Doppler-free Saturated Absorption Spectroscopy Research Articles

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.

Mid-infrared Doppler-free saturation absorption spectroscopy of the Q branch of CH4ν3 = 1 band using a rapid-scanning continuous-wave optical parametric oscillator.

We have developed a mid-infrared Doppler-free saturation absorption spectroscopy apparatus that employs a commercial continuous-wave optical parametric oscillator (CW OPO), complemented by a home-built automation and wavelength scanning system. Here, we report a comprehensive spectral scan of the Q branch transitions of the ν3 = 1 band of methane (CH4) with an average linewidth (FWHM) of 4.5 MHz. The absolute frequency calibration was achieved using previously reported transition frequencies determined using optical frequency combs, while a Fabry-Perot etalon was used for the relative frequency calibration. We report 15 transitions with improved accuracies of 1.13 MHz (3.76 × 10-5 cm-1).

Hyperfine structure and isotope shifts of xenon measured for near-infrared transitions with Doppler-free saturated absorption spectroscopy

Hyperfine structure and isotope shifts of Xe were investigated with Doppler-free saturated absorption spectroscopy for all transitions in the 820-841 nm spectral interval. The Xe samples were commercial gases of natural isotopic abundances. The measurements were performed by employing a widely tunable narrow line Ti:sapphire laser. The hyperfine structures for 129Xe and 131Xe were well resolved. For the transitions with the wavelengths in vacuum near 820.860 nm and 841.150 nm also isotope shifts of the even isotopes were clearly observed. The modeling of the shapes of the observed absorption lines qualitatively reproduces experimental spectral profiles. The measured absorption peaks of the hyperfine structure and isotope shifts of Xe isotopes present characteristic spectral fingerprints for their identification. Eventually, quantitative spectral analysis will provide isotopic abundances of natural, as well as radioactive Xe gas samples.

Saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride molecules

We report an experimental investigation on the Doppler-free saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride (BaF) molecules in a 4~K cryogenic cell. The obtained spectra with a resolution of 19~MHz, much smaller than previously observed in absorption spectroscopy, clearly resolve the hyperfine transitions. Moreover, we use these high-resolution spectra to fit the hyperfine splittings of excited $A(v=0)$ state and find the hyperfine splitting of the laser-cooling-relevant $A^2\Pi_{1/2}(v=0, J=1/2, +)$ state is about 18 MHz, much higher than the previous theoretically predicted value. This provides important missing information for laser cooling of BaF molecules.

Compact frequency-stabilized pump laser for wavelength conversion in long-distance quantum communication

We demonstrate a compact frequency-stabilized laser at 1064 nm using Doppler-free saturation absorption spectroscopy of molecular iodine. The achieved laser frequency stability and linewidth are 5.7 10-12 (corresponding to an uncertainty of the laser frequency of 1.6 kHz) and 400 kHz, respectively. The developed frequency-stabilized laser can be used as a pump laser for wavelength conversion from visible to telecom (or vice versa) to connect quantum memories utilizing nitrogen-vacancy centers in diamond at remote nodes in fiber-based quantum communication.

Frequency Measurement of Tellurium Lines Near Calcium

We report measurement of frequencies of tellurium lines with respect to atomic calcium employing a 423 nm commercial violet laser diode placed in an extended cavity. Doppler-free saturated absorption spectroscopy of molecular tellurium is performed on three lines, which are lower and higher in energy to the calcium 4s2 1S0–4s4p 1P1 transition. The measured frequency difference of 717(13) MHz between the strong absorption line, #1508 in the tellurium atlas and the calcium transition is in agreement within 10% of the values available from literature. Wavenumbers of two new tellurium lines are derived from the measurement. In addition, spectroscopy and laser cooling and trapping of francium (n = 7) on the ns 2S1/2–(n + 1)p 2P3/2 transition and spectroscopy of Te2 lines near francium could be performed employing the 423 nm diode laser.

Improved measurement of the hyperfine structure of the laser cooling level $$4f^{12}(^3H_6)5d_{5/2}6s^2$$ 4 f 12 ( 3 H 6 ) 5 d 5 / 2 6 s 2 $$(J=9/2)$$ ( J = 9 / 2 ) in $${}^{169}_{\,\,69}{{\mathrm {Tm}}}$$ 69 169 Tm

We report on the improved measurement of the hyperfine structure of $4f^{12}(^3 H_6)5d_{5/2}6s^2$ $(J=9/2)$ excited state in Tm-169 which is involved in the second-stage laser cooling of Tm. To measure the absolute value of the hyperfine splitting interval we used Doppler-free frequency modulation saturated absorption spectroscopy of Tm atoms in a vapor cell. The sign of the hyperfine constant was determined independently by spectroscopy of laser cooled Tm atoms. The hyperfine constant of the level equals $A_J=-422.112(32)$ MHz that corresponds to the energy difference between two hyperfine sublevels of $-2110.56(16)$~MHz. In relation to the saturated absorption measurement we quantitatively treat contributions of various mechanisms into the line broadening and shift. We consider power broadening in the case when Zeeman sublevels of atomic levels are taken into account. We also discuss the line broadening due to frequency modulation and relative intensities of transitions in saturated-absorption experiments.

Interference Cancellation for Hollow-Core Fiber Reference Cells

Doppler-free saturated absorption spectroscopy of gases in hollow-core fiber (HCF)-based cells can be used for realizing new compact, robust, and portable frequency standards. In this paper, methods for cancelling interferences resulting from the optical connections between standard fiber and HCF and other factors such as varying coupling to HCF modes are investigated. Laser power modulation with simultaneous detection of ac and dc signal is used to separate saturated absorption from interferences. In addition, a technique of two piezoelectric stack actuators stretching the fiber at different locations is described. The presented experimental results demonstrate that 99% interference attenuation is readily attainable with the techniques. Frequency comb-referenced measurement of saturated acetylene absorption features near $1.54~\mu \text{m}$ , with fiber length and power modulation, is presented. For comparison, measurements and results of the same acetylene fiber, using a system having pump and probe beams at mutually shifted frequencies, are also given.

High spectral resolution test and calibration of an ultra-narrowband Faraday anomalous dispersion optical filter for use in daytime mesospheric resonance Doppler lidar

We present a high-spectral-resolution test and calibration station for precision measurement of ultra-narrow bandwidth optical filters, and how this is used in the processing of daytime measurements from a resonance Doppler potassium lidar at Arecibo. The test station consists of Doppler-free saturation–absorption spectroscopy coupled with a small free-spectral-range Fabry–Perot etalon, which produces a precise measurement of the filter passband over a range of 20GHz (40pm) or more with a resolution of under 2MHz. This setup is used to measure the bandpass function of a Faraday anomalous dispersion optical filter with a band center at 770nm and full width at half maximum of about 3.64GHz (∼7.2pm), which is the principal spectral filter in the Arecibo lidar. This bandpass function is then used to calibrate the Doppler-broadened returns from the K lidar. As the Faraday filter passband is narrow enough, the return lidar signals in both the resonance fluorescence and Rayleigh scattering are affected. We describe a calibration process to deconvolve the measured filter function from the return signals in order to achieve accurate temperature measurements. Our approach is demonstrated with actual lidar measurements.

Spectroscopic study of the cycling transition4s[3/2]2–4p[5/2]3at 811.8 nm inAr39: Hyperfine structure and isotope shift

Doppler-free saturated absorption spectroscopy is performed on an enriched radioactive $^{39}\mathrm{Ar}$ sample. The spectrum of the $3{s}^{2}3{p}^{5}4s[3/2]{}_{2}$--$3{s}^{2}3{p}^{5}4p[5/2]{}_{3}$ cycling transition at 811.8 nm is recorded, and its isotope shift between $^{39}\mathrm{Ar}$ and $^{40}\mathrm{Ar}$ is derived. The hyperfine coupling constants $A$ and $B$ for both the $4s[3/2]{}_{2}$ and $4p[5/2]{}_{3}$ energy levels in $^{39}\mathrm{Ar}$ are also determined. The results partially disagree with a recently published measurement of the same transition. Based on earlier measurements as well as the current work, the isotope shift and hyperfine structure of the corresponding transition in $^{37}\mathrm{Ar}$ are also calculated. These spectroscopic data are essential for the realization of laser trapping and cooling of $^{37,39}\mathrm{Ar}$.

Doppler-free laser spectroscopy of buffer-gas-cooled molecular radicals

We demonstrate Doppler-free saturated absorption spectroscopy of cold molecular radicals formed by laser ablation inside a cryogenic buffer gas cell. By lowering the temperature, congested regions of the spectrum can be simplified, and by using different temperatures for different regions of the spectrum a wide range of rotational states can be studied optimally. We use the technique to study the optical spectrum of YbF radicals with a resolution of 30 MHz, measuring the magnetic hyperfine parameters of the electronic ground state. The method is suitable for high-resolution spectroscopy of a great variety of molecules at controlled temperature and pressure, and is particularly well suited to those that are difficult to produce in the gas phase.

Development of a wavelength-stabilized distributed Bragg reflector laser diode to the Cs-D2 line for field use in accurate geophysical measurements

We have developed a wavelength-stabilized laser diode (LD) for geophysical measurement devices, which benefit from the uniformity of laser light. Regarding this purpose, a system that has such characteristics as low power consumption, sturdiness against mechanical disturbances, and a long life with long-term frequency stability is especially required. Therefore, we adopt as the light source a distributed Bragg reflector (DBR) LD because it has various advantages concerning such properties. This paper describes the durable and compact wavelength-stabilized laser system. Since our DBR-LD oscillates at 852 nm, we selected the Cs-D2 line (6 2S1/2-6 2P3/2 transition) as a frequency reference to obtain a long-term stability in wavelength. Stabilization is performed by a feedback system using a modulation transfer (MT) method, which is a kind of Doppler-free saturated absorption spectroscopy, to acquire a saturated absorption signal with a high signal-to-noise ratio. Using this system, we could continuously lock the laser frequency to the hyperfine component of the Cs-D2 line for more than one week. By an Allan standard deviation measurement, the uncertainty of the stabilized laser frequency was found to be better than 1 x 10(-10) (<40 kHz) in a Gatetime region longer than 100 s.

High-precision frequency measurements of the ν1 + ν3 combination band of 12C 2H 2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to transitions of 12C 2H 2 and 13C 2H 2, using cavity-enhanced Doppler-free saturation absorption spectroscopy. The absolute frequencies of 41 lines of the ν 1 + ν 3 band of 12C 2H 2, covering the spectral region 1520–1545 nm, have been measured by use of a passive optical frequency comb generator, referenced to 13C 2H 2 transitions of known frequency. The mean experimental uncertainties (coverage factor k = 1) of the frequency values are 3.0 kHz (type A) and 10 kHz (type B). Improved values of the band origin ν 0, rotational constants B′ and B″, and centrifugal distortion coefficients D′, D″, H′, and H″ are presented.

High-resolution spectroscopy of Sm I performed with an extended-cavity violet diode laser

We performed high-resolution spectroscopy of Sm I in the near-UV transitions by using an extended-cavity violet diode laser. By adopting traditional Doppler-free saturated-absorption spectroscopy, we made accurate measurements of the isotope shifts for Sm I. For an atomic excitation laser we used an extended-cavity violet diode laser that was operated in the wavelength range 398–400 nm. As for the experimental results, Doppler-free spectra of the 399.002- and 399.102-nm transition lines of Sm were obtained and the isotope shifts between the even-mass isotopes were measured for the first time to our knowledge. Additionally, we used the King-plot method to check the consistency of the measured isotope shifts and to analyze them as mass shifts and field shifts. For a more quantitative analysis, we performed an ab initio calculation by using the relativistic multiconfiguration Dirac–Fock method.

Isotope shift studies in Zr I by Doppler-freesaturated absorption spectroscopy and pseudo-relativistic Hartree-Fockcalculations: II. Transitions 4d25s2-4d25s5p

High-resolution Doppler-free saturated absorption spectroscopyhas been employed to determine accurate (about ±1 MHz)isotope shifts for twenty-seven 4d25s2-4d25s5p transitions of Zr I in the green, blue andyellow-red spectral regions. These transitions, which involve anelectron jump 5s→5p, represent a class in which thefield shift (FS) component is larger than the specific mass shift (SMS).The SMSs and FSs were separated using aKing plot procedure, in which the SMS of the468.78 nm reference transition was estimated from scaled ab initio calculations. The SMSs for thesetransitions are found to lie between zero and about three timesthe normal mass shifts. Using refined multiconfigurationalfine-structure calculations and scaled pseudo-relativisticHartree-Fock estimates, FSs and SMSshave been computed and found to be in broad agreement with the experimentally determined values. A detailed comparison of thecalculated FSs and SMSs with theaccurate experimental values for this large sample of zirconiumtransitions is found to provide stringent tests of the Vintiintegral and electron density values calculated from the radialwavefunctions and also of the admixture coefficients of the eigenvector components determined from the multiconfigurationalfine-structure calculations. Finally, the results of this workhave been used to predict the SMS and FS values for 20 relevant even- and odd-parity Zr Iconfigurations.

Isotope shiftstudies in Zr I by Doppler-free saturated absorptionspectroscopy and pseudo-relativistic Hartree-Fock calculations:I. Transitions 4d35s-4d25s5p

The isotope shifts of twelve Zr I 4d35s-4d25s5ptransitions in the green and the 4d35s a 5F5-4d35py 5G6 `reference' transitionat 468.78 nm have been determined by the technique of Doppler-free saturated absorption spectroscopy in a sputteredvapour. The specific mass shift (SMS) and the field shift (FS)contributions were separated using a King-plot analysis, inwhich the SMS of the 468.78 nm referencetransition was estimated from ab initio calculations.The 4d35s-4d25s5p transitions, which involve anelectron jump 4d→5p, represent an importantclass in which the SMS is large compared with the FS. This enables SMSs to bedetermined to high accuracy (1-2%), thus affording stringenttests of ab initio calculations. An interpretation ofthe isotope shifts was performed using refined multiconfigurational fine-structure calculations andpseudo-relativistic Hartree-Fock (PSUHFR) calculations. TheSMS values deduced from the PSUHFR calculationsare found to be systematically higher than the experimentalSMS values for all levels, by an average factor of 1.45±0.07 (where the uncertainty represents the standarddeviation of the distribution). Using PSUHFR estimates for theelectron density at the nucleus together with the experimentalFS for the 4d35s a 5F5-4d25s5p y 5G6 transition,the 90Zr-92Zr FSs for some relevantodd-parity configurations are predicted to be FS(4d35p)=-419 MHz, FS(4d25s6p) = + 281 MHz and FS(4d5s25p) = + 1012 MHz, relative to the lower-levelconfiguration 4d35s.

Competition of dark states: Optical resonances with anomalous magnetic field dependence

A different type of optical resonance has been observed in Doppler-free saturated absorption spectroscopy when the pump beam has elliptical polarization slightly deviating from the ${\ensuremath{\sigma}}^{+}$ and the probe has ${\ensuremath{\sigma}}^{\ensuremath{-}}$ polarization. An interpretation in terms of competition between two trap states and a dressed-atom model is presented. The observed extreme sensitivity of the resonance frequency to the external magnetic field is attributed to the ``scissors effect'' of the dressed states' crossing point.

Hyperfine-structure intervals and isotope shifts in the2p33s5S2→2p33p5PJ′transitions of atomic oxygen

We have measured hyperfine-structure splittings and isotope shifts in the ${2p}^{3}3s{}^{5}{S}_{2}\ensuremath{\rightarrow}{2p}^{3}3p{}^{5}{P}_{1,2,3}$ transitions of atomic oxygen using Doppler-free saturated absorption spectroscopy near 778 nm. Values for the hyperfine-structure coupling constants of the ${}^{5}{S}_{2}$ and ${}^{5}{P}_{1,2,3}$ states in ${}^{17}\mathrm{O}$ and the ${}^{18}{\mathrm{O}\mathrm{\ensuremath{-}}}^{17}\mathrm{O}$ and ${}^{18}{\mathrm{O}\mathrm{\ensuremath{-}}}^{16}\mathrm{O}$ isotope shifts of the ${2p}^{3}3s{}^{5}{S}_{2}\ensuremath{\rightarrow}{2p}^{3}3p{}^{5}{P}_{1,2,3}$ transitions were found. The set of values for hyperfine-structure coupling constants and isotope shifts is more complete and generally more precise than previously reported results.

Hyperfine-structure intervals and isotope shifts in the3p44s4PJ→3p44p4DJ′fine-structure multiplet of atomic chlorine by diode laser spectroscopy

We have measured hyperfine-structure splittings and isotope shifts in the $4s{}^{4}{P}_{J}\ensuremath{\rightarrow}4p{}^{4}{D}_{{J}^{\ensuremath{'}}}$ multiplet in atomic chlorine using Doppler-free saturated absorption spectroscopy with an external cavity diode laser. Spectra of seven of the eight components of this multiplet, which have wavelengths between 798 and 859 nm, were obtained. Values for the magnetic dipole and electric quadrupole hyperfine-structure constants of the ${}^{4}{P}_{1/2\ensuremath{-}5/2}$ and ${}^{4}{D}_{1/2\ensuremath{-}7/2}$ states in both ${}^{35}\mathrm{Cl}$ and ${}^{37}\mathrm{Cl}$ were found, and the isotope shifts of the seven transitions studied were measured. The data were also analyzed in an attempt to extract values for magnetic octupole coupling constants for some of the levels investigated, but these were found to be zero at the level of the experimental uncertainty of our measurements.

Hyperfine structure intervals and absolute frequency measurement in the2p43s2PJ→2p43p2DJ′fine-structure multiplet of atomic fluorine by diode laser spectroscopy

We have measured the hyperfine structure splittings of the three components of the ${2p}^{4}3s{}^{2}{P}_{J}\ensuremath{\rightarrow}{2p}^{4}3p{}^{2}{D}_{{J}^{\ensuremath{'}}}$ multiplet in atomic fluorine using both Doppler-free saturated absorption spectroscopy with an external cavity diode laser and Doppler-limited absorption spectroscopy with a noncavity diode laser. Specifically, we have obtained spectra of the $J=1/2\ensuremath{\rightarrow}{J}^{\ensuremath{'}}=3/2$ transition 780 nm, the $J=3/2\ensuremath{\rightarrow}{J}^{\ensuremath{'}}=5/2$ transition at 775 nm, and the $J=3/2\ensuremath{\rightarrow}{J}^{\ensuremath{'}}=3/2$ transition at 761 nm. The fluorine atoms were generated from a 10% mix of ${\mathrm{F}}_{2}$ in He using a 2.45-GHz microwave generator and cavity pressures of approximately 0.5 torr. We report here values for hyperfine splittings and constants for the upper and lower states of these transitions. In addition, the absolute frequency of one of the hyperfine components of the $J=1/2\ensuremath{\rightarrow}{J}^{\ensuremath{'}}=3/2$ transition at 780 nm was measured using a recent absolute frequency measurement of the ${D}_{2}$ transition in Rb.