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1. Efficient pathway to NaCs ground state molecules

   https://doi.org/10.1088/1367-2630/acd411  

   Warner, Claire ; Bigagli, Niccolò ; Lam, Aden Z. ; Yuan, Weijun ; Zhang, Siwei ; Stevenson, Ian ; Will, Sebastian ( June 2023 , New Journal of Physics)

   We present a study of two-photon pathways for the transfer of NaCs molecules to their rovibrational ground state. Starting from NaCs Feshbach molecules, we perform bound-bound excited state spectroscopy in the wavelength range from 900 nm to 940 nm, covering more than 30 vibrational states of the$c^3{\mathrm{\Sigma }}^{+}$,$b^3\mathrm{\Pi }$, and$B^1\mathrm{\Pi }$electronic states. Analyzing the rotational substructure, we identify the highly mixed$c^3{\mathrm{\Sigma }}_1^{+}|v=22⟩\sim b^3{\mathrm{\Pi }}_1|v=54⟩$state as an efficient bridge for stimulated Raman adiabatic passage. We demonstrate transfer into the NaCs ground state with an efficiency of up to 88(4)%. Highly efficient transfer is critical for the realization of many-body quantum phases of strongly dipolar NaCs molecules and high fidelity detection of single molecules, for example, in spin physics experiments in optical lattices and quantum information experiments in optical tweezer arrays.

    

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2. Can ozone be used to calibrate aerosol photoacoustic spectrometers?

   https://doi.org/10.5194/amt-11-6419-2018  

   Fischer, D. Al ; Smith, Geoffrey D. ( January 2018 , Atmospheric Measurement Techniques)

   Abstract. Photoacoustic spectroscopy (PAS) has become a popular technique for measuringabsorption of light by atmospheric aerosols in both the laboratory andfield campaigns. It has low detection limits, measures suspended aerosols,and is insensitive to scattering. But PAS requires rigorous calibration to beapplied quantitatively. Often, a PAS instrument is either filled with a gasof known concentration and absorption cross section, such that the absorptionin the cell can be calculated from the product of the two, or the absorptionis measured independently with a technique such as cavity ring-downspectroscopy. Then, the PAS signal can be regressed upon the known absorptionto determine a calibration slope that reflects the sensitivity constant ofthe cell and microphone. Ozone has been used for calibrating PAS instrumentsdue to its well-known UV–visible absorption spectrum and the ease with whichit can be generated. However, it is known to photodissociate up toapproximately 1120nm via the O₃ + $h\mathit{\nu }(\>\mathrm{1.1}\mathrm{eV})\to {\mathrm{O}}_{\mathrm{2}}{(}^{\mathrm{3}}{\mathrm{\Sigma }}_g^{-})$ + O(³P) pathway, which is likely tolead to inaccuracies in aerosol measurements. Two recent studies haveinvestigated the use of O₃ for PAS calibration but have reachedseemingly contradictory conclusions with one finding that it results in asensitivity that is a factor of 2 low and the other concluding that it isaccurate. The present work is meant to add to this discussion by exploringthe extent to which O₃ photodissociates in the PAS cell and the rolethat the identity of the bath gas plays in determining the PAS sensitivity.We find a 5% loss in PAS signal attributable to photodissociation at 532nmin N₂ but no loss in a 5% mixture of O₂ in N₂.Furthermore, we discovered a dramatic increase of more than a factor of 2in the PAS sensitivity as we increased the O₂ fraction in the bathgas, which reached an asymptote near 100% O₂ that nearly matched thesensitivity measured with both NO₂ and nigrosin particles. Weinterpret this dependence with a kinetic model that suggests the reason forthe observed results is a more efficient transfer of energy from excitedO₃ to O₂ than to N₂ by a factor of 22–55 depending onexcitation wavelength. Notably, the two prior studies on this topic useddifferent bath gas compositions, and although the results presented here donot fully resolve the differences in their results, they may at leastpartially explain them.

    

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3. Formation and evolution of post-solitons following a high intensity laser-plasma interaction with a low-density foam target

   https://doi.org/10.1088/1361-6587/abf85c  

   Blackman, David R. ; Adak, Amitava ; Singh, Prashant K. ; Lad, Amit D. ; Chatterjee, Gourab ; Ridgers, Christopher P. ; Del Sorbo, Dario ; Trines, Raoul M. G. M. ; Robinson, A. P. L. ; Nazarov, Wigen ; et al ( May 2021 , Plasma Physics and Controlled Fusion)

   The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a$0.03\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$TMPTA foam target with a focused intensity$I_{\mathrm{l}}=9.5\times {10}^{17}\mathrm{W}\mathrm{c}{\mathrm{m}}^{-2}$. A third harmonic (${\lambda }_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{b}\mathrm{e}}\simeq 266$nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.

    

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4. Detection of Cosmological 21 cm Emission with the Canadian Hydrogen Intensity Mapping Experiment

   https://doi.org/10.3847/1538-4357/acb13f  

   The CHIME Collaboration ; Amiri, Mandana ; Bandura, Kevin ; Chen, Tianyue ; Deng, Meiling ; Dobbs, Matt ; Fandino, Mateus ; Foreman, Simon ; Halpern, Mark ; Hill, Alex S. ; et al ( April 2023 , The Astrophysical Journal)

   We present a detection of 21 cm emission from large-scale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1σ(LRG), 5.7σ(ELG), and 11.1σ(QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (Hi), defined as${\mathit{}}_{\mathrm{H}\mathrm{I}}\equiv {10}^3{\mathrm{\Omega }}_{\mathrm{H}\mathrm{I}}\left(b_{\mathrm{H}\mathrm{I}}+〈f{\mu }^2〉\right)$, where Ω_Hiis the cosmic abundance of Hi,b_Hiis the linear bias of Hi, and 〈fμ²〉 = 0.552 encodes the effect of redshift-space distortions at linear order. We find${\mathit{}}_{\mathrm{H}\mathrm{I}}={1.51}_{-0.97}^{+3.60}$for LRGs (z= 0.84),${\mathit{}}_{\mathrm{H}\mathrm{I}}={6.76}_{-3.79}^{+9.04}$for ELGs (z= 0.96), and${\mathit{}}_{\mathrm{H}\mathrm{I}}={1.68}_{-0.67}^{+1.10}$for QSOs (z= 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δv= − 66 ± 20 km s⁻¹for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin atz= 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far.

    

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5. Laboratory Study of the Cameron Bands and UV Doublet in the Middle Ultraviolet 180–300 nm by Electron Impact upon CO 2 with Application to Mars

   https://doi.org/10.3847/1538-4357/ac88c8  

   Lee, Rena A. ; Ajello, Joseph M. ; Malone, Charles P. ; Evans, J. Scott ; Veibell, Victoir ; Holsclaw, Gregory M. ; McClintock, William E. ; Hoskins, Alan C. ; Jain, Sonal K. ; Gérard, Jean-Claude ; et al ( October 2022 , The Astrophysical Journal)

   We have observed electron impact fluorescence from CO₂to excite the Cameron bands (CBs), CO (a³Π →X¹Σ⁺; 180–280 nm), the first-negative group (1NG) bands, CO⁺(B²Σ⁺→X²Σ⁺; 180–320 nm), the fourth-positive group (4PG) bands, CO (A¹Π →X¹Σ⁺; 111–280 nm), and the UV doublet, CO₂⁺($\tilde{B}{}^2{\mathrm{\Sigma }}_u^{+}\to \tilde{X}{}^2{\mathrm{\Pi }}_g;$288.3 and 289.6 nm) in the ultraviolet (UV). This wavelength range matches the spectral region of past and present spacecraft equipped to observe UV dayglow and aurora emissions from the thermospheres (100–300 km) of Mars and Venus. Our large vacuum system apparatus is able to measure the emission cross sections of the strongest optically forbidden UV transitions found in planetary spectra. Based on our cross-sectional measurements, previous CB emission cross-sectional errors exceed a factor of 3. The UV doublet lifetime is perturbed through$\tilde{B}{}^2{\mathrm{\Sigma }}_u^{+}-\tilde{A}{}^2{\mathrm{\Pi }}_u$spin–orbit coupling. Forward modeling codes of the Mars dayglow have not been accurate in the mid-UV due to systematic errors in these two emission cross sections. We furnish absolute emission cross sections for several band systems over electron energies 20–100 eV for CO₂. We present a CB lifetime, which together with emission cross sections, furnish a set of fundamental physical constants for electron transport codes such as AURIC (Atmospheric Ultraviolet Radiance Integrated Code). AURIC and Trans-Mars are used in the analysis of UV spectra from the Martian dayglow and aurora.

    

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