arXiv subjects

Timothy C. Steimle

Publications and source records attributed to Timothy C. Steimle.

15 recordsLinked to original sources

arXiv2025

Production and spectroscopy of cold radioactive molecules

Molecules with heavy, radioactive nuclei promise extreme sensitivity to fundamental nuclear and particle physics. However, these nuclei are available in limited quantities, which challenges their use in precision measurements. Here we demonstrate the gas-phase synthesis, cryogenic cooling, and high-resolution laser spectroscopy of radium monohydroxide, monodeuteroxide, and monofluoride molecules ($^{226}$RaOH, $^{226}$RaOD, and $^{226}$RaF) in a tabletop apparatus by combining novel radioactive target production protocols, optically driven chemistry in a cryogenic buffer gas, and low-background spectroscopic detection methods. The molecules are cooled in the lab frame, creating conditions that are the same starting points as many current molecular precision measurement and quantum information experiments. This approach is readily applied to a wide range of species and establishes key capabilities for molecular quantum sensing of exotic nuclei.

physics.atom-ph↗

arXiv2025

Rapid, Broadband, Optical Spectroscopy of Cold Radicals

Optical spectroscopy of molecular radicals is an important tool in physical chemistry, and is a prerequisite for many experiments which use molecules for quantum science and precision measurement. However, even the simplest molecules have complex spectra which can be very time consuming to measure. Here we present an approach which offers the ability to measure the optical spectra of cryogenically-cooled molecular radicals with much greater efficiency. By combining a supercontinuum laser with a cryogenic buffer gas molecular source and a commercial optical spectrometer, we realize 15 nm of simultaneous bandwidth with 0.56 pm $(\approx 0.5$ GHz) resolution and high sensitivity. As a demonstration we measure and assign hundreds of lines and dozens of molecular constants from 15 bands in the $B^2Σ^+-X^2Σ^+$ system of CaF, including a low-abundance isotopologue, in a few hours. The setup is robust, simple, and should enable spectroscopy of molecular radicals with much higher throughput.

physics.chem-ph↗

arXiv2025

A Molecular Beam Study of the (0,0) A2Π<- X2Σ+ Band of CaF Isotopologues

This study presents an experimental determination of spectroscopic parameters for the less-abundant isotopologues $^{42}$CaF and $^{44}$CaF, alongside $^{40}$CaF, using high-resolution laser-induced fluorescence spectroscopy in a skimmed free jet expansion. We recorded spectra near the natural linewidth limit and derived spectroscopic constants for both the $X^2Σ^+$ and $A^2Π$ electronic states, including the fine and $^{19}$F magnetic hyperfine parameters. We also estimated the isotope amount ratio $r(^{44}\mathrm{Ca}/^{40}\mathrm{Ca})$, demonstrating the potential use of optical spectroscopy for calcium isotope analysis.

physics.chem-ph↗

arXiv2023

Optical cycling in polyatomic molecules with complex hyperfine structure

We have developed and demonstrated a scheme to achieve rotationally-closed photon cycling in polyatomic molecules with complex hyperfine structure and sensitivity to hadronic symmetry violation, specifically $^{171}$YbOH and $^{173}$YbOH. We calculate rotational branching ratios for spontaneous decay and identify repumping schemes which use electro-optical modulators (EOMs) to address the hyperfine structure. We demonstrate our scheme by cycling photons in a molecular beam and verify that we have achieved rotationally-closed cycling by measuring optical pumping into unaddressed vibrational states. Our work makes progress along the path toward utilizing photon cycling for state preparation, readout, and laser cooling in precision measurements of polyatomic molecules with complex hyperfine structure.

physics.atom-ph↗

arXiv2022

Zeeman-Sisyphus Deceleration for Heavy Molecules with Perturbed Excited-State Structure

We demonstrate and characterize Zeeman-Sisyphus (ZS) deceleration of a beam of ytterbium monohydroxide (YbOH). Our method uses a combination of large magnetic fields ($\sim$ 2.5 T) and optical spin-flip transitions to decelerate molecules while scattering only $\sim$ 10 photons per molecule. We study the challenges associated with the presence of internal molecular perturbations among the excited electronic states and discuss the methods used to overcome these challenges, including a modified ZS decelerator using microwave and optical transitions.

physics.atom-ph↗

arXiv2022

Direct observation of the Yb(4f13 6s2)F states and accurate determination of the YbF ionization energy

YbF has been identified as a molecule that can be used to investigate charge-parity symmetry violations that are beyond the Standard Model of particle physics. Cooling to sub-milli-Kelvin is advantageous for experiments that probe manifestations of these symmetry violations. One approach involves laser cooling of YbF via the A2P1/2-X2S+ transition. However, it appears that cooling by means of this transition may be limited by the radiative loss of population from the cooling cycle. YbF has low-energy states that arise from the Yb+(4f136s2)F- configuration. Recent theoretical calculations predict (Zhang et al J. Mol. Spectrsc. 386 11625 (2022)) that radiative decay from A2Π1/2 to the 4f136s2 states occurs with a branching fraction of approximately 10-3. In the present study we have used dispersed laser induced fluorescence spectroscopy to the observe the lowest energy 4f136s2 states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. An accurate ionization energy (IE) for YbF is also reported. A two-color photoionization technique was used to determine the IE and observe the v+=0-3 vibrational levels of YbF+ X1S+.

physics.chem-ph↗

arXiv2022

Inner-shell excitation in the YbF molecule and its impact on laser cooling

The YbF molecule is a sensitive system for measuring the electron's electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these "4f hole" states lies below the $A^2Π_{1/2}$ excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as $10^{-5}$, can be a hindrance. Other 4f hole states lie very close to the $A^2Π_{1/2}$ state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the $A^2Π_{1/2}$ state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of the ground state, $X ^{2}Σ^+$. We use electronic structure calculations to characterise the 4f hole states and the strengths of transitions between these states and the $A^2Π_{1/2}$ and $X ^{2}Σ^+$ states. We identify a leak out of the cooling cycle with a branching ratio of roughly $5 \times 10^{-4}$, dominated by the contribution of the ground state configuration in a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules with similar structure.

physics.atom-ph↗

arXiv2021

Fine and hyperfine interactions in $^{171}$YbOH and $^{173}$YbOH

The odd isotopologues of ytterbium monohydroxide, $^{171,173}$YbOH, have been identified as promising molecules in which to measure parity (P) and time reversal (T) violating physics. Here we characterize the $\tilde{A}^{2}Π_{1/2}(0,0,0)-\tilde{X}^2Σ^+(0,0,0)$ band near 577 nm for these odd isotopologues. Both laser-induced fluorescence (LIF) excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. Additionally, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and utilized in the absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the $\tilde{A}^{2}Π_{1/2}(0,0,0)$ and $\tilde{X}^2Σ^+(0,0,0)$ states. A comparison of the determined $\tilde{X}^2Σ^+(0,0,0)$ hyperfine parameters with recently predicted values (M. Denis, et al., J. Chem. Phys. $\bf{152}$, 084303 (2020), K. Gaul and R. Berger, Phys. Rev. A $\bf{101}$, 012508 (2020), J. Liu et al., J. Chem. Phys. $\bf{154}$, 064110 (2021)) is made. The measured hyperfine parameters provide experimental confirmation of the computational methods used to compute the P,T-violating coupling constants $W_d$ and $W_M$, which correlate P,T-violating physics to P,T-violating energy shifts in the molecule. The dependence of the fine and hyperfine parameters of the $\tilde{A}^{2}Π_{1/2}(0,0,0)$ and $\tilde{X}^2Σ^+(0,0,0)$ states for all isotopologues of YbOH are discussed and a comparison to isoelectronic YbF is made.

physics.atom-ph↗

arXiv2020

Observation and laser spectroscopy of ytterbium monomethoxide, YbOCH$_3$

We describe a laser spectroscopic study of ytterbium monomethoxide, YbOCH$_3$, a species of interest to searches for time-reversal symmetry violation using laser-cooled molecules. We report measurements of vibrational structure in the $\tilde{X}$ and $\tilde{A}$ states, vibrational branching ratios for several components of the $\tilde{A}$ state, and radiative lifetimes of low-lying electronic states. $\textit{Ab initio}$ calculations are used to aid the assignment of vibronic emission bands and provide insight into the electronic and vibrational structure. Our results demonstrate that rapid optical cycling is feasible for YbOCH$_3$, opening a path to orders-of-magnitude increased sensitivity in future measurements of P- and/or T-violating physics.

physics.atom-ph↗

arXiv2020

Branching ratios, radiative lifetimes and transition dipole moments for YbOH

Medium resolution ($Δν$ ~ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm$^{-1}$ range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution ($Δλ$ ~ 0.65 nm) dispersed laser induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the $\tilde{X} \, ^2Σ^+$ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution ($Δν$ < 10 MHz) LIF excitation of individual low-rotational lines in the $\tilde{A} \, ^2Π_{1/2}(0,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$, $\tilde{A} \, ^2Π_{1/2}(1,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$, $[17.73]Ω=0.5(0,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$ bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

physics.atom-ph↗

arXiv2019

Laser-Cooled Polyatomic Molecules for Improved Electron Electric Dipole Moment Searches

Doppler and Sisyphus cooling of $^{174}$YbOH are achieved and studied. This polyatomic molecule has high sensitivity to physics beyond the Standard Model and represents a new class of species for future high-precision probes of new T-violating physics. The transverse temperature of the YbOH beam is reduced by nearly two orders of magnitude to $< 600 \, μ$K and the phase-space density is increased by a factor of $>6$ via Sisyphus cooling. We develop a full numerical model of the laser cooling of YbOH and find excellent agreement with the data. We project that laser cooling and magneto-optical trapping of long-lived samples of YbOH molecules are within reach and these will allow a high sensitivity probe of the electric dipole moment (EDM) of the electron. The approach demonstrated here is easily generalized to other isotopologues of YbOH that have enhanced sensitivity to other symmetry-violating electromagnetic moments.

physics.atom-ph↗

arXiv2018

Determination of CaOH and CaOCH$_3$ vibrational branching ratios for direct laser cooling and trapping

Alkaline earth monoalkoxide free radicals (MORs) have molecular properties conducive to direct laser cooling to sub-millikelvin temperatures. Using dispersed laser induced fluorescence (DLIF) measurements from a pulsed supersonic molecular beam source we determine vibrational branching ratios and Franck-Condon factors for the MORs CaOH and CaOCH$_{3}$. With narrow linewidth continuous-wave dye laser excitation, we precisely measure fluorescence branching for both $\tilde{X}-\tilde{A}$ and $\tilde{X}-\tilde{B}$ electronic systems in each molecule. Weak symmetry-forbidden decays to excited bending states with non-zero vibrational angular momentum are observed. Normal mode theoretical analysis combined with ab initio structural calculations are performed and compared to experimental results. Our measurements and analysis pave the way for direct laser cooling of these (and other) complex nonlinear polyatomic molecules. We also describe a possible approach to laser cooling and trapping of molecules with fewer symmetries like chiral species.

physics.atom-ph↗

arXiv2018

The pure rotational spectrum of YbOH

The pure rotational spectrum of YbOH has been recorded and analyzed to produce fine and magnetic hyperfine parameters for the $\tilde{X}^2Σ^+$(0,0,0) state. These parameters are compared with those determined from the optical study [Melville and Coxon, J. Chem. Phys. 115, 6974-6978 (2001)] and with the values for YbF [Dickinson et al. 115, 6979-6989 (2001)]. The results support the existence of an unobserved perturbing state near the $\tilde{A}^2Π_{1/2}$ state, similar to that previously found in YbF. The precisely determined parameters lay the foundation for laser cooling YbOH, which will aid in the search for new physics beyond the standard model.

physics.chem-ph↗

arXiv2017

Fluorescence branching ratios and magnetic tuning of the visible spectrum of SrOH

The magnetic tuning of the low rotational levels in the Xsigma+(0,0,0), Api(0,0,0), and Bsigma+ (0,0,0) electronic states of strontium hydroxide, SrOH, have been experimentally investigated using high resolution optical Zeeman spectroscopy of a cold molecular beam sample. The observed Zeeman shifts and splittings are successfully modeled using a traditional effective Hamiltonian approach to account for the interaction between the Api and Bsigma+ states. The determined magnetic g-factors for the Xsigma+, Api , and Bsigma+ states are compared to those predicted by perturbation theory. The dispersed fluorescence resulting from laser excitation of rotationally resolved branch features of the Bsigma+ (0,0,0)<Xsigma+(0,0,0) Api(0,0,0)< Xsigma+(0,0,0) transitions have been recorded and analyzed. The measured fluorescence branching ratios are compared with Franck-Condon calculations. The required bending motion wave functions are derived using a discrete variable representation (DVR) method. Implications for laser slowing and magneto-optical trapping experiments for SrOH are described.

physics.chem-ph↗

arXiv2011

Franck-Condon Factors and Radiative Lifetime of the A^{2}Π_{1/2} - X^{2}Σ^{+} Transition of Ytterbium Monoflouride, YbF

The fluorescence spectrum resulting from laser excitation of the A^{2}Π_{1/2} - X^{2}Σ^{+} (0,0) band of ytterbium monofluoride, YbF, has been recorded and analyzed to determine the Franck-Condon factors. The measured values are compared with those predicted from Rydberg-Klein-Rees (RKR) potential energy curves. From the fluorescence decay curve the radiative lifetime of the A^{2}Π_{1/2} state is measured to be 28\pm2 ns, and the corresponding transition dipole moment is 4.39\pm0.16 D. The implications for laser cooling YbF are discussed.

physics.atom-ph↗