Wytze E. van der Veer

Light-Triggered Charge Reversal of Organic–Silica Hybrid Nanoparticles

A functional nanoparticle with light-triggered charge reversal based on a protected amine-bridged polysilsesquioxane was designed. An emulsion- and amine-free sol-gel synthesis was developed to prepare uniform nanospheres. Photolysis of suspensions of these nanoparticles results in a reversal of the ζ potential. This behavior has been used to trigger nanoparticle self-assembly, nanocomposite hydrogel formation, and nanoparticle release, showing the potential of this material in nanoscale manipulation and nanoparticle therapy.

Photoluminescent macrocyclic Pd(II) and Pt(II) dimeric complexes with Ph2P–CC–PPh2 spacer

Abstract The synthesis and characterization of macrocyclic Pd(II)/Pt(II) dimers and their monomeric precursors with diphosphine spacer Ph 2 P–CC–PPh 2 (C 2 P 2 ) are reported. Their excited-state properties, including solvent-dependent absorption, emission and quantum yield, are studied. When the solvent polarity increases, solvatochromic absorption band shifts to higher energy, emission maximum shifts to lower energy, and quantum yield decreases. In addition, the host–guest behavior of these new inorganic macrocycles is also reported here.

Conductive Carbon Filled Polymeric Electrodes: Novel Ion Optical Elements for Time-of-Flight Mass Spectrometers

A new technique employing conductive polymeric electrodes for the generation of linear electric fields is proposed and validated. A hollow cylinder comprised of DuPont’s Vespel SP-22, a polymer loaded with conductive carbon particles, is used to enhance the performance of a hybrid reflectron compared to a conventional dual stage gridless reflectron composed of discrete metal ring electrodes. Both devices have comparable physical dimensions and nearly identical ion optical properties. Instrumental resolution measurements are used to validate this novel design.

Fluorescence and Nonradiative Properties of Nd3

We demonstrate new series of heavy metal containing fluorophosphate glass system. The fluorescence and nonradiative properties of Nd3

Probing Dense Sprays with Gated, Picosecond, Digital Particle Field Holography

This paper describes work that demonstrated the feasibility of producing a gated digital holography system that is capable of producing high-resolution images of three-dimensional particle and structure details deep within dense particle fields of a spray. We developed a gated picosecond digital holocamera, using optical Kerr cell gating, to demonstrate features of gated digital holography that make it an exceptional candidate for this application. The Kerr cell gate shuttered the camera after the initial burst of ballistic and snake photons had been recorded, suppressing longer path, multiple scattered illumination. By starting with a CW laser without gating and then incorporating a picosecond laser and an optical Kerr gate, we were able to assess the imaging quality of the gated holograms, and determine improvement gained by gating. We produced high quality images of 50–200 μm diameter particles, hairs and USAF resolution charts from digital holograms recorded through turbid media where more than 98% of the light was scattered from the field. The system can gate pulses as short as 3 mm in pathlength (10 ps), enabling image-improving features of the system. The experiments lead us to the conclusion that this method has an excellent capability as a diagnostics tool in dense spray combustion research.

Optical absorption and emission properties of Nd3-doped fluorophosphates glass for broadband fiber amplifier applications

A new series of fluorophosphate glass is developed which can be doped with an extremely high concentration of Nd3+. The dependence of the optical absorption and emission properties on dopant concentration is reported here for the concentration range 2.5×1020 to 1.25×1021 ions/cm3. Absorption and emission measurements are performed in order to evaluate the spontaneous emission probability, absorption cross-section, emission cross-section, and laser performance parameters. We have synthesized two glass systems: MBBA/NdI with an Nd3+ concentration of 2.50×1020 cm3 and MBBA/NdII with an Nd3+ concentration 6.26×1020 cm3. The stimulated emission cross sections are 1.14 and 1.64×104 cm2 for the 4F3/2→4I13/2 transition and 3.68 and 6.68×104 cm2 for the 4F3/2→4I13/2 transition in MBBA/NdI and MBBA/NdII, respectively. Similarly, the extraction efficiencies are measured to be 1.91, 2.31 (4FI3/2→4I13/2) and 6.18, 9.41 (4F3/2→4I11/2) in MBBA/NdI and the MBBA/NdII, respectively. This new (Mg, Ba)F2-based fluorophosphate glass (MBBA system) is promising for broadband compact optical fiber and waveguide amplifier applications.

Raman spectroscopy of solutions and interfaces containing nitrogen dioxide, water, and 1,4 dioxane: Evidence for repulsion of surface water by NO2 gas

The interaction of water, 1,4 dioxane, and gaseous nitrogen dioxide, has been studied as a function of distance measured through the liquid-vapour interface by Raman spectroscopy with a narrow (<0.1 mm) laser beam directed parallel to the interface. The Raman spectra show that water is present at the surface of a dioxane-water mixture when gaseous NO2 is absent, but is virtually absent from the surface of a dioxane-water mixture when gaseous NO2 is present. This is consistent with recent theoretical calculations that show NO2 to be mildly hydrophobic.

Simple induction probe electric field meter for the detection of electrical fields generated by ion-optical electrodes

A simple electric field probe was developed and used to assess the electrical fields produced inside an ion-optical system. When attached to an XYZ translation stage, this induction probe electrometer is capable of spatially mapping the electrical fields generated by a variety of ion-optical arrangements. Measurements of the electrical fields produced by a conventional reflectron consisting of discrete electrodes and monolithic volume and surface conductive polymeric reflectrons are compared. The performance of the system is validated and a correction is introduced to compensate for capacitive coupling between the probe and the electrode system investigated.

Time-gated holography to provide a glimpse into dense sprays

In all combustion devices, the flame stability and thermal efficiency are strongly influenced by the fuel and oxidizer mixing processes. In spray combustion (e.g., in gas turbines), mixing is associated with breakup and atomization of dense sprays. It is necessary to view these processes in detail to obtain knowledge vital for improving them.1 Photography, holography, and x-ray imaging, which have been used for many years in such research,2, 3 have failed to provide clear views because noise from multiple scattering obscures the signal needed to acquire a useful recording. In recent years, new methods of separating the signal from the noise have been developed, including pseudo-ballistic photon imaging,4–7 in which high-speed optical gates separate ballistic (not scattered) and only-once-scattered, near-ballistic, ‘snake’ photons from multiply scattered photons. Another problem in imaging spray particles is the wide depth of field needed to bring all of them into focus. Current ballistic imaging systems provide only the shadows of particles without resolving the third dimension.4–7 We are combining pseudo-ballistic imaging with digital holography for the first time to resolve the digitally recorded hologram of a dense spray in three dimensions. The hologram is the out-of-focus diffraction pattern of all of the spray particles, which we can reconstruct numerically at different depths throughout the viewed volume. This procedure brings every particle into focus and detects its position. Figure 1 shows the digital holocamera design. The laser output is split into three different beams: the fundamental 1.06 m beam, which is used to open the Kerr gate, a second-harmonic Figure 1. Picosecond digital holography system design. DM: Dichroic mirror. !: Fundamental beam. 2!: Second-harmonic beam. BS: Beam splitter cube. F1: Focal plane. OP: Optical path length compensation. L1: Lens, f D 400mm. L2: Lens, f D 200mm. WP: Wave plate. P1, P2: Cross polarizer. OKC: Optical Kerr cell.

Stabilization technique for injection seeding Nd:Yag lasers using microwave range mode beating

The conventional technique for matching and stabilizing the cavity length of seeded Q-switched Nd:YAG lasers is to minimize the pulse build-up time in a lock-in scheme. A disadvantage of this technique is that in order to obtain a robust feedback signal the opening speed of the Q-switch needs to be reduced, which causes timing issues, loss of power, and lengthening the generated pulse. Here an alternative method is presented which mediates these problems. A feedback signal is obtained using microwave frequency range detection of the beating between the longitudinal cavity modes. This novel technique can be implemented with only a minimal modification of the cavity optics and electronics of conventional free-running Nd:YAG lasers.The conventional technique for matching and stabilizing the cavity length of seeded Q-switched Nd:YAG lasers is to minimize the pulse build-up time in a lock-in scheme. A disadvantage of this technique is that in order to obtain a robust feedback signal the opening speed of the Q-switch needs to be reduced, which causes timing issues, loss of power, and lengthening the generated pulse. Here an alternative method is presented which mediates these problems. A feedback signal is obtained using microwave frequency range detection of the beating between the longitudinal cavity modes. This novel technique can be implemented with only a minimal modification of the cavity optics and electronics of conventional free-running Nd:YAG lasers.