Two Nd:YAG lasers at 1064 nm are independently frequency-stabilized to two separately located, vertically mounted ultrastable Fabry-Perot reference cavities. Measurements show that each laser system has achieved a most probable linewidth of 0.6 Hz and fractional frequency instability of ∼1.2 × 10 −15 between 1 and 40 s averaging time. Systematic evaluation shows that the performance of each laser system is limited by thermal noise of the reference cavity.
An optical atomic clock with 171Yb atoms is devised and tested. By using a two-stage Doppler cooling technique, the 171Yb atoms are cooled down to a temperature of 6±3 μK, which is close to the Doppler limit. Then, the cold 171Yb atoms are loaded into a one-dimensional optical lattice with a wavelength of 759 nm in the Lamb—Dicke regime. Furthermore, these cold 171Yb atoms are excited from the ground-state 1S0 to the excited-state 3P0 by a clock laser with a wavelength of 578 nm. Finally, the 1S0–3P0 clock-transition spectrum of these 171Yb atoms is obtained by measuring the dependence of the population of the ground-state 1S0 upon the clock-laser detuning.
We demonstrate a narrow-linewidth optical frequency comb based on a femtosecond Ti:sapphire laser by precisely phase-locking it to a subhertz-linewidth Nd:YAG laser at 1064 nm. Each comb tooth inherits the phase coherence and frequency stability of the subhertz-linewidth laser. By comparing against other independent narrow-linewidth lasers, we measured the absolute linewidth of the comb teeth to be 0.6 Hz-1.2 Hz over an octave spectrum. V
A laser at 578 nm is phase-locked to an optical frequency comb (OFC) which is optically referenced to a subhertzlinewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavitystabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3 × 10 −15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.
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