The Pound-Drever-Hall (PDH) cavity-locking scheme has found prevalent uses in precision optical interferometry and laser frequency stabilization. A form of frequency modulation spectroscopy, PDH enjoys superior signal-to-noise recovery, large acquisition dynamic range, wide servo bandwidth, and robust rejection of spurious effects. However, residual amplitude modulation at the signal frequency, while significantly suppressed, still presents an important concern for further advancing the state-of-the-art performances. Here we present a simplified and improved scheme for PDH using an acousto-optic modulator to generate digital phase reference sidebands instead of the traditionally used electro-optic modulator approach. We demonstrate four key advantages: (1) the carrier and two modulation tones are individually synthesized and easily reconfigured, (2) robust and orthogonal control of the modulated optical field is applied directly to the amplitude and phase quadratures, (3) modulation synthesis, demodulation, and feedback are implemented in a self-contained and easily reproducible electronic unit, and (4) superior active and passive control of residual amplitude modulation is achieved, especially when the carrier power is vanishingly low. These distinct merits stimulate new ideas on how we optimally enact PDH for a wide range of applications.

Frequency combs measure optical frequencies with an unprecedented precision, allowing myriad applications in optical metrology, high-precision spectroscopy, optical atomic clocks, attosecond science, astronomy and, recently, quantum information processing.

We present the thermal noise limited performance of a cryogenic ultrastable silicon optical cavity operated at 4 K. A three-cornered comparison with two other ultrastable resonators shows that the 4 K system is largely limited by a flicker frequency floor near 7×10 -17 for averaging times from 5 seconds to 30 seconds.

We report on a laser locked to a silicon cavity operating continuously at 4 K with 1×10^{-16} instability and a median linewidth of 17 mHz at 1542 nm. This is a tenfold 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 an ultranarrow linewidth and long-term stability without user intervention.

It is interesting to try to understand the rate-limiting processes in scientific and technical research and applications. In this invited paper, I use data about the introduction of the maser, the laser, and the optical comb to see if unnecessary delays can be identified. The general result is that it all depends-on circumstances and breadth of awareness, and luck! (C) 2017 Optical Society of America

We demonstrate here a RAM cancellation method of reaching locking accuracy at shot-noise sensitivity level, and with a reserve precision sufficient to still be free of RAM-induced problems when the bandwidth has been narrowed to some tens of milliHz. Non-optical rf pickup sets the current limit at 2.8 ppm. Basically this paper announces the RAM-Buster approach needed to achieve the ideal spectroscopic accuracy, shotnoise-limited, as had been anticipated in the 1983 Drever et al. paper.

We demonstrate here a RAM cancellation method of reaching locking accuracy at shot-noise sensitivity level, and with a reserve precision sufficient to still be free of RAM-induced problems when the bandwidth has been narrowed to some tens of milliHz. Non-optical rf pickup sets the current limit at 2.8 ppm. Basically this paper announces the RAM-Buster approach needed to achieve the ideal spectroscopic accuracy, shotnoise-limited, as had been anticipated in the 1983 Drever et al. paper.

A panel discussion: Nine specialists foresee an expanded frequency range, new kinds of lasers, and many novel applications.

Active control and cancellation of residual amplitude modulation (RAM) in phase modulation of an optical carrier is one of the key technologies for achieving the ultimate stability of a laser locked to an ultrastable optical cavity. Furthermore, such techniques are versatile tools in various frequency modulation-based spectroscopy applications. In this Letter we report a simple and robust approach to actively stabilize RAM in an optical phase modulation process. We employ a waveguide-based electro-optic modulator (EOM) to provide phase modulation and implement an active servo with both DC electric field and temperature feedback onto the EOM to cancel both the in-phase and quadrature components of the RAM. This technique allows RAM control on the parts-per-million level where RAM-induced frequency instability is comparable to or lower than the fundamental thermal noise limit of the best available optical cavities.

Submitted for the 4CF14 Meeting of The American Physical Society Five Decades of Lasers, Six Decades of Progress, and a Proposed Space Experiment to Test Einstein’s Assumptions JOHN L. HALL1, JILA, University of Colorado — Even though this is the 52nd year of the Laser, progress in its control and application in precision measurements is still accelerating. The Optical Frequency Comb technology exploded in 1999-2000 from the synthesis of advances in independent fields of Laser Stabilization, UltraFast Lasers, and NonLinear Optical Fibers, enabling a thousand-fold advance in optical frequency measurement, and searches (in the 17th digit) for time-variation of physical “constants.” Current advances in ultra-precise locking are making possible stable optical frequencies defined by length and the speed of light, as well as by locking lasers to the resonant frequency of atoms. These two “clocks” represent our current prototypes of the clocks postulated by Einstein in 1905 in formulating the theory of Special Relativity, which can now be tested into the 18th decimal in a proposed Space-based experiment now being planned by our Space-Time Asymmetry Research collaboration (STAR). 1Boulder CO 80309-0440 John Hall Univ of Colorado Boulder Date submitted: 04 Sep 2014 Electronic form version 1.4

Many factors are coming together to make this an exciting time in the development of optical frequency standards. These include improved strategies for interrogation of the resonant quantum reference sample, improved accuracy and control of the modulation process, demonstration of an external modulation-removal strategy, and a rich field of new possibilities for frequency measurement, particularly the arrival of broad optical comb generation techniques. Frequencydomain methods based on broad femtosec laser combs are very promising, as made clear by the work of Udem and Hänsch. We easily see beats at 805 nm with optical comb lines whose center is at 840 nm, a 16 THz interval. Adjustment of the laser compensation broadens the comb to >140 nm width at – 3 dB ! Stabilization of both optical center frequency and pulse rate has been implemented. Interesting combs are also generated near 1060 nm with Kourogi’s modulator-in-a-cavity approach, augmented by an intracavity LiNbO3 crystal which provides OPO gain and frequency connection to the stable pump. So far, about 15 000 coherent comb lines are generated, limited by uncompensated dispersion in the OPO cavity. Useful data regarding S/N necessary for accurate counting and a powerful adaptive Phase-Tracking Filter/Oscillator are discussed.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text J. L. Hall, "Making a new SI System of Measurement by Learning from the Metre Redefinition," in Frontiers in Optics 2012/Laser Science XXVIII, OSA Technical Digest (online) (Optica Publishing Group, 2012), paper LW1I.1. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

After discussing several issues in a future redefinition of the kilogram, this paper considers the lessons that one might have learned from the analogous redefinitions of the metre and the second. The progress of length metrology was slow and steady, from seven digits reproducibility with the 1889 X-shaped metre prototype, to nine digits with Kr lamps, to 11 digits with the 1983 redefinition of the metre using the speed of light. With laser cooling, the Cs clock improved to 15, now 16, digits (and so also astronomical distance measurements could improve). Laser-cooled ions, and now atoms captured and cooled in an optical lattice, enable accuracy capability of three different optical frequency references to exceed 17 digits, i.e. better than time itself. The optical comb and related techniques vastly simplify frequency comparisons. Such progress stimulates a new satellite experiment, the STAR Mission (Space-Time Asymmetry Research). The goal is to test at the 1E-18 level frequency shifts owing to spatial anisotropy, position, gravitational potential and boost. The onboard optical clock will use stabilization to a molecular transition in I-2 or HCCH or CO2. The length etalons will be multiply redundant, with stability at the thermo-mechanical mirror motion limit. For a ULE glass etalon spacer (1987), I measure length creep approximately -1.5E-12/d, i.e. below 1E-14 over the 500 s satellite spin period.

The Space Time Asymmetry Research (STAR), recently proposed as a NASA Small Explorer Mission (SMEX) will test isotropy and symmetry of space time at unprecedented precision. We will use precision molecular iodine stabilized Nd:YAG laser interferometers to search for small deviations from Lorentz Invariance, a cornerstone of relativity and particle physics and thus our understanding of the Universe. A Lorentz violation would have profound implications for cosmology and particle physics. An improved null result will constrain theories attempting to unite particle physics and gravity. We have previously submitted a Science White Paper to Astro 2010. While self contained, this White Paper mainly outlines technology development for the STAR mission, with emphasis on the science payload and spacecraft. With a funding level compatible with SMEX, we plan to develop a high performance, high reliability science payload in a 4~5 year time frame. The STAR mission is designed to work one-year in space, with possible extension to indefinitely longer as long as the payload remains functional.

The Space-Time Asymmetry Research (STAR) project, a jointly-proposed concept by the NASA Ames Research Center (NASA ARC), Stanford University, and international partners from Saudi Arabia (KACST), Germany, and the United Kingdom, will test isotropy and symmetry of spacetime at unprecedented precision. We will use precision molecular iodine stabilized Nd:YAG laser interferometers to search for small deviations from Lorentz Invariance, a cornerstone of relativity and particle physics and thus our understanding of the Universe. A Lorentz violation would have profound implications for cosmology and particle physics. An improved null result will constrain theories attempting to unite particle physics and gravity. The STAR program can be built upon a series of focused, small satellite missions at a fraction of the cost of larger space science missions. STAR will take an incremental mission approach, flying instruments with progressively increased precision and measurement scope in each of five flights. The program is designed specifically to attract extensive research participation and leadership by university students; STAR will challenge curious young minds and train the next generation of space scientists and engineers.

Abstract Improved accuracy in measurement of the gravitational time delay of electromagnetic waves passing by the sun may be achieved with two drag-free spacecraft, one with a stable clock and laser transmitter and one with a high-stability transponder. We consider one spacecraft near the Earth-Sun L1 point with an advanced optical clock, and the transponder on a second satellite, which has a 2 year period orbit and eccentricity e = 0.37. Superior conjunctions will occur at aphelion 1, 3, and 5 years after launch of the second spacecraft. The measurements can be made using carrier phase comparisons on the laser beam that would be sent to the distant spacecraft and then transponded back. Recent development of clocks based on optical transitions in cooled and trapped ions or atoms indicate that a noise spectral amplitude of about 5 × 10−15/ at frequencies down to at least 1 microhertz can be achieved in space-borne clocks. An attractive candidate is a clock based on a single laser-cooled Yb+ trapped ion. Both spacecraft can be drag-free at a level of 1×10−13m/s2/ at frequencies down to at least 1 microhertz. The corresponding requirement for the LISA gravitational wave mission is 3 × 10−15m/s2/ at frequencies down to 10−4 Hz, and Gravitational Reference Sensors have been developed to meet this goal. They will be tested in the LISA Pathfinder mission, planned by ESA for flight in 2011. The requirements to extend the performance to longer times are mainly thermal. The achievable accuracy for determining the PPN parameter γ is about 1 × 10−8.

Special and General Relativity and the Standard Model (SM) of physics all rely on the postulate that the speed of light is invariant, regardless of the relative velocity of the source and observer, the direction of the light beam, or its wavelength. Indeed, the whole of modern physics is based on a class of invariances, or symmetries, describing how all measured quantities are seen by different observers in relative motion, and contained in the famous Lorentz transformations. A verifiable detection of any dependence of the speed of light on motion or direction, the object of this proposal, would signal the first needed modification of special relativity since its inception and would have profound implications for the development of cosmology, high energy astrophysics, particle astrophysics, and basic physics, including particle physics and relativity. While the impact of a successful search would be dramatic, even a non-detection would have significant value. An improved upper limit would give new direction to theoreticians and reduce the parameter space available to attempts to unite quantum mechanics, particle physics and gravity. We will use precision molecular iodine stabilized Nd:YAG laser interferometers to search for small deviations from Lorentz Invariance, a cornerstone of relativity and particle physics and thus our understanding of the Universe. A Lorentz violation would have profound implications for cosmology and particle physics. An improved null result will constrain theories attempting to unite particle physics and gravity.

Recent scientific and technological advances in atomic, molecular, and optical physics (AMOP) have produced new generation of high-precision instruments such as advanced atomic clocks and atomic quantum inertial sensors. Unique performance of these instruments allows addressing many challenging questions related to our understanding of the universe and of the physical laws of Nature. Although remarkably precise, the performance of these instruments is often limited by terrestrial conditions. On the other hand, space offers superior experimental conditions and a wide range of unique scientific opportunities. In particular, AMOP technologies are expected to bring about a new generation of high-accuracy tests of Einstein’s general theory of relativity, to improve sensitivities of future gravitational wave observatories, to offer unique methods of probing the physics beyond the Standard Model, etc. In addition, cold-atom-based atomic clocks and quantum inertial sensors are naturally suited for precision investigations in many areas of astronomy and astrophysics. We describe the new AMOP-based technologies, their benefits for space research and the rational for dedicated support of their development, size and power reduction, and space qualification efforts in the next decade. Programs in fundamental physics will be a unique opportunity to consolidate this new technology and prepare key instruments for future space missions. A well-defined program with modest investments on the order of $70M will beget new capabilities that could enable major scientific advances in fundamental physics, astronomy and astrophysics. We emphasizes that the development of the AMOP-based technologies will bring about outstanding scientific results and mature space-proved technology within a plausible time frame of 5 to 10 years. Additional benefits include more robust and advanced ground-based experiments that will further advance the art of measurement science. An Astro2010 Technology White Paper: AMOP-based Technologies for Fundamental Physics Experiments in Space Page 1 of 10 1 AMOP-based technologies to addresses the challenges in gravitational physics Today physics stands at the threshold of major discoveries. Growing observational evidence points to the need for new physics. Efforts to discover new fundamental symmetries, investigations of the limits of established symmetries, tests of the general theory of relativity, searches for gravitational waves, and attempts to understand the nature of dark matter were among the topics at the focus of scientific research at the end of the last century. These efforts intensified with the unexpected discovery of the accelerated expansion of the universe (i.e., “dark energy”) made in the late 1990s, triggering many new activities aimed at answering important questions related to the most fundamental laws of Nature (Turyshev et al., 2009). The fundamental physical laws of Nature are currently described by the Standard Model and Einstein’s general theory of relativity. However, there are important reasons to question the validity of this description. Despite the beauty and simplicity of general relativity and the success of the Standard Model, our present understanding of the fundamental laws of physics has several shortcomings. In particular, if gravity is to be quantized, general relativity will have to be modified; however, the search for a realistic theory of quantum gravity remains a challenge. This continued inability to merge gravity with quantum mechanics together with the challenges posed by the discovery of dark energy indicates that the pure tensor gravity of general relativity needs modification or augmentation. It is believed that new physics is needed to resolve this issue. Theoretical models of the kinds of new physics that can solve the problems above typically involve new physical interactions, some of which could manifest themselves as violations of the Equivalence Principle, variation of fundamental constants, modification of the inverse square law of gravity at various distances, Lorentz-symmetry breaking, large-scale gravitational phenomena, and introduce corrections to the current model of spacetime around massive bodies. Each of these manifestations offers an opportunity for experiment and could lead to a major discovery. Space is one of the most likely places where these manifestations may be investigated. While providing access to greater variation of gravitational potentials, greater velocities, and full orientation coverage, space also extends the well-understood and controlled laboratory environments. Ground-based laboratories have seen spectacular developments in Atomic, Molecular and Optical Physics (AMOP) to access measurement regimes with unprecedented sensitivity and accuracy. Progress has led to new instruments and technologies including more accurate atomic clocks, atom-wave interferometers, and femto-second laser combs. Today’s new generation of high performance atomic quantum sensors (accelerometers, gyroscopes, gravimeters, gravity gradiometers) is surpassing previous state-of-the-art instruments with novel experimental techniques based on engineered atomic systems. Atomic clocks and quantum inertial sensors represent key technologies for precise measurements of time, frequency, displacement, acceleration, and rotation. Combined with access to large spatial and gravitational variations, these new tools enable more precise experiments in a search for physics beyond the Standard Model and in tests of the general theory of relativity. The questions that can be addressed by space experiments are: “Does gravity behave as Einstein predicted?”; “What will be the nature of a theory of quantum gravity?”; “Where and how will the Standard Model fail?”; “Are the fundamental constants of nature truly constant?”; “What is the nature of dark matter and dark energy?” Many projects in fundamental physics would greatly benefit from having access to measurement precisions that have already been demonstrated by atomic quantum sensors based on cold atom physics. Today, atomic clocks approach a precision of few parts in 10 in the measurement of time and frequency; on the ground, atom interferometers promise sensitivities of 10 m/s/Hz An Astro2010 Technology White Paper: AMOP-based Technologies for Fundamental Physics Experiments in Space Page 2 of 10 for acceleration measurements and of 10 rad/s/Hz for the detection of tiny rotations. These accuracies are already surpassing the performances of instruments presently in use. However, putting these instruments in space can further improve their already remarkable precision by additional orders of magnitude, thus enabling new classes of fundamental physics investigations. A new generation of high-precision fundamental physics experiments requires ultra-high accuracy metrology of distance, accelerations, rotations, and time. For instance, the present generation of ground-based torsion-balance tests of gravitational inverse-square law (ISL) operates at distances of tens of microns limited by the terrestrial conditions. At the same time, many modern fundamental physics theories predict violations of the ISL at shorter distances, typically below 1 micron. New technologies are needed to access such short ranges. Similarly, future space-based gravitational wave observatories will have to control proof mass acceleration noise below the level of 10 m/s/Hz at very low frequency, currently a significant challenge. On the other hand, instruments in space relying on cold-atom-based technologies with truly drag-free atoms as proof masses offer an unmatched potential in resolving these challenges. Among the promising new AMOP-based technologies are highly stable and accurate frequency standards and clocks, atomic quantum sensors, and octave-spanning femtosecond laser combs. Space is a unique environment for improving the performances of these new devices and pushing to the limits the experiments testing the fundamental laws of physics. Space can ensure infinitely long and unperturbed “free fall” conditions, long interaction times, quiet environmental conditions and absence of seismic noise, absence of atmosphere, large free-propagation distances and variations in altitude, large velocities, and large variations of the gravitational potential. In this white paper we discuss these new AMOP-based technologies, including their current status, anticipated performance, challenges of space deployment, and science benefits from their use in space-based research. We also argue for dedicated support for their development, miniaturization, and space qualification efforts in the next decade. 2 Emerging Technologies: frequency standards and atomic quantum sensors The field of AMOP has had an incredibly productive decade marked by Nobel Prizes awarded for discoveries in laser cooling (1997), Bose-Einstein condensation and atom lasers (2001), and laser-based precision spectroscopy and the optical frequency comb technique (2005). The field is now mature both from the point of view of the understanding of the basic physics underlying laser cooling and laser manipulation of atoms and for the development of a solid technology for the experimental implementation of new quantum devices. Below we present the details. 2.1 Highly-accurate optical clocks 2.1.1 The nature of technology innovation For many years microwave transitions have served as the basis for highly accurate and ultrastable atomic clock systems. Laser cooling and trapping of ions and neutral atoms achieve extremely low temperatures where systems of confined atoms can be well controlled. New ultrastable optical reference cavities achieve laser stabilization to one part in 10 in 1 sec. A new type of clocks based on optical atomic transitions promises dramatic improvements. In an optical atomic clock, a laser in the visible region of the electromagnetic spectrum is used to induce a forbidden atomic transiti