Doppler-free Saturation Spectroscopy Research Articles

Optical frequency stabilization of a 10 GHz Ti:sapphire frequency comb by saturated absorption spectroscopy inr87ubidium

The high power per mode of a recently developed 10 GHz femtosecond Ti:sapphire frequency comb permits nonlinear Doppler-free saturation spectroscopy in 87 Rb with a single mode of the comb. We use this access to the natural linewidth of the rubidium D2 line to effectively stabilize the optical frequencies of the comb with an instability of 7 10 �12 in 1so faveraging. The repetition rate is stabilized to a microwave reference leading to a stabilized and atomically referenced comb. The frequency stability of the 10 GHz comb is characterized using optical heterodyne with an independent self-referenced 1 GHz comb. In addition, we present alternative stabilization approaches for high repetition rate frequency combs and evaluate their expected stabilities.

Molecular fine structure and transition dipole moment of NO 2 using an external cavity quantum cascade laser

Rotational vibrational fine structure and transition dipole moment of NO 2 is measured using Doppler free saturation spectroscopy with an external grating cavity quantum cascade laser (QCL). The QCL wavelength is calibrated using a 310 cm long internally coupled Fabry–Perot interferometer. We obtain a frequency splitting of 139.68 ± 0.06 MHz (0.0047 cm −1) between the spin doublets P 4 ± (17) of 000 → 001 transition of NO 2. The resolution of the QCL based saturation spectrometer is limited by the QCL linewidth of ∼ 3.99 MHz (∼ 0.00013 cm −1) deduced from the half width of the Lamb dips. The Lamb dip spectroscopy is utilized to obtain a vibrational dipole moment of ∼0.37 Debye for the P 4 ± (17) transitions.

Laser-frequency locking using light-pressure-induced spectroscopy in a calcium beam

We demonstrate a spectroscopy method that can be applied in an atomic beam, light-pressure-induced spectroscopy (LiPS). A simple pump and probe experiment yields a dispersivelike spectroscopy signal that can be utilized for laser frequency stabilization. The underlying principles are discussed and compared to Monte Carlo simulations. The shape of the dispersive signal is well described by the simulations. The zero crossing point of the signal is redshifted with respect to the atomic resonance by $\ensuremath{\sim}3\text{ }\text{MHz}$ (one-tenth of the natural linewidth) and depends slightly on the laser intensity. The shift of the zero crossing is determined by laser-induced fluorescence and compared with results of Doppler-free saturation spectroscopy. To check the potential of LiPS for frequency stabilization purposes, it was used to frequency-stabilize the laser for 400 min. Frequency fluctuations of only 0.12 MHz were measured.

Absolute frequency measurements and comparisons in iodine at 735 nm and 772 nm

We report frequency measurements at the rovibronic transition P(42)1-14 (772 nm) and R(114)2-11 (735 nm) from the electronic X 1 Σ g + → B 3 Π 0 u + transition of the iodine molecule 127I 2 with the help of a frequency comb as a reference. By using Doppler-free saturation spectroscopy a frequency precision in the 7 × 10 −10 region is reached and two iodine cells both operated at 550–600 °C are compared. To relate our results to other measurements, the absolute transition frequency of the hyperfine structure line P(148)1-14 a 1 at 780 nm with an already known transition frequency was also determined.

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.

Modulation-free sub-Doppler laser frequency stabilization to molecular iodine with a common-path, two-color interferometer

Recently, a simple common-path, two-color interferometer has been used for Doppler-free saturated dispersion spectroscopy of iodine. We have used such a set-up to stabilize a Nd:YAG laser for the first time, to our knowledge. This method requires only a small number of low-cost optical components compared to frequency modulation techniques.We have measured a root Allan variance of 5 . 10(-12) for 0.2 s, and below 5 . 10 (-11) for integration times up to 300 s.

High resolution Doppler-free spectroscopy of molecular iodine using a continuous wave optical parametric oscillator

We report the application of an all solid-state optical parametric oscillator (OPO) system as a versatile light source for high resolution spectroscopy in the visible wavelength range. The new designed CW OPO showed a high frequency stability and a broad tuning range. We were able to perform Doppler-free saturation spectroscopy thereby resolving the hyperfine structure of molecular iodine at 580 nm. Possible applications and future improvements are discussed.

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.

Isotope shifts and hyperfine structure in near-ultraviolet transitions of Pb I by Doppler-free saturation spectroscopy

Isotope shifts and hyperfine structures have been determined for the three near-ultraviolet transitions 405.8 nm ${(6s}^{2}{6p}^{2}{}^{3}{P}_{2}--{6s}^{2}6p7s{}^{3}{P}_{1}^{o}),$ 368.3 nm ${(6s}^{2}{6p}^{2}{}^{3}{P}_{1}--{6s}^{2}6p7s{}^{3}{P}_{0}^{o}),$ and 364.0 nm ${(6s}^{2}{6p}^{2}{}^{3}{P}_{1}--{6s}^{2}6p7s{}^{3}{P}_{1}^{o})$ in stable isotopes of Pb I using the technique of saturated absorption spectroscopy in a sputtered vapor. The isotope shifts for these transitions and the magnetic hyperfine interaction constants for the ${6s}^{2}{6p}^{2}{}^{3}{P}_{1,2}$ metastable levels are the first Doppler-free determinations for these systems reported in the literature to our knowledge. Combined with experimental data, previously given in the literature, and pseudorelativistic Hartree-Fock estimates, the field shifts (FS's) of seven relevant configurations are deduced: $\mathrm{FS}{(6s}^{2}6p7s)=2461\mathrm{MHz},$ $\mathrm{FS}{(6s}^{2}6p9p)=1838\mathrm{MHz},$ $\mathrm{FS}{(6s}^{2}6p6d)=1820\mathrm{MHz},$ $\mathrm{FS}{(6s}^{2}6p7d)=1668\mathrm{MHz},$ $\mathrm{FS}{(6s}^{2}6p8s)=2132\mathrm{MHz},$ $\mathrm{FS}{(6s}^{2}6p7p)=395\mathrm{MHz},$ and $\mathrm{FS}{(6s}^{2}6p5f)=\ensuremath{-}461\mathrm{MHz},$ referred to ${6s}^{2}{6p}^{2}.$ The hyperfine-structure integrals deduced from the experimental A factors for p electrons of the ground configuration ${6s}^{2}{6p}^{2}$ are in good agreement with results of ab initio calculations.

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.

Obtaining frequency markers of variable separation with a spherical mirror Fabry-Perot interferometer

A compact (L≈5 cm) spherical Fabry-Pérot interferometer with adjustable mirror spacing is used to produce interference fringes with frequency separation (c/2L)/N, N≲20. These fringes are used as frequency markers in a Doppler-free saturation spectroscopy experiment. The conditions for observation of the fringes are discussed in terms of the eigenmodes of the cavity with high transverse indices.

A Dense Grid of Reference Iodine Lines for Optical Frequency Calibration in the Range 595–655 nm

A dense grid of reference lines in the hyperfine structure of the B–X transitions of molecular iodine (127I2) is presented. Frequencies of 481 “t”-hyperfine components in 15 vibrational bands covering the wavelength range 595–655 nm were determined with an absolute accuracy of 1.0 MHz (1ς uncertainty). Spectra were obtained by Doppler-free saturation spectroscopy using a cw ring-dye laser of 1-MHz bandwidth. Center-of-gravity frequencies of rovibronic lines, determined by correcting for the calculated hyperfine shift, are included separately in a least-squares parametrization for each band. From the obtained molecular constants a prediction is made for all t-hyperfine components of the 15 bands covering 595–655 nm. Hence a dense grid of reference lines of 1 MHz (1ς) absolute accuracy is created, with a line in each interval of 1 cm−1 in the entire range. This spectral atlas of about 3400 lines may provide a useful calibration tool in many laboratories.

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.

Isotope selective element analysis by diode laser atomic absorption spectrometry

The analytical figures of merit of isotope selective diode laser atomic absorption spectrometry (DLAAS) in low-pressure graphite furnaces are given for lithium and rubidium. While6Li and7Li were measured by Doppler-limited as well as by Doppler-free absorption spectroscopy of the 670.79 nm resonance line, Doppler-free saturation spectroscopy was applied for analysis of the85Rb and87Rb D2 resonance line at 780.03 nm. Three different modulation techniques were applied and compared: (i) intensity modulation, (ii) wavelength modulation, and (iii) a combination of intensity and wavelength modulation.

A new precise value of the absolute , , transition frequency in

The absolute frequency of the optical electric-dipole transition between the metastable 1 s 2 s 3 S1, F =5/2 and the short-lived 1 s 2 p 3 P2, F =7/2 hyperfine structure sublevels of the helium-like ion in its rest frame was determined by combining Doppler-free saturation spectroscopy and laser heterodyning. One of two cw single-mode dye lasers was locked to the calibrated w-component of the [R(85) 26-0]-line in the (B-X)-system of the -molecule at MHz. While crossing two counterpropagating beams of the other laser perpendicularly (lab angle ) with a low-velocity ion beam and tuning its frequency over the transition under study, the distance of the Lamb-dip center frequency from was obtained by mixing both laser frequencies with an avalanche diode and registering their beat frequency at about 4 GHz with a quartz-stabilized high-frequency counter. The Lamb-dip position was measured for different ion velocities (in units of the velocity of light) in the range of . The parameters and of the relativistic Doppler formula were extracted via a fit to the experimental data set , providing MHz and . This result of differs noticeably from MHz, measured by another group in a collinear-beam configuration at an ion beam propagating with .

A Dense Grid of Reference Iodine Lines for Optical Frequency Calibration in the Range 571–596 nm

A high precision dense grid of reference lines in the hyperfine structure of theB–Xsystem of molecular iodine (127I2) is presented. A simple parametrization has been derived, predicting the hyperfine line positions of the “t” components for vibrational bands (13-1) up to (18-1) and rotational quantum numbersJ= (9–140). The analysis in this paper is based on Doppler-free saturation spectroscopy spectra used for calibration of more than 100 new components in the hyperfine structure of127I2. The data presented contains a prediction (with 2 MHz accuracy) for the positions of 1584 “t” components in the rotational structure of iodine, covering the wavelength interval 571–596 nm.

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.

Observation of strongly subhomogeneous linewidths using high-contrast transmission spectroscopy: Experiment and theory.

Several papers have recently addressed the issue of ob- taining subnatural linewidth and subnatural resolution by performing Doppler-free spectroscopy on samples of high optical density ~so-called high-contrast transmission spec- troscopy !@ 1-7#. In this paper we experimentally and theo- retically demonstrate that lines with strongly subnatural linewidths can be obtained using high-contrast transmission spectroscopy ~HCTS!. Linewidths close to half the natural linewidth are obtained by using the so-called ''tandem ar- rangement'' @2 #@ standard and ''tandem'' experimental con- figurations are schematically shown in Figs. 1~a! and 1~b! respectively#. In the latter configuration the Doppler-free out- put signal from a saturation spectroscopy measurement on a high optical density cell is used as the input light source for a Doppler-free saturation spectroscopy measurement in a second cell, which also is of high optical density. Due to the line-narrowing effect of HCTS the Doppler-free output sig- nal from this second cell may have a linewidth substantially lower than the natural linewidth. The observed line narrowing is explained and supported by theoretical calculations. The theoretical modeling is based on rate equations specifically including velocity-selective op- tical pumping. Previous theoretical analyses have included rate equations @2,7# as well as optical Bloch equations @3-6 #. The present experiment and calculations have been per- formed on the 3s 2 S 1/2 -3 p 2 P 1/2 transition in sodium. We will briefly describe the prerequisites for the calculations. The coupling of the total angular momentum with the nuclear spin of I5 3 2 turns this transition into a four-level system ~neglecting the Zeeman degeneracy! with total angu- lar momentum F51 and F52 in the upper as well as lower electronic state. The optically induced transparency is then caused by velocity-selective optical pumping between the two ground-state hyperfine levels. At sample temperatures below 200 °C the mean free path of the sodium atoms is.1 m. This means that redistribution of optically hyperfine pumped atoms essentially then only occurs when the atoms collide with the walls of the cell and other collision pro- cesses can be neglected. An atomic velocity of 600 m/s per- pendicular to the laser beam and a 2-mm-diameter beam yields a transit time through the beam for the atoms of about 3 ms. This consequently would more or less be the average time until an optically pumped atom is replaced by an un- pumped atom. With an upper state lifetime of 16 ns the tran- sit time through the beam is much longer than any coherence between the ground and excited state. Although use of the

Diode-pumped, continuous-wave, single-mode, tunable Cr^3+:LiSrAlF_6 ring laser

We describe an all-solid-state, tunable, single-frequency, continuous-wave Cr(3+):LiSrAlF(6) ring laser. When pumped with 360 mW of power from a single laser diode the laser has tuning range from 814 to 892 nm and a free-running frequency stability relative to a reference cavity of 60 kHz rms. Further stabilization promises to be possible by use of standard servo electronics. We demonstrate the use of the laser by performing Dopplerfree saturation spectroscopy of the cesium D2 line.