Precision Spectroscopy Research Articles

Fully phase-stabilized 1 GHz turnkey frequency comb at 1.56 µm

Low noise and high repetition rate optical frequency combs are desirable for many applications, from timekeeping to precision spectroscopy. For example, gigahertz repetition rate sources greatly increase the acquisition speed of spectra in a dual-comb modality when compared to lower repetition rate sources, while still maintaining sufficient instantaneous resolution to resolve ro-vibrational signatures from molecules in a variety of conditions. In this paper, we present the stabilization and characterization of a turnkey commercial 1 GHz mode-locked laser that operates at telecom wavelengths (1.56 µm). Fiber amplification and spectral broadening result in high signal-to-noise ratio detection and stabilization of f ceo with 438 mrad of residual phase noise (integrated from 102 to 107 Hz). Simultaneously, we stabilize the beatnote between the nearest comb mode and a cavity stabilized continuous-wave laser at 1.55 µm with 41 mrad of residual phase noise (integrated from 102 to 107 Hz). This robust, self-referenced comb system is built with off-the-shelf polarization-maintaining fiber components and will be useful for a wide range of low noise frequency comb applications that benefit from the increased repetition rate.

Accurate non-destructive prediction of peach fruit internal quality and physiological maturity with a single scan using near infrared spectroscopy

The development of precise and reliable near infrared spectroscopy (NIRS)-based non-destructive tools to assess physicochemical properties of fleshy fruit has been challenging. A novel crop load × fruit developmental stage protocol for multivariate NIRS-based prediction models calibration to non-destructively assess peach internal quality and maturity was followed. Regression statistics of the prediction models highlighted that dry matter content (DMC, R2 = 0.98, RMSEP = 0.41%), soluble solids concentration (SSC, R2 = 0.96, RMSEP = 0.58%) and index of absorbance difference (IAD, R2 = 0.96, RMSEP = 0.08) could be estimated accurately with a single scan during fruit growth and development. Thus, the impact of preharvest factors such as crop load and canopy position on peach quality and maturity was evaluated. Large-scale field validation showed that heavier crop loads reduced peach quality (DMC, SSC) and delayed maturity (IAD) and upper canopy position advanced both mainly in the moderate crop loads. This calibration protocol can enhance NIRS adaptation across tree fruit supply chain.

Precision spectroscopy of cesium-137 from the ground to 150 m above in Fukushima

After the Fukushima nuclear disaster in 2011, large amounts of radioisotopes (mainly 137Cs and 134Cs) were released into the environment. Various monitoring activities have revealed radiation on the ground both in local and wide areas; however, aerial dose variation in the vertical direction is poorly known. This paper presents the results of airborne gamma-ray spectroscopy of a contamination field in Namie, Fukushima, as measured from 0 m to 150 m above the ground by drone. We found that the gamma-ray dose rate measured at 100 m height is about seven times higher than that expected based on ground measurements, which is caused by two factors: (1) the integrated dose includes contamination of upward scattered 662-keV gamma rays and (2) radiation from 137Cs is vertically collimated because 137Cs is buried in the soil. We also propose a novel method to obtain the distribution of radioactive substances in the soil only through aerial mapping.

Spectroscopy of HD+: Proton Charge Radius and the Rydberg Constant

The problem of the proton charge radius, its correlation with the Rydberg constant, difficulties in determination of the Rydberg constant using hydrogen atom spectroscopy, and redetermination of fundamental constants in the new CODATA18 revision are discussed. Theoretical and experimental aspects of precision spectroscopy of the molecular hydrogen ion HD+ are considered. It is shown that new experiments allow the Doppler broadening of spectral lines to be eliminated and a relative error of ~10–11 to be achieved in the transition frequency measurements. A comparison of these experiments and theoretical calculations leads to an unambiguous conclusion that the proton charge radius should be determined from the muonic hydrogen experiment and the Rydberg constant from the $$1S$$ – $$2S$$ transition in the ordinary hydrogen atom. Only in this case experiment and theory in HD+ are in reasonable consent.

Advances in soliton microcomb generation

Optical frequency combs, a revolutionary light source characterized by discrete and equally spaced frequencies, are usually regarded as a cornerstone for advanced frequency metrology, precision spectroscopy, high-speed communication, distance ranging, molecule detection, and many others. Due to the rapid development of micro/nanofabrication technology, breakthroughs in the quality factor of microresonators enable ultrahigh energy buildup inside cavities, which gives birth to microcavity-based frequency combs. In particular, the full coherent spectrum of the soliton microcomb (SMC) provides a route to low-noise ultrashort pulses with a repetition rate over two orders of magnitude higher than that of traditional mode-locking approaches. This enables lower power consumption and cost for a wide range of applications. This review summarizes recent achievements in SMCs, including the basic theory and physical model, as well as experimental techniques for single-soliton generation and various extraordinary soliton states (soliton crystals, Stokes solitons, breathers, molecules, cavity solitons, and dark solitons), with a perspective on their potential applications and remaining challenges.

Toward Stand-Alone Alkali-Based Mid-Infrared Frequency References

Highly accurate and precise spectroscopy in the mid-infrared (MIR) spectral region is a versatile tool that finds great interest in fundamental scientific research as well as in mitigating myriad a...

Ramsey-comb precision spectroscopy in xenon at vacuum ultraviolet wavelengths produced with high-order harmonic generation

The remarkable progress in the field of laser spectroscopy induced by the invention of the frequency-comb laser has enabled many new high-precision tests of fundamental theory and searches for new physics. Extending frequency-comb based spectroscopy techniques to the vacuum (VUV) and extreme ultraviolet (XUV) spectral range would enable measurements in e.g. heavier hydrogen-like systems and open up new possibilities for tests of quantum electrodynamics and measurements of fundamental constants. The main approaches rely on high-harmonic generation (HHG), which is known to induce spurious phase shifts from plasma formation. After our initial report (Physical Review Letters 123, 143001 (2019)), we give a detailed account of how the Ramsey-comb technique is used to probe the plasma dynamics with high precision, and enables accurate spectroscopy in the VUV. A series of Ramsey fringes is recorded to track the phase evolution of a superposition state in xenon atoms, excited by two up-converted frequency-comb pulses. Phase shifts of up to 1 rad induced by HHG were observed at ns timescales and with mrad-level accuracy at $110$ nm. Such phase shifts could be reduced to a negligible level, enabling us to measure the $5p^6 \rightarrow 5p^5 8s~^2[3/2]_1$ transition frequency in $^{132}Xe$ at 110 nm (seventh harmonic) with sub-MHz accuracy. The obtained value is $10^4$ times more precise than the previous determination and the fractional accuracy of $2.3 \times 10^{-10}$ is $3.6$ times better than the previous best spectroscopic measurement using HHG. The isotope shifts between $^{132}Xe$ and two other isotopes were determined with an accuracy of $420$ kHz. The method can be readily extended to achieve kHz-level accuracy, e.g. to measure the $1S-2S$ transition in $He^+$. Therefore, the Ramsey-comb method shows great promise for high-precision spectroscopy of targets requiring VUV and XUV wavelengths.

Tritium Processing Systems and First Tritium Operation of the KATRIN Experiment

The KArlsruhe TRItium Neutrino (KATRIN) Experiment aims for the determination of the effective mass of the electron-antineutrino. KATRIN uses a strong, gaseous, windowless tritium source for precision spectroscopy of the β-electrons. The 70-m-long experiment has been set up at the Tritium Laboratory Karlsruhe (TLK) and was commissioned with traces of tritium during two measurement campaigns in 2018. In spring 2019, the first campaign with full source luminosity started. KATRIN uses a complex gas-handling system called Loops for stabilized injection of tritium into the source and tritium gas handling. It also makes use of the unique facilities and possibilities found at the TLK for gas handling, cleanup, and purification. This paper describes the integration of KATRIN into TLK’s existing infrastructure and the current status of the experiment and concludes with a summary of the tritium measurements.

Spectroscopic-network-assisted precision spectroscopy and its application to water

Frequency combs and cavity-enhanced optical techniques have revolutionized molecular spectroscopy: their combination allows recording saturated Doppler-free lines with ultrahigh precision. Network theory, based on the generalized Ritz principle, offers a powerful tool for the intelligent design and validation of such precision-spectroscopy experiments and the subsequent derivation of accurate energy differences. As a proof of concept, 156 carefully-selected near-infrared transitions are detected for H216O, a benchmark system of molecular spectroscopy, at kHz accuracy. These measurements, augmented with 28 extremely-accurate literature lines to ensure overall connectivity, allow the precise determination of the lowest ortho-H216O energy, now set at 23.794 361 22(25) cm−1, and 160 energy levels with similarly high accuracy. Based on the limited number of observed transitions, 1219 calibration-quality lines are obtained in a wide wavenumber interval, which can be used to improve spectroscopic databases and applied to frequency metrology, astrophysics, atmospheric sensing, and combustion chemistry.

Precision spectroscopy with single ions

Spectroscopy Spectroscopy is a powerful tool that can identify chemical species used in a wide range of settings. Usually, the samples are formed of ensembles, and this can limit the resolution with which the different species can be detected or identified. Chou et al. demonstrate an optical frequency comb technique with a single pair of trapped ions, Ca+ and CaH+, to obtain the rotational spectrum of a single trapped ion, CaH+. With the ions isolated and the ensemble interactions removed, the rotational structure of the trapped molecular ion can then be obtained with high precision. As the trapping and manipulation process is general, this technique could be applied to a number of chemical species for specific purposes. Science , this issue p. [1458][1] [1]: /lookup/doi/10.1126/science.aba3628

A novel digitally optimized rapid quantification of carcinogenic aryl azo amines from various food matrices by HPTLC-MS

A rapid, precise and reproducible high-performance thin-layer chromatography-mass spectroscopy (HPTLC-MS) method was developed and validated for identification and quantification of toxic aryl azo amines from chili oils, pickles and related food matrices using Merck thin-layer chromatography (TLC) silica gel F-254 plates, as a stationary phase adsorbent by CAMAG HPTLC system. Extraction of azo food colors was done using method specified as per ISO standard. The use of tert-butyl-methyl ether as final extraction solvent resulted in minimal sample clean up and high efficiency. Calibration was performed to combat matrix effect. Good linearity levels were observed for the concentrations of aniline, 2, 4-xylidine and 4 aminoazobenzene of 2–14 ppm per band. The limits of detection and quantification found for aniline, 2,4-xylidine and 4-aminoazobenzene were found to be 0.0015, 200, and 400 ppm and limit of quantification (LOQ) values were found to be 0.004, 600, and 1200 ppm, respectively, with a correlation coefficient of 99.94 %. This study thus highlights an economically viable, commercially sustainable yet highly scientific technique of HPTLC-MS methodology with structural elucidation of banned azo amines in food and related products for their identification duly detectable at trace levels in a digitized form, which can enable material integrity-related prediction capacity of suspected food matrices.

Tritium Supply and Processing for the First KATRIN Tritium Operation

The main task of the Tritium Laboratory Karlsruhe (TLK) in 2018 was the commissioning and First Tritium (FT) operation of the windowless gaseous tritium source (WGTS) of the Karlsruhe Tritium Neutrino (KATRIN) experiment. It was paramount to enable the FT measurement run of the KATRIN experiment, to yield first scientific results with the complete KATRIN beamline.The aim of KATRIN is to determine the mass of the electron-antineutrino by precise spectroscopy of the tritium β-spectrum close to its maximum energy of 18.6 keV. KATRIN uses an ultraluminous source (WGTS) and a high-resolution electrostatic spectrometer. While the inner loop system of KATRIN has the task of providing stabilized tritium circulation with a throughput of 40 g·day−1 for the WGTS, the outer loop incorporates the entire TLK infrastructure for tritium cleanup, purification, and accountancy prior to reinjection of tritium into the inner loop.For KATRIN’s FT run, ≈5 × 1013 Bq (2.3 × 10−2 mol) of tritium was provided in 3.2 mol of deuterium. In contrast to the high isotopic purity of >95% tritium necessary for future KATRIN operation, a concentration of 7 × 108 Bq·m−3 (resulting in 0.5% nominal source luminosity) had to be kept constant during the entire FT campaign. This required a processing scheme deviating from the later KATRIN outer loop processing procedure.This paper describes the procedures used to supply the KATRIN inner loop with its FT gas. Furthermore, experience gained during operation of the different gas processing steps and tritium accountancy is presented.

Production of HD Molecules in Definite Hyperfine Substates.

Polarized atomic beam sources have been in operation for many years to produce either nuclear polarized atomic hydrogen or deuterium beams. In recent experiments, such a source was used to polarize both isotopes independently at the same time. By recombination of the atoms, hydrogen-deuterium molecules with all possible nuclear spin combinations can be created. Those spin isomers are useful for further applications, like precision spectroscopy, as polarized targets for laser-particle acceleration, polarized fuel for fusion reactors, or as an option for future measurements of electric dipole moments.

Reading a molecule without destroying it

Spectroscopy Achieving efficient quantum control of ultracold molecular systems may open opportunities in molecular precision spectroscopy, quantum information, and related fields. Sinhal et al. report a quantumnondemolition protocol for the detection of the spin-rovibronic state of a single trapped cold molecular ion co-trapped with an atomic ion. They show that monitoring the motion of Ca+ after coherent motional excitation of the Ca+-N2+ string makes it possible to detect the N2+ state without destroying either the molecule or the state itself. The procedure can be repeated multiple times while preserving the high readout fidelity. Science , this issue p. [1213][1] [1]: /lookup/doi/10.1126/science.aaz9837

Quantum-nondemolition state detection and spectroscopy of single trapped molecules.

Trapped atoms and ions, which are among the best-controlled quantum systems, find widespread applications in quantum science. For molecules, a similar degree of control is currently lacking owing to their complex energy-level structure. Quantum-logic protocols in which atomic ions serve as probes for molecular ions are a promising route for achieving this level of control, especially for homonuclear species that decouple from blackbody radiation. Here, a quantum-nondemolition protocol on single trapped [Formula: see text] molecules is demonstrated. The spin-rovibronic state of the molecule is detected with >99% fidelity, and a spectroscopic transition is measured without destroying the quantum state. This method lays the foundations for new approaches to molecular spectroscopy, state-to-state chemistry, and the implementation of molecular qubits.

Ultranarrow Linewidth Photonic‐Atomic Laser

AbstractLasers with high spectral purity can enable a diverse application space, including precision spectroscopy, coherent high‐speed communications, physical sensing, and manipulation of quantum systems. Already, meticulous design and construction of bench Fabry–Perot cavities has made possible dramatic achievements in active laser‐linewidth reduction, predominantly for optical‐atomic clocks. Yet, there is increasing demand for miniaturized laser systems operating with high performance in ambient environments. Here, a compact and robust photonic‐atomic laser comprising a 2.5 centimeter long, 20 000 finesse, monolithic Fabry–Perot cavity integrated with a micromachined rubidium vapor cell is presented. By leveraging the short‐time frequency stability of the cavity and the long‐time frequency stability of atoms, an ultranarrow‐linewidth laser that enables integration for extended measurements is realized. Specifically, the laser supports a fractional‐frequency stability of at an averaging time of 20 millisecond, at 300 second, an integrated linewidth of 25 Hz that results from thermal noise, frequency noise floor as low as 0.06 Hz2 Hz−1, and a passive vibration immunity as low as 10−10 g−1. The present work explores hybrid laser systems with monolithic photonic and atomic packages based on physical design.

457-nm radiation source based on a diode laser for precision spectroscopy of magnesium atoms

We report on the development of a highly stable source of 457-nm radiation based on a diode laser and a tapered amplifier operating in a double-pass scheme. The diode laser frequency was stabilised by a high-Q reference Fabry – Perot interferometer and doubled in a PPSLT nonlinear crystal placed in an enhancement cavity. At a maximum output power of 200 mW at a wavelength of 457 nm, the laser linewidth was less than 5 kHz. The radiation source operation was demonstrated in experiments on precision spectroscopy of cold magnesium atoms in a magneto-optical trap.

Two types of highly efficient electrostatic traps for single loading or multi-loading of polar molecules**Project supported by the National Natural Science Foundation of China (Grant Nos. 11834003, 91536218, 11034002, 11274114, 11504112, and 11874151), the National Key Basic Research and Development Program of China (Grant No. 2011CB921602), the Fundamental Research Funds for the Central Universities, China, Shanghai Pujiang Talents Plan, China

Two novel electrostatic traps named octopole-based disk electrostatic trap (ODET) and tubular-based disk electrostatic trap (TDET) are proposed for trapping cold polar molecules in low-field-seeking states. Using MgF as the target molecule, single loading and multi-loading methods are numerically simulated with varied incident velocities of slow molecular beams in the two types of traps, respectively. In ODET, with an incident velocity of 10 m/s, a highest loading efficiency of 78.4% or 99.9% has been achieved under the single loading or multi-loading operation mode. In TDET, with an incident velocity of 11 m/s, a highest loading efficiency of 81.6% or 106.5% has been achieved using the two loading methods, respectively. With such high loading efficiencies, the trapped cold molecules can be applied in the researches of cold collisions, high precision spectroscopy, and precision measurements. Especially, together with a blue-detuned hollow beam, the new electrostatic traps proposed here offer a new platform for the following gradient-intensity cooling of MgF molecules, which may provide a new way to produce high density ultracold molecules.

Microbubble resonators combined with a digital optical frequency comb for high-precision air-coupled ultrasound detectors

Fast and sensitive air-coupled ultrasound detection is essential for many applications such as radar, ultrasound imaging, and defect detection. Here we present a novel approach based on a digital optical frequency comb (DOFC) technique combined with high- Q optical microbubble resonators (MBRs). DOFC enables precise spectroscopy on resonators that can trace the ultrasound pressure with its resonant frequency shift with femtometer resolution and sub-microsecond response time. The noise equivalent pressure of air-coupled ultrasound as low as 4.4 mPa / √ Hz is achieved by combining a high- Q ( ∼ 3 × 10 7 ) MBR with the DOFC method. Moreover, it can observe multi-resonance peaks from multiple MBRs to directly monitor the precise spatial location of the ultrasonic source. This approach has a potential to be applied in 3D air-coupled photoacoustic and ultrasonic imaging.

Seeded optical parametric oscillator light source for precision spectroscopy.

Precision spectroscopy of fundamental bands of molecules in the mid-infrared (MIR) region is of great interest in applications of trace detection and testing fundamental physics, where high-power and narrow-linewidth MIR lasers are needed. By using a frequency-stabilized near-infrared laser as a seed of the signal light of a continuous-wave optical parametric oscillator, we established a broadly tunable MIR light source that has an output power of several hundred milliwatts and a linewidth of a few tens of kilohertz. The MIR laser frequency drift was reduced to below 1 kHz by using an optical frequency comb to stabilize the frequency of the 1064 nm pumping laser. The performance of the light source was investigated and tested by measuring the saturated absorption spectroscopy of a few molecular transitions at 3.3 µm.