Colin J Dedman

Optimum design and construction of a Zeeman slower for use with a magneto-optic trap

A method for optimizing the design and construction of a Zeeman slower coil is presented. Unlike traditional designs, the measured magnetic field profile very accurately matches the desired field profile, enabling significant advantages for loading a magneto-optic trap.

ForceForm: a dynamically deformable interactive surface

We present the design and implementation of ForceForm, a prototype dynamically deformable interactive surface that provides haptic feedback. We use an array of electromagnets and a deformable membrane with permanent magnets attached to produce a deformable interactive surface. The system has a fast reaction time, enabling dynamic interaction. ForceForm supports user input by physically deforming the surface according to the users touch and can visualise data gathered from other sources as a deformed plane. We explore possible usage scenarios that illustrate benefits and features of the system and we outline the performance of the system

Elastic electron scattering from sulfur hexafluoride

Absolute differential cross sections for elastic scattering of electrons from sulfur hexafluoride (SF6) have been measured at 11 incident energies between 2.7 and 75 eV and for scattering angles between 10° and 130°. The magnetic angle-changing device of Read and co-workers has been used to extend these measurements to backward angles (130°-180°) for incident energies below 15 eV. The measurements reveal some substantial differences with several previous determinations and a reasonably good level of agreement with a recent close-coupling calculation.

Active cancellation of stray magnetic fields in a Bose-Einstein condensation experiment

A method of active field cancellation is described, which greatly reduces the stray magnetic field within the trap region of a Bose-Einstein condensation experiment. An array of six single-axis magnetic sensors is used to interpolate the field at the trap center, thus avoiding the impractical requirement of placing the sensor within the trap. The system actively suppresses all frequencies from dc to approximately 3000 Hz, and the performance is superior to conventional active Helmholtz cancellation systems. A method of reducing the field gradient, by driving the six Helmholtz coils independently, is also investigated.

Fast switching of magnetic fields in a magneto-optic trap

Magneto-optic traps which employ current windings to generate pulsed magnetic fields require rapid switch-off times for many applications. Practical difficulties in attaining rapid switch-off of the magnetic field, including the generation of induced currents, are addressed. Several methods for minimizing the switch-off time are presented which do not require complex feedback mechanisms involving direct measurement of the magnetic field.

Fast 8 kV metal-oxide semiconductor field-effect transistor switch

A fast, high-voltage switch based on cheap and readily available components is described. This simple circuit can switch 1 kV to ground with a fall time of ∼2.5 ns, and has proved a cost-effective means of driving electrostatic gating and rereferencing devices in pulsed ion-beam experiments.

An ion gating, bunching, and potential re-referencing unit

A novel design to achieve the gating, bunching, and potential re-referencing of an ion beam, suitable for use in a photofragment spectrometer, is presented. The device simultaneously performs all three functions in a simple, compact, and easily aligned unit. It requires only a single digital signal and one high voltage supply for operation, and provides higher flux density than previous designs. The unit uses lensing to perform beam gating, an approach which has not been reported previously. The design does not require grids, and does not introduce divergence into the ion beam. Experimental results for the combined gating, bunching, and re-referencing unit are presented, and compared with modeled performance.

Widely tunable, narrow linewidth external-cavity gain chip laser for spectroscopy between 1.0 – 1.1 µm

We have developed and characterised a stable, narrow linewidth external-cavity laser (ECL) tunable over 100 nm around 1080 nm, using a single-angled-facet gain chip. We propose the ECL as a low-cost, high-performance alternative to fibre and diode lasers in this wavelength range and demonstrate its capability through the spectroscopy of metastable helium. Within the coarse tuning range, the wavelength can be continuously tuned over 30 pm (7.8 GHz) without mode-hopping and modulated with bandwidths up to 3 kHz (piezo) and 37(3) kHz (current). The spectral linewidth of the free-running ECL was measured to be 22(2) kHz (Gaussian) and 4.2(3) kHz (Lorentzian) over 22.5 ms, while a long-term frequency stability better than 40(20) kHz over 11 hours was observed when locked to an atomic reference.

New magnetic dipole transition of the oxygen molecule: B′ 3Πg←X 3Σg−(0,0)

Through the use of isotopically pure gas at a temperature of 77 K, a weak photoabsorption band of 16O2 is found near 1856 A, underlying the stronger Schumann–Runge (SR) band B 3Σu−←X 3Σg−(8,0). The location, structure, and intensity of this new band are consistent with expectation for the magnetic dipole transition B′ 3Πg←X 3Σg−(0,0), where the designation B′ is chosen to represent the II 3Πg valence state. This electronic transition contributes to the “excess absorption” underlying the SR bands [B. R. Lewis, S. T. Gibson, and E. H. Roberts, J. Chem. Phys. 115, 245 (2001)].Through the use of isotopically pure gas at a temperature of 77 K, a weak photoabsorption band of 16O2 is found near 1856 A, underlying the stronger Schumann–Runge (SR) band B 3Σu−←X 3Σg−(8,0). The location, structure, and intensity of this new band are consistent with expectation for the magnetic dipole transition B′ 3Πg←X 3Σg−(0,0), where the designation B′ is chosen to represent the II 3Πg valence state. This electronic transition contributes to the “excess absorption” underlying the SR bands [B. R. Lewis, S. T. Gibson, and E. H. Roberts, J. Chem. Phys. 115, 245 (2001)].

Precision temperature controlled filtered laminar air enclosure

We demonstrate a novel temperature controlled filtered laminar air enclosure composed of primarily off-the-shelf components that can be applied to a broad class of systems to significantly enhance their performance. An air mixing method is employed to provide variable cooling of the incoming filtered air, providing a temperature stability of ± 0.02 °C within the enclosure. The method is inexpensive to implement, and is suitable for a wide range of temperature controlled enclosures, with dimensions in the approximate range from 1 m to 5 m, making it ideal for many scientific applications.