Hyun-Gue Hong

Improved absolute frequency measurement of the 171Yb optical lattice clock at KRISS relative to the SI second

We measured the absolute frequency of the 1S0–3P0 transition of 171Yb atom confined in a one-dimensional optical lattice relative to the SI second. The determined frequency was 518 295 836 590 863.38(57) Hz. The uncertainty was reduced by a factor of 14 compared with our previously reported value in 2013 due to the significant improvements in decreasing the systematic uncertainties. This result is expected to contribute to the determination of a new recommended value for the secondary representations of the second.

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.

Mie resonance-enhanced pumping and detection efficiency for shallow nitrogen-vacancy centers in diamond

We investigate Mie resonances of a diamond nano-resonator as a means to enhance the pumping and detection efficiency of shallow nitrogen-vacancy color centers. We show it is possible to tune a couple of high-order modes of a single resonator to each absorption and emission spectrum of the color center, and thereby the resonator plays a dual role of pump field concentration and emission field guiding. Furthermore superposition of the resonator field and the uncoupled near field results in even stronger pump intensity in the shallow top layer of the resonator. We also examine possible coupling between adjacent resonators when they form a periodic array. This approach allows us to achieve lower excitation power and higher signal intensity at local sites defined by resonators providing a way to enhance wide-field metrology in the sampled region of shallow color centers.

Operating atomic fountain clock using robust DBR laser system

We operate an atomic fountain clock KRISS-F1 using a laser system based on a DBR (Distributed Bragg Reflector) laser. We have found that there is no major difference in the fountain performance between laser systems with an ECDL (Extended-Cavity Diode Laser) and the DBR laser, even though spectral properties of the DBR is worse than that of ECDL. Moreover, quantum projection-noise limited stability is observed using DBR lasers. After replacing the ECDL to the DBR laser, laser system of the fountain clock became robust against acoustic and vibration noise mainly from mechanical shutters. Therefore, currently KRISS-F1 can be operated without failure of laser locking.

Improved absolute frequency measurement of the 1S 0 –3P 0 transition of 171Yb at KRISS

We measured the absolute frequency of the ¹S<inf>0</inf>–³P<inf>0</inf> transition of ¹⁷¹Yb atom relative to the SI second with an uncertainty reduced by a factor of 14 compared with our previous measurement. The determined frequency was 518 295 836 590 863.38(57) Hz. The experimental setup is being improved for the independent uncertainty evaluation by measuring the frequency shift coefficients of our own system.

Increasement of effective number of detected atoms in KRISS-F1(Cs) fountain clock by optical pumping

We have performed optical pumping (OP) technique to increase the effective number of detected atoms in the KRISS-F1 (Cs) fountain clock using two laser frequencies. The maximum gain of detected signal is 3.5. We anticipate the short-term stability of KRISS-F1(Cs) will be improved with OP.

Continuous cold atomic beam in a Zerodur chamber for atom interferometry

We generated a continuous cold atomic beam using a two-dimensional magneto-optical trap for atom interferometry. The vacuum system is made of Zerodur glass with a large optical access for a compact system.

Progress of an atomic gravimeter at KRISS

This paper introduces an atomic gravimeter under development at KRISS for precise measurement of gravitational acceleration. The gravimeter based on atom interferometer uses two counter-propagating Raman lasers of π/2-π-π/2 pulse sequence and laser cooled 87Rb atoms in free fall. Atomic interference fringes caused by Raman lasers were observed at various time intervals between the three Raman pulses. The frequency sweep rate α which compensates Doppler shift due to gravitational acceleration g was obtained from the interference fringes. In the presentation, the current status and recent results of the KRISS atomic gravimeter will be discussed.