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Narrow linewidth visible light lasers are critical for atomic, molecular and optical (AMO) applications including atomic clocks, quantum computing, atomic and molecular spectroscopy, and sensing. Historically, such lasers are implemented at the tabletop scale, using semiconductor lasers stabilized to large optical reference cavities. Photonic integration of high spectral-purity visible light sources will enable experiments to increase in complexity and scale. Stimulated Brillouin scattering (SBS) is a promising approach to realize highly coherent on-chip visible light laser emission. While progress has been made on integrated SBS lasers at telecommunications wavelengths, barriers have existed to translate this performance to the visible, namely the realization of Brillouin-active waveguides in ultra-low optical loss photonics. We have overcome this barrier, demonstrating the first visible light photonic integrated SBS laser, which operates at 674 nm to address the 88Sr+ optical clock transition. To guide the laser design, we use a combination of multi-physics simulation and Brillouin spectroscopy in a 2 meter spiral waveguide to identify the 25.110 GHz first order Stokes frequency shift and 290 MHz gain bandwidth. The laser is implemented in an 8.9 mm radius silicon nitride all-waveguide resonator with 1.09 dB per meter loss and Q of 55.4 Million. Lasing is demonstrated, with an on-chip 14.7 mW threshold, a 45% slope efficiency, and linewidth narrowing as the pump is increased from below threshold to 269 Hz. To illustrate the wavelength flexibility of this design, we also demonstrate lasing at 698 nm, the wavelength for the optical clock transition in neutral strontium. This demonstration of a waveguide-based, photonic integrated SBS laser that operates in the visible, and the reduced size and sensitivity to environmental disturbances, shows promise for diverse AMO applications., 23 pages, 10 figures

Atomic, molecular and optical (AMO) visible light systems are the heart of precision applications including quantum, atomic clocks and precision metrology. As these systems scale in terms of number of lasers, wavelengths, and optical components, their reliability, space occupied, and power consumption will push the limits of using traditional laboratory-scale lasers and optics. Visible light photonic integration is critical to advancing AMO based sciences and applications, yet key performance aspects remain to be addressed, most notably waveguide losses and laser phase noise and stability. Additionally, a visible light integrated solution needs to be wafer-scale CMOS compatible and capable of supporting a wide array of photonic components. While the regime of ultra-low loss has been achieved at telecommunication wavelengths, progress at visible wavelengths has been limited. Here, we report the lowest waveguide losses and highest resonator Qs to date in the visible range, to the best of our knowledge. We report waveguide losses at wavelengths associated with strontium transitions in the 461 nm to 802 nm wavelength range, of 0.01 dB/cm to 0.09 dB/cm and associated intrinsic resonator Q of 60 Million to 9.5 Million, a decrease in loss by factors of 6x to 2x and increase in Q by factors of 10x to 1.5x over this visible wavelength range. Additionally, we measure an absorption limited loss and Q of 0.17 dB/m and 340 million at 674 nm. This level of performance is achieved in a wafer-scale foundry compatible Si3N4 platform with a 20 nm thick core and TEOS-PECVD deposited upper cladding oxide, and enables waveguides for different wavelengths to be fabricated on the same wafer with mask-only changes per wavelength. These results represent a significant step forward in waveguide platforms that operate in the visible, opening up a wide range of integrated applications that utilize atoms, ions and molecules including sensing, navigation, metrology and clocks.

For more than 100 years, optical atomic/molecular frequency references have played important roles in science and technology, and provide standards enabling precision measurements. Frequency-stable optical sources have been central to experimental tests of Einstein's relativity, and also serve to realize our base unit of length. The technology has evolved from atomic discharge lamps and interferometry, to narrow atomic resonances in laser-cooled atoms that are probed by frequency-stabilized cw lasers that in turn control optical frequency synthesizers (combs) based on ultra-fast mode-locked lasers. Recent technological advances have improved the performance of optical frequency references by almost four orders of magnitude in the last eight years. This has stimulated new enthusiasm for the development of optical atomic clocks, and allows new probes into nature, such as searches for time variation of fundamental constants and precision spectroscopy.

A high-power picosecond optical parametric oscillator (OPO) based on a 47-mm periodically poled lithium niobate crystal is described. More than 12 W of total average power-almost 8 W of signal power at 1.85 microm and more than 4 W of idler radiation at 2.5 microm -is simultaneously extracted from less than 18 W of average pump power. The OPO is synchronously pumped by 80-ps (FWHM) cw mode-locked pulses at 1.064 microm , and its output is tunable from 1.7 to 2.84microm . Nearly transform-limited signal pulses are obtained following the introduction of two intracavity etalons.

We present an experimental study of the lattice induced light shifts on the 1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The ``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394 799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz on the 518 THz clock transition. Also investigated were the hyperpolarizability shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the two-photon resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the magic wavelength. In addition, we have confirmed that a circularly polarized lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10^-17., Accepted to PRL

This talk presents two different types of neutral atom optical clocks and emphasizes the systems' differences in potential performance and complexity. Approaches in attaining high stability, high accuracy, and transportable optical atomic clocks are discussed in detail.

We describe a new laser system we have developed to probe the ultra-narrow 1S0 harr 3P0 clock transition at 578 nm in neutral ytterbium. The yellow light is produced by sum frequency generation in a periodically poled waveguide. With approximately 100 mW each from a fiber laser and Nd:YAG laser, we produce 10 mW of visible light. Stabilization of the laser to a resonance of a high finesse, environmentally isolated cavity has enabled resolution of spectroscopic features as narrow as 5 Hz.

Revolutionary advances in the performance of atomic clocks results from some new ideas, precision spectroscopy of ultra-cold atoms, and maturing technologies of stable lasers. Frequency stabilized solid-state lasers are playing an increasingly important roles.

We report on two optical clocks: one uses freely expanding calcium atoms, while the other is based on lattice-confined ytterbium. We measure a fractional instability between the clocks of 4 x 10-16@ 100 s.

The paper describes two types of optical atomic clocks. The first is based on freely expanding calcium atoms and is optimized for experimental simplicity and high stability. The second is based on Yb atoms confined to an optical lattice that is designed to yield minimal shifts for the clock transition at 578 nm. Measurements of the effective beatnote between the clocks via a femtosecond-laser frequency comb show a fractional frequency instability of

We report direct single-laser excitation of the strictly forbidden clock transition in atoms confined to a 1D optical lattice. A small () static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of . The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be . This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

We report high resolution spectroscopy of optical lattice-confined 174Yb atoms. We demonstrate spectroscopic linewidths as narrow as 4 Hz (full-width at half-maximum) using the highly forbidden clock transition (1S0-3P0) in a one-dimensional optical lattice.

We report the first spectroscopy of optical lattice-confined Yb atoms. We demonstrate 20 Hz linewidths using the highly forbidden clock transition (1S 0 -3P 0 ) in metrologically superior even-isotope 174Yb atoms in a one-dimensional optical lattice.

We report direct single-laser excitation of the strictly forbidden (6s2)1S0--(6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

This work has focused on two atoms, Sr and Yb, due in part to the relatively high abundance of their odd isotopes, the use of which is necessary for appreciable direct excitation probability. The Sr clock transition has been measured (with an uncertainty of 20 kHz) using atoms in a magneto-optic trap (MOT), and has been excited with atoms confined in a one dimensional lattice. Here we report direct excitation of the Yb clock transition (at 578 nm) with atoms in a second-stage MOT, and the first fs-laser comb-based absolute measurements of the clock frequency for two different isotopes. These measurements lead to a nearly millionfold improvement in our knowledge of the transition frequencies, an important step toward Doppler-free spectroscopy of Yb atoms in a lattice.

We report the direct excitation of the highly forbidden $(6{s}^{2})^{1}S_{0}\ensuremath{\leftrightarrow}(6s6p)^{3}P_{0}$ optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at $\ensuremath{\sim}70\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$ in a magneto-optical trap. The measured frequency in $^{171}\mathrm{Yb}$ ($\mathrm{F}=1/2$) is $518\text{ }295\text{ }836\text{ }591.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. The measured frequency in $^{173}\mathrm{Yb}$ ($\mathrm{F}=5/2$) is $518\text{ }294\text{ }576\text{ }847.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a ${10}^{6}$-fold reduction in uncertainty. The natural linewidth of these $J=0$ to $J=0$ transitions is calculated to be $\ensuremath{\sim}10\text{ }\text{ }\mathrm{mHz}$, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

We report the direct excitation of the highly forbidden (6s2) 1S0--(6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method -- a single clock laser combined with a DC magnetic field-- relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10^-17 for the metrologically preferred even isotopes.

This paper discusses an optical atomic clock that uses a narrow atomic resonance to control the frequency of a spectrally narrow laser source. The atomically controlled frequency of the laser gives the clock oscillation frequency as an optical output and provides the stable reference for frequency and timing.

In the past four years have shown a dramatic improvement in the performance of optical frequency references and in the methods by which they are calibrated and utilized. These revolutionary changes result from better stabilized lasers that probe narrow-linewidth transitions in laser-cooled atoms and ions, and from the development of a convenient method for synthesizing, measuring and distributing optical frequencies based on mode-locked lasers.

Optical cooling of solids was first demonstrated in 1995. Since that time our efforts have concentrated on using this phenomenon to produce a viable optical cryocooler. A bench-top, solid-state optical cooler was demonstrated recently with 54 °C of cooling from room temperature and a heat lift of 25 mW when it was pumped with 1.6 watts of laser light. Based on the bench-top cooler results a compact, rugged, self-contained system with laser-diode pumping is being constructed as a prototype for research and commercial applications. Recent results, designs and plans for future work are discussed. In addition to prototype work, our efforts have continued on producing additional optical materials which demonstrate optical cooling and will improve the efficiency and useful temperature range of optical coolers. New materials with promising results are discussed.

We report the first observation of anti-Stokes fluorescence cooling in a thulium-doped solid with pump excitation at $1.82\ensuremath{\mu}\mathrm{m}l\ensuremath{\lambda}l1.97\ensuremath{\mu}\mathrm{m}$. At a pump wavelength of $1.9\ensuremath{\mu}\mathrm{m}$ and incident average power of $\ensuremath{\sim}3\mathrm{W}$, a ${\mathrm{Tm}}^{3+}$:ZBLANP ( ${\mathrm{ZrF}}_{4}\ensuremath{-}{\mathrm{BaF}}_{2}\ensuremath{-}{\mathrm{LaF}}_{3}\ensuremath{-}{\mathrm{AlF}}_{3}\ensuremath{-}\mathrm{NaF}\ensuremath{-}{\mathrm{PbF}}_{2}$) sample cooled to $\ensuremath{-}1.2\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ from room temperature for a single pass of the pump beam. This corresponds to an absorbed pump power of $\ensuremath{\sim}40\mathrm{mW}$ and a peak temperature change per absorbed power of $\ensuremath{\sim}\ensuremath{-}30\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}/\mathrm{W}$ from room temperature.

Recent developments in cooling thulium-doped heavy-metal fluoride glass are presented. Thulium-doped fluorozirconate (ZBLANP) is cooled to 19 K below ambient with a multiple-pass pump scheme. This represents over an order of magnitude increase from the previously reported single-pass geometry. The results agree with a simple model for anti-Stokes fluorescence cooling that includes considerations of quantum efficiency and parasitic heating mechanisms. Issues relating to a practical optical refrigerator are examined, including a general model for the effects of multiple pump passes.

At the previous Symposium on Frequency Standards and Metrology, H. Katori proposed using IS0 ---->3pO transitions in alkaline earth like atoms to make high performance optical clocks based on large numbers of neutral atoms tightly confined in an optical lattice. 1 This proposal was based on the use of Sr atoms, as were the initial experiments.24 In 2004 Porsev et al. proposed the use of the analogous transition in Yb at 578 nm,5 and we have been developing lattice clocks based on Yb over the past four years. While there are considerable similarities between the Sr and Yb atomic systems, there are also some important differences. Most significantly, Yb has an