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Schematic diagram of the experimental setup: EDFA, erbium-doped f iber amplifier; SMFs, single-mode fibers; APDs, avalanche photodiodes; AOM, acousto-optic modulator; DMs, dichroic mirrors; SHG, second-harmonic generation; PLLs, phase-locked loops; PZT, piezoelectric transducer.
Source publication
The absolute frequency of an acetylene-stabilized laser at 1542 nm is measured at its second harmonic (771 nm) by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. Frequency stability and reproducibility of the acetylene-stabilized laser are evaluated by the femtosecond comb with a H maser as a frequency reference. The abs...
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Citations
... Moreover, it occupies a special place for its P(16) transition at 1542.38 nm, which has been chosen by the CIPM as a primary wavelength standard [2]. Thus, acetylene spectroscopy in this region has been carefully studied, and high stability and accuracy references have been demonstrated, based on the detection of sub-Doppler resonances in acetylene vapor probed in a cell [3][4][5] or in a cavity [6][7][8][9]. In both configurations, frequency stabilities (the relative frequency fluctuations) in the 10 −14 range have been reached [5,9]. ...
We present an experimental investigation of the stability limits specific to optical frequency standards using fiber optic architecture and semiconductor lasers. A compact setup composed of a semiconductor laser frequency-locked onto an acetylene transition detected in saturated absorption has been implemented using only fiber optic components. Fiber optic technology allows compact and reliable solutions for various applications. However, for high sensitivity and stability applications such as metrology, residual reflections induced by optical index inhomogeneities in connectors and fiber-coupled components leading to spurious interference significantly limit performance. We have examined the origin of the interference fringes superimposed on the detected signal and the limitations they cause to the frequency stability of the reference. The effects of temperature and beam power fluctuations are also examined. Our results show that the frequency stability is limited in the ${{10}^{- 13}}$ 10 − 13 range by the effect of interference fringes due to use of fiber components.
... The R(73)46-0 transition is different from the R(34)44-0 transition studied in Ref. [17] and the P(13)43-0 transition recommended by the CIPM at 515 nm, which are 125 GHz higher and 620 GHz lower, respectively 26, compared to the absolute frequency of the present transition. The frequency of the 1.5 µm laser was stabilized using the observed iodine transition and a frequency stability of 1.1 × 10 −12 was obtained at an average of 1 s, which is approximately one order of magnitude better than that of the acetylene-stabilized laser [27]. The absolute frequency of the a 1 component of the R(73)46-0 transition was also determined at 583 109 956 557 kHz ± 6 kHz, following the evaluation of frequency uncertainty. ...
... Since the stability of the UTC(NMIJ) is better than that of the developed iodine-stabilized laser, the Allan standard deviation observed indicates the stability of the laser. The black dashed line in Fig. 7 shows the frequency stability of an acetylene-stabilized laser [27]. Compared to typical acetylene-stabilized lasers, the iodine-stabilized laser developed reached a stability that was superior by approximately one order of magnitude over a short time, and approximately a factor of 5 over longer time periods. ...
We demonstrate the third harmonic generation of a 1542-nm laser using a dual-pitch periodically poled lithium niobate waveguide with a conversion efficiency of 66%/W². The generated 514-nm light is used for saturation spectroscopy of molecular iodine and laser frequency stabilization. The achieved laser frequency stability is 1.1×10⁻¹² at an average time of 1 s, which is approximately one order of magnitude better than the acetylene-stabilized laser at 1542 nm. Uncertainty evaluation and absolute frequency measurement are also performed. The developed frequency-stabilized laser can be used as a reliable frequency reference at the telecom wavelength for various applications including optical frequency combs and precision interferometric measurement.
... Yamada and colleagues [54] studied the transition P(16) in the 1+3 band near 1.56 µm. The isotope substituted 13 C2H2 was chosen because the frequency of the line in question had previously been determined with great accuracy [57]: it lies close to half the frequency of the two-photon transition near 778 nm in Rb [58] used for some determinations of the Rydberg constant [59]. The uncertainty in the value of the Boltzmann constant, some 1200 ppm, was due mainly to the temperature measurement (T=295.65(30) ...
We review measurements of the Boltzmann constant, k, the value of which is soon to be fixed at exactly 1.380649×10⁻²³ J⋅K⁻¹ for the future revised Système international of units. In addition to a description of the theoretical background and of diverse experimental techniques (acoustic thermometry, Johnson noise thermometry, dielectric constant gas thermometry, and Doppler broadened molecular spectroscopy), the article highlights the decisive role of ab initio calculations of the thermophysical properties of gases, especially helium-4. Perspectives for improvements in thermometry are outlined in the wake of the new definition.
... The invention of optical frequency combs at the end of the past millennium enabled the calibration of optical frequencies against primary frequency standards, whose fractional frequency uncertainty may easily attain ∼10 −11 at 1 s. This made it possible, at least on single transitions, to retrieve line centers with uncertainties down to a few kHz [2][3][4][5][6][7] . ...
... On the other hand, optical frequency combs have been seldom applied to broad line surveys to extract spectroscopic parameters of molecular absorption bands. In the near-infrared (near-IR), extended measurements have been performed only on a few bands of C 2 H 2 , NH 3 and H 2 O in a sub-Doppler regime [6][7][8][9][10] and of CO, CO 2 and H 2 O in a Doppler broadening regime [11][12][13][14][15] , quite often in conjunction with optical cavities to ex- * Corresponding author. ...
The ν1 fundamental band of N2O is examined by a novel spectrometer that relies on the frequency locking of an external-cavity quantum cascade laser around 7.8 µm to a near-infrared Tm:based frequency comb at 1.9 µm. Due to the large tunability, nearly 70 lines in the 1240–1310 cm⁻¹ range of the ν1 band of N2O, from P(40) to R(31), are for the first time measured with an absolute frequency calibration and an uncertainty from 62 to 180 kHz, depending on the line. Accurate values of the spectroscopic constants of the upper state are derived from a fit of the line centers (rms ≈ 4.8 × 10⁻⁶ cm⁻¹ or 144 kHz). The ν1 transitions presently measured in a Doppler regime validate high accuracy predictions based on sub-Doppler measurements of the ν3 and ν3-ν1 transitions.
... Since their invention, optical frequency combs have revitalized the field of precision molecular spectroscopy, making it possible to achieve accuracies at the kHz or even sub-kHz level on absorption line centers [1][2][3][4] . In order to bring such a comb revolution to the point of redefining spectroscopic databases such as HITRAN 5 , which are still mostly based on a pre-comb spectroscopy era, it is crucial to develop spectrometers that join an accurate frequency axis to a wide spectral coverage (>100 cm −1 ), which is the typical extension of absorption bands. ...
We report the first experimental demonstration of frequency-locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locking scheme is applied to carry out absolute spectroscopy of N2O lines near 7.87 {\mu}m with an accuracy of ~60 kHz. Thanks to a single mode operation over more than 100 cm^{-1}, the comb-locked EC-QCL shows great potential for the accurate retrieval of line center frequencies in a spectral region that is currently outside the reach of broadly tunable cw sources, either based on difference frequency generation or optical parametric oscillation. The approach described here can be straightforwardly extended up to 12 {\mu}m, which is the current wavelength limit for commercial cw EC-QCLs.
... Rotation-resolved molecular transitions are convenient natural frequency grids used in spectroscopy, communication, 1 metrology, 2 and astrophysics. 3 Their precise positions are also concerned in fundamental physics, being used to determine physical constants, either the values 4 or the space-time variation, [5][6][7] to find parity-violation effects, 8 and even to search new physics beyond the standard model. ...
... The method has been applied to determine absolute infrared line positions from Lamb-dip measurements of several molecules. 1,[14][15][16][20][21][22][23][24][25][26][27][28][29] Most of the reported molecular line positions have an uncertainty at the kHz level (fractional accuracy 10 11 ), including the C 2 H 2 line positions near 1.54 µm recommended by Bureau International des Poids et Mesures for practical realization of the metre and secondary representations of the second. ...
Precise molecular transition frequencies are of great interest in the test of fundamental physics and also in various applications. Two well isolated ro-vibrational transitions of $^{12}$C$^{16}$O at 1.57 $\mu$m, R(9) and R(10) in the second overtone band molecule, were measured by a comb-locked cavity ring-down spectrometer. Despite the weakness of the lines (Einstein coefficient $A\simeq 0.008$ s$^{-1}$), Lamb-dip spectra were recorded with a signal-to-noise ratio over 1000, and the line positions were determined to be 191 360 212 763.7 and 191 440 612 664.8 kHz respectively, with an uncertainty of 0.5 kHz ($\delta\nu/\nu=2.6\times 10^{-12}$). The present work demonstrated the possibility to explore extensive molecular lines in the near-infrared with sub-kHz accuracy.
... On the other hand, fiber lasers are now capable of delivering pulse energies as high as those of solid-state lasers in addition to their key advantages such as compactness, low cost, passive cooling, and turn-key operability. Historically, ultrafast fiber lasers have been extensively involved in the areas of optical frequency metrology applications since 2003 [11][12][13][14][15]. Erbium (Er) fiber lasers with the GHz or multi-GHz repetition rate were reported in literatures [16,17]. ...
This study focuses on presenting a fully stabilized, self-referenced Yb:fiber frequency comb respectively phase locked to a microwave standard and an optical reference employing the highest, fundamental repetition rate of 750-MHz without additional external amplifiers and compressors. In addition, the challenge of phase locking the carrier envelop offset frequency for this high-repetition-rate fiber frequency comb is separately investigated in two schemes, namely, f-2f self-referencing and an approach of phase locking a beat note between the Yb: fiber frequency comb and a continuous wave laser.
... The authors motivations was to measure frequency of their reference laser against optical frequency comb generator and then compare measurement results with results obtained earlier using different methods. The application of SHG technique in case of frequency measurement of laser emitting light in 1550 nm region against optical frequency comb generator was reported in [13]. In conducted experiment, in contrast to the cited work we did not use "lab developed" technology but commercially available comb generator which is installed in Central Office of Measures (Warsaw, Poland). ...
... In order to measure 1533 nm reference laser we decided to use second harmonic generation (SHG) technique using Periodically Poled Lithium Niobate (PPLN) crystal to get 766.4 nm signal, which is in the measurement range of the optical frequency comb synthesizer. Similar solution has been reported in case of 1542 nm laser stabilized to P(16) absorption line of 13 C 2 H 2 [13]. In our case the maximum output power of the reference laser was only 0.5 mW, which is too low to achieve effective frequency conversion in PPLN crystal. ...
The second harmonic generation process in Periodically Poled Lithium Niobate (PPLN) has been applied in order to measure frequency of reference laser locked to acetylene absorption peak 12C2H2 (P13) (1533 nm) against optical frequency synthesizer. The measurement results have been compared to the results obtained using different techniques for the same reference laser during the past 10 years in other laboratories.
... In terms of fundamental physics, optical clocks can be used to demonstrate relativistic effects in daily life and to verify the constancy of fundamental constants [11,12]. In practice, high-resolution laser spectroscopy can provide new tools for improving telecommunication systems [13,14] and medical diagnostics systems [15]. High performance optical clocks are expected to open the door to new research frontiers such as relativistic geodesy [16]. ...
... In the third part of the list, iodine-or Rb-stabilized lasers are shown as practical wavelength standards for length applications. The 1.54 µm acetylene-stabilized laser is used as a wavelength standard for telecommunication applications [13,14,42]. Since the light source of the 778 nm 85 Rb-stabilized laser can be either a direct 778 nm diode laser or a frequency-doubled laser using a 1.56 µm diode laser, this optical frequency standard can be used for either length applications at 778 nm or telecommunication applications at 1.56 µm. ...
The last decade has witnessed tremendous progress in research on optical frequency metrology. Optical frequency standards using optical lattice and single-ion trap technologies have reached levels of stability and accuracy that surpass the performance of the best Cs fountain atomic clocks by orders of magnitude. Optical frequency standards are also used for various applications including length metrology. Optical frequency measurement and links using optical frequency combs and optical fibres play important roles in the development of optical frequency standards. This article introduces optical frequency standards recommended by the International Committee for Weights and Measures (CIPM) along with updates provided by recent research results. Frequency ratio measurements and remote frequency comparisons are addressed in relation to the work whose goal is to redefine the second. Optical frequency standard and optical frequency comb applications are also described.
... Repeatability is a key feature whenever highly accurate absorption profiles have to be measured, enabling the acquisition of traceable spectroscopic data and the study of the physics underlying linebroadening mechanisms [2][3][4]. On the other hand, absolute frequency calibration enables the comparison of spectroscopic data acquired in different laboratories and at different times [5], as well as comparison with theoretical predictions or existing databases [6]. ...
We report on a comprehensive theoretical and experimental analysis of the feed-forward method for external frequency stabilization of a continuous wave laser against a frequency comb. Application of the method to a distributed feedback diode laser at 1.55 μm allows line narrowing from 800 to 10 kHz, with frequency noise reduction by more than 2 decades up to a Fourier frequency of 100 kHz and a maximum control bandwidth of 0.8 MHz. The results are consistent with a relative phase fluctuation of 1.4 rad rms, as limited by uncompensated high-frequency noise of the slave laser.
