Taeg Yong Kwon

Sweep optical frequency synthesizer with a distributed-Bragg-reflector laser injection locked by a single component of an optical frequency comb

A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser.

Absolute frequency measurement of 1S0(F = 1/2)–3P0(F = 1/2) transition of 171Yb atoms in a one-dimensional optical lattice at KRISS

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.

Dispersion-like signals in velocity-selective saturated-absorption spectroscopy

We observed a dispersion-like signal from a caesium-vapour cell configured for saturated-absorption spectroscopy. Two parallel laser beams used as probes intersected a pump laser beam at a finite crossing angle. The dispersion-like signal was obtained from the difference in intensities of the two probe lasers passing through the vapour cell. The shape of the dispersion-like signal depended on the crossing angle and the crossing position of the intersecting beams. Using the dispersion-like signal as a frequency discriminator, we were able to stabilize the laser frequency without any frequency modulation. The frequency fluctuation was reduced to 22 kHz using a proportional amplifier and an integrator as a feedback circuit.

Generation of 578-nm yellow light over 10 mW by second harmonic generation of an 1156-nm external-cavity diode laser

578-nm yellow light with an 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, which is the highest output power at this wavelength using second harmonic generation of a solid state laser source without an enhancement ring cavity, to our knowledge. To achieve this result we made a high power 1156-nm external-cavity diode laser with the maximum output power of more than 250 mW. This system is expected to be an excellent alternative to the system using the sum-frequency generation with the advantage of simplicity and cost-effectiveness, and will be used as a clock laser of the ytterbium optical lattice clock with robust and reliable operation.

A compact extended-cavity diode laser with a Littman configuration

We have constructed a compact extended-cavity diode laser (ECDL) that is based on a Littman configuration with a grating and a reflector. The whole structure is installed in a 2-inch kinematic mount. ECDLs operating at 852 nm (Cs D/sub 2/ line), 894 nm (Cs D/sub 1/ line), 780 nm (Rb D/sub 2/ line), and 794 nm (Rb D/sub 1/ line) were fabricated and tested. As a result of the performance test, up to 9 GHz continuous tuning without mode hopping could be obtained by tuning with a piezoelectric transducer only. The linewidth from the beat-note spectrum of two ECDLs was about 200 kHz.

Production of Raman laser beams using injection-locking technique

We produced two Raman-laser beams with a frequency offset of 9.2-GHz using a simple injection-locking technique. A slave diode-laser is injection-locked to one f first-order sidebands of a master diode-laser produced by a 9.2 GHz EOM (electro-optic modulator). Using these Raman-laser beams, we observed CPT resonance in a cesium vapor cell.

Toward a cesium frequency standard based on a continuous slow atomic beam: preliminary results

A continuous beam of slow cesium atoms was produced from a thermal atomic beam by laser cooling. This beam was used as the source for the frequency standard. The Rabi-Ramsey spectrum was observed with the cold atomic beam. The Ramsey fringe of 62-Hz linewidth was obtained from a 21-cm-long microwave cavity. We found that the Rabi-Ramsey spectrum exhibited little dependence on the frequency of the pumping laser because of the long interaction time with the pumping light.

Collimation of a beam of caesium atoms by optical molasses, with resulting reduction in longitudinal beam velocity

Abstract We report on the collimation of a beam of caesium atoms by a one- or two-dimensional σ + – σ − optical molasses installed transverse to the atomic-beam direction. The width of the spatial distribution of atomic beam was reduced from 15 to 2 mm. We found that the collimation process strongly affects the longitudinal velocity; after collimation the mean of longitudinal velocity was reduced within a finite detection area. This result is due to longitudinal velocity selection by the collimation process. A computer simulation based on the two-photon laser-cooling theory was made, and the results were in a good agreement with the experiment.

Second-Order Zeeman Frequency Shift in the Optically Pumped Cesium Beam Frequency Standard with a Dual Servo System

The second-order Zeeman effect produces the largest frequency shift among several causes to alter the reference frequency in the optically pumped cesium beam frequency standard. We introduce a novel way to reduce the uncertainties due to the Zeeman effect by adopting a dual servo system, one for stabilizing the current for static magnetic field and the other for normal clock operation. As a result, the combined uncertainty of the second-order Zeeman frequency shift is reduced to 3.2 ×10-15, which is smaller by one order of magnitude than that without the servo system.

Drift-compensated low-noise frequency synthesis based on a CryoCSO for the KRISS-F1(Cs)

This paper reports implementation and operation of a frequency synthesizer based on a cryocooled cryogenic Sapphire oscillator (cryoCSO) for the Cesium atomic fountain clock developing at KRISS, KRISS-Fl(Cs). With use of this highly stable local oscillator, the short-term stability of KRISS-F1(Cs) was greatly improved and reaches the quantum projection noise limit, resulting in the measured lowest Allan deviation of 2.6×10-14. In addition, the long-term drift (4.8×10-14/day) of the cryoCSO could be compensated and reach below 5×10-16/day as low as state-of-the-art active hydrogen masers.