2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007
ABSTRACT The selected and amplified optical frequency comb by using diode laser is used in an opt... more ABSTRACT The selected and amplified optical frequency comb by using diode laser is used in an optical clock configuration to measure the absolute frequency of stabilized ECDL. The ECDL is stabilized to F = 4 rarr F = 5 transition line of cesium D2 line with modulation transfer spectroscopy. The measured frequency is fECDL = 351 721 960 529 kHz with a statistical uncertainty of 3.5 kHz.
We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band ... more We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band wavelength region. The wavelength of the laser can be tuned continuously over 102 nm between 1510.4-1612.6 nm by insertion of the fiber Fabry-Perot tunable filter (FFP-TF) in the ring cavity. By use of the wavelength tunable characteristics of our fiber laser, we measured absorption spectra of more than fifty transition lines of the acetylene (13C2H2) molecule with high signal to noise ratio (SNR).
We investigate the generation of the dark spatial soliton and its role of waveguiding in Fe doped... more We investigate the generation of the dark spatial soliton and its role of waveguiding in Fe doped LiNbO3. A cw Ar+ laser of 488 nm is used for the generation of the dark spatial soliton. The generation of the dark spatial soliton is observed even at the laser intensity as low as 10 mW/cm2. The self-defocusing effect is observed when the direction of the intensity variation is parallel to the optic axis, while it can't be seen when perpendicular to the axis. So, it is verified that the refractive index change is generated parallel to the optic axis. When 633 nm He-Ne laser beam is injected into the dark spatial soliton, the beam propagates just as in the diffraction free medium. So, it is verified that the dark spatial soliton can act as a waveguide.
This paper describes the current status of an ytterbium lattice clock under development at KRISS.... more This paper describes the current status of an ytterbium lattice clock under development at KRISS. After the success of 399 nm magneto-optical-trap (MOT) at a temperature 1 mK, we constructed the 2nd stage cooling laser system at a wavelength of 556 nm to cool atoms further down to several muK. We are also developing an ultra-narrow linewidth laser at a wavelength of 578 nm to probe the clock transition by doubling the frequency output of a commercial 1156 nm ECDL. Efforts to reduce the linewidth are under way.
We have transferred highly stable 100 MHz RF through a 23 km fiber network. The fiber-induced pha... more We have transferred highly stable 100 MHz RF through a 23 km fiber network. The fiber-induced phase noise due to the vibration and the temperature fluctuation in the optical path is detected and is compensated by configuring a noise-canceling servo. The transfer instability was 6×10-14 at 1 s of averaging time and 2×10-17 at 10000 s of averaging time. The single sideband phase noise was greatly reduced by more than 20 dB below the Fourier frequency of 1 kHz. The transferred RF has nearly the same stability as the original reference frequency.
The excited states of an atom consist of several sub-states which can be split by certain perturb... more The excited states of an atom consist of several sub-states which can be split by certain perturbations. An external magnetic eld causes the Zeeman splitting whose frequency lies in the radio-frequency region. When a short pulse, whose inverse of pulse width is larger than that mentioned above splitting, is used, a coherence between splitted levels is generated. If the pulse train is incident on the atom under an external magnetic the coherence depends on the relative phase relation and the repetition rate of the pulse train. We study time-dependent Hertzian coherences and for slow and fast decay rates by using a density matrix formalism in the case of excitation by a commonly used mode-locked lasers (repetition rate : a few tens of MHz).-1-2
We report on accuracy test results on the comparison of two different types of optical frequency ... more We report on accuracy test results on the comparison of two different types of optical frequency combs, each of those referenced to a microwave frequency standard and an optical frequency standard. One of those combs is based on a mode-locked erbium-doped fiber laser and the other is based on a Ti:sapphire femtosecond laser. The comb comparison was carried out by measuring an absolute frequency of an acetylene-stabilized diode laser with both combs simultaneously.
A fiber-phase-noise compensating system was constructed for a 1.4 GHz reference frequency transfe... more A fiber-phase-noise compensating system was constructed for a 1.4 GHz reference frequency transferred through a 13-km-long fiber spool. The transfer instability was dependent on the temperature variation of the compensating system. With the room temperature variation stabilized within , the transfer instability was at 0.8 s of average time and at 1000 s of average time with the fiber phase noise compensated. However, with the room temperature changed by , the transfer instability was at 1.2 s of average time and at 1000 s of average time. From this result, the temperature stability condition for the experimental setup could be determined to obtain a transfer instability of at 1000 s of average time.
CPEM Digest (Conference on Precision Electromagnetic Measurements)
A laser source at 578 nm with output power of more than 10 mW was obtained using a waveguide peri... more A laser source at 578 nm with output power of more than 10 mW was obtained using a waveguide periodically-poled-lithium-niobate crystal as a nonlinear medium for second harmonic generation. To achieve this result, we made a high power 1156-nm external-cavity diode laser with maximum output power of more than 250 mW. This system is expected to be an excellent alternative to systems using sum-frequency generation with advantages of simplicity and cost-effectiveness, and will be used as a clock laser of an ytterbium optical lattice clock with robust and reliable operation.
We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) ... more We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) of 171Yb atoms confined in a one-dimensional optical lattice and it was determined to be 518 295 836 590 863.5(8.1) Hz. The frequency was measured against Terrestrial Time (TT; the SI second on the geoid) by using an optical frequency comb of which the frequency was phase-locked to an H-maser as a flywheel oscillator traceable to TT. The magic wavelength was also measured as 394 798.48(79) GHz. The results are in good agreement with two previous measurements of other institutes within the specified uncertainty of this work.
We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose... more We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose-Einstein condensates by using a double magneto-optical trap (MOT) system that consists of a two-dimensional MOT (2D MOT) and a three-dimensional MOT (3D MOT). As an atomic beam source for loading the 3D MOT, we use a unique 2D MOT system with two-color pushing beams, which increase the loading rate and the total number of atoms in the 3D MOT, compared to a pure 2D MOT by a factor of 20. After MOT compression and polarization gradient cooling, atoms are optically pumped into a magnetically trappable hyperfine state |F = 1, m F = −1〉 to be loaded into a quadrupole-Ioffe-configuration (QUIC) trap. We enhance this optical pumping process by up to 300% by using two laser beams. After rf evaporative cooling, a Bose-Einstein condensate (BEC) with more than 2 × 107 atoms is achieved.
Recent Developments in Traceable Dimensional Measurements III, 2005
ABSTRACT This paper describes a fringe scanning Fourier transform method to automatically measure... more ABSTRACT This paper describes a fringe scanning Fourier transform method to automatically measure the fractional interference order in gauge block interferometry. The advantages of the proposed method are presented with the comparison of measurement results between the existing Fourier transform method and the fringe scanning Fourier Transform method. The configuration of automatic gauge block measuring system is also described, where the proposed method is applied. The standard uncertainty evaluation of the fractional interference order measurement with this method is given.
2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007
ABSTRACT The selected and amplified optical frequency comb by using diode laser is used in an opt... more ABSTRACT The selected and amplified optical frequency comb by using diode laser is used in an optical clock configuration to measure the absolute frequency of stabilized ECDL. The ECDL is stabilized to F = 4 rarr F = 5 transition line of cesium D2 line with modulation transfer spectroscopy. The measured frequency is fECDL = 351 721 960 529 kHz with a statistical uncertainty of 3.5 kHz.
We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band ... more We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band wavelength region. The wavelength of the laser can be tuned continuously over 102 nm between 1510.4-1612.6 nm by insertion of the fiber Fabry-Perot tunable filter (FFP-TF) in the ring cavity. By use of the wavelength tunable characteristics of our fiber laser, we measured absorption spectra of more than fifty transition lines of the acetylene (13C2H2) molecule with high signal to noise ratio (SNR).
We investigate the generation of the dark spatial soliton and its role of waveguiding in Fe doped... more We investigate the generation of the dark spatial soliton and its role of waveguiding in Fe doped LiNbO3. A cw Ar+ laser of 488 nm is used for the generation of the dark spatial soliton. The generation of the dark spatial soliton is observed even at the laser intensity as low as 10 mW/cm2. The self-defocusing effect is observed when the direction of the intensity variation is parallel to the optic axis, while it can't be seen when perpendicular to the axis. So, it is verified that the refractive index change is generated parallel to the optic axis. When 633 nm He-Ne laser beam is injected into the dark spatial soliton, the beam propagates just as in the diffraction free medium. So, it is verified that the dark spatial soliton can act as a waveguide.
This paper describes the current status of an ytterbium lattice clock under development at KRISS.... more This paper describes the current status of an ytterbium lattice clock under development at KRISS. After the success of 399 nm magneto-optical-trap (MOT) at a temperature 1 mK, we constructed the 2nd stage cooling laser system at a wavelength of 556 nm to cool atoms further down to several muK. We are also developing an ultra-narrow linewidth laser at a wavelength of 578 nm to probe the clock transition by doubling the frequency output of a commercial 1156 nm ECDL. Efforts to reduce the linewidth are under way.
We have transferred highly stable 100 MHz RF through a 23 km fiber network. The fiber-induced pha... more We have transferred highly stable 100 MHz RF through a 23 km fiber network. The fiber-induced phase noise due to the vibration and the temperature fluctuation in the optical path is detected and is compensated by configuring a noise-canceling servo. The transfer instability was 6×10-14 at 1 s of averaging time and 2×10-17 at 10000 s of averaging time. The single sideband phase noise was greatly reduced by more than 20 dB below the Fourier frequency of 1 kHz. The transferred RF has nearly the same stability as the original reference frequency.
The excited states of an atom consist of several sub-states which can be split by certain perturb... more The excited states of an atom consist of several sub-states which can be split by certain perturbations. An external magnetic eld causes the Zeeman splitting whose frequency lies in the radio-frequency region. When a short pulse, whose inverse of pulse width is larger than that mentioned above splitting, is used, a coherence between splitted levels is generated. If the pulse train is incident on the atom under an external magnetic the coherence depends on the relative phase relation and the repetition rate of the pulse train. We study time-dependent Hertzian coherences and for slow and fast decay rates by using a density matrix formalism in the case of excitation by a commonly used mode-locked lasers (repetition rate : a few tens of MHz).-1-2
We report on accuracy test results on the comparison of two different types of optical frequency ... more We report on accuracy test results on the comparison of two different types of optical frequency combs, each of those referenced to a microwave frequency standard and an optical frequency standard. One of those combs is based on a mode-locked erbium-doped fiber laser and the other is based on a Ti:sapphire femtosecond laser. The comb comparison was carried out by measuring an absolute frequency of an acetylene-stabilized diode laser with both combs simultaneously.
A fiber-phase-noise compensating system was constructed for a 1.4 GHz reference frequency transfe... more A fiber-phase-noise compensating system was constructed for a 1.4 GHz reference frequency transferred through a 13-km-long fiber spool. The transfer instability was dependent on the temperature variation of the compensating system. With the room temperature variation stabilized within , the transfer instability was at 0.8 s of average time and at 1000 s of average time with the fiber phase noise compensated. However, with the room temperature changed by , the transfer instability was at 1.2 s of average time and at 1000 s of average time. From this result, the temperature stability condition for the experimental setup could be determined to obtain a transfer instability of at 1000 s of average time.
CPEM Digest (Conference on Precision Electromagnetic Measurements)
A laser source at 578 nm with output power of more than 10 mW was obtained using a waveguide peri... more A laser source at 578 nm with output power of more than 10 mW was obtained using a waveguide periodically-poled-lithium-niobate crystal as a nonlinear medium for second harmonic generation. To achieve this result, we made a high power 1156-nm external-cavity diode laser with maximum output power of more than 250 mW. This system is expected to be an excellent alternative to systems using sum-frequency generation with advantages of simplicity and cost-effectiveness, and will be used as a clock laser of an ytterbium optical lattice clock with robust and reliable operation.
We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) ... more We measured the absolute frequency of the optical clock transition 1S0 (F = 1/2) - 3P0 (F = 1/2) of 171Yb atoms confined in a one-dimensional optical lattice and it was determined to be 518 295 836 590 863.5(8.1) Hz. The frequency was measured against Terrestrial Time (TT; the SI second on the geoid) by using an optical frequency comb of which the frequency was phase-locked to an H-maser as a flywheel oscillator traceable to TT. The magic wavelength was also measured as 394 798.48(79) GHz. The results are in good agreement with two previous measurements of other institutes within the specified uncertainty of this work.
We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose... more We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose-Einstein condensates by using a double magneto-optical trap (MOT) system that consists of a two-dimensional MOT (2D MOT) and a three-dimensional MOT (3D MOT). As an atomic beam source for loading the 3D MOT, we use a unique 2D MOT system with two-color pushing beams, which increase the loading rate and the total number of atoms in the 3D MOT, compared to a pure 2D MOT by a factor of 20. After MOT compression and polarization gradient cooling, atoms are optically pumped into a magnetically trappable hyperfine state |F = 1, m F = −1〉 to be loaded into a quadrupole-Ioffe-configuration (QUIC) trap. We enhance this optical pumping process by up to 300% by using two laser beams. After rf evaporative cooling, a Bose-Einstein condensate (BEC) with more than 2 × 107 atoms is achieved.
Recent Developments in Traceable Dimensional Measurements III, 2005
ABSTRACT This paper describes a fringe scanning Fourier transform method to automatically measure... more ABSTRACT This paper describes a fringe scanning Fourier transform method to automatically measure the fractional interference order in gauge block interferometry. The advantages of the proposed method are presented with the comparison of measurement results between the existing Fourier transform method and the fringe scanning Fourier Transform method. The configuration of automatic gauge block measuring system is also described, where the proposed method is applied. The standard uncertainty evaluation of the fractional interference order measurement with this method is given.
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Papers by Won-Kyu Lee