Optical frequency standards and measurements

Abstract

We describe the performance characteristics and frequency measurements of two high-accuracy high-stability lasercooled atomic frequency standards. One is a 657-nm (456-THz) reference using magneto-optically trapped Ca atoms, and the other is a 282-nm (1064-THz) reference based on a single Hg + ion confined in an RF-Paul trap. A femtosecond mode-locked laser combined with a nonlinear microstructure fiber produces a broad and stable comb of optical modes that is used to measure the frequencies of the reference lasers locked to the atomic standards. The measurement system is referenced to the primary frequency standard NIST F-1, a Cs atomic fountain clock. Both optical standards demonstrate exceptional short-term instability ( 5 10 15 at 1 s), as well as excellent reproducibility over time. In light of our expectations for the future of optical frequency standards, we consider the present performance of the femtosecond optical frequency comb, along with its limitations and future requirements. (NIST)], Boulder, CO, where he is currently a NIST Fellow and Ion-Storage Group Leader in the Time and Frequency Division. His research has concentrated on laser cooling and spectroscopy of trapped atomic ions with applications to atomic clocks, cold plasmas, and fundamental tests. More recent work has focused on quantum-state engineering with applications to quantum information processing and quantum-limited measurements.

Study of the excess noise associated with demodulation of ultra-short infrared pulses

“…Introduction K err-lens femtosecond lasers have revolutionized the entire field of optical frequency metrology by allowing quick and precise measurements of optical frequencies with the resolution close to the limit of the best microwave frequency standards based on the laser-cooled Cs atoms [1]- [3]. By making use of femtosecond lasers, it also is possible to convert the lightwave output of an optical frequency standard (optical "clock") into an ultra-stable microwave signal [4], [5]. The frequency/time transfer from optical to microwave domain is realized by synchronizing the pulse repetition rate of a femtosecond laser with a beat rate of an optical "clock" and detecting the optical pulse train with a high-speed photodetector.…”

Femtosecond optical frequency combs

“…With the frequency comb at hand one has a simple tool to count up 5 orders of magnitude faster. In fact one can show that any clock limited by quantum noise will possess an instability that decreases with the inverse of the averaging time and is proportional to the observed line width divided by the transition frequency [25]. For practical reasons one cannot simply pick a transition with an arbitrary small line width, because this will at the same time increase the required observation time.…”

Design and control of femtosecond lasers for optical clocks and the synthesis of low-noise optical and microwave signals

“…A 2-mm-Iong Ti:sapphire crystal is placed at Brewster's angle between two concave mirrors Ml and M2 with radius of curvature of 30 mm. It is pumped through lens L (focal length 30 mm) by 8.5 W from a frequency-doubled Nd:YV0 4 laser. The resonator is completed by mirror M3 and the output coupler OC.…”