Saturation Spectroscopy Research Articles

Saturated absorption spectroscopy of 87Rb atoms using structured light: Observation of narrow hyperfine and crossover resonances

Abstract An experiment on the saturated absorption spectroscopy (SAS) of 87Rb-D2 line is performed using the Laguerre-Gaussian (LG) beam as structured light. The theoretical simulation of which is done by considering a four-level atom-laser coupled system. The theoretically simulated spectra fairly match with the experimentally observed spectra. The line-width narrowing behavior of both the observed hyperfine and crossover resonances in the Doppler-broadened probe absorption spectra is attributed by the spatially dependent Rabi frequency of the pump LG beam irrespective of the characteristics of the probe beam. The results also illustrated that the narrowing behavior of the line shapes of the hyperfine structure using the LG beam is universal in nature, i.e. irrespective of hyperfine or crossover transitions. This structured light-induced narrowing of line-width of the sub Doppler hyperfine and crossover resonances can be utilized for high-precision laser frequency locking at a particular hyperfine or crossover transition. Moreover, a significant narrowing of hyperfine and crossover resonances with the variation of the orbital angular momentum (OAM) number of the LG beam shows that the generated SAS signal can be manipulated by using the OAM of the structured light as a control knob.

Exploration of a vapor cell optical frequency standard scheme implemented using Doppler-free spectroscopy.

We implement a compact optical frequency standard scheme with laser frequency locked to the 5S1/2 (F = 2) - 6P3/2 (F' = 3) transition of the second excited state of 87Rb atoms in a 3 mm cubic glass cell, using a Doppler-free saturated absorption spectroscopy. The experimental results show the frequency stability at the level of 2.2 × 10-12 at 1 s. Furthermore, we conduct an experimental study on the effect of a repump laser on the frequency performance of the saturated absorption spectroscopy optical frequency standard, providing valuable experimental results with reference values for implementing this type of optical atomic clock.

A Network Approach for the Accurate Characterization of Water Lines Observable in Astronomical Masers and Extragalactic Environments.

The water molecule, crucial to the chemical composition and dynamics of the universe, is typically identified in its gas phase via radio and submillimeter transitions, with frequencies up to a few THz. To understand the physicochemical behavior of astronomical objects, accurate transition frequencies are required for these lines. From a set of 26 new and 564 previous Lamb dip measurements, utilizing our ultrasensitive laser-based spectrometers in the near-infrared region, ultrahigh-precision spectroscopic networks were set up for H2 16O and H2 18O, augmented with 40 extremely accurate frequencies taken from the literature. Based on kHz-accuracy paths of these networks, considerably improved line-center frequencies have been obtained for 35 observed or predicted maser lines of H2 16O, as well as for 14 transitions of astronomical significance of H2 18O. These reference frequencies, attached with 5-25 kHz uncertainties, may help future studies in various fields of astrochemistry and astrophysics, in particular when precise information is demanded about Doppler-velocity components, including the gas flows of galactic cores, the kinematics of planetary nebulae, or the motion in exoplanetary atmospheres.

Twin-Field Quantum Key Distribution with Local Frequency Reference.

Twin-field quantum key distribution (TFQKD) overcomes the linear rate-loss limit, which promises a boost of secure key rate over long distance. However, the complexity of eliminating the frequency differences between the independent laser sources hinders its practical application. We analyzed and determined the frequency stability requirements for implementing TFQKD using frequency-stabilized lasers. Based on this analysis, we proposed and demonstrated a simple and practical approach that utilizes the saturated absorption spectroscopy of acetylene as an absolute reference, eliminating the need for fast frequency locking to achieve TFQKD. Adopting the 4-intensity sending-or-not-sending TFQKD protocol, we experimentally demonstrated the TFQKD over 502, 301, and 201km ultralow-loss optical fiber, respectively. We expect this high-performance scheme will find widespread usage in future intercity and free-space quantum communication networks.

Laser Ablation Saturated Absorption Spectroscopy (LA-SAS) for In Situ Detection of Neodymium Isotopes.

This study introduces a novel optical system integrating laser ablation with saturated absorption spectroscopy (LA-SAS) for the detection of neodymium isotopes, crucial for the characterization process in nuclear forensics. Conventional methods for isotope analysis have encountered challenges, such as the inability to perform on-site detection or difficulty in distinguishing minor isotope differences. The LA-SAS system overcomes these limitations by combining pulsed laser for ablation and counter-propagated diode laser for saturated absorption, enabling preparation-free detection with enhanced spectral resolution. The analytical capability was demonstrated through the successful detection of seven neodymium isotopes (142Nd, 143Nd, 144Nd, 145Nd, 146Nd, 148Nd, and 150Nd) with a line width narrowed to 0.1 pm, significantly improving upon the resolution limit of conventional LA-based methods. In addition, quantitative analysis of isotope abundance was facilitated by evaluating the signals from saturated absorption spectra. Special attention was given to the hyperfine structure of odd isotopes, which was resolved by multiple fitting in spectra, thereby refining the accuracy of isotope quantification up to an average bias of 0.45%. The established LA-SAS system offers on-site detection capability based on LA, and also the high resolution from SAS, making it a promising method for in situ nuclear forensics. Consequently, the study enhances the academic understanding of neodymium isotopes and underscores the potential of LA-SAS in fields requiring detailed isotopic information.

Accurate measurement of the frequency offset of the laser based on electromagnetically induced transparency

We propose a method using electromagnetically induced transparency (EIT) to measure the frequency offset of the laser relative to a cavity’s resonance frequency, thereby reducing the laser detuning when preparing Rydberg atoms. Laser reflection by the vapor cell enables observation of two EIT peaks corresponding to the co-propagating and counter-propagating beams, and the peaks’ position is related to laser detuning, allowing us to estimate the frequency offset of the probe and coupling lasers. The method reduces the measurement uncertainty compared to directly observing saturated absorption spectroscopy (SAS) and EIT, making it suitable for applications that require strict control over laser detuning.

Spectroscopic study of the 4f76s2 8 S7/2∘ – 4f7(8S°) 6s6p(1P°) 8P5/2,7/2 transitions in neutral europium-151 and europium-153: absolute frequency and hyperfine structure

We report on spectroscopic measurements on the 4f76s28S7/2∘−4f7(8S∘)6s6p(1P∘)8P5/2,7/2 transitions at 466.32 nm and 462.85 nm, respectively, in neutral europium-151 and europium-153. The center of gravity frequencies for the 151 and 153 isotopes for both transitions are reported for the first time using saturated absorption spectroscopy. For the 6s6p(1P∘)8P5/2 state, the center of gravity frequencies were found to be 642,894,493.3(4) MHz and 642,891,693.3(9) MHz for the 151 and 153 isotopes, respectively. The hyperfine constants for the upper state were found to be A(151)=−157.01(3)MHz, B(151)=74.5(4)MHz and A(153)=−69.43(14)MHz, B(153)=191.0(26)MHz. These hyperfine values are all consistent with previously published results except for B(151) that has a small discrepancy. The isotope shift was found to be 2799.54(20) MHz, a small discrepancy with previously published results. For the 6s6p(1P∘)8P7/2 state, the center of gravity frequencies were found to be 647,708,930.6(6) MHz and 647,705,958.4(26) MHz for the 151 and 153 isotopes, respectively. The hyperfine constants for the upper state were found to be A(151)=−218.66(4)MHz, B(151)=−293.4(8)MHz and A(153)=−97.15(13)MHz, B(153)=−750(3)MHz. These values are all consistent with previously published results except for A(151) that has a small discrepancy. The isotope shift was found to be 2972.8(5) MHz, a small discrepancy with previously measured results.

High-Field Optical Cesium Magnetometer for Magnetic Resonance Imaging

We present a novel high-field optical quantum magnetometer based on saturated absorption spectroscopy on the extreme angular-momentum states of the cesium D2 line. With key features including continuous readout, high sampling rate, and sensitivity and accuracy in the ppm range, it represents a competitive alternative to conventional techniques for measuring magnetic fields of several teslas. The prototype has four small separate field probes, and all support electronics and optics are fitted into a single 19-inch rack to make it compact, mobile, and robust. The field probes are fiber coupled and made from nonmetallic components, allowing them to be easily and safely positioned inside a 7 T MRI scanner. We demonstrate the capabilities of this magnetometer by measuring two different MRI sequences, and we show how it can be used to reveal imperfections in the gradient coil system, to highlight the potential applications in medical MRI. We propose the term EXAAQ (EXtreme Angular-momentum Absorption-spectroscopy Quantum) magnetometry, for this novel method. Published by the American Physical Society 2024

Rovibrational Energies of 13C16O2 Determined with Kilohertz Accuracy.

Accurate spectroscopic data of carbon dioxide are widely used in many important applications, such as carbon monitoring missions. Here, we present comb-locked cavity ring-down saturation spectroscopy of the second most abundant isotopologue of CO2, 13C16O2. We determined the positions of 88 lines in three vibrational bands in the 1.6 μm region, 30011e/30012e/30013e-00001e, with an accuracy of a few kHz. Based on the analysis of combination differences, we obtained for the first time the ground-state rotational energies with kHz accuracy. We also provide a set of hybrid line positions for 150 13C16O2 transitions. The rotational energies (J < 50) in the 30013e vibrational state can be fitted by a set of rotational and centrifugal constants with deviations within a few kHz, indicating that the 30013e state is free of perturbations. These precise isotopic line positions will be utilized to improve the Hamiltonian model and quantitative remote sensing of carbon dioxide. Moreover, they will help to track changes in the carbon source and sink through isotopic analysis.

Analysis of the interaction-length dependence of frequency stability in an iodine-stabilized Nd:YAG laser.

We report a numerical simulation and an experimental study on the interaction-length dependence of frequency stability in an iodine-stabilized neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. A saturation spectroscopy model was used in the simulation to calculate the interaction-length dependence of the linewidth and signal-to-noise ratio of the iodine saturation spectrum. We determined that 2m was the optimal interaction length for laser-frequency stabilization. We confirmed the simulation results by performing modulation transfer spectroscopy and laser-frequency stabilization using 45-cm- and 2-m-long iodine cells and multipass configurations. The results of this study are useful for designing compact and highly stable iodine-stabilized lasers.

Presurgical Use of Hypoxic Mixture for Systemic Perfusion Improvement in Neonates With Complex Congenital Heart Disease: A Systematic Review and Meta-Analysis.

Oxygen therapy is essential for the survival of preterm babies and critically ill newborns; however, it has the potential to cause harm through hypoxemia or hyperoxemia. Newborns with complex congenital heart diseases (CHD) suffer from oxygen fluctuations due to the disease and its treatments, altering pre and postnatal development. The objective of this study is to evaluate the evidence for using a hypoxic mixture to decrease pulmonary over-circulation and improve systemic perfusion before surgical interventions in newborns with complex CHD that course with pulmonary over-circulation and systemic hypoperfusion. A search was conducted in PubMed, EMBASE, LILACS, Scielo, Taylor and Francis, SAGE, and Science Direct databases from 2000 to 2022 by two independent authors, including articles with hypoxic mixture treatment in observational studies or trials, with pre-treatment and post-treatment measurements in the same patient, or two groups or more comparisons. Six articles were selected, with a total of 75 patients. The primary outcome was improved systemic circulation and decreased pulmonary over-circulation measured directly with Qp/Qs and indirectly with oxygen saturation and cerebral near-infrared spectroscopy (NIRS). In addition, we performed a meta-analysis for oxygen saturation and cerebral NIRS. Oxygen saturation was the value uniformly reported; three studies reported a significantly lower oxygen saturation after the hypoxic mixture. The cerebral NIRS was measured in 4 studies, with inconsistent results. After using the hypoxic mixture, the Qp/Qs calculation was lower in the two studies but was not statistically significant. The meta-analysis for oxygen saturation showed a fixed effect post-hypoxic therapy of -0.7 (-1.06; -0.35), p < 0.001. The meta-analysis of two studies that measured cerebral NIRS did not show a statistically significant difference at 12 and 24 hours. In conclusion, this is the first systematic review and meta-analysis regarding the pre-operative use of hypoxic gas mixtures for newborns with complex congenital heart disease. Treatment results in lower oxygen saturations, but there is a lack of evidence of improvement in systemic perfusion. The utilization of this therapy is controversial, and better evidence is necessary.

Chirp asymmetry as an analogue of leptogenesis

The effective conjugation symmetry that arises in the rotating wave frame is the analogue of the charge conjugation symmetry in field theory. Breaking this effective conjugation symmetry leads to asymmetries between up-chirped and down-chirped excitation in quantum optical systems. We use semiclassical quantum optics theory to describe these processes and experimentally characterize the asymmetry in the optical response in chirped, two-color saturated absorption spectroscopy (SAS) in an atomic vapor cell. Doing so demonstrates a theoretical and phenomenological correspondence to the simplest model of leptogenesis, the process by which our universe purportedly went from equal amounts of matter and antimatter to its present matter excess. The understanding of the asymmetry as due to a broken discrete symmetry under chirp illuminates the underlying processes responsible for other chirp asymmetries previously noted in the literature.

Hyperfine structure in a vibrational quadrupole transition of ortho-H2

ABSTRACT A Lamb dip spectroscopic measurement of the Q(1) transition in the (2-0) overtone band of ortho- H 2 is performed with the ultra-sensitive NICE-OHMS intracavity absorption technique at 1238 nm . For the first time individual hyperfine components of a vibrational transition in H 2 are resolved, displaying a pattern of 4 overlapping components with singly isolated components at the red and blue side. Weak components at a line strength of 4.4 × 10 − 28 cm/molecule could be observed as a Lamb dip. Analysis yields a hyperfineless purely rovibrational transition frequency for the Q(1) (2-0) line in H 2 at unprecedented accuracy for any rovibrational transition in a molecular hydrogen isotopologue. Its frequency is 242,091,630,140 ( 9 ) kHz under the assumption that only a blue recoil component is observed. A 1.7σ deviation from the most advanced quantum electrodynamics calculations is obtained, forming a challenge for theory.

Frequency-stabilized improvement of saturated absorption spectroscopy based on laser linewidth-control strategy.

Single-frequency fiber lasers (SFFLs), 1083 nm, have been extensively applied in 4He optical pumping magnetometers (OPMs) for magnetic field detection. However, the sensitivity and accuracy of OPMs are constrained by the frequency stability of SFFLs. Focusing on this concern, the frequency-stabilized performance of the 1083 nm SFFLs is successfully improved by externally tailoring the laser linewidth to match the spectral width of the error signal in saturated absorption spectroscopy. Thereinto, a high-intensity error signal of saturated absorption is generated as a large number of 4He atoms with a wide range of velocities interacting with the 1083 nm laser. Consequently, the root mean square value of the fluctuating frequency after locking is effectively decreased from 24.6 to 13.6 kHz, which achieves a performance improvement of 44.7%. Such a strategy can provide a technical underpinning for effectuating an absolute frequency stabilization with higher precision based on atomic and molecular absorption spectroscopy techniques.

Controlled multiple spectral hole burning via a tripod-type atomic medium

In limit of saturation spectroscopy, we theoretically study the spectral hole burning (SHB) in the absorption spectrum of a probe field through a tripod atomic system. The response function for the probe field is calculated in a Doppler-broadened medium. Burning of spectral holes is observed only for the counter propagation of either one or both the coupling fields in the medium. The SHB is not observed below some critical temperature which is a condition for the electromagnetically induced transparency (EIT) in the medium. The most interesting and significant feature is that the Doppler broadening acts as a decoherence effect in case of EIT, however, the Doppler broadening acts inversely in case of SHB and consequently the burning effect enhances. The SHB is further enhanced and controlled by classes of the average velocity of atoms. The classes of high average atomic velocity in the medium increase the number of spectral hole burns (HBs). The widths of HBs can be controlled by the intensity of the driving fields. A single HB can be switched to multiple HBs in a well-controlled manner using different classes of high average atomic velocity. The various switchable holes can be burned in a desired position of the absorption spectrum which in turn simultaneously slow down multiple probe fields. The phenomenon of SHB may be useful in the construction of multichannel optical switching and storage devices.

Frequency stable and low phase noise THz synthesis for precision spectroscopy

We present a robust approach to generate a continuously tunable, low phase noise, Hz linewidth and mHz/s stability THz emission in the 0.1 THz to 1.4 THz range. This is achieved by photomixing two commercial telecom, distributed feedback lasers locked by optical-feedback onto a single highly stable V-shaped optical cavity. The phase noise is evaluated up to 1.2 THz, demonstrating Hz-level linewidth. To illustrate the spectral performances and agility of the source, low pressure absorption lines of methanol and water vapors have been recorded up to 1.4 THz. In addition, the hyperfine structure of a water line at 556.9 GHz, obtained by saturation spectroscopy, is also reported, resolving spectral features displaying a full-width at half-maximum of 10 kHz. The present results unambiguously establish the performances of this source for ultra-high resolution molecular physics.

Two species–one wavelength detection based on selective optical saturation spectroscopy

Cross-sensitivity limits accurate quantitative detection of species concentrations in all sensor technologies, including laser-based absorption techniques. Absorption sensors capture a signal that combines contributions from all interfering species at a given detection wavelength. Careful selection of the probed spectral line, broadband detection, or upstream separation can partially mitigate cross-sensitivity, however, weak or unidentified signal interference remains a challenge for accuracy. Here, we present a proof-of-principle study to overcome cross-sensitivity by taking advantage of the distinct optical saturation characteristics of different gas mixture components. By controlling the absorption contribution of a selected species by intentional optical saturation, simultaneous and quantitative detection of two interfering species becomes possible even without the need for spectral scanning, hence offering two species–one wavelength detection (2S1W) capability. Demonstrated with direct absorption and cavity-ringdown setups, the method offers a new, previously unexploited opportunity to further enhance laser-based analyzers for complex gas mixture analysis in environmental, medical, and technical applications.

Saturated cavity ringdown spectroscopy at Balmer-α lineof atomic hydrogen for estimating sheath electric field in plasma

We applied saturated cavity ringdown spectroscopy (CRDS) to the measurement of the Doppler-free absorption spectrum of the Balmer-α line of atomic hydrogen in an inductively coupled hydrogen plasma. The spectrum was used for estimating the electric field in the sheath region in the vicinity to a biased electrode. The absorption frequency (the absorption coefficient multiplied by the speed of light) and the saturation parameter were estimated by fitting the experimental ringdown curve with the theory reported by Giusfredi and coworkers (Phys. Rev. Lett. 104 (2010) 110801). We detected the Lamb dip corresponding to the 2p 2 P o 3/2 - 3d 2 D 5/2 transition in the absorption spectrum in the field-free condition. We observed the change in the Lamb dip spectrum when we repeated the measurement in the sheath, and we succeeded in estimating the sheath electric field of 220–230 V/cm at a distance of 1.8 mm from the electrode which was biased at -100 V with respect to the ground potential. The experimental results indicate the potential of saturated CRDS for the measurement of sheath electric fields in plasmas.

Artifact side peaks in saturated absorption spectroscopy caused by inappropriate lock-in amplification

Saturated absorption spectroscopy is a powerful technique that provides valuable information about gas-phase atomic targets, including not only the precise positions of transitions but also the effects of velocity-changing collisions, which manifest as changes in the shape of the peaks. However, using a lock-in amplifier inappropriately can generate artifact side peaks, potentially leading to a misinterpretation of results. To investigate the emergence of these artifacts, we conducted numerical calculations based on the basic Lambert–Beer’s law. Our model reproduced the artifact side peaks and revealed that these artifacts become more significant as the transmittance of the probe laser decreases.

Age, sex, endurance capacity, and chronic heart failure affect central and peripheral factors of oxygen uptake measured by non-invasive and continuous technologies: support of pioneer work using invasive or non-continuous measures.

It is known that maximum oxygen uptake depends on age, sex, endurance capacity, and chronic heart failure. However, due to the required invasive or often applied non-continuous approaches, less is known on underlying central and peripheral factors. Thus, this study aimed to investigate the effects of age, sex, endurance capacity, and chronic heart failure on non-invasively and continuously measured central and peripheral factors of oxygen uptake. 15 male children (11 ± 1 years), 15 male (24 ± 3 years) and 14 female recreationally active adults (23 ± 2 years), 12 male highly trained endurance athletes (24 ± 3 years), and 10 male elders (59 ± 6 years) and 10 chronic heart failure patients (62 ± 7 years) were tested during a cardiopulmonary exercise test on a cycling ergometer until exhaustion for: blood pressure, heart rate, stroke volume, cardiac output, cardiac power output, vastus lateralis muscle oxygen saturation, and (calculated) arterio-venous oxygen difference. For the non-invasive and continuous measurement of stroke volume and muscle oxygen saturation, bioreactance analysis and near-infrared spectroscopy were used, respectively. A two-factor repeated measure ANOVA and partial eta-squared effect sizes () were applied for statistical analyses at rest, 80, and 100% of oxygen uptake. For the age effect, there were statistically significant group differences for all factors (p ≤ .033; ). Concerning sex, there were group differences for all factors (p ≤ .010; ), except diastolic blood pressure and heart rate (p ≥ .698; ). For the effect of endurance capacity, there were no group differences for any of the factors (p ≥ .065; ). Regarding chronic heart failure, there were group differences for the heart rate and arterio-venous oxygen difference (p ≤ .037; ). Age, sex, endurance capacity, and chronic heart failure affect central and peripheral factors of oxygen uptake measured by non-invasive and continuous technologies. Since most of our findings support pioneer work using invasive or non-continuous measures, the validity of our applied technologies is indirectly confirmed. Our outcomes allow direct comparison between different groups serving as reference data and framework for subsequent studies in sport science and medicine aiming to optimise diagnostics and interventions in athletes and patients.