We describe the first precision measurement of the electron’s electric dipole moment ($d_e$) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on ${}^{180}\mathrm{Hf}{}^{19}{\mathrm{F}}^{+}$ in its metastable ${{}^3\mathrm{\Delta }}_1$ electronic state, we obtain $d_e=(0.9\pm 7.7_{\mathrm{stat}}\pm 1.7_{\mathrm{syst}})\times {10}^{-29}e\mathrm{cm}$, resulting in an upper bound of $|d_e|<1.3\times {10}^{-28}e\mathrm{cm}$ (90% confidence). Our result provides independent confirmation of the current upper bound of $|d_e|<9.4\times {10}^{-29}e\mathrm{cm}$ [J. Baron et al., New J. Phys. 19, 073029 (2017)], and offers the potential to improve on this limit in the near future.

We present a high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region. The system employs periodically poled lithium niobate and is singly resonant for the signal. It is synchronously pumped by a $10\mathrm{W}$ femtosecond Yb:fiber laser centered at $1.07\mu \mathrm{m}$. The idler (signal) wavelength can be continuously tuned from $2.8\text{to}4.8\mu \mathrm{m}$ $\left(1.76\text{to}1.37\mu \mathrm{m}\right)$ with a simultaneous bandwidth as high as $0.3\mu \mathrm{m}$ and a maximum average idler output power of $1.50\mathrm{W}$. We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.

We present a first implementation of optical-frequency-comb-based rapid trace gas detection in the molecular fingerprint region in the mid-infrared. Near-real-time acquisition of broadband absorption spectra with 0.0056 cm⁻¹ maximum resolution is demonstrated using a frequency comb Fourier transform spectrometer which operates in the 2100-to-3700-cm⁻¹ spectral region. We achieve part-per-billion detection limits in 30 seconds of integration time for several important molecules including methane, ethane, isoprene, and nitrous oxide. Our system enables precise concentration measurements even in gas mixtures that exhibit continuous absorption bands, and it allows detection of molecules at levels below the noise floor via simultaneous analysis of multiple spectral features.

Cavity-enhanced direct frequency comb spectroscopy combines broad bandwidth, high spectral resolution, and ultrahigh detection sensitivity in one experimental platform based on an optical frequency comb efficiently coupled to a high-finesse cavity. The effective interaction length between light and matter is increased by the cavity, massively enhancing the sensitivity for measurement of optical losses. Individual comb components act as independent detection channels across a broad spectral window, providing rapid parallel processing. In this review we discuss the principles, the technology, and the first applications that demonstrate the enormous potential of this spectroscopic method. In particular, we describe various frequency comb sources, techniques for efficient coupling between comb and cavity, and detection schemes that utilize the technique's high-resolution, wide-bandwidth, and fast data-acquisition capabilities. We discuss a range of applications, including breath analysis for medical diagnosis, trace-impurity detection in specialty gases, and characterization of a supersonic jet of cold molecules.

Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broadband spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly used techniques. We finish this review by discussing potential future advances in techniques and applications of broadband spectroscopy.

Toward a New Physics: The search for physics beyond the Standard Model is carried out at accelerator facilities such as the Large Hadron Collider but also on a smaller scale in atomic and molecular physics experiments. One of the signatures of this “new physics” would be a nonvanishing electric dipole moment of the electron, but experiments designed to look for it need to distinguish between the signal and many potential artifacts. Loh et al. (p. 1220 ) introduce a method based on the spectroscopy of polarized molecular ions that avoids some of the sources of systematic error.