Takuya Kohno

A multi-branch, fiber-based frequency comb with millihertz-level relative linewidths using an intra-cavity electro-optic modulator.

We demonstrate that fiber-based frequency combs with multi-branch configurations can transfer both linewidth and frequency stability to another wavelength at the millihertz level. An intra-cavity electro-optic modulator is employed to obtain a broad servo bandwidth for repetition rate control. We investigate the relative linewidths between two combs using a stable continuous-wave laser as a common reference to stabilize the repetition rate frequencies in both combs. The achieved energy concentration to the carrier of the out-of-loop beat between the two combs was 99% and 30% at a bandwidth of 1 kHz and 7.6 mHz, respectively. The frequency instability of the comb was 3.7x10(-16) for a 1 s averaging time, improving to 5-8x10(-19) for 10000 s. We show that the frequency noise in the out-of-loop beat originates mainly from phase noise in branched optical fibers.

One-Dimensional Optical Lattice Clock with a Fermionic 171Yb Isotope

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.

Improved absolute frequency measurement of the 171 Yb optical lattice clock towards a candidate for the redefinition of the second

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.

Evaluation of the clock laser for an Yb lattice clock using an optic fiber comb

A light source to drive the 1S0-3P0 transition in Yb atoms is generated by 2 solid state lasers: a Nd:YAG laser and an Yb:YAG laser, using a sum-frequency generation (SFG) scheme. With a ridge waveguide (WG) periodically poled lithium niobate (PPLN) device, SFG power of about 150 mW is obtained at the required frequency. The zero-expansion temperature of a Fabry-Perot etalon was determined by using a home-made fiber-based optical frequency comb running continuously for weeks. Frequency stabilization of the clock laser system was also evaluated by the optical frequency comb.

Spectroscopy of 171Yb in an optical lattice based on laser linewidth transfer using a narrow linewidth frequency comb.

We propose a novel, high-performance, and practical laser source system for optical clocks. The laser linewidth of a fiber-based frequency comb is reduced by phase locking a comb mode to an ultrastable master laser at 1064 nm with a broad servo bandwidth. A slave laser at 578 nm is successively phase locked to a comb mode at 578 nm with a broad servo bandwidth without any pre-stabilization. Laser frequency characteristics such as spectral linewidth and frequency stability are transferred to the 578-nm slave laser from the 1064-nm master laser. Using the slave laser, we have succeeded in observing the clock transition of (171)Yb atoms confined in an optical lattice with a 20-Hz spectral linewidth.

A compact light source at 461 nm using a periodically poled LiNbO 3 waveguide for strontium magneto-optical trapping

We have developed a compact light source at 461 nm using a single-pass periodically poled LiNbO3 waveguide for second-harmonic (SH) generation. The obtained optical power at 461 nm is 76 mW when the power of the 922-nm fundamental light coupled into the waveguide is 248 mW. Although a narrowing of the phase-matching temperature acceptance bandwidth is observed at a high SH power, stable overnight operation is realized by carefully controlling the device temperature within an uncertainty of 0.01 °C.

Optical Frequency Stability Measurement of an External Cavity Blue Diode Laser with an Optical Frequency Comb

We present experimental results of the frequency stability measurement of an external cavity blue diode laser stabilized with the saturated absorption signal of the 1S0–1P1 transition of Yb at 398.9 nm. Frequency stability and reproducibility of the stabilized laser were evaluated by using an optical frequency comb. Allan standard deviation of 5.4×10-12 with an averaging time of 256 s is achieved. The results show that our laser system has long-term stability and good performance for laser cooling and trapping experiments of Yb atom.

Fiber-comb-stabilized light source at 556 nm for magneto-optical trapping of ytterbium

A frequency-stabilized light source emitting at 556 nm is realized by frequency doubling a 1112 nm laser, which is phase locked to a fiber-based optical frequency comb. The 1112 nm laser is either an ytterbium (Yb)-doped distributed feedback fiber laser or a master-slave laser system that uses an external cavity diode laser as a master laser. We have achieved the continuous frequency stabilization of the light source over a 5 day period. With the light source, we have completed the second-stage magneto-optical trapping (MOT) of Yb atoms using the S10–P31 intercombination transition. The temperature of the ultracold atoms in the MOT was 40 μK when measured using the time-of-flight method, and this is sufficient for loading the atoms into an optical lattice. The fiber-based frequency comb is shown to be a useful tool for controlling the laser frequency in cold-atom experiments.

Present Status of the Development of the Yb Optical Lattice Clock at NMIJ/AIST

The present status of the development of the Yb optical lattice clock at NMIJ and future prospects are presented.

Present status of the development of an Yb optical lattice clock at NMIJ/AIST (National Metrology Institute of Japan / National Institute of Advanced Industrial Science and Technology)

The present status of the development of the Yb optical lattice clock at NMIJ/AIST and future prospects are presented. Experimental equipments such as vacuum systems and laser sources are explained in detail.