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All-polarization-maintaining, single-port Er:fiber combs offer long-term robust operation as well as high stability. We have built two such combs and evaluated the transfer noise for linking optical clocks. A uniformly broadened spectrum over 135-285 THz with a high signal-to-noise ratio enables the optical frequency measurement of the subharmonics of strontium, ytterbium, and mercury optical lattice clocks with the fractional frequency-noise power spectral density of $(1-2)\times 10^{-17}$ Hz$^{-1/2}$ at 1 Hz. By applying a synchronous clock comparison, the comb enables clock ratio measurements with $10^{-17}$ instability at 1 s, which is one order of magnitude smaller than the best instability of the frequency ratio of optical lattice clocks., Comment: 14 pages, 4 figures

We report on the wideband frequency stabilization of a 100-W injection-locked Nd:YAG laser using an external electrooptic modulator made of MgO-doped stoichiometric LiNbO3 crystals. In order to circumvent a phase delay in the frequency control loop caused by an injection-locked slave cavity, the electrooptic modulator was placed at the optical path of the slave output. The realized control bandwidth was 85 kHz, which was four-times wider than that obtained without an external electrooptic modulator. We achieved the frequency noise level suppressed relative to a reference cavity of 6×10-2 Hz/√Hz at around 100 Hz.

We have developed an electrooptic modulator (EOM) using stoichiometric MgO-doped LiNbO3 (MgO-doped SLN) crystals, and evaluated this EOM for the phase control of a high-power laser whose power is over 100 W. We succeeded in the phase modulation of a 100 W laser without a decrease in phase modulation index, due to a nonlinear optical effect, which can occur when a high-power laser beam enters the EOM. We also estimated wavefront distortions caused by passing through the EOM with a Shack–Hartmann wavefront sensor, and found that the additional wavefront distortion was negligible. Thus, we confirmed that MgO-doped SLN crystals are a suitable material for use in a high-power laser system.