode, thereby allowing continuous generation of desired particle formulations. The generation of semiconductor quantum dots, metal colloids, emulsions, and liposomes is considered. To emphasize the potential benefits of the continuous-flow microfluidic methodology for nanoparticle generation, preliminary data on the size distribution of liposomes formed using the microfluidic approach is compared to the traditional bulk alcohol injection method.     

Quantum transmission of atoms through a slab of superfluid helium

We describe a measurement of the transmission probability of 4He atoms through a freely suspended slab of superfluid 4He at low temperatures. In our experiment the slab is realized by using an array of parallel cylindrical holes of diameter 51 microm in a glass disc of thickness 190 microm. By controlling the chemical potential, the holes can be made to fill or empty with liquid, and the surface curvature varied. We have measured the transmission of atom beams, generated by a thin-film heater and detected with a sensitive bolometer, through this structure. The results show that the dominant transmission channel is atom-R+ roton-atom with a probability p approximately 0.12 and that R+ rotons can undergo total internal reflection at the free liquid surfaces.     

Self-referencing, spectrally, or spatially encoded spectral interferometry for the complete characterization of attosecond electromagnetic pulses

We propose a method for the complete characterization of attosecond duration electromagnetic pulses produced by high harmonic generation in an atomic gas. Our method is based on self-referencing spectral interferometry of two spectrally sheared extreme ultraviolet pulses, which is achieved by pumping the harmonic source with two sheared optical driving pulses. The resulting interferogram contains sufficient information to completely reconstruct the temporal behavior of the electric field. We demonstrate that such a method is feasible, and outline two possible experimental configurations.