Inertial navigation systems (INSs) are a redundant form of navigation for modern naval platforms and a primary form in Global Positioning System (GPS) denied environments. Current technologies like ring laser gyroscopes (RLG) are used by INSs to measure rotation and acceleration. These measurements are then used to determine position via dead reckoning. There are, however, limitations to the accuracy and stability of this technology. The fundamental sensitivity of an RLG is determined by the effective mass of the photon, which is very small. RLGs are also prone to measurement drift, leading to errors that compound over time. Atomic interferometers show increases in both accuracy and stability over time. Atomic interferometer measurements are fundamentally tied to the mass of an atom, which is ten orders of magnitude larger than the photon’s effective mass. These systems have significantly reduced measurement drift because atomic parameters, which can be tied to gyroscope parameters like scale factors, do not change over time. We discuss the complications of using atomic interferometers as gyroscopes. Two area-reversed interferometers are needed for an atomic gyroscope to distinguish between rotation and acceleration. We explore the addition of a second atomic beam to form a second interferometer in the NPS apparatus. Both atomic beams are characterized separately to verify optimal apparatus settings before a laser is used to simultaneously detect counter-propagating beams.
Inertial navigation systems (INSs) are a redundant form of navigation for modern naval platforms and a primary form in Global Positioning System (GPS) denied environments. Current technologies like ring laser gyroscopes (RLG) are used by INSs to measure rotation and acceleration. These measurements are then used to determine position via dead reckoning. There are, however, limitations to the accuracy and stability of this technology. The fundamental sensitivity of an RLG is determined by the effective mass of the photon, which is very small. RLGs are also prone to measurement drift, leading to errors that compound over time. Atomic interferometers show increases in both accuracy and stability over time. Atomic interferometer measurements are fundamentally tied to the mass of an atom, which is ten orders of magnitude larger than the photon’s effective mass. These systems have significantly reduced measurement drift because atomic parameters, which can be tied to gyroscope parameters like scale factors, do not change over time. We discuss the complications of using atomic interferometers as gyroscopes. Two area-reversed interferometers are needed for an atomic gyroscope to distinguish between rotation and acceleration. We explore the addition of a second atomic beam to form a second interferometer in the NPS apparatus. Both atomic beams are characterized separately to verify optimal apparatus settings before a laser is used to simultaneously detect counter-propagating beams.
Modern Naval vessels utilize Inertial Navigation System (INS) as a navigation tool. Roll, pitch, and yaw data, commonly referred to as attitude data, require onboard gyroscopes and accelerometers. Many weapon systems such as the Navy’s Standard Missile (SM) family require inertial navigation data for operation. Current inertial navigation data for linear acceleration is provided by accelerometers, and rotational acceleration data by optical gyroscopes. However, there are inherent sensitivity limitations to these systems that are fundamentally related to the properties of measuring acceleration changes with a massless photon. If an INS system is being used as a primary method of navigation, it does not have the ability to be checked against another source to reset the drift. This happens when operating in a GPS-denied environment or other situations. Atom interferometry shows promise to provide both linear and rotational data simultaneously with an increase in sensitivity by orders of magnitude relative to current systems, all while being less affected by drift due to the intrinsic characteristics of the atoms which, by definition, do not change over time. Improving the attitude data that INS have access to will significantly enhance both the duration of time they are accurate, and the degree to which they maintain accuracy. This research will continue to investigate the physics of atom interferometry, and the application of this technology as an accelerometer and gyroscope.
The Department of Defense relies on many platforms that require inertial sensors to operate in Global Positioning System (GPS)–compromised environments to provide or verify navigational data. The current generation of sensors in use are subject to sensitivity limitations and drift errors that can compound significantly over time in GPS-contested areas. Inertial sensors based on atom interferometers could provide navigational data that is significantly more accurate and less prone to drift (and therefore navigational errors). This research builds upon previous work (Manicchia in 2020, Gervis in 2021) in which an atomic interferometer was constructed and studied. In this thesis, I demonstrate a path toward making inertially sensitive measurements with this apparatus. In contrast to the previous work, I use counter-propagating Raman fields that can achieve inertial sensitivity. However, these Raman fields are sensitive to non-trivial transverse velocities of our atom beam. I demonstrate a method to reduce these transverse velocities using an optical molasses, but do not pursue this in the apparatus due to spatial considerations. I explore the difference between Ramsey and spin echo spectroscopies, forms of atomic interference, in co- and counter-propagating configurations, the second of which is inertially sensitive. I also demonstrate that interference is still visible in the counter-propagating geometry, laying the foundation for a fully inertially sensitive interferometer.
Current sensors used for inertial navigation are based on technology with inherent sensitivity limitations. Atom interferometry is a very promising replacement, which could yield many orders of magnitude of improvement in sensitivity, leading to more accurate navigation over longer periods of time relative to current technology. This research investigates the physics of atom interferometry through the construction and characterization of an atomic accelerometer/gyroscope combination. In contrast to current state-of-the-art atomic sensors, which use pulsed cold atom sources and pulsed laser beams, the apparatus investigated relies purely on continuous atomic and laser beams. These differences would result in a sensor that lends itself more readily to smaller sizing, lower power consumption, and reduced complexity. This change in approach to atomic interferometry also introduces challenges resulting from laser and atomic beam divergences and the velocity averaging due to both longitudinal and transverse temperature, which this dissertation shows how to overcome. The work contained herein explores many stages of construction of an atomic gyro including the demonstration and characterization of two-dimensional laser cooling of atoms, stimulated Raman transitions, and Ramsey and spin echo interference. The implications for future research are also outlined and discussed.
Recent technological advancements in atom interferometry have demonstrated extremely precise inertial measurements of acceleration and rotation. These could be used to develop ultra-precise inertial navigation systems that approach GPS navigation. The paper presents a rudimentary exposition of the interferometer which is based on beams of atoms cooled by lasers to a velocity of the order of 1 m/s and launched along two trajectories that re-combine, as in a classical interferometer. Using the dual wave-particle quantum mechanical properties of atoms, the differential phase of the interfering beams is indicative of inertial acceleration and rotation, similar to the Sagnac effect. Due to the much shorter wavelength of the atomic beam, the sensitivity is many orders of magnitude greater. Concluding analyses show that an inertial navigation system with 5/hr drift is technically possible.
The use of atom interferometers in inertial systems holds the promise of improvement of several orders of magnitude in sensitivity over sensors using current technology such as micro-electro-mechanical (MEMS) devices or ring laser gyroscopes (RLGs). This paper describes the construction and characterization of an atomic interferometry system for eventual use in a dual-atom-beam accelerometer/gyroscope sensor. In contrast with current state-of-the-art atomic sensors which use pulsed cold atom sources and pulsed laser beams, the investigated apparatus relies purely on continuous atomic and laser beams. These differences can result in a sensor with reduced complexity, a smaller physical footprint, and reduced power consumption. However, these differences also introduce challenges resulting from laser and atomic beam divergences and from velocity averaging due to both longitudinal and transverse velocity spreads. In this work, we characterize our rubidium-based atom beam system and show that Ramsey-style interference can still be observed. The implications for future research are also outlined and discussed.
Inertial sensors based on cold atom interferometry exhibit many interesting features for applications related to inertial navigation, particularly in terms of sensitivity and long-term stability. However, at present the typical atom interferometer is still very much an experiment—consisting of a bulky, static apparatus with a limited dynamic range and high sensitivity to environmental effects. To be compliant with mobile applications further development is needed. In this work, we present a compact and mobile experiment, which we recently used to achieve the first inertial measurements with an atomic accelerometer onboard an aircraft. By integrating classical inertial sensors into our apparatus, we are able to operate the atomic sensor well beyond its standard operating range, corresponding to half of an interference fringe. We report atom-based acceleration measurements along both the horizontal and vertical axes of the aircraft with one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g. The same technology can be used to develop cold-atom gyroscopes, which could surpass the best optical gyroscopes in terms of long-term sensitivity. Our apparatus was also designed to study multi-axis atom interferometry with the goal of realizing a full inertial measurement unit comprised of the three axes of acceleration and rotation. Finally, we present a compact and tunable laser system, which constitutes an essential part of any cold-atom-based sensor. The architecture of the laser is based on phase modulating a single fiber-optic laser diode, and can be tuned over a range of 1 GHz in less than 200 μs.