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High-accuracy two-color heterodyne interferometry based on fundamental and second harmonic of frequency combs for air refractive index correction is developed. A monitor interferometer as well as a probe interferometer is constructed to compensate the phase noises and drifts, which are caused by introducing the acousto-optic modulators for heterodyne interferometer, to realize high-accuracy measurement of optical distance. A relative stability of 10−10 to the total length for 500 s is achieved in the measurement of an optical path length difference between two wavelengths. In long-term measurements, the interferometric measurement results and the calculations from empirical equation of air refractive indices are in good agreement with a standard deviation of 4.1 × 10−10 throughout the 10 h period. By applying the two-color method, high-accuracy correction of air refractive index with an uncertainty of 8.9 × 10−8 is achieved during 10 h continuous measurements while the total refractive index changes with a range of 2.0 × 10−6.

We demonstrate an improved absolute frequency measurement of the 1S0–3P0 clock transition at 578 nm in 171Yb atoms in a one-dimensional optical lattice. The clock laser linewidth is reduced to ≈2 Hz by phase-locking the laser to an ultrastable neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 1064 nm through an optical frequency comb with an intracavity electrooptic modulator to achieve a high servo bandwidth. The absolute frequency is determined as 518 295 836 590 863.1(2.0) Hz relative to the SI second, and will be reported to the International Committee for Weights and Measures.

A narrow linewidth diode laser system at 689 nm is realized by phase-locking an extended cavity diode laser to one tooth of a narrow linewidth optical frequency comb. The optical frequency comb is phase-locked to a narrow linewidth laser at 1064 nm, which is frequency stabilized to a high-finesse optical cavity. We demonstrate the magneto-optical trapping of Sr using an intercombination transition with the developed laser system.

The spectral resolution and accuracy of asynchronous-optical-sampling terahertz time-domain spectroscopy (ASOPS-THz-TDS) were evaluated by examining low-pressure gas-phase samples. Use of dual 56-MHz, erbium (Er)-doped, mode-locked femtosecond fiber lasers enhanced the spectral resolution to as low as 50.5 MHz and the spectral accuracy to as low as 6.2 × 10(-6). The results indicate that ASOPS-THz-TDS has the potential to achieve high spectral resolution, high spectral accuracy, and wide spectral coverage at the same time. ASOPS-THz-TDS will open a new door to gas-phase spectroscopy of multiple chemical species in the field of atmospheric gas analysis.

We determine the absolute frequencies of 56 rotation-vibration transitions of the ν(3) band of CH(4) from 88.2 to 90.5 THz with a typical uncertainty of 2 kHz corresponding to a relative uncertainty of 2.2 × 10(-11) over an average time of a few hundred seconds. Saturated absorption lines are observed using a difference-frequency-generation source and a cavity-enhanced absorption cell, and the transition frequencies are measured with a fiber-laser-based optical frequency comb referenced to a rubidium atomic clock linked to the international atomic time. The determined value of the P(7) F(2)((2)) line is consistent with the International Committee for Weights and Measures recommendation within the uncertainty.

We constructed a widely and continuously tunable terahertz frequency synthesizer traceable to a hydrogen maser linked to coordinated universal time. Photomixing of two optical frequency synthesizers, linked to the hydrogen maser via dual optical frequency combs, gave this THz synthesizer frequency uncertainty of 10⁻¹². To demonstrate the potential of wide and continuous tunability in the THz synthesizer, we tuned its output frequency up to 50 GHz discretely and 1.26 GHz continuously in the F-band while maintaining the unprecedented frequency uncertainty by using a uni-traveling-carrier photodiode as a photomixer. This THz synthesizer will be a powerful tool for broadband, high-precision THz spectroscopy and THz frequency metrology.

A continuously tunable, phase-locked, single-frequency, continuous-wave (cw) terahertz generator has been demonstrated around 120 GHz, corresponding to the spectral bandwidth of the F-band unitraveling-carrier photodiode (UTC-PD) used as a photomixer in this study. This cw-terahertz generator is based on photomixing of an accurately tunable cw laser and a tightly fixed cw laser in the optical frequency region, phase locked to two independent optical combs. The continuous tuning range of the presented method was three orders of magnitude around 0.1 THz and two orders around 1 THz broader than that of a previous photomixing method in which two cw lasers are phase locked to a single optical comb, and fully covered the available spectral bandwidth of the F-band UTC-PD. The spectral behavior of the tight locking and continuous tuning of 120 GHz cw-terahertz radiation was confirmed in real time by use of a terahertz-comb-referenced spectrum analyzer. This cw-terahertz generator shows promise as a terahertz clock and synthesizer for terahertz frequency metrology.

We demonstrate a one-dimensional optical lattice clock with ultracold 171Yb atoms, which is free from the linear Zeeman effect. The absolute frequency of the 1S0(F = 1/2) - 3P0(F = 1/2) clock transition in 171Yb is determined to be 518 295 836 590 864(28) Hz with respect to the SI second., Comment: 11 pages, 5 figures, Appl. Phys. Express (Open Select Paper: open access)

Lasers from three national metrological institutes (NMIs) have been measured following the protocol of the BIPM.L-K11 ongoing key comparison initiated by the Comit? Consultative des Longueurs (CCL) 11th meeting in 2003. The absolute frequency of the f component of the R(127) 11-5 transition at 633 nm was measured for two of these lasers in their home institutes, AIST/NMIJ and UME, while the b5 component of the R(106) 28-0 transition at 543 nm was measured on a standard from NIM at the BIPM. The results of these measurements are compiled in the present paper. The comparison reports, as communicated by each participant, are included as Appendices. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A phase-shifting interferometry (PSI) with equal phase steps by use of a frequency-tunable diode laser and a Fabry-Perot cavity is proposed for the Carré algorithm. The measurement accuracy of the Carré algorithm depends on the equality of the phase steps. Using the Fabry-Perot cavity as a highly stable optical frequency reference, a high degree of phase step equality can be realized in PSI with an optical frequency shift. Our experimental scheme realizes an optical frequency step equality higher than 5.1 x 10(-5) and a measurement repeatability of lambda/800.

We present an arbitrary optical single-frequency generator based on a femtosecond optical frequency comb. The functions of this device are comparable to those of a radio-frequency synthesizer. However, this device operates at hundreds of terahertz. The absolute frequency accuracy of this synthesizer is approximately 1 kHz at a 282 THz carrier frequency. The stability is approximately 2 x 10(-14) at 100 s, and the tuning speed exceeds 30 GHz/s. This source demonstrates the integration of a phase-locked optical comb into a versatile and easy-to-use system for the generation of tunable, absolute optical frequencies. By using downconversion, one could generate tunable terahertz frequencies that are phase locked to a microwave reference, such as a Cs atomic clock, and high-precision interferometry could benefit greatly from the stability and accuracy of this widely tunable source.

An Rb-stabilized diode laser has been developed for use in a high-precision interferometer. The light source is a commercially available external-cavity tunable diode laser. The laser frequency is stabilized to a Doppler-free absorption line of Rb by the third-harmonic technique. The laser emits an output beam with a high power (more than 7 mW) and fast frequency modulation (10 kHz). The relative optical frequency uncertainty of 4.3×10 –10 is achieved for a 0.01-s averaging time.

Absolute frequency measurements of the R(85)33‐0 transition of molecular iodine at the blue end of the tuning range of a frequency-doubled Nd:YAG laser are implemented with a femtosecond optical comb based on a mode-locked Ti:sapphire laser. The hyperfine structure of the R(85)33‐0 transition is observed by use of high-resolution laser spectroscopy and is measured by the femtosecond optical comb. The observed hyperfine transitions are good frequency references for both frequency-doubled Nd:YAG and Nd:YVO4 lasers in the 532-nm region. High-accuracy hyperfine constants are obtained by our fitting the measured hyperfine splittings to a four-term Hamiltonian, which includes the electric quadrupole, spin‐rotation, tensor spin‐spin, and scalar spin‐spin interactions. © 2004 Optical Society of America OCIS codes: 120.3940, 300.6390, 320.7160, 300.6360, 020.2930, 120.6200.

A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 microm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.

A master/slave/slave laser spectrometer in the blue-wavelength region has been developed, comprising a master/slave laser combination coupled with a second-harmonic generation (SHG) enhancement cavity and an SHG-injected blue diode laser.

In this paper,five groups of stronger hyperfine transitions of iodine molecule ( 127 I 2) are reported,which are to our knowledge first observed by us.Frequency separations and relative intensities of each transition are calculated.The calculated results and the observed values match very well.With the calculated results,we assigned the vib rotational bands of each transition.Because the intensities of the newly observed transitions are hundreds of times stronger than transition R(127)11 5,which is applied to frequency stabilized He Ne laser,we use them as reference lines of iodine frequency stabilized tunable diode laser and get an output laser of 3mW.This kind of frequency stabilized diode laser may become a new kind of frequency standard.

Frequency tuning of internal-mirror 543 nm He–Ne lasers was realized using a piezo-electric transducer (PZT) through an elastic deformation of the laser tube. Two 543 nm He–Ne lasers were locked on the saturated absorption lines of iodine with the third-derivative signal of a signal-to-noise ratio of about 50. From the beat signal between them the frequency stability was measured to be σ(τ, 2)=1.2×10-11τ-1/2(10-4 s

オーチャードグラス乾草摂取めん羊から採取したルーメン液(微生物)の凍結乾燥標品を調製し,標品中に保持される飼料消化能の活性について検討した.採取したルーメン液を直ちに-20°Cまたは-70°Cで凍結した後凍結乾燥機で乾燥し,標品を調製した.脱気蒸留水で標品を元の量に復元したものまたは新鮮ルーメン液に人工唾液を加えて培養液として,セルロース(ろ紙粉末),オーチャードグラス乾草,アルファルファミール,フスマ,大麦およびトウモロコシを基質としin vitro消化試験を行なった.いずれの標品もセルロースを全く消化しなかったが新鮮ルーメン液では32%のin vitro消化率(IVDMD)を示した.2種類の標品によるIVDMDはアルファルファミールを除くすべての基質においてほぼ同じ値を示した.オーチャードグラス乾草およびアルファルファミールの標品によるIVDMDは新鮮ルーメン液によるそれより明らかに低かったが,フスマ,大麦およびトウモロコシのIVDMDは両者でほぼ同じ値を示した.標品による培養液中のVFA濃度はいずれの基質においても新鮮ルーメン液のそれより有意に低かったが,乳酸濃度は著しく高かった.以上の結果は標品中にはデンプン分解菌群の活性は保持されるがセンイ分解菌群の活性は保持されないことを示している.

Frequency comb spanning more than one octave has been achieved by injecting the second harmonic generation (780 nm) of a mode-locked fiber laser (1.56 /spl mu/m) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency.

We demonstrate a precision frequency measurement using a phase-stabilized 120-km optical fiber link over a physical distance of 50 km. The absolute frequency of the 87Sr optical lattice clock is measured to be 429228004229874.1(2.4) Hz.

Two fiber-based frequency combs were compared at 633 nm. An offset laser was locked to a frequency comb, and the locked laser was measured with another comb. Consequently, the frequency uncertainty of the combs was less than 3 times 10-16 at 10 000 s averaging, which is sufficiently lower than the uncertainty of UTC.

We demonstrate a fast control of an octave-spanning fiber-based frequency comb with an intracavity electro-optic modulator. The servo bandwidth of both repetition and carrier-envelope offset frequency is greater than 200 kHz.

A phase-locked 110-GHz continuously-tunable optical-single-frequency generator is developed based on a phase-stabilized fiber-based comb. Stability of the optical frequencies at 1s are 3.0 and 31×10−12 at scanning speeds of 0.17 and 1 GHz/s, respectively.

Distance measurements using the 821st-harmonic of the intermode beat frequency in an optical comb with optical-sub-wavelength accuracy are demonstrated. Direct comparison with a laser interferometer for the same optical setup reveals good agreement to 20-nm.

The repetition-rate and carrier envelope offset frequency of a turnkey, all-fiber-based continuum generator are phase-locked to a highly-stable atomic clock, H-maser. The performance of the system is evaluated and compared to a traditional Ti:sapphire-based comb.

We fully interpolated frequency gaps between THz-comb modes by their incremental sweeping at intervals of their linewidth, showing the possibility of enhancing the spectral resolution in THz spectroscopy to the linewidth of THz comb mode.

We demonstrated gapless THz comb spectroscopy for high-resolution THz spectroscopy. Frequency sweeping of THz comb mode enables us to enhance the spectral resolution in THz spectroscopy down to the linewidth of THz comb mode.

We report on a displacement metrology setup that provides sub-pm resolution in air. The setup is based on a Fabry-Perot cavity. However, unlike current Fabry-Perot cavity based displacement setups we incorporate a novel fs-laser based arbitrary wavelength synthesizer that provides efficient suppression of atmospheric disturbances while providing very wide and precise tuning of the output wavelength. The wavelength synthesizer provides sub-10 attometer wavelength resolution. The setup provides subpm length stability for integration times of up to one minute and sub-10 pm for up to half an hour without airtight enclosure of the Fabry-Perot cavities.

We proposed frequency-swept asynchronous-optical-sampling terahertz time-domain spectroscopy to further improve the spectral resolution. The spectral resolution achieved here was 2.2 MHz, which is two orders of magnitude smaller than the mode-locked frequency.

We demonstrated combination of spectrally interleaved terahertz (THz) frequency comb with dual-comb spectroscopy, enabling us to achieve the spectral sampling equal to linewidth of the comb tooth in the low-pressure gas spectroscopy in THz region.

We demonstrated a frequency measurement of CW-THz wave referring to dual THz frequency comb in real time. The absolute frequency of the CW-THz wave is measured with an accuracy of 3.5*10^-11 10ms each.

We observed detailed spectrum of THz frequency comb by extending the measured time window of the pulsed THz electric field up to ten pulse periods with asynchronous-optical-sampling THz-TDS (ASOPS-THz-TDS). Observed spectrum of THz comb mode has a linewidth of 5.6 MHz and a frequency interval of 56 MHz.

We develop an all-fiber-based frequency comb with an intra-cavity waveguide electro-optic modulator. A comb mode is successfully phase-locked to an optical reference. The servo bandwidth of repetition rate is approximately 400 kHz.

Arbitrary single-frequency CW-THz-wave generator based on two-independent femtosecond fiber-combs is presented. Continuous tuning of a 120-GHz CW wave was demonstrated across several MHz, which is limited by electric bandwidth of THz-spectrum analyzer for evaluation.