arXiv subjects

Danielle Pizzey

Publications and source records attributed to Danielle Pizzey.

18 recordsLinked to original sources

arXiv2026

Transformation of vector modes by the Faraday effect in strong magnetic fields

Large Faraday rotations can be generated by circular birefringence of atomic samples in an axial magnetic field in the vicinity of atomic resonance lines. The Faraday angle is a function of the magnetic field strength, the optical density of the atomic sample which may be varied by changing the temperature of the atomic gas, and of course the optical detuning from the transition frequencies. More generally, magneto-optical effects in atomic samples include circular dichroism in addition to birefringence, resulting in a modification of the ellipticity as well as the polarisation alignment. Usually such effects are investigated for homogeneous linear polarisations, but the mechanisms apply also to polarisation structures such as vector vortices. We investigate the effect of optical activity of a rubidium vapour in the Hyperfine Paschen-Back regime, for the example of an azimuthally polarised input light beam. We show that for low atomic densities, circular birefringence dominates over dichroism, and azimuthal polarisation is rotated towards radial polarisation. The rotation angle increases with increasing optical densities. At high vapour temperatures, dichroism becomes more and more relevant, leading to intricate variations of both alignment and ellipticity.

physics.atom-ph↗

arXiv2025

Experimental and theoretical characterisation of Stokes polarimetry of the potassium D1 line with neon buffer gas broadening

This study presents a comprehensive experimental and theoretical characterisation of Stokes polarimetry in potassium (K) vapour on the D1 line. Measurements were performed in the weak-probe regime, investigating the influence of neon buffer gas in the presence of an applied magnetic field in the Faraday geometry. While previous Stokes polarimetry studies in alkali-metal vapours have been conducted, the specific effects of buffer gas-induced broadening and shifts on the observed Stokes parameters remained largely underexplored. Here, experimental measurements of absolute absorption and dispersion were compared with a theoretical model for the electric susceptibility of the vapour, calculated using the established software package $ElecSus$. This work marks the first application of $ElecSus$ to model buffer gas polarimetry of the potassium D1 line, with validation performed against experimental spectra for magnetic fields up to 1.2 kG. Our findings provide new insight into how the presence of buffer gas influences the observed Stokes parameters, thereby enhancing the predictive capabilities of theoretical frameworks for atom-light interactions in buffer-gas environments.

physics.atom-ph↗

arXiv2025

Visualizing strongly focused 3D light fields in an atomic vapor

Structured light, when strongly focused, generates highly confined vectorial electromagnetic field distributions which may feature a polarization component along the optical axis. Manipulating and detecting such 3D light fields is challenging, as conventional optical elements and detectors do not interact with the axial polarization component. Vector light can, however, be mapped onto atomic polarizations, making electric dipole transitions an ideal candidate to sense such 3D light configurations. Working in the hyperfine Paschen-Back regime, where the electric dipole transitions are spectrally resolved, we demonstrate direct evidence of the axial polarization component of strongly focused radial light. We investigate the influence of various input polarization states, including radial, azimuthal, and higher-order optical vortices, on atomic absorption profiles. Our results confirm a clear mapping between the 3D vector light and the atomic transition strength. This work provides new insights into vectorial light-matter interaction, and opens avenues for novel quantum sensing applications.

physics.atom-ph↗

arXiv2025

Light propagation through an atomic vapor with non-orthogonal electric field modes

Alkali-metal atomic vapors are the foundation of an ever-growing range of applications, driven by a comprehensive understanding of their interaction with light. In particular, many models have been developed which characterize this interaction for low intensity laser fields. An atomic medium subject to an external magnetic field of arbitrary direction exhibits two electric field modes that, in general, are non-orthogonal. Mode non-orthogonality is currently neglected by the models used in this context. We derive a new light propagation formalism which takes into account the non-zero overlap of the two modes. We verify the theory using weak-probe spectroscopy of the Rb D$_{2}$ line, showing excellent agreement with experiment. The predictions of the new theory can be exploited, and optimized, to design better atomic photonic devices.

physics.atom-ph↗

arXiv2025

The Role of Buffer Gas in Shaping the D1 Line Spectrum of Potassium Vapour

In this study, we investigate the effect of buffer gas and magnetic field on the spectral line shapes of the potassium D1 transition using sealed vapour cells filled with varying amounts of neon as a buffer gas. Employing a dual-temperature control system, we independently manipulate the cell body and stem temperatures to explore Doppler and collisional effects on the spectrum. Our results show how the Voigt spectral profile changes from Gaussian- to Lorentzian-dominated forms due to pressure broadening and shifts caused by collisions between potassium atoms and neon. Our measurements are in excellent agreement with the literature values for potassium-neon collisions. For the first time we were able to incorporate the buffer-gas shift and broadening into the modified Voigt profile via the ElecSus code, and found excellent agreement between the predicted and measured line profiles. We also analyse the potassium D1 spectral lines in the hyperfine Paschen-Back regime using strong magnetic fields, demonstrating how Zeeman splitting modifies the pressure-broadened line shape. This work provides valuable insights into collision-induced broadening and shifts, enhancing our understanding of potassium spectroscopy and its application in the development of advanced magneto-optical filters for solar physics and other applications.

physics.atom-ph↗

arXiv2024

Modelling spectra of hot alkali vapour in the saturation regime

Laser spectroscopy of hot atomic vapours has been studied extensively. Theoretical models that predict the absolute value of the electric susceptibility are crucial for optimising the design of photonic devices that use hot vapours, and for extracting parameters, such as external fields, when these devices are used as sensors. To date, most of the models developed have been restricted to the weak-probe regime. However, fulfilling the weak-probe power constraint may not always be easy, desired or necessary. Here we present a model for simulating the spectra of alkali-metal vapours for a variety of experimental parameters, most distinctly at intensities beyond weak laser fields. The model incorporates optical pumping effects and transit-time broadening. We test the performance of the model by performing spectroscopy of Rb-87 in a magnetic field of 0.6 T, where isolated atomic resonances can be addressed. We find very good agreement between the model and data for three different beam diameters and a variation of intensity of over five orders of magnitude. The non-overlapping absorption lines allow us to differentiate the saturation behaviour of open and closed transitions. While our model was only experimentally verified for the D2 line of rubidium, the software is also capable of simulating spectra of rubidium, sodium, potassium and caesium over both D lines.

physics.atom-ph↗

arXiv2024

Fine-structure changing collisions in $^{87}$Rb upon D2 excitation in the hyperfine Paschen-Back regime

We investigate fine structure changing collisions in $^{87}$Rb vapour upon D2 excitation in a thermal vapour at 350 K; the atoms are placed in a 0.6 T axial magnetic field in order to gain access to the hyperfine Pashen-Back regime. Following optical excitation on the D2 line, the exothermic transfer 5P$_{3/2}$$\rightarrow$5P$_{1/2}$ occurs as a consequence of buffer-gas collisions; the $^{87}$Rb subsequently emits a photon on the D1 transition. We employ single-photon counting apparatus to monitor the D1 fluorescence, with an etalon filter to provide high spectral resolution. By studying the D1 fluorescence when the D2 excitation laser is scanned, we see that during the collisional transfer process the $m_{J}$ quantum number of the atom changes, but the nuclear spin projection quantum number, $m_{I}$, is conserved. A simple kinematic model incorporating a coefficient of restitution in the collision accounted for the change in velocity distribution of atoms undergoing collisions, and the resulting fluorescence lineshape. The experiment is conducted with a nominally ``buffer-gas free" vapour cell; our results show that fine structure changing collisions are important with such media, and point out possible implications for quantum-optics experiments in thermal vapours producing entangled photon pairs with the double ladder configuration, and solar physics magneto-optical filters.

physics.atom-ph↗

arXiv2024

Indirect measurement of atomic magneto-optical rotation via Hilbert transform

The Kramers-Kronig relations are a pivotal foundation of linear optics and atomic physics, embedding a physical connection between the real and imaginary components of any causal response function. A mathematically equivalent, but simpler, approach instead utilises the Hilbert transform. In a previous study, the Hilbert transform was applied to absorption spectra in order to infer the sole refractive index of an atomic medium in the absence of an external magnetic field. The presence of a magnetic field causes the medium to become birefringent and dichroic, and therefore it is instead characterised by two refractive indices. In this study, we apply the same Hilbert transform technique to independently measure both refractive indices of a birefringent atomic medium, leading to an indirect measurement of atomic magneto-optical rotation. Key to this measurement is the insight that inputting specific light polarisations into an atomic medium induces absorption associated with only one of the refractive indices. We show this is true in two configurations, commonly referred to in literature as the Faraday and Voigt geometries, which differ by the magnetic field orientation with respect to the light wavevector. For both cases, we measure the two refractive indices independently for a Rb thermal vapour in a 0.6 T magnetic field, finding excellent agreement with theory. This study further emphasises the application of the Hilbert transform to the field of quantum and atomic optics in the linear regime.

physics.atom-ph↗

arXiv2023

A device for magnetic-field angle control in magneto-optical filters using a solenoid-permanent magnet pair

Atomic bandpass filters are used in a variety of applications due to their narrow bandwidths and high transmission at specific frequencies. Predominantly these filters in the Faraday (Voigt) geometry, using an applied axial(transverse) magnetic field with respect to the laser propagation direction. Recently, there has been interest in filters realized with arbitrary-angle magnetic fields, which have been made by rotating permanent magnets with respect to the $k$-vector of the interrogating laser beam. However, the magnetic-field angle achievable with this method is limited as field uniformity across the cell decreases as the rotation angle increases. In this work, we propose and demonstrate a new method of generating an arbitrary-angle magnetic field, using a solenoid to produce a small, and easily alterable, axial field, in conjunction with fixed permanent magnets to produce a large transverse field. We directly measure the fields produced by both methods, finding them to be very similar over the length of the vapor cell. We then compare the transmission profiles of filters produced using both methods, again finding excellent agreement. Finally, we demonstrate the sensitivity of filter profile to changing magnetic-field angle (solenoid current), which becomes easier to exploit with the much improved angle control and precision offered by our new design.

physics.optics↗

arXiv2023

Exploiting non-orthogonal eigenmodes in a non-Hermitian optical system to realize sub-100 MHz magneto-optical filters

Non-Hermitian physics is responsible for many of the counter-intuitive effects observed in optics research opening up new possibilities in sensing, polarization control and measurement. A hallmark of non-Hermitian matrices is the possibility of non-orthogonal eigenvectors resulting in coupling between modes. The advantages of propagation mode coupling have been little explored in magneto-optical filters and other devices based on birefringence. Magneto-optical filters select for ultra-narrow transmission regions by passing light through an atomic medium in the presence of a magnetic field. Passive filter designs have traditionally been limited by Doppler broadening of thermal vapors. Even for filter designs incorporating a pump laser, transmissions are typically less than 15\% for sub-Doppler features. Here we exploit our understanding of non-Hermitian physics to induce non-orthogonal propagation modes in a vapor and realize better magneto-optical filters. We construct two new filter designs with ENBWs and maximum transmissions of 181~MHz, 42\% and 140~MHz, 17\% which are the highest figure of merit and first sub-100~MHz FWHM passive filters recorded respectively. This work opens up a range of new filter applications including metrological devices for use outside a lab setting and commends filtering as a new candidate for deeper exploration of non-Hermitian physics such as exceptional points of degeneracy.

physics.optics↗

arXiv2022

Voigt transmission windows in optically thick atomic vapours: a method to create single-peaked line centre filters

Cascading light through two thermal vapour cells has been shown to improve the performance of atomic filters that aim to maximise peak transmission over a minimised bandpass window. In this paper, we explore the atomic physics responsible for the operation of the second cell, which is situated in a transverse (Voigt) magnetic field and opens a narrow transmission window in an optically thick atomic vapour. By assuming transitions with Gaussian line shapes and magnetic fields sufficiently large to access the hyperfine Paschen-Back regime, the window is modelled by resolving the two transitions closest to line centre. We discuss the validity of this model and perform an experiment which demonstrates the evolution of a naturally abundant Rb transmission window as a function of magnetic field. The model results in a significant reduction in two-cell parameter space, which we use to find theoretical optimised cascaded line centre filters for Na, K, Rb and Cs across both D lines. With the exception of Cs, these all have a better figure of merit than comparable single cell filters in literature. Most noteworthy is a Rb-D2 filter which outputs >92% of light through a single peak at line centre, with maximum transmission 0.71 and a width of 330 MHz at half maximum.

physics.atom-ph↗

arXiv2022

Better magneto-optical filters with cascaded vapor cells in the Faraday-Faraday and Faraday-Voigt geometries

Single-cell magneto-optical Faraday filters find great utility and are realized with either 'wing' or 'line center' spectral profiles. We show that cascading a second cell with independent axial (Faraday) or transverse (Voigt) magnetic field leads to improved performance in terms of figure of merit (FOM) and spectral profile. The first cell optically rotates the plane of polarization of light creating the high transmission window; the second cell selectively absorbs the light eliminating unwanted transmission. Using naturally-abundant Rb vapor cells, we realize a Faraday-Faraday wing filter and the first recorded Faraday-Voigt line center filter which show excellent agreement with theory. The two filters have FOM values of 0.86 and 1.63 GHz$^{-1}$ respectively, the latter of which is the largest FOM atomic line filter recorded.

physics.optics↗

arXiv2021

High resolution nanosecond spectroscopy of even-parity Rydberg excitons in Cu$_{2}$O

We present a study of even parity Rydberg exciton states in cuprous oxide using time-resolved second harmonic generation (SHG). Excitonic states with principal quantum number n = 5 - 12 were excited by nanosecond pulses around 1143 nm. Using time-resolved single-photon counting, the coherently generated second harmonic was isolated both temporally and spectroscopically from inelastic emission due to lower-lying free and bound excitonic states, which included narrow resonances at 1.99 eV associated with an exceptional lifetime of 641 $\pm$ 7 $μ$s. The near transform-limited excitation bandwidth enabled detailed measurements of the exciton lineshape and position, from which we obtained values for the quantum defects of the S and D excitonic states associated with the appropriate crystal symmetries. Odd parity P and F excitonic states were also observed, in accordance with predicted quadrupole-allowed two-photon excitation processes. We compared our measurements to conventional one-photon spectroscopy in the same sample, and find that the SHG spectrum is cut off at a lower principal quantum number (n = 12 vs n = 15). We attribute this effect to a combination of spatial inhomogeneities and local heating, and discuss the prospects for observing higher principal quantum number even parity states in future experiments.

cond-mat.mes-hall↗

arXiv2021

Microwave-optical coupling via Rydberg excitons in cuprous oxide

We report exciton-mediated coupling between microwave and optical fields in cuprous oxide (Cu$_2$O) at low temperatures. Rydberg excitonic states with principal quantum number up to $n=12$ were observed at 4~K using both one-photon (absorption) and two-photon (second harmonic generation) spectroscopy. Near resonance with an excitonic state, the addition of a microwave field significantly changed the absorption lineshape, and added sidebands at the microwave frequency to the coherent second harmonic. Both effects showed a complex dependence on $n$ and angular momentum, $l$. All of these features are in semi-quantitative agreement with a model based on intraband electric dipole transitions between Rydberg exciton states. With a simple microwave antenna we already reach a regime where the microwave coupling (Rabi frequency) is comparable to the nonradiatively broadened linewidth of the Rydberg excitons. The results provide a new way to manipulate excitonic states, and open up the possibility of a cryogenic microwave to optical transducer based on Rydberg excitons.

cond-mat.mes-hall↗

arXiv2021

Tuneable homogeneous kG magnetic field production using permanent magnets

We present a permanent magnet arrangement that can achieve a tuneable axial magnetic field from 1.80(8)-2.67(2) kG along the z-axis, where (x,y) = (0,0), with a rms field variation of less than 1% over a length of 25 mm. The instrument consists of an arrangement of off-the-shelf N42 neodymium-iron-boron (NdFeB) axially magnetized ring magnets, of varying outer and inner diameters. The magnets are organized into four cylindrical brass holders, whose relative separation can be manipulated to achieve the desired magnetic field strength and homogeneity over the region of interest. We present magnetic field computations and Marquardt-Levenberg fits to experimental data and demonstrate excellent agreement between theory and experiment. The apparatus has been designed to accommodate a cylindrical atomic vapor cell of length 25 mm and diameter 25 mm to lie within the bore of the ring magnets. The design has a clear aperture of 20 mm in the x-y plane along the z-axis, which opens up new avenues for imaging exploration in atomic spectroscopy.

physics.atom-ph↗

arXiv2020

The Raspberry Pi Auto-aligner: Machine Learning for Automated Alignment of Laser Beams

We present a novel solution to automated beam alignment optimization. This device is based on a Raspberry Pi computer, stepper motors, commercial optomechanics and electronic devices, and the open source machine learning algorithm M-LOOP. We provide schematic drawings for the custom hardware necessary to operate the device and discuss diagnostic techniques to determine the performance. The beam auto-aligning device has been used to improve the alignment of a laser beam into a single-mode optical fiber from manually optimized fiber alignment with an iteration time of typically 20~minutes. We present example data of one such measurement to illustrate device performance.

physics.ins-det↗

arXiv2020

Rydberg Excitons in Synthetic Cuprous Oxide (Cu$_2$O)

High-lying Rydberg states of Mott-Wannier excitons are receiving considerable interest due to the possibility of adding long-range interactions to the physics of exciton-polaritons. Here, we study Rydberg excitation in bulk synthetic cuprous oxide grown by the optical float zone technique and compare the result with natural samples. X-ray characterization confirms both materials are mostly single crystal, and mid-infrared transmission spectroscopy revealed little difference between synthetic and natural material. The synthetic samples show principal quantum numbers up to $n=10$, exhibit additional absorption lines, plus enhanced spatial broadening and spatial inhomogeneity. Room temperature and cryogenic photoluminescence measurements reveal a significant excess of copper vacancies in the synthetic material. These measurements provide a route towards achieving \mbox{high-$n$} excitons in synthetic crystals, opening a route to scalable quantum devices.

cond-mat.mtrl-sci↗

arXiv2020

Atomic line versus lens cavity filters: A comparison of their merits

We present a comparison between lens cavity filters and atomic line filters, discussing their relative merits for applications in quantum optics. We describe the design, characterization and stabilization procedure of a lens cavity filter, which consists of a high-reflection coated commercially available plano-convex lens, and compare it to an ultra-narrow atomic band-pass filter utilizing the D$_{2}$ absorption line in atomic rubidium vapor. We find that the cavity filter peak transmission frequency and bandwidth can be chosen arbitrarily but the transmission frequency is subject to thermal drift and the cavity needs stabilization to better than a few mK, while the atomic filter is intrinsically stable and tied to an atomic resonance frequency such that it can be used in a non-laboratory environment.

physics.ins-det↗