James L. Archibald

Identification and Control of a Grating-Stabilized External-Cavity Diode Laser

Diode lasers have many useful properties and have found a variety of uses including CD and DVD players, barcode scanners, laser surgery, water purification, quantum-key cryptography, spectroscopic sensing, etc. Nevertheless, their intrinsic linewidth or the precision of their emitted wavelengths, is not good enough for many cutting-edge applications such as atomic interferometry or high-performance atomic clocks. Using active feedback control, we can narrow the linewidth of a diode laser by not allowing the frequency of emitted light to drift away from a reference value. Nevertheless, such feedback designs are challenging because of a lack of first principles models and difficult sensor dynamics. This brief describes our diode laser system and reports our results identifying the system using black-box techniques, validating the empirical models, and designing controllers to achieve desired performance while preserving stability and satisfying implementation constraints.

Black-Box Identification of a Grating-Stabilized External-Cavity Diode Laser

Diode lasers have many useful properties and have found a variety of uses including CD and DVD players, barcode scanners, laser surgery, water purification, quantum-key cryptography, spectroscopic sensing, etc. Nevertheless, their intrinsic linewidth, or the precision of their emitted wavelengths, is not good enough for many cutting-edge applications such as atom interferometry or high-performance atomic clocks. Using active feedback control we can narrow the linewidth of a diode laser, not allowing the frequency of emitted light to drift away from a reference value. Nevertheless, such feedback designs are challenging because of a lack of first principles models and difficult sensor dynamics. This paper describes our diode laser system and reports our results identifying the system using black-box techniques.

Light splitting with imperfect wave plates

We discuss the use of wave plates with arbitrary retardances, in conjunction with a linear polarizer, to split linearly polarized light into two linearly polarized beams with an arbitrary splitting fraction. We show that for non-ideal wave plates, a much broader range of splitting ratios is typically possible when a pair of wave plates, rather than a single wave plate, is used. We discuss the maximum range of splitting fractions possible with one or two wave plates as a function of the wave plate retardances, and how to align the wave plates to achieve the maximum splitting range possible when simply rotating one of the wave plates while keeping the other one fixed. We also briefly discuss an alignment-free polarization rotator constructed from a pair of half-wave plates.

Applying classical geometry intuition to quantum spin

Using concepts of geometric orthogonality and linear independence, we logically deduce the form of the Pauli spin matrices and the relationships between the three spatially orthogonal basis sets of the spin-1/2 system. Rather than a mathematically rigorous derivation, the relationships are found by forcing expectation values of the different basis states to have the properties we expect of a classical, geometric coordinate system. The process highlights the correspondence of quantum angular momentum with classical notions of geometric orthogonality, even for the inherently non-classical spin-1/2 system. In the process, differences in and connections between geometrical space and Hilbert space are illustrated.

Precision Metrology with a Strontium Ion Interferometer

We present a strontium ion interferometer for use as an electromagnetic field sensor with unprecedented sensitivity. Applications include measurements of fringing fields, studies of image charge scattering in superconductors, and ultra-precise tests of electromagnetism.

Achieving High Precision with a Thermal Beam Atom Interferometer

We report on the progress of a thermal calcium-beam Ramsey-Borde atom interferometer. Our efforts have led to the development of precision electronic and laser systems whose design allows them to be implemented as lab standards.