Frequency stabilization of CO laser using RF optogalvanic Lamb-dip

The Lamb dip of CO rovibrational transition is detected by a room temperature extracavity RF optogalvanic cell and employed to stabilize the frequency of a CO laser. The S/N ratio of optogalvanic signal is about 2000  at optical power < 1 W. The relative depth of Lamb dip is 2.3%. The S/N ratios of first and third harmonic demodulated saturation signals are about 40  and 10  , respectively. The CO laser is stabilized using the first harmonic demodulated signal, and the frequency stability is better than 300 kHz. Concurrently, the influences of operational parameters, which include the coil current, partial pressures of gas mixture, are investigated. A simple model for the influence of coil current is presented, and further improvements are addressed as well.     

A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy

We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS) technology with good reproducibility. A frequency stability of 2.5 × 10~(-14) at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10~(-13), demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated, especially the contribution of the residual amplitude modulation(RAM). The contribution of the RAM in MTS cannot be evaluated directly. To solve this problem, we theoretically deduce the MTS signal with RAM under large modulation depth, and prove that the nonsymmetric shape of the MTS signal is directly related to the MTS effect. The non-symmetric shape factor r can be calibrated with a frequency comb, and in real experiments, this r value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift. The full frequency uncertainty is evaluated to be 5.3 k Hz(corresponding to a relative frequency uncertainty of 9.4×10~(-12)). The corrected transition frequency has a difference from the BIPM-recommended value of 2 k Hz, which is within 1σ uncertainty, proving the validity of our evaluation.     

Laser cooling and trapping of Yb from a thermal source

We have successfully loaded a magneto-optic trap for Yb atoms from a thermal source without the use of a Zeeman slower. The source is placed close to the trapping region so that it provides a large flux of atoms that can be cooled and captured. The atoms are cooled on the transition at 398.9 nm. We have loaded all seven stable isotopes of Yb into the trap including the rarest isotope, ¹⁶⁸Yb. For the most abundant isotope (¹⁷⁴Yb), we load more than 10⁸ atoms into the trap within 1 s. We have characterized the source by studying the loading rate and the loss rate for different isotopes and at different trapping powers. We extract values for the loss rate due to collisions and due to branching into low-lying metastable levels. At the highest trap densities, we find evidence of additional loss due to intra-trap collisions.Received: 15 February 2004, Published online: 23 March 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 42.50.Vk Mechanical effects of light on atoms, molecules, electrons, and ions     

A new analysis of the ν2 fundamental band of H2O^＋＊

This paper reports that the absorption spectra of H2O^＋ have been measured by tunable mid-infrared diode laser spectroscopy in the spectral range of 1100-1380 cm^-1. The H2O＋ ions are generated in an AC glow discharge of the gaseous mixtures of H2O/He and detected with the velocity modulation technique. Forty new lines are assigned to the ν2 fundamental band of H2O^＋ （X^2B1）. The observed lines together with other data published previously are fitted to the standard effective Hamiltonian of an asymmetric top, yielding a set of improved rotational constants, spin-rotation constants and their quartic and sextic centrifugal distortion constants for the ν2=1 vibrational state of H2O＋.     

Pressure broadening parameters of the hydroxyl radical A 2 Σ+ (υ’=0) ← X 2 Π3/2 (υ=0) transitions at ca. 308 nm

Pressure broadening widths and pressure-induced frequency shifts for the hydroxyl radical Q11([see full textsee full text]), Q21([see full textsee full text]), Q11(2), Q21(2) absorption lines in the A band at ca. 308 nm have been determined in the presence of a variety of gases (N2, Ar, Ne and He). Hydroxyl radicals were formed using either a microwave discharge or a vacuum ultra-violet photolysis of water vapour and were detected using direct absorption spectroscopy with a bandwidth normalised noise equivalent absorption sensitivity of 5 ×10-5 Hz-1/2. A tunable external cavity diode laser at 835 nm and a single-frequency continuous-wave intracavity frequency-doubled diode laser at 488 nm were used to produce tunable continuous-wave light at 308 nm by sum-frequency generation in a -BaB2O4 crystal.     

A DFG-based cavity ring-down spectrometer for trace gas sensing in the mid-infrared

Continuing studies into an all-diode laser-based 3.3 μm difference frequency generation cavity ring-down spectroscopy system are presented. Light from a 1,560 nm diode laser, amplified by an erbium-doped fibre amplifier, was mixed with 1,064 nm diode laser radiation in a bulk periodically poled lithium niobate crystal to generate 16 μW of mid-IR light at 3,346 nm with a conversion efficiency of $0.05\,\%\,{\text{W}}^{-1}\,{\text{cm}}^{-1}$ . This radiation was coupled into a 77 cm long linear cavity with average mirror reflectivities of 0.9996, and a measured baseline ring-down time of $6.07\pm 0.03\,\upmu{\rm s}$ . The potential of such a spectrometer was illustrated by investigating the $P(3)$ transition in the fundamental $\nu_{3}(F_{2})$ band of ${\text{CH}}_4$ both in a 7.5 ppmv calibrated mixture of ${\text{CH}}_4$ in air and in breath samples from methane and non-methane producers under conditions where the minimum detectable absorption coefficient ( $\alpha_{\rm min}$ ) was $2.8 \times 10^{-8}\,{\rm cm}^{-1}$ over 6 s using a ring-down time acquisition rate of 20 Hz. Allan variance measurements indicated an optimum $\alpha_{\rm min}$ of $2.9\times 10^{-9}\,{\rm cm}^{-1}$ over 44 s.     

Nd:GSAG-pulsed laser operation at 943 nm and crystal growth

Laser activity of neodymium-doped gadolinium scandium aluminum garnet (Nd:GSAG) on the transition with an output wavelength around 943 nm was investigated. The emission cross-section was measured with spectroscopic and amplifier approaches demonstrating the applicability of the Nd:GSAG laser for water vapor detection. A Q-switched laser setup delivered 150 ns pulses with 26 mJ output energy and 9% optical to optical efficiency. The laser was diode pumped with up to 50 Hz repetition rate. In the long pulse mode a pulse energy of 83 mJ with 32% optical efficiency was achieved. The output wavelength was controlled by injection seeding. PACS 42.55.Xi; 42.70.Hj     

Accurate spectroscopy of Sr atoms

We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr: 1S0-3P1 at 689 nm, 3P1-3S1 at 688 nm and 3P0-3S1 at 679 nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden transition of 87Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for 88Sr and 87Sr, allowing the determination of 3P0, 3P1 and 3S1 isotope shifts, as well as the 3S1 hyperfine constants.     

Loss of collectivity in 79Rb

High-spin states in ⁷⁹Rb were populated in the reaction at E(beam) = 60 MeV. The lifetimes of the excited states of the positive-parity yrast band and of the negative-parity band in ⁷⁹Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Q_t are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. An erratum to this article is available at .     

Linewidth of a quantum-cascade laser assessed from its frequency noise spectrum and impact of the current driver

We report on the measurement of the frequency noise properties of a 4.6-??m distributed-feedback quantum-cascade laser (QCL) operating in continuous wave near room temperature using a spectroscopic set-up. The flank of the R(14) ro-vibrational absorption line of carbon monoxide at 2196.6?cm^?1 is used to convert the frequency fluctuations of the laser into intensity fluctuations that are spectrally analyzed. We evaluate the influence of the laser driver on the observed QCL frequency noise and show how only a low-noise driver with a current noise density below ${\approx} 1~\mbox{nA/}\sqrt{}\mbox{Hz}$ allows observing the frequency noise of the laser itself, without any degradation induced by the current source. We also show how the laser FWHM linewidth, extracted from the frequency noise spectrum using a simple formula, can be drastically broadened at a rate of ${\approx} 1.6~\mbox{MHz/}(\mbox{nA/}\sqrt{}\mbox{Hz})$ for higher current noise densities of the driver. The current noise of commercial QCL drivers can reach several $\mbox{nA/}\sqrt{}\mbox{Hz}$ , leading to a broadening of the linewidth of our QCL of up to several megahertz. To remedy this limitation, we present a low-noise QCL driver with only $350~\mbox{pA/}\sqrt{}\mbox{Hz}$ current noise, which is suitable to observe the ??550?kHz linewidth of our QCL.     

Characterization of a large core photonic crystal fiber made of lead–bismuth–gallium oxide glass for broadband infrared transmission

We report on characterization of a large solid core, photonic crystal fiber dedicated to broadband transmission range from visible to mid-infrared. We have fabricated a multi-mode photonic crystal fiber, made of a heavy metal-oxide glass based on the $\hbox {PbO}{-}\hbox {Bi}_{2}\hbox {O}_{3}{-}\hbox {Ga}_{2}\hbox {O}_{3}$ system, modified with $\hbox {SiO}_{2}$ and CdO, synthesized in-house, which shows good transmission up to $4.5\,\upmu \hbox {m}$ , as well as good rheological properties that permit multiple thermal processing steps without crystallization. The core of the fiber is created by replacement of central 60 tubes with solid rods. The photonic cladding is composed of 8 rings of air holes with a filling factor of 0.42. Simulation results shows that the fiber can be used for broadband transmission in the range of 430–3,000 nm. Calculated effective mode area of the fiber is $295\,\upmu \hbox {m}^{2}$ . We have measured attenuation of the fiber in the range 800–1,700 nm and its sensitivity to bending losses. Attenuation ranges from 1 to 4 dB/m in the considered range and bending losses are below 0.7 dB.     

High-resolution laser spectroscopy of ultracold ytterbium atoms using spin-forbidden electric quadrupole transition

We have successfully observed high-resolution spectra of spin-forbidden electric quadrupole transition (¹ S ₀→³ D ₂) in ytterbium (¹⁷⁴Yb) atoms. The differential light shifts between the ¹ S ₀ and the ³ D ₂ states in a far-off resonant trap at 532 nm are also measured. For the spectroscopy, we developed simple, narrow-linewidth, and long-term frequency stabilized violet diode laser systems. Long-term drifts of the excitation laser (404 nm) is suppressed by locking the laser to a length stabilized optical cavity. The optical path length of the cavity is stabilized to another diode laser whose frequency is locked to a strong ¹ S ₀→¹ P ₁ transition (399 nm) of Yb. Both lasers are standard extended-cavity diode lasers (ECDLs) in the Littrow configuration. Since the linewidth of a violet ECDL (～10 MHz) is broader than a typical value of a red or near infra-red ECDL (<1 MHz), we employ optical feedback from a narrow-band Fabry–Perot cavity to reduce the linewidth. The linewidth is expected to be <20 kHz for 1 ms averaging time, and the long-term frequency stability is estimated to be ～200 kHz/h.     

Observation of four-wave mixing in caesium atoms using a noncycling transition

In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition $6{\rm S}_{1/2}F=4\to6{\rm P}_{3/2}F'=4$, and meanwhile the probe frequency is scanned across the $6{\rm S}_{1/2}F=4 \to6{\rm P}_{3/2}$ transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with $6{\rm S}_{1/2} F=3\to 6{\rm P}_{3/2}F'=4$ transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.     

Femtosecond relaxation kinetics of highly excited \mathrm{M}_{\mathrm{Na}}^{**} states in CaF2 at 3.2 eV and 4.7 eV

Femtosecond (fs) laser pulses at variable delay times allowed us to track the fast non-radiative transitions between the manifold of highly excited $\mathrm{M}_{\mathrm{Na}}^{**}$ states to the lower lying fluorescent $\mathrm{M}_{\mathrm{Na}}^{*}$ state in CaF₂. Two distinct $\mathrm{M}_{\mathrm{Na}}^{**}$ states of the manifold at 3.16?eV ( $\mathrm{M}_{\mathrm{Na}2}^{**}$ ) and 4.73?eV ( $\mathrm{M}_{\mathrm{Na}3}^{**}$ ) were populated using the second (SH) and third harmonics (TH) of fs laser light at 785?nm. The population kinetics of the fluorescent $\mathrm{M}_{\mathrm{Na}}^{*}$ state in the 2?eV excitation energy range was revealed by depleting its fluorescence centered at 740?nm using fundamental near infrared (NIR) fs laser pulses. The related time constants for $\mathrm{M}_{\mathrm{Na}2,3}^{**}{\sim}{>} \mathrm{M}_{\mathrm{Na}}^{*}$ relaxation amounted to 1.0±0.14?ps and 3.0±0.3?ps upon SH and TH excitation, respectively.     

The Algebraic Structure of an Approximately Universal System of Quantum Computational Gates

Shi and Aharonov have shown that the Toffoli gate and the Hadamard gate give rise to an approximately universal set of quantum computational gates. We study the basic algebraic properties of this system by introducing the notion of Shi-Aharonov quantum computational structure. We show that the quotient of this structure is isomorphic to a structure based on a particular set of complex numbers (the closed disc with center and radius ). Dedicated to Pekka Lahti.     

A high-resolution Ramsey-Bordé spectrometer for optical clocks based on cold Mg atoms

We report on recent progress in our Ramsey-Bordé interferometer with cold magnesium atoms at 457.2 nm. A resolution as high as was achieved, which corresponds to a quality factor of Q = 2.3×10¹². An upper limit of 170 Hz for the laser oscillator line width is inferred from the interferometric analysis of the contrast decay induced by the residual atomic motion and spontaneous emission. The performance of the spectrometer allows to realize an optical frequency standard at 457.2 nm with a short-term stability of up to with 10⁵ atoms similar to state-of-the art, non-cryogenic microwave clocks or oscillators.     

Growth of strongly textured FeCO 3 thin films for application in research of nuclear quantum optics with ultrashort-pulsed laser deposition

Growth of strongly textured $\mathrm{FeCO}_{3}$ thin films on substrates was achieved with ultrashort-pulsed laser deposition using 810-nm, 46-fs ablation pulses. The crystallinity and composition were verified with X-ray diffraction and Raman spectroscopy. Using Mössbauer spectroscopy, it is shown that the deposited $\mathrm{FeCO}_{3}$ thin films possess the film quality required for application in research of nuclear quantum optics. It is found that a relatively low substrate temperature is crucial for growing a strongly textured film of $\mathrm{FeCO}_{3}$ while avoiding decomposition of $\mathrm{FeCO}_{3}$ into $\mathrm{Fe}_{2}\mathrm{O}_{3}$ and $\mathrm{CO}_{2}$ . This supports the importance of the use of ultrashort-pulsed laser deposition in providing adatoms with high mobility for attaining good crystallinity. The surface morphology was characterized by surface profilometry, scanning electron microscopy and atomic force microscopy. It is found to be significantly affected by changing the ablation laser parameters, including laser fluence, pulse duration, and on-target spot size. The results show that the peak deposition flux must be below approximately 0.03 nm/pulse in order to grow a flat film.     

Empirical formulas for the fermion spectra and Yukawa matrices

We present empirical relations that connect the dimensionless ratios of low energy fermion masses for the charged lepton, up-type quark and down-type quark sectors and the CKM elements: and . Explaining these relations from first principles imposes strong constraints on the search for the theory of flavor. We present a simple set of normalized Yukawa matrices, with only two real parameters and one complex phase, which accounts with precision for these mass relations and for the CKM matrix elements and also suggests a simpler parametrization of the CKM matrix. The proposed Yukawa matrices accommodate the measured CP-violation, giving a particular relation between standard model CP-violating phases, . According to this relation the measured value of is close to the maximum value that can be reached, for . Finally, the particular mass relations between the quark and charged lepton sectors find their simplest explanation in the context of grand unified models through the use of the Georgi-Jarlskog factor.Received: 31 July 2004, Revised: 22 September 2004, Published online: 9 November 2004     

The hyperfine and isotope structure of the Cd intercombination line – revisited

Careful analysis of the intercombination 5¹S₀–5³P₁ line of the ¹¹³Cd isotope with two hfs components and was carried out. The hyperfine splitting of this line was determined to uncertainty less than 10^-3 cm^-1 using neon-perturbed Doppler limited spectra.