Saturation Spectroscopy Research Articles

Silicon nitride waveguide polarization rotator and polarization beam splitter for chip-scale atomic systems

The design, fabrication, and characterization of a silicon nitride waveguide polarization rotator and polarization beam splitter that operate with a polarization extinction ratio (PER) of ∼30 dB at the rubidium atomic transition of 780 nm wavelength are demonstrated. These polarization devices are fabricated on the same chip using a self-aligned process for integration of the rib and ridge waveguide structures. The polarization rotator is based on the mode evolution approach using adiabatic tapers and demonstrates a PER of ≥20 dB over a 100 nm bandwidth (730–830 nm wavelengths) with an insertion loss (IL) ≤1 dB. The polarization beam splitter is based on a cascaded tapered asymmetric directional coupler with phase matching between the fundamental and higher order TM modes, whereas the TE mode is separated by the through port. This provides a PER ≥ 20 dB with IL ≤ 1 dB over a 50 nm bandwidth for the cross port and a PER ≥ 15 dB with an IL ≤ 1 dB over an 18 nm bandwidth for the through port. These polarization control waveguide devices will enable photonic integrated circuits for saturated absorption spectroscopy of atomic vapors for laser stabilization on-chip.

High stability in near-infrared spectroscopy: part 1, adapting clock techniques to optical feedback

Optical feedback is an efficient way to narrow and stabilise semi-conductor lasers. As a step forward for ultra-stable, yet highly tunable sources, we developed a new prototype of a three-mirror V-shaped optical cavity (VCOF). It is made of a precisely machined Zerodur spacer, that holds 3 optical contacted mirrors forming a high finesse V-shaped cavity. This arrangement allows the resonant light to be sent back to the seeding laser, triggering a drastic narrowing of the emission linewidth well below the cavity mode width without the need for high-bandwidth active electronic lock of the laser on the cavity. Low expansion material and precise temperature control of the reference cavity leads to a source with Hz level frequency drift and 70 Hz-level emission linewidth at 215 THz. We discuss the benefits of this new prototype compared to its predecessor for high-sensitivity cavity ring down spectroscopy (CRDS). To serve this purpose, the frequency stabilised laser was characterised on short, mid and long time scales, using a high finesse etalon, a self referenced optical frequency comb and a long term saturated CRDS absorption Lamb dip measurement on water.

Cavity-enhanced saturated absorption spectroscopy of the (30012) - (00001) band of 12C16O2.

The (30012) ← (00001) band of 12C16O2 in the 1.6 μm region is used for satellite observation of carbon dioxide in the Earth's atmosphere. Here, we report a Doppler-free spectroscopy study of this band with comb-locked wavelength-modulated cavity-enhanced absorption spectroscopy. Frequencies of 18 transitions with the rotational quantum numbers up to 42 were determined with sub-kHz accuracy, corresponding to a fractional uncertainty at the 10-12 level. With this precision, we revealed an anomalous decrease of the line shift and an increase of the line broadening for the Lamb dips of CO2 in the low-pressure regime compared to values obtained from Doppler-limited spectra at higher pressures.

Comb coherence-transfer and cavity ring-down saturation spectroscopy around 1.65 μm: kHz-accurate frequencies of transitions in the 2ν3 band of 12CH4.

Comb Coherence Transfer (CCT) uses a feed-forward frequency correction to transfer the optical phase of a frequency comb to the beam of a free-running diode laser. This allows the amplification of a selected comb tooth by 50 dB while adding agile and accurate frequency tuning. In the present work, SI-traceable frequency calibration and comb tooth narrowing down to 20 kHz is additionally provided by comb frequency locking to an ultrastable optical frequency reference distributed from Paris to Grenoble through the RENATER optical fiber network [Lisdat et al., Nat. Commun., 2016, 7, 12443]. We apply this CCT broadly tunable source for saturated cavity ring-down spectroscopy of ro-vibrational R0 to R10 multiplets in the 2ν3 band of 12CH4 (from 6015 to 6115 cm-1). Indeed, efficient cavity injection with large intra-cavity power build-up induces saturation of the ro-vibrational transitions at low pressure and Doppler-free Lamb dips are observed with high signal/noise. kHz-accurate transition frequencies are derived improving by three orders of magnitude previous values from spectra in the Doppler regime, which are strongly affected by line blending. While previous saturation spectroscopy investigations addressed specific 2ν3 multiplets (R6 or R9), the CCT approach allowed for a rapid coverage of the entire R0-R10 series. Measured transition frequencies are compared with experimental and theoretical line lists available in the literature.

Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm

Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C2H2 between 7167 and 7217 cm−1, using a frequency-comb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers. We measured the absolute center frequency of sixteen lines belonging to the 2 band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a ‘V’-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 3 and 13 kHz. This is over three orders of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene.

Frequency-based dispersion Lamb-dip spectroscopy in a high finesse optical cavity.

Frequency-based cavity mode-dispersion spectroscopy (CMDS), previously applied for Doppler-limited molecular spectroscopy, is now employed for the first time for saturation spectroscopy. Comparison with two intensity-based, cavity-enhanced absorption spectroscopy techniques, i.e. cavity mode-width spectroscopy (CMWS) and the well-established cavity ring-down spectroscopy (CRDS), shows the predominance of the CMDS. The method enables measurements in broader pressure range and shows high immunity of the Lamb dip position to the incomplete model of saturated cavity mode shape. Frequencies of transitions from the second overtone of CO are determined with standard uncertainty below 500 Hz which corresponds to relative uncertainty below 3 × 10-12. The pressure shift of the Lamb dips, which has not been detected for these transitions in available literature data, is observed.

Coherent Surface Plasmon Hole Burning via Spontaneously Generated Coherence.

Surface plasmon (SP)—induced spectral hole burning (SHB) at the silver-dielectric interface is investigated theoretically. We notice a typical lamb dip at a selective frequency, which abruptly reduces the absorption spectrum of the surface plasmons polaritons (SPP). Introducing the spontaneous generated coherence (SGC) in the atomic medium, the slope of dispersion becomes normal. Additionally, slow SPP propagation is also noticed at the interface. The spectral hole burning dip is enhanced with the SGC effect and can be modified and controlled with the frequency and intensity of the driving fields. The SPP propagation length at the hole-burning region is greatly enhanced under the effect of SGC. A propagation length of the order of 600 µm is achieved for the modes, which is a remarkable result. The enhancement of plasmon hole burning under SGC will find significant applications in sensing technology, optical communication, optical tweezers and nano-photonics.

Observation of photon recoil effects in single-beam absorption spectroscopy with an ultracold strontium gas

We report on observing photon recoil effects in the absorption of a single monochromatic light at 689 nm through an ultracold 88Sr gas, where the recoil frequency is comparable to natural linewidth of the narrow-line transition 5s2 1S0–5s5p 3P1 in strontium. In the regime of high-saturation, the absorption profile becomes asymmetric due to the photon-recoil shift, which is of the same order as the natural linewidth. The lineshape is described by an extension of the optical Bloch equations including the momentum transfers to atoms during emission and absorption of photons. Our work reveals the photon recoil effects in a simplest single-beam absorption setting, which is of significant relevance to other applications such as saturation spectroscopy, Ramsey interferometry, and absorption imaging.

Saturated absorption spectroscopy near 1.57 μm and revised rotational line list of 12C16O

Molecular transitions provide natural frequency standards for spectroscopy, telecommunication, and astrophysics. The frequency accuracy is also crucial in various tests of fundamental physics. A comb-locked cavity ring-down spectrometer measured lamb dips of sixty-one 12C16O transitions around 1.57 μm in the second overtone band. The positions were determined with an accuracy of a few kHz. A new set of rotational spectroscopic parameters was derived with 30 ground state combination difference for the ground vibrational state with a standard deviation of 4.5 kHz. It results in a refinement of the ro-vibrational spectroscopic constants for the v=3 vibrational state. These parameters allow the pure rotational line lists of the υ=0←0 and υ=3←3 in the 112 GHz – 3.89 THz regions.

Structural characterization of the interaction between α M I‐domain of the integrin Mac‐1 (α M β 2 ) and the cytokine pleiotrophin

Integrin receptors are involved in numerous physiological processes, including inflammation, cell migration, extracellular matrix recognition, survival, and growth. Integrin Mac-1 (αMβ2) is a monocyte adhesion receptor that can undergo rapid activation yielding conformational changes that subsequently allow increased affinity for its ligands and enable cellular responses such as rolling, adhesion, and transmigration of phagocytes to the inflammatory sites. αMβ2 is also the most promiscuous integrin receptor because it recognizes a large number of distinct ligands that share no homologous recognition motif. In particular, αMI-domain is known to bind cationic proteins/peptides depleted in acidic residues. This contradicts the canonical ligand-binding mechanism of αI-domains, which requires an acidic amino acid in the ligand to coordinate the divalent cation within the metal ion-dependent adhesion site (MIDAS) of αI-domains. The lack of acidic amino acids in the αMI-domain-binding sequences suggests the existence of an as-yet uncharacterized interaction mechanism. In the present study, we analyzed interactions of αMI-domain with a representative Mac-1 ligand, the cationic cytokine pleiotrophin (PTN). Through nuclear magnetic resonance (NMR) chemical shift perturbations, cross saturation, and nuclear Overhauser effect spectroscopy (NOESY), we found the interaction between αMI-domain and PTN is divalent cation-independent and mediated mostly by hydrophobic contacts between the N-terminal domain of PTN and residues in the α5-β5 loop of αMI-domain. The mutation I265 in the α5-β5 region confirms this area as a binding site of αMI-domain for PTN. The observation that both increased ionic strength and mutations of acidic residues in the α5-β5 loop weaken the interaction between the proteins indicates electrostatic interaction may also play a significant role in the binding. Based on results from these experiments, we formulated a model of the interaction between αMI-domain and PTN. This unique mechanism of interaction between PTN and αMI-domain should explain ligand recognition specificity of αMβ2.

Methods of tunable diode laser absorption saturation spectroscopy to gas sensing under optically thick conditions

AbstractThe absorption saturation under optically thick conditions will bring difficulties to laser spectroscopy gas sensing. We report the spectrum two wings reconstruction method and the transmitted laser intensity fitting method for tunable diode laser absorption saturation spectroscopy gas absolute measurements under optically thick conditions, and used the modified Lambert Beer's law to calculate methane concentration based on the incomplete spectrum of absorption saturation. The maximum deviation between the experimental measurement results and the standard methane concentration is about 4.7%, which verifies the feasibility of these new methods and also show that they have great potential for expanding the gas sensing range of a single absorption line.

Isotope shifts in the metastable a5F and excited y5Go terms of atomic titanium

We measure and analyze the isotope shifts the multiplet of transitions between the metastable a$^5$F and excited y$^5$G$^\circ$ terms of neutral titanium by probing a titanium vapor in a hollow cathode lamp using saturated absorption spectroscopy. We resolve the five $J\to J+1$ and the four $J\to J$ transitions within the multiplet for each of the the three $I=0$ stable isotopes ($^{46}$Ti, $^{48}$Ti, and $^{50}$Ti). The isotope shifts on these transitions allow us to determine the isotope-dependent variation in the fine-structure splitting of the a$^5$F and y$^5$G$^\circ$ levels themselves. Combined with existing knowledge of the nuclear charge radii of titanium nuclei, we derive the specific mass and field shifts, which arise from correlated electronic motion and electronic density at the nucleus respectively, and further observe a strong $J$-dependent variation in each. Our results yield insight into the electronic and nuclear structure of transition metal atoms like titanium, and also characterize optical transitions that may allow for optical manipulation of ultracold gases of transition metal species.

Low-cost external cavity diode laser for cold atom experiments

In this article, the construction of an external cavity diode laser (ECDL) with the wavelength selection and stabilization given by an interference filter in a cateye reflector mirror type instead of using a common grating Littrow configuration is described. We show that our ECDL can be locked for several hours to a given frequency with the broad temperature variation of about 0.2-0.4 °C. A rubidium saturated absorption spectroscopy was used to check our ECDL with the D2 hyperfine transitions. Our low-cost and stabilized ECDL can be used for cold atom experiments as well as in quantum and atom optics applications.

Theoretical calculation of saturated absorption spectroscopy of atomic ytterbium beam

Saturated absorption spectroscopy is a technique of measuring the transmission of a probe beam induced by a counter-propagating pump beam, which can achieve a nearly Doppler-free spectral resolution. In this study, the saturated absorption spectra of individual isotopes of ytterbium atoms are calculated using rate equations for various polarizations of the probe and pump beams under an assumption that the distribution of velocities for atoms within the atomic beam is a Maxwell-Boltzmann distribution. The fourth-order Runge-Kutta method is used for calculation of the rate equations, then the absorption coefficient in the vicinity of the atomic transitions is calculated, and the transmission of the probe beam is obtained by Beer-Lambert law. We compare the calculations with an experimental result from the literature and obt ain a good agreement.

Bone Marrow Reconversion With Reambulation: A Prospective Clinical Trial.

In a prospective clinical trial, 20 healthy men participated in a 60-day, 6-degree head-down tilt bed rest study. Serial 3-T magnetic resonance (MR) imaging measures of the lumbar spine were performed at baseline, after 57 days of bed rest, and at 30, 360, and 720 days of reambulation (100 MR imaging scans). Proton density with and without fat saturation, 2-point Dixon, and single-voxel MR spectroscopy techniques were used to assess bone marrow composition (300 measures). Erythropoiesis was measured using hematocrit, reticulocyte, and ferritin. Also, participants randomly received either a nutritional intervention composed of polyphenols, omega-3, vitamin E, and selenium or a normal diet. Thirty days of reambulation after 60 days of bed rest caused a marked decrease of the mean lumbar vertebral fat fraction (VFF) (-9.2 ± 1.6 percentage points, -8.0 ± 1.3 percentage points, and -12.7 ± 1.2 percentage points compared with baseline using proton density, Dixon, MR spectroscopy, respectively; all 3, P < 0.05). Reambulation also decreased the fat saturation index (-5.3 ± 1.1 percentage points compared with baseline; P < 0.05). These coincided with lower hematocrit and ferritin and with increased reticulocytes at reambulation day 13 compared with baseline (all 3, P < 0.05). After 57 days of bed rest, the VFF was unchanged from baseline (all 3 MR techniques, P > 0.05); reambulation for 2 years returned the lumbar VFF to baseline values. This longitudinal trial established that 30 days of reambulation after 60 days of bed rest constituted a powerful stimulus for bone marrow reconversion. In this model, the enhanced erythropoiesis coupled with preferential consumption of fatty acids from regulated marrow adipose tissue to supply energy for erythropoiesis and bone anabolism may explain the lumbar vertebrae reconversion. These results will help interpreting bone marrow signal in ambulatory patients after long periods of bed rest.

Probing atomic and nuclear properties with precision spectroscopy of fine and hyperfine structures in the Li+7 ion

Precision spectroscopy of ${\mathrm{Li}}^{+}$ is a promising testing ground for bound-state quantum electrodynamics (QED) and for measurements of nuclear properties such as the Zemach radius. We investigate the hyperfine and fine-structure splittings of the $2\phantom{\rule{0.16em}{0ex}}^{3}S_{1}$ and $2{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{J}$ states of $^{7}\mathrm{Li}^{+}$ using saturated fluorescence spectroscopy based on a $\ensuremath{\sim}460\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ metastable ion beam. We measure in particular the $2\phantom{\rule{0.16em}{0ex}}^{3}S_{1}--2\phantom{\rule{0.16em}{0ex}}^{3}P_{J}$ transitions in $^{7}\mathrm{Li}^{+}$. With a triple nested loop scanning method, the long-term drift and systematic uncertainties are reduced or eliminated, resulting in a total uncertainty of less than 100 kHz. Our results are in good agreement with QED calculations. For the hyperfine splittings of $2\phantom{\rule{0.16em}{0ex}}^{3}S_{1}$, our measured values have a similar accuracy to previous measurements and theoretical calculations. For the $2{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{J}$ fine and hyperfine splittings, our measured results are one order of magnitude more accurate than those of previous measurements and have a similar accuracy to the theoretical values. The measurements lay the foundation for future work on the ${\mathrm{Li}}^{+}$ isotopes and their theoretical interpretation in terms of nuclear charge radii and the Zemach radii.

Continuum and undefine hole burning regions via pulse propagation in a four-level Doppler broadened atomic system

In this paper, we have theoretically examined and modified the spectral hole burning (SHB) in a tripod-type four-level Doppler broadened atomic medium. We have investigated a narrow spectral hole (Lamb dip) in the absorption spectrum, and subluminal/superluminal light propagation in the dispersion spectrum through Doppler broadened atomic medium as well. Furthermore, a theoretical demonstration is presented for the group index, advance/delay time and group velocity. Moreover, we investigate that the detuning of the control fields considerably shift the SHB at either side of the resonance line. For the first time, we have investigated the undefined hole burning regions by showing that the group index, advance/delay time, and group velocity are undefined in these regions. The results may have important applications in the developing technology of quantum optics and will open up new ways to investigate different phenomena inside the hole burning regions.

Dispersion-like lineshape observed in cavity-enhanced saturation spectroscopy of HD at 1.4 µm.

Precision measurement of ro-vibrational transitions in the electronic ground state of the hydrogen molecule can be used to test quantum electrodynamics and also to determine the dimensionless proton-to-electron mass ratio. Saturation spectroscopy of the 2-0 overtone transitions of hydrogen deuterium (HD) were measured with three cavity-enhanced spectroscopy methods. With a sensitivity at the 10-13cm-1 level, we revealed a dispersion-like lineshape instead of a conventional Lamb "dip," which explains the significant discrepancy among previous independent measurements. The spectra can be fit well by using the Fano profile. Centers of R(1) and R(3) lines were determined as 217 105 182 111 (19)stat(240)syskHz and 220 704 305 234 (20)stat(240)syskHz, respectively.

Lamb-peak spectrum of the HD (2-0) P(1) line

A saturation spectroscopy measurement of the P(1) line of the ($2-0$) band in HD is performed in a sensitive cavity-enhanced optical setup involving frequency comb calibration. The spectral signature is that of a Lamb-peak, in agreement with a density-matrix model description involving 9 hyperfine components and 16 crossover resonances of $\Lambda$-type. Comparison of the experimental spectra with the simulations yields a rovibrational transition frequency at 209,784,242,007 (20) kHz. Agreement is found with a first principles calculation in the framework of non-adiabatic quantum electrodynamics within 2$\sigma$, where the combined uncertainty is fully determined by theory.

Role of velocity induced coherent population oscillation in saturated fluorescence spectroscopy

In this paper we present a theoretical framework to identify the role of coherent population oscillation (CPO) in saturated fluorescence spectroscopy in a two-level system which is a very useful spectroscopic technique for weak transitions. The fluorescence dip in a fluorescence spectra is generally explained as a saturation effect. However in this work, we find that the Doppler-free dip in a fluorescence spectra is due to saturation effect and CPO effect. The fluorescence dip is further modified by Doppler averaging and its linewidth and dip height are dependent on the temperature of the atomic gas and the applied laser beam intensity. For an atomic beam, the shift of the fluorescence dip from the line center is dependent on the average velocity of the atomic beam and the misalignment of the laser beams with respect to the atomic beam.