Laser Frequency Standards Research Articles

A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304401), Key-Area Research and Development Program of GuangDong Province, China (Grant No. 2019B030330001), and the National Natural Science Foundation of China (Grant Nos. 11174095, 61875065, 91536116, and 11804108).

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 non-symmetric 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 kHz (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 kHz, which is within 1 σ uncertainty, proving the validity of our evaluation.

Excited-state population distributions of alkaline-earth metal in a hollow cathode lamp

The intensities of fluorescence spectral lines of Ca atoms and Sr atoms in two different hollow cathode lamps (HCLs) are measured by element-balance-detection technology. In the wavelength range of 350–750 nm in the visible spectral region, using the individual strongest line (Ca 422.67 nm, Sr 460.73 nm) as the bench mark, the population ratios between the excited states of Ca atoms and Sr atoms are calculated by rate equations and the spontaneous transition probabilities. The HCLs with populations at excited states can be used to realize the frequency stabilization reference of the laser frequency standard.

High-contrast sub-Doppler absorption spikes in a hot atomic vapor cell exposed to a dual-frequency laser field

The saturated absorption technique is an elegant method widely used in atomic and molecular physics for high-resolution spectroscopy, laser frequency standards and metrology purposes. We have recently discovered that a saturated absorption scheme with a dual-frequency laser can lead to a significant sign reversal of the usual Doppler-free dip, yielding a deep enhanced-absorption spike. In this paper, we report detailed experimental investigations of this phenomenon, together with a full in-depth theoretical description. It is shown that several physical effects can support or oppose the formation of the high-contrast central spike in the absorption profile. The physical conditions for which all these effects act constructively and result in very bright Doppler-free resonances are revealed. Apart from their theoretical interest, results obtained in this manuscript are of great interest for laser spectroscopy and laser frequency stabilization purposes, with applications in laser cooling, matter-wave sensors, atomic clocks or quantum optics.

A novel method to drive semiconductor laser for optical frequency standard based on constant voltage source

The semiconductor laser is the important part in the semiconductor laser frequency standard. The quality of light frequency standard depends on line width and stability of laser. Semiconductor laser is very sensitive to environmental changes, such as the temperature, humidity and so on. The driving voltage and circuit and the temperature compensation are significant to laser output stability. The paper put forward a novel method to drive the semiconductor laser based on constant voltage source. The experimental results show that the circuit is simple, reliable, and high-precision. After improvement, the driving source of laser can promise parameters: constant-current range is from 0 to 250mA, and the drift of current is less than 10−6, and stability is 10−5. The drift of frequency of laser drive with the circuit is within 10−5nm.

Atomic population distribution of excited states in He electrodeless discharge lamp

Population ratios between excited states are measured to build the excited state Faraday anomalous dispersion optical filter (ESFADOF). We calculate these values between the excited states according to the spontaneous transition probabilities using rate equations and the measured intensities of fluorescence spectral lines of He atoms in an electrodeless discharge lamp in the visible spectral region from 350 to 730 nm. The electrodeless discharge lamp with populations in excited states can be used to realize the frequency stabilization reference of the laser frequency standard. This lamp can also build ESFADOFs for submarine communication application in the blue-green wavelength to simplify the system without the use of a pump laser.

Transparency or spectral narrowing for two-mode squeezing and entanglement

We analyze the nonadiabatic effects on the propagation of a two-mode squeezed field inside a medium of three-level $\ensuremath{\Lambda}$ atoms that display the dark resonance. We identify the different effects for the two-mode quantum properties: (i) unconditional transparency for the sum squeezing and (ii) induced transparency or spectral narrowing for the difference squeezing depending on the relative widths of the initial correlation spectrum to the transparency window. These effects combine to induce transparency or spectrum narrowing for the bipartite entanglement. The potential applications range from quantum information to laser spectroscopy and frequency standards.

Narrow band noise rejection technique for laser frequency and length standards: application to frequency stabilization to I2 lines near dissociation limit at 501.7 nm

An opto-electronic device for the stabilization of laser beam intensity in a narrow frequency band based on a numeric corrector driving the radio-frequency signal of an acousto-optic modulator is applied to improve the signal-to-noise ratio of the detected signal in saturation spectroscopy of iodine in a cell at 501.7 nm, both in the FM spectroscopy technique and in the transfer modulation technique. In the latter case, a 30 dB rejection of the amplitude noise of the probe beam is achieved and, when the laser frequency is locked to the saturation signal, the enhancement of the sensitivity of the frequency jitter detection is demonstrated in a frequency band extending up to 1 kHz. For the long term stabilization the laser is locked to a narrow line detected in a low pressure cell. A relative Allan deviation of about 10−13 is found for 1 s integration time and a deviation of 10−14 is reached for 500 s. Linewidths smaller than 40 kHz (FWHM) are also demonstrated at low saturating power for hyperfine components of the transition R(26)62-0 at 501.7 nm.

Лазерные стандарты частоты в ФИАНе

Лазерные стандарты частоты в ФИАНе

Traceability of Laser Frequency Calibrations at MIKES

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the Practical Realization of the Definition of the Meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers. </para>

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers

Preface to Topical Papers on Laser and New Atomic Frequency Standards

Preface to Topical Papers on Laser and New Atomic Frequency Standards

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.

Development and absolute frequency measurement of a pair of 778 nm two-photon rubidium standards

A pair of diode laser frequency standards stabilized to 778 nm two-photon rubidium transitions have been developed and characterized. Their sensitivity to vapour pressure, modulation depth and optical power have been investigated, along with their relative stability and day-to-day reproducibility. The Allan deviation of the standards locked to the 5 2S1/2(Fg = 3)–5 2D5/2(Fe = 5) transition of 85Rb is 9.3 × 10−13τ−1/2 for 1 s < τ < 100 s, reaching a floor of 1 × 10−13 at 100 s. The long-term repeatability of an individual system locked to this line is 1.2 kHz, corresponding to 3.1 parts in 1012. The system-to-system reproducibility is limited by cell impurities to 4.9 kHz and 4.5 kHz, respectively, for this line and the 5 2S1/2(Fg = 2)–5 2D5/2(Fe = 4) transition in 87Rb. The mean observed frequencies for these transitions, averaged for the two systems and corrected for light shift and second-order relativistic Doppler effect, are 385 285 142 375.1 (4.9) kHz and 385 284 566 374.2 (4.5) kHz, respectively.

Fifty years of atomic time-keeping at VNIIFTRI

Time metrology in Russia in the second half of the twentieth century has been marked, as in other advanced countries, by the rapid development of time and frequency quantum standards and the beginning of atomic time-keeping. This brief review presents the main developments and studies in time and frequency measurement, and the improvement of accuracy and atomic time-keeping at the VNIIFTRI—the National Metrology Institute keeping primary time and frequency standards and ensuring unification of measurement. The milestones along the way have been the ammonia and hydrogen masers, primary caesium beam and fountain standards and laser frequency standards. For many years, VNIIFTRI was the only world laboratory that applied hydrogen-maser clock ensembles for time-keeping. VNIIFTRI's work on international laser standard frequency comparisons and absolute frequency measurements contributed greatly to the adoption by the CIPM of a highly accurate value for the He–Ne/CH4 laser frequency. VNIIFTRI and the VNIIM were the first to establish a united time, frequency and length standard.

High-accuracy frequency atlas of 13C2H2 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 Doppler-free transitions of the ν1 + ν3 and ν1 + ν2 + ν4 + ν5 combination bands of 13C2H2. The Allan deviation σ/f for a laser locked to line P(10) of the former band follows a slope of 1.6 × 10−12τ−1/2, reaching a minimum of 5.7 × 10−14 at τ = 4000 s. The absolute frequencies of 61 lines of the ν1 + ν3 band and 43 lines of the ν1 + ν2 + ν4 + ν5 band, covering the spectral region 1520 nm to 1552 nm, have been measured by use of a combined frequency chain and femtosecond comb, together with a passive optical frequency comb generator. The mean uncertainties for the line frequencies within each band are 1.4 kHz for the ν1 + ν3 band and 1.9 kHz for the ν1 + ν2 + ν4 + ν5 band, representing improvements on the precision of previously published data by factors of 100 and 104, respectively. Improved values of the rotational constant B″ and centrifugal distortion coefficients D″, H″ and L″ of the vibrational ground state are presented.

Absolute frequency measurement of a 1.5-microm acetylene standard by use of a combined frequency chain and femtosecond comb.

We have developed and characterized a pair of Doppler-free acetylene-stabilized diode laser frequency standards as optical communications references. The Allan deviation sigma/f of an individual system reaches a minimum of 4 x 10(-14) at a sampling time of 5000 s, and the long-term lock-point repeatability is found to be 0.4 kHz (one standard uncertainty), corresponding to a fractional uncertainty of 2 x 10(-12). Using a combination of a frequency chain and a self-referenced femtosecond comb, we have measured the frequency of line P(16) of the v1 + v3 overtone band of 13C2H2 to be 194,369,569,385.9 (3.0) kHz. The uncertainty of this number is limited solely by the reproducibility of the standards.

Portable frequency standard at 633 nm with compact external-cavity diode laser

A portable (32 cm × 13 cm × 6 cm) laser frequency standard has been constructed by frequency-stabilizing a miniaturized external-cavity diode laser to the Doppler-free spectrum of iodine. Compact structure is achieved using a novel transmission grating. The laser has excellent noise properties, which leads to a high signal-to-noise ratio (SNR) of detection and allows direct observation of the inverse Lamb dips. The frequency stability matches that of iodine-stabilized He-Ne lasers at 633 nm; the relative frequency stability (square root of the Allan variance) follows a slope of 7.9 × 10−12τ−1/2 (10 s < τ < 4000 s). The best stability, 1 × 10−13 (47 Hz), is reached at an integration time of τ = 4000 s. The observed day-to-day repeatability (1σ) is 4 × 10−12 (1.6 kHz). Extensive measurements were made to evaluate the dependence of the laser frequency on the various operational parameters.

Cancellation of laser dither modulation from optical frequency standards

We demonstrate the removal of the dither modulation from an iodine-stabilized He-Ne laser by using a frequency-modulated acousto-optic modulator and feed-forward techniques. This procedure reduces the linewidth of the beat between this laser and a flywheel He-Ne laser from 6 MHz to 8 kHz, the undithered beat linewidth being ~7 kHz. Dither suppression greatly reduces counter errors during beat measurements from stroboscopic effects between the counter's gate and the frequency of the dither modulation and increases the utility of the already formidable array of dithered laser frequency standards by making locking to them an easier task.

Accuracy of the computer-controlled laser frequency standards based on resolved hyperfine structure of a methane line

Results of 2-year frequency comparisons of our transportable He-Ne laser standard stabilized on a component of the magnetic hyperfine structure (MHFS) of the F/sub 2//sup 2/ line of methane /spl lambda/=3.39 /spl mu/m, with our stationary laser using resolved recoil doubler as reference are presented. The absolute frequency of the transportable laser measured at PTB (Physikalisch-Technische Bundesanstalt, Braunschweig, Germany), using the radio-optical frequency chain, was transferred to the stationary device. On the basis of the theoretical model of the line shape, the frequency of unperturbed transition has peen calculated. >

Ultranarrow ^13C_2H_2 saturated-absorption lines at 15 μm

The saturation spectroscopy of molecular transitions at 1.5microm is reported. We show that it is possible, with a low-power laser diode, to obtain 2-MHz-wide acetylene saturated-absorption lines, and we give what is to our knowledge the first experimental estimation of (13)C(2)H(2) saturation intensity. To our knowledge, these lines are the narrowest reported 1.5-microm frequency references and should be suitable for high-quality 1.5-microm laser frequency standards.