LeGrand Shumway

Ion Trap Electric Field Characterization Using Slab Coupled Optical Fiber Sensors

AbstractThis paper presents a method for characterizing electric field profiles of radio frequency (rf) quadrupole ion trap structures using sensors based on slab coupled optical-fiber sensor (SCOS) technology. The all-dielectric and virtually optical fiber-sized SCOS fits within the compact environment required for ion traps and is able to distinguish electric field orientation and amplitude with minimal perturbation. Measurement of the fields offers insight into the functionality of traps, which may not be obtainable solely by performing simulations. The SCOS accurately mapped the well-known field profiles within a commercially available three-dimensional quadrupole ion trap (Paul trap). The results of this test allowed the SCOS to map the more complicated fields within the coaxial ion trap with a high degree of confidence as to the accuracy of the measurement. Figureᅟ

High voltage measurements using slab coupled optical sensors (SCOS)

One of the most common methods used to measure high voltage is using a voltage divider. While this method is fairly reliable for most low frequency high voltage measurements, the voltage divider encounters difficulty when measuring higher frequency voltage signals. In these instances, the signal measured by the voltage divider becomes susceptible to distortion and inaccuracy. One solution to measuring voltages where a voltage divider would not suffice is using an electrode structure in conjunction with a fiber-based electric field sensor. A high voltage generator was constructed utilizing automotive ignition coils and was used in a capacitor-charging circuit. The voltage on the capacitor was measured using a common resistive voltage divider as well as with a fiber-based electric field sensor. Where a resistor divider was not reliable in characterizing the system, the optical sensor was successful in measuring the charge and discharge voltages of the capacitor circuit.

Optical sensing of electrical fields in harsh environments

This paper shows a method allowing electric field sensing in high vibration environments. The vibration sensitivity is reduced using a push-pull configuration and external phase modulation. This paper provides both theoretical description and experimental verification.

Split Hopkinson bar measurement using high-speed full-spectrum fiber Bragg grating interrogation.

The development and validation of a high-speed, full-spectrum measurement technique is described for fiber Bragg grating (FBG) sensors. A FBG is surface-mounted to a split-Hopkinson tensile bar specimen to induce high strain rates. The high strain gradients and large strains that indicate material failure are analyzed under high strain rates up to 500  s-1. The FBG is interrogated using a high-speed full-spectrum solid-state interrogator with a repetition rate of 100 kHz. The captured deformed spectra are analyzed for strain gradients using a default interior point algorithm in combination with the modified transfer matrix approach. This paper shows that by using high-speed full-spectrum interrogation of an FBG and the modified transfer matrix method, highly localized strain gradients and discontinuities can be measured without a direct line of sight.

Push–pull slab coupled optical sensor for measuring electric fields in a vibrational environment

Vibration-insensitive fiber optic electric field sensor is created by fabricating two sensing elements in close proximity onto the same optical fiber and subtracting the two signals. The device is used to measure an electric field of 10  kV/m, while the sensor is being bent and impacted.

Ion trap electric field measurements using slab coupled optical sensors

Ion traps are widely used in the field of mass spectrometry. These devices use high electric fields to mass-selectively trap, eject, and count the particles of a material, producing a mass spectrum of the given material. Because of their usefulness, technology pushes for smaller, more portable ion traps for field use. Making internal ion trap field measurements not yet feasible because current electric field sensors are often too bulky or their metallic composition perturbs field measurements. Using slab coupled optical sensor (SCOS) technology, we are able to build sensors that are compatible with the spacing constraints of the ion trap. These sensors are created by attaching a nonlinear crystal slab waveguide to an optical fiber. When a laser propagates through the fiber, certain wavelengths of light couple out of the fiber via the crystal and create “resonances” in the output light spectrum. These resonances shift in proportion to a given applied electric field, and by measuring that shift, we can approximate the electric field. Developing a sensor that can effectively characterize the electric fields within an ion trap will greatly assist in ion trap design, fabrication, and troubleshooting techniques.

Optical Sensing of Electric Fields in Harsh Environments

Fiber optic electric field sensors are ideal for characterizing the electric field in many different systems. Unfortunately, many of these systems produce one or more noise types, like vibrational noise which contribute to a harsh sensing environment on the fiber optic sensor. When fiber optic sensors are placed in a harsh vibration environment, multiple noise types can overwhelm the measurements. This work shows how to simultaneously eliminate three different noise types in a fiber optic sensor induced by a harsh vibration environment. Specifically, nonlocalized vibration-induced interferometric noise is up converted to higher frequency bands by single-tone phase modulation. Then, localized vibrational noise, and radio frequency noise are all eliminated using a push–pull slab coupled optical sensor configuration to allow for an optical measurement of an electric field in a harsh environment.

Optical electric field sensor sensitivity direction rerouting and enhancement using a passive integrated dipole antenna

This work introduces a passive dipole antenna integrated into the packaging of a slab-coupled optical sensor to enhance the directional sensitivity of electro-optic electric field measurements parallel to the fiber axis. Using the passive integrated dipole antenna described in this work, a sensor that can typically only sense fields transverse to the fiber direction is able to sense a 1.25 kV/m field along the fiber direction with a gain of 17.5. This is verified through simulation and experiment.

Measuring arc dynamics using a slab coupled optical sensor (SCOS)

Electric arcs are a form of electric discharge through a non-conductive media caused by a high electric potential between two points. The timing of this discharge serves as an important parameter in high pulse power applications and a short discharge time is often desirable. We put together a circuit which operates on the principle of inducing a high voltage pulse on an ignition coil controlled by a MOSFET. Slab coupled optical sensor (SCOS) technology was used to characterize arc dynamics such as the discharge time, charge time, slope of the discharge, and effects of changing spark gap distance. In triggering the spark gap, we were able to characterize the discharge of pulses with times between 100 ms and 170 ns.

High electric field measurement with slab coupled optical sensors using nonlinear calibration

We describe the application of SCOS technology in non-intrusive, directional and spatially localized measurements of high electric fields. When measuring electric fields above a certain threshold, SCOS measurement sensitivity starts varying to a great extent and the linear approximation that assumes sensitivity to be constant breaks down. This means that a comprehensive nonlinear calibration method is required for accurate calibration of both low and high electric fields, while linear calibration can only be accurately applied for low fields. Nonlinear calibration method relies on the knowledge of the variability of sensitivity, while linear calibration relies on approximation of sensitivity with a constant value, which breaks down for high fields. We analyze and compare the two calibration methods by applying them to a same set of measurements. We measure electric field pulses with magnitudes from 1 MV/m to 8.2 MV/m, with sub-300 ns rise time and fall-off time constant of 60 μs. We show that the nonlinear calibration very accurately predicts all measured fields, both high and low, while the linear calibration becomes increasingly inaccurate for fields above 1 MV/m.