Leo W. Hollberg

Impact of atmospheric anisoplanaticity on earth-to-satellite time transfer over laser communication links

The need for an accurate time and position reference on orbiting platforms motivates the study of time transfer over satellite optical communication links. The transfer of precise optical clock signals to space would benefit many fields in fundamental science and applications. However, the precise role of atmospheric turbulence during the optical time transfer process is not well-known and documented. In free-space optical links, atmospheric turbulence represents a major impairment, since it causes degradation of the spatial and temporal coherence of the optical signals. We present possible link scenarios in which the atmospheric channel behavior for time transfer between ground and space can be investigated, and have identified the major challenges to be overcome. We found in our analysis that, despite the limited reciprocity in uplink and downlink propagation, partial two-way cancellation of atmospheric effects still occurs. We established that laser communication links make possible high-quality time transfer in most practical propagation scenarios and over a single satellite visibility period. Our results demonstrate that sharing of optical communication resources for optical time transfer and range determination is an effective and relevant scheme for space clock developments and enabling for future space missions.

Effect of atmospheric anisoplanatism on earth-to-satellite time transfer over laser communication links

The need for an accurate time reference on orbiting platforms motivates study of time transfer via free-space optical communication links. The impact of atmospheric turbulence on earth-to-satellite optical time transfer has not been fully characterized, however. We analyze limits to two-way laser time transfer accuracy posed by anisoplanatic non-reciprocity between uplink and downlink. We show that despite limited reciprocity, two-way time transfer can still achieve sub-picosecond accuracy in realistic propagation scenarios over a single satellite visibility period.

Optical phase-noise dynamics of Titanium:sapphire optical frequency combs

Abstract Stabilized optical frequency combs (OFC) can have remarkable levels of coherence across their broad spectral bandwidth. We study the scaling of the optical noise across hundreds of nanometers of optical spectra. We measure the residual phase noise between two OFC׳s (having offset frequencies f 0 ( 1 ) and f 0 ( 2 ) ) referenced to a common cavity-stabilized narrow linewidth CW laser. Their relative offset frequency Δ f 0 = f 0 ( 2 ) − f 0 ( 1 ) , which appears across their entire spectra, provides a convenient measure of the phase noise. By comparing Δ f 0 at different spectral regions, we demonstrate that the observed scaling of the residual phase noise is in very good agreement with the noise predicted from the standard frequency comb equation.

Self-Referenced and Optically Stabilized 10 GHz Frequency Comb

We demonstrate a self-referenced 10 GHz Ti:sapphire frequency comb where the continuum is generated in microstructured fiber. In addition, we discuss optical stabilization of the comb via saturated absorption in87Rb with a single mode.

20 GHz Pulse Generation with a Stabilized Optical Frequency Comb Generator

20 GHz pulses were generated by a Fabry-Perot modulator based optical frequency comb generator. We demonstrate high-fidelity 20 GHz sub-picosecond pulses with low residual microwave AM and PM noises.

Sr Optical Clock with High Stability and Accuracy

We report on our recent evaluations of stability and accuracy of the JILA Sr optical lattice clock. We discuss precision tools for the lattice clock, including a stabilized clock laser with sub-Hz linewidth, fs-comb based technology allowing accurate clock comparison in both the microwave and optical domains, and clock transfer over optical fiber in an urban environment. High resolution spectroscopy (Q > 2 × 10) of lattice-confined, spin-polarized strontium atoms is used for both a high-performance optical clock and atomic structure measurement. Using a Ca optical standard for comparison, the overall systematic uncertainty of the Sr clock is reduced to < 2 × 10.

Sub-10 fs Residual Timing Jitter on a 10 GHz Optical Frequency Comb Generator

With a narrow linewidth seed laser, residual timing jitter on a 10 GHz optical frequency comb generator is reduced to 6 fs. We present analysis connecting spectral phase and laser linewidth to the timing jitter.

Phase Coherence of Ti:sapphire Optical Frequency Combs across Hundreds of Nanometers

We demonstrate the scaling of the relative phase noise across hundreds of nanometers of spectra from stabilized Ti:sapphire frequency combs. We show good agreement between the predicted and measured phase noise.

Optical oscillators with high stability and low timing jitter

Frequency stabilized cw lasers achieve exceptional frequency stability using high finesse Fabry-Perot cavities. That stability can be transferred to other optical frequencies with mode-locked lasers and provides optical and electronic pulses with ultra-low timing jitter.

The mercury single-ion optical clock and a test of the stability of the fundamental constants

Summary form only given. Results of the measurements which compare the frequency ν/sub Hg/ of the /sup 199/Hg/sup +2/ S/sub 1/2/ (F=0) - /sup 2/D/sub 1/2/ (F=2, m/sub F/=0) optical transition to the SI second as realized at NIST are reported. Since the NIST time scale is calibrated with a cesium fountain primary frequency standard, the ratio of ν/sub Hg/ ( ≈ 10/sup 15/ Hz) to the cesium ground-state hyperfine splitting ν/sub Cs/ (≈ 9.2 GHz) is measured. These measurements show better reproducibility than 10 Hz at ν/sub Hg/, and constrain any possible variation of the ratio ν/sub Hg/ /ν/sub Cs/ to ± 7·10/sup -15/ yr/sup -1/.