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State-of-the-art laser frequency stabilization by high-finesse optical cavities is limited fundamentally by thermal noise-induced cavity length fluctuations. We present a novel design to reduce this thermal noise limit by an order of magnitude as well as an experimental realization of this new cavity system, demonstrating the most stable oscillator of any kind to date for averaging times of 0.1–10 s. The cavity spacer and the mirror substrates are both constructed from single-crystal silicon and are operated at 124 K, where the silicon thermal expansion coefficient is zero and the mechanical loss is small. The cavity is supported in a vibration-insensitive configuration, which, together with the superior stiffness of the silicon crystal, reduces the vibration-related noise. With rigorous analysis of heterodyne beat signals among three independent stable lasers, the silicon system demonstrates a fractional frequency instability of 1 × 10 −16 at short timescales and supports a laser linewidth of <40 mHz at 1.5 µm. Frequency stabilization in a high-finesse optical cavity is limited fundamentally by thermal-noise-induced cavity length fluctuations. Scientists have now developed a single-crystal silicon system that offers a fractional frequency instability of 1 × 10 −16 at short timescales and supports a laser linewidth of less than 40 mHz at 1.5 µm.

This article presents an exploratory study that examines how 11 first-year writing instructors’ conceptualizations of information literacy evolved over the course of their participation in an inquiry group co-developed and co-facilitated by the Libraries’ teaching faculty and the Director of Composition & Rhetoric at a public university in the United States. The authors developed a coding schema to identify the presence of information literacy-related themes and practices in pre- and post-program course syllabi and in reflective pieces submitted by instructors. The findings revealed that instructors’ use and applications of the ACRL Framework increased after the program, showing greater personal engagement as evidenced by more preferential application of frames most relevant to their learning goals. Moreover, instructors integrated those frames more fully into their instructional practices. The authors’ analysis of instructor-created artifacts provides a unique lens into disciplinary instructors’ conceptualizations of and approaches to information literacy while examining the impact of one path for collaboration and scalability of information literacy integration within a curriculum.

We have investigated crystalline AlGaAs/GaAs optical coatings with three ultra-stable cavities operating at 4 K, 16 K, 124 K and 297 K. The response of the cavities’ resonance frequencies to variations in optical power indicates non-thermal effects beyond the photo-thermo-optic effect observed in dielectric coatings. These effects are strongly dependent on the intensity of the intracavity light at 1.5 μm. When the rear side of the mirrors is illuminated with external light, we observe a prominent photo-modified birefringence for photon energies above the GaAs bandgap, which points to a possible mechanism relating our observations to the semiconductor properties of the coatings. Separately, we also present a low maintenance evolution of our 124 K silicon cavity system where the liquid nitrogen based cooling system is replaced with closed cycle cooling from a pulse-tube cryo-cooler.

We have set up an improved vertically mounted silicon cavity operating at the zero-crossing temperature of the coefficient of thermal expansion (CTE) near 123 K with estimated thermal noise limited instability of 4 x 10-17 in the modified Allan deviation. Owing to the anisotropic elasticity of single-crystal silicon, the vertical acceleration sensitivity was minimized in situ by axially rotating the resonator with respect to the mounting frame. The control of the resonator temperature is greatly improved by using a combination of two thermal shields, monitoring with several temperature sensors, and employing low-thermal conductivity materials. The instability of the resonator stabilized laser was characterized by comparing with another low-noise system based on a 48 cm long room temperature cavity of PTB's strontium lattice clock, resulting in a modified Allan deviation of 7 x 10-17 at 100 s.

Optical atomic clocks require local oscillators with exceptional optical coherence owing to the challenge of performing spectroscopy on their ultranarrow-linewidth clock transitions. Advances in laser stabilization have thus enabled rapid progress in clock precision. A new class of ultrastable lasers based on cryogenic silicon reference cavities has recently demonstrated the longest optical coherence times to date. Here we utilize such a local oscillator with two strontium (Sr) optical lattice clocks to achieve an advance in clock stability. Through an anti-synchronous comparison, the fractional instability of both clocks is assessed to be \\[4.8 \\times 10^{ - 17}/\\sqrt \\tau\\] for an averaging time τ (in seconds). Synchronous interrogation enables each clock to average at a rate of \\[3.5 \\times 10^{ - 17}/\\sqrt \\tau\\], dominated by quantum projection noise, and reach an instability of 6.6 × 10−19 over an hour-long measurement. The ability to resolve sub-10−18-level frequency shifts in such short timescales will affect a wide range of applications for clocks in quantum sensing and fundamental physics.

Background Undefined pathophysiologic mechanisms likely contribute to unsuccessful antihypertensive drug therapy. The renin test–guided therapeutic (RTGT) algorithm is based on the concept that, irrespective of current drug treatments, subnormal plasma renin activity (PRA) (<0.65 ng/ml/h) indicates sodium-volume excess “V” hypertension, whereas values ≥0.65 indicate renin–angiotensin vasoconstriction excess “R” hypertension. Methods The RTGT algorithm was applied to treated, uncontrolled hypertensives and compared to clinical hypertension specialists' care (CHSC) without access to PRA. RTGT protocol: “V” patients received natriuretic anti-“V” drugs (diuretics, spironolactone, calcium antagonists, or α1-blockers) while withdrawing antirenin “R” drugs (converting enzyme inhibitors, angiotensin receptor antagonists, or β-blockers). Converse strategies were applied to “R” patients. Eighty-four ambulatory hypertensives were randomized and 77 qualified for the intention-to-treat analysis including 38 in RTGT (63.9 ± 1.8 years; baseline blood pressure (BP) 157.0 ± 2.6/87.1 ± 2.0 mm Hg; PRA 5.8 ± 1.6; 3.1 ± 0.3 antihypertensive drugs) and 39 in CHSC (58.0 ± 2.0 years; BP 153.6 ± 2.3/91.9 ± 2.0; PRA 4.6 ± 1.1; 2.7 ± 0.2 drugs). Results BP was controlled in 28/38 (74% (RTGT)) vs. 23/39 (59% (CHSC)), P = 0.17, falling to 127.9 ± 2.3/73.1 ± 1.8 vs. 134.0 ± 2.8/79.8 ± 1.9 mm Hg, respectively. Systolic BP (SBP) fell more with RTGT (−29.1 ± 3.2 vs. −19.2 ± 3.2 mm Hg, P = 0.03), whereas diastolic BP (DBP) declined similarly (P = 0.32). Although final antihypertensive drug numbers were similar (3.1 ± 0.2 (RTGT) vs. 3.0 ± 0.3 (CHSC), P = 0.73) in “V” patients, 60% (RTGT) vs. 11% (CHSC) of “R” drugs were withdrawn and BP medications were reduced (−0.5 ± 0.3 vs. +0.7 ± 0.3, P = 0.01). Conclusions In treated but uncontrolled hypertension, RTGT improves control and lowers BP equally well or better than CHSC, indicating that RTGT provides a reasonable strategy for correcting treated but uncontrolled hypertension.

We have investigated crystalline AlGaAs/GaAs optical coatings with three ultra-stable cavities operating at 4 K, 16 K, 124 K and 297 K. The response of the resonance frequencies of cavities to variations in optical power indicates effects beyond the photo-thermo-optic effect observed in dielectric coatings. These effects are strongly dependent on the intensity of the intracavity light at 1.5~\\textmu m. When the rear side of the mirrors is illuminated with external light, we observe a prominent photo-modified birefringence for photon energies above the GaAs bandgap, which points to a possible mechanism relating our observations to the semiconductor properties of the coatings. Separately, we also present a low maintenance evolution of our 124 K silicon cavity system where the liquid nitrogen based cooling system is replaced with closed cycle cooling from a pulse-tube cryo-cooler.

We report on a laser locked to a silicon cavity operating continuously at 4 K with \\(1 \\times 10^{-16}\\) instability and a median linewidth of 17 mHz at 1542 nm. This is a ten-fold improvement in short-term instability, and a \\(10^4\\) improvement in linewidth, over previous sub-10 K systems. Operating at low temperatures reduces the thermal noise floor, and thus is advantageous toward reaching an instability of \\(10^{-18}\\), a long-sought goal of the optical clock community. The performance of this system demonstrates the technical readiness for the development of the next generation of ultrastable lasers that operate with ultranarrow linewidth and long-term stability without user intervention.

Optical clocks are not only powerful tools for prime fundamental research, but are also deemed for the re-definition of the SI base unit second as they now surpass the performance of caesium atomic clocks in both accuracy and stability by more than an order of magnitude. However, an important obstacle in this transition has so far been the limited reliability of the optical clocks that made a continuous realization of a timescale impractical. In this paper, we demonstrate how this situation can be resolved and that a timescale based on an optical clock can be established that is superior to one based on even the best caesium fountain clocks. The paper also gives further proof of the international consistency of strontium lattice clocks on the \\(10^{-16}\\) accuracy level, which is another prerequisite for a change in the definition of the second.