Saturation Spectroscopy Research Articles

The effects of saturation and velocity selective population in two-step 6S 1/2 → 6P 3/2 → 6D 5/2 laser excitation in cesium

Excited states population distributions created by two-step 6S 1/2 → 6P 3/2 → 6D 5/2 laser excitation in room temperature cesium vapor were quantitatively analyzed applying absorption and saturation spectroscopy. A simple method for the determination of the excited state population in a single excitation step that is based on the measurements of the saturated and unsaturated absorption coefficients was proposed and tested. It was shown that only ≈ 2% of the ground state population could be transferred to the first excited state by pumping the Doppler broadened line with a single-mode narrow-line laser. With complete saturation of the second excitation step, the population amounting to only ≈ 1% of the ground state can be eventually created in the 6D 5/2 state. The fluorescence intensity emerging at 7P 3/2 → 6S 1/2 transition, subsequent to the radiative decay of 6D 5/2 population to the 7P 3/2 state, was used to assess the efficiency of the population transfer in the chosen two-step excitation scheme. The limitations imposed on the sensitivity of such resonance fluorescence detector caused by velocity-selective excitation in the first excitation step were pointed out and the way to overcome this obstacle is proposed.

Hyperfine Structure Measurement of Rubidium Atom and Tunable Diode Laser Stabilization by Using Sagnac Interferometer

The Rubidium saturated absorption spectra for D2 transition lines are used to measure the Fabry-Perot interferometer free spectral range (FSR). The scale linearity of the laser frequency tuning is determined. The Sagnac interferometer has been used for the laser stabilization. The result shows that the laser frequency is stabilized upto sub-mega Herz level. Also the hyperfine structure [5(2)S(1/2) F = 3 --> F' = 2, 3, 4 5(2)P(3/2) 85Rb] of the rubidium atom has been measured by using the tilt locking method, which shows the same result as the conventional saturation spectroscopy.

Accurate absolute reference frequencies from 1511 to 1545 nm of the ν1+ν3 band of ^12C2H2 determined with laser frequency comb interval measurements

Absolute frequency measurements, with uncertainties as low as 2 kHz (1×10−11), are presented for the ν1+ν3 band of 12C2H2 at 1.5 μm (194-198 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line of 13C2H2 and a system stabilized to the line in 12C2H2 whose frequency was to be determined, a Cr:YAG laser-based frequency comb was employed to measure the frequency intervals. The systematic uncertainty is notably reduced relative to that of previous studies, and the region of measured lines has been extended. Improved molecular constants are obtained.

Assessment of Cerebral Oxygen Balance During Deep Hypothermic Circulatory Arrest by Continuous Jugular Bulb Venous Saturation and Near-Infrared Spectroscopy

The purpose of this study was to compare jugular venous bulb saturation (SjvO(2)) and regional cerebral oximetry (rSO(2)) by near-infrared spectroscopy (NIRS) during procedures with deep hypothermic circulatory arrest (DHCA). Prospective observational study. Academic hospital. Patients undergoing aortic reconstructive surgery with DHCA from July 2001 to January 2005. The authors examined cerebral oxygenation by continuous NIRS monitoring and by blood gas analysis of intermittently sampled jugular bulb blood (SjvO(2)). Data were obtained during various stages of the procedure in 29 patients. NIRS measurements were compared with SjvO(2). NIRS and SjvO(2) trends were similar. Overall, cerebral venous oxygen saturation obtained from NIRS was lower compared with SjvO(2) (p < 0.05), especially during periods of low temperature. The mean correlation between NIRS and SjvO(2) was 0.363, and the individual correlations varied from -0.11 to 0.91. The low mean correlation was because of a high degree of variability in the NIRS data between patients. It was concluded that NIRS does not closely correlate with SjvO(2) in this patient population. Cerebral oximetry measured by NIRS could not replace jugular bulb saturation as an intraoperative marker of adequate metabolic suppression.

Narrow Lamb Dip of 3.4 µm Band Transition of Methane with Difference Frequency Generation and Enhancement Cavity

We have developed a sub-Doppler-resolution spectrometer tunable in the 3.4 µm region on the basis of difference frequency generation and an enhancement cavity cell. The spectrometer has allowed us to record the Lamb dips of the ν3 fundamental band of methane even with an IR power level of 3.9 µW, and the linewidth of the Lamb dips can be as narrow as 0.33 MHz. The spectrometer is also so sensitive that a Lamb dip of a less abundant isotopomer, 13CH4, has been successfully observed.

Accurate absolute frequencies of the ν_1+ν_3 band of ^13C_2H_2 determined using an infrared mode-locked Cr:YAG laser frequency comb

Absolute frequency measurements, with up to 1×10−11 level accuracies, are presented for 60 lines of the P and R branches for the ν1+ν3 band of 13C2H2 at 1.5 μm (194 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line and a second laser system stabilized to the line whose frequency was to be determined, a Cr:YAG frequency comb was employed to accurately measure the tetrahertz level frequency intervals. The results are compared with recent work from other groups and indicate that these lines would form a basis for a high-quality atlas of reference frequencies for this region of the spectrum.

Two-photon spectroscopy of rubidium using a grating-feedback diode laser

We describe an experiment for investigating the 5S1∕2→5D5∕2 two-photon transition in rubidium using a single grating-feedback diode laser operating at 778.1nm (385THz). Continuous tuning of the laser frequency over 4GHz allows for the clear resolution of the Doppler-free spectral features and allows accurate measurement of the hyperfine ground-state splitting. A direct comparison between Doppler-broadened and Doppler-free spectral features is possible because both are distinctly evident in the two-photon spectra. By independently modifying the polarization state of the two laser fields, the impact of electric dipole selection rules on the two-photon transition spectra is investigated. This experiment is a valuable addition to the advanced undergraduate laboratory because it uses much of the same equipment as the single-photon saturated absorption spectroscopy experiment performed on the 5S1∕2→5P3∕2 transition in rubidium (λ=780.24nm) and provides students with an opportunity to investigate characteristics of atomic spectra not evident in the single-photon experiment.

Development of a highly intense state-selected CH radical beam source for the study on the collision energy dependent reaction dynamics

A velocity-variable highly intense pulsed supersonic CH (X 2Π) radical beam source was newly developed for the study on the collision energy dependent reaction dynamics of the state-selected CH radical. CH radicals were state-selected by an electrostatic hexapole field. The focusing curves and the CH flux intensities for the ∣ J, F i, M〉 states were measured by a saturated laser-induced fluorescence spectroscopy. As a demonstration, the rotational state dependence of the reaction cross section of CH + O 2 → OH(A) + CO reaction was determined at the collision energy of 0.06 eV.

The hyperfine structure of 129 I 2 and 127 I 129 in the B band system

In a double saturation spectroscopy experiment, using the radiation from one single frequency cw laser, the spectra of 129I2 and 127I129I from one saturation setup were recorded simultaneously and with respect to the spectrum of 127I2 from another setup while tuning the laser. The hyperfine patterns of 129I2 and 127I129I were analysed to determine the nuclear electric quadrupole interaction and the nuclear spin–rotation interaction parameters. Models are presented describing the observations and giving reliable predictions for the hyperfine parameters of all isotopomers.

Arc fusion splicing of hollow-core photonic bandgap fibers for gas-filled fiber cells

The difficulty of fusion splicing hollow-core photonic bandgap fiber (PBGF) to conventional step index single mode fiber (SMF) has severely limited the implementation of PBGFs. To make PBGFs more functional we have developed a method for splicing a hollow-core PBGF to a SMF using a commercial arc splicer. A repeatable, robust, low-loss splice between the PBGF and SMF is demonstrated. By filling one end of the PBGF spliced to SMF with acetylene gas and performing saturation spectroscopy, we determine that this splice is useful for a PBGF cell.

Multiple frequency stabilization of lasers using double saturation spectroscopy

We have developed a method of stabilizing multiple lasers based on double saturation spectroscopy. Compared with other laser-stabilization methods based on conventional saturation spectroscopy, ours provides numerous reference spectra constructed with several velocity groups of atoms. Two independent laser sources can be simultaneously stabilized by using combined optical-pumping processes associated with a single Rb reference. We analyzed the stability of the feedback loop taking the correlation effect of the saturation spectra into consideration. We experimentally demonstrated two stabilized laser sources with a frequency difference of 6,109MHz in the 87Rb D2 line. The results were in good agreement with theory within errors in measurement.

Quantum optical properties of a singleInxGa1−xAs−GaAsquantum dot two-level system

We report on a two-level system, defined by the ground-state exciton of a single $\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot. Saturation spectroscopy combined with ultrahigh spectral resolution gives us a complete description of the system in the steady-state limit. Rabi oscillations and quantum interference experiments, on the other hand, provide a detailed insight into the coherent high excitation regime. All fundamental properties of the two-level system show an excellent quantitative agreement in both domains, even though obtained under entirely different experimental conditions. We thus are able to demonstrate control over an almost ideal two-level system, suitable for possible applications in quantum information processing.

Base units of the SI, fundamental constants and modern quantum physics

Over the past 40 years, a number of discoveries in quantum physics have completely transformed our vision of fundamental metrology. This revolution starts with the frequency stabilization of lasers using saturation spectroscopy and the redefinition of the metre by fixing the velocity of light c. Today, the trend is to redefine all SI base units from fundamental constants and we discuss strategies to achieve this goal. We first consider a kinematical frame, in which fundamental constants with a dimension, such as the speed of light c, the Planck constant h, the Boltzmann constant k(B) or the electron mass m(e) can be used to connect and redefine base units. The various interaction forces of nature are then introduced in a dynamical frame, where they are completely characterized by dimensionless coupling constants such as the fine structure constant alpha or its gravitational analogue alpha(G). This point is discussed by rewriting the Maxwell and Dirac equations with new force fields and these coupling constants. We describe and stress the importance of various quantum effects leading to the advent of this new quantum metrology. In the second part of the paper, we present the status of the seven base units and the prospects of their possible redefinitions from fundamental constants in an experimental perspective. The two parts can be read independently and they point to these same conclusions concerning the redefinitions of base units. The concept of rest mass is directly related to the Compton frequency of a body, which is precisely what is measured by the watt balance. The conversion factor between mass and frequency is the Planck constant, which could therefore be fixed in a realistic and consistent new definition of the kilogram based on its Compton frequency. We discuss also how the Boltzmann constant could be better determined and fixed to replace the present definition of the kelvin.

Absolute wave-number measurements in ^130Te_2: reference lines spanning the 4209-4646-nm region

We have measured the absolute wave numbers of 39 transitions of ^130Te_2 spanning the spectral region of 420.9-464.6 nm to an accuracy of better than 2 parts in 10^9 by use of saturation spectroscopy and Fabry-Perot interferometry. These measurements provide a set of convenient and accurate transfer standards for laser wavelength calibration spanning the entire Stilbene-420 dye-tuning curve.

Theoretical analysis of cavity saturation spectroscopy of weak molecular absorbance

A theoretical analysis of sub-Doppler molecular saturation spectroscopy by use of a confocal Fabry–Perot (CFP) cavity is presented. The effects of gas pressure, cavity length and mirror reflectivity on the saturation dip amplitude are analysed. Such a treatment can provide the optimum conditions and a guidance for the experiment of saturating the weak molecular absorption lines.

High-power frequency-stabilized laser for laser cooling of metastable helium at 389 nm

A high-power, frequency-stabilized laser for cooling of metastable helium atoms using the 2S13→3P23 transition at 389 nm has been developed. The 389 nm light is generated by frequency doubling of a titanium:sapphire laser in an external enhancement cavity containing a lithium–triborate nonlinear crystal. With a maximum conversion efficiency of 75%, 1 W of useful 389 nm power is produced out of 2 W at 778 nm. While being stabilized to the 2S13→3P23 transition, the 389 nm frequency is tunable over ±150MHz with respect to the field-free atomic resonance frequency. This is accomplished by Zeeman tuning of the absorption lines used in the frequency-stabilization scheme. The setup for saturated absorption spectroscopy in an rf discharge cell, used to stabilize the 389 nm laser to the atomic transition, is described in detail.

Observation of large atomic-recoil-induced asymmetries in cold atom spectroscopy

The atomic recoil effect leads to large (25 %) asymmetries in simple spectroscopic investigations of Ca atoms that have been laser-cooled to 10 microkelvin. Starting with spectra from the more familiar Doppler-broadened domain, we show how the fundamental asymmetry between absorption and stimulated emission of light manifests itself when shorter spectroscopic pulses lead to the Fourier transform regime. These effects occur on frequency scales much larger than the size of the recoil shift itself, and have not been observed before in saturation spectroscopy. These results are relevant to state-of-the-art optical atomic clocks based on freely expanding neutral atoms.

Inelastic state-to-state scattering of OH (Π3∕22,J=3∕2,f) by HCl

Parity resolved state-to-state cross sections for inelastic scattering of OH (X2Pi) by HCl were measured in a crossed molecular beam experiment at the collision energy of 920 cm(-1). The OH (X2Pi) radicals were prepared in a single quantum state, Omega=3/2, J=3/2, MJ=3/2, f, by means of electrostatic state selection in a hexapole field. The rotational distribution of the scattered OH radicals by HCl was probed by saturated LIF spectroscopy of the 0-0 band of the A 2Sigma+ - X 2Pi transition. Relative state-to-state cross sections were measured for rotational excitations up to J=9/2 within the Omega=3/2 spin-orbit manifold and up to J=7/2 within the Omega=1/2 spin-orbit manifold. A propensity for spin-orbit conserving transitions was found, but no propensity for excitation into a particular Lambda-doublet component of the same rotational state was evident. The data are presented and discussed in comparison with results previously obtained for collisions of OH with CO (Ecoll=450 cm(-1)) and N2 (Ecoll=410 cm(-1)) and with new data we have measured for the OH+CO system at a comparable collision energy (Ecoll=985 cm(-1)). This comparison suggests that the potential energy surface (PES) governing the interaction between OH and HCl is more anisotropic than the PES's governing the intermolecular interaction of OH with CO and N2.

Sub-Doppler RQ-branch spectra and ab initio dipole derivative calculation for the ν11 ( au) CH 2-wagging mode of 1,3-butadiene

The infrared spectrum of the ν 11 ( a u) out-of-plane CH 2-wagging vibrational mode of the environmentally important 1,3-butadiene molecule has been investigated at sub-Doppler resolution with a CO 2-laser/microwave-sideband spectrometer in order to fully resolve the rotational structure in a number of compact RQ-branch heads. The center frequencies of over 90 saturation Lamb dips in the 11 μm region have been measured with an estimated absolute accuracy of 200 kHz. The new data have been combined with previous Fourier transform results to refine the parameters in the molecular Hamiltonian. A value of |d μ c/d Q 11|=0.3135 debye has been obtained for the transition dipole derivative for the ν 11 mode on the basis of ab initio calculations.

Frequency Measurement of an Ar&amp;lt;tex&amp;gt;$^+$&amp;lt;/tex&amp;gt;Laser Stabilized on Narrow Lines of Molecular Iodine at 501.7 nm

A spectrometer for ultrahigh-resolution spectroscopy of molecular iodine at wavelength of 501.7 nm, near the dissociation limit is described. Line shapes about 30 kHz wide half-width half-maximum (HWHM) were obtained using saturation spectroscopy in a pumped cell. The frequency of an Ar/sup +/ laser was locked to a hyperfine component of the R(26)62-0 transition and the first absolute frequency measurement of this line is reported.