12183523
Colloquium: Femtosecond optical frequency combs
Recently there has been a remarkable synergy between the technologies of precision laser stabilization and mode-locked ultrafast lasers. This has resulted in control of the frequency spectrum produced by mode-locked lasers, which consists of a regular comb of sharp lines. Thus such a controlled mode-locked laser is a ``femtosecond optical frequency comb generator.'' For a sufficiently broad comb, it is possible to determine the absolute frequencies of all of the comb lines. This ability has revolutionized optical frequency metrology and synthesis. It has also served as the basis for the recent demonstrations of atomic clocks that utilize an optical frequency transition. In addition, it is having an impact on time-domain applications, including synthesis of a single pulse from two independent lasers. In this Colloquium, we first review the frequency-domain description of a mode-locked laser and the connection between the pulse phase and the frequency spectrum in order to provide a basis for understanding how the absolute frequencies can be determined and controlled. Using this understanding, applications in optical frequency metrology and synthesis and optical atomic clocks are discussed. This is followed by a brief overview of how the comb technology is affecting and will affect time-domain experiments.
2486417
Precision test of mass-ratio variations with lattice-confined ultracold molecules.
We propose a precision measurement of time variations of the proton-electron mass ratio using ultracold molecules in an optical lattice. Vibrational energy intervals are sensitive to changes of the mass ratio. In contrast to measurements that use hyperfine-interval-based atomic clocks, the scheme discussed here is model independent and does not require separation of time variations of different physical constants. The possibility of applying the zero-differential-Stark-shift optical lattice technique is explored to measure vibrational transitions at high accuracy.
119207145
Mid-Infrared Frequency Comb Fourier Transform Spectrometer
Optical frequency-comb-based-high-resolution spectrometers offer enormous potential for spectroscopic applications. Although various implementations have been demonstrated, the lack of suitable mid-infrared comb sources has impeded explorations of molecular fingerprinting. Here we present for the first time a frequency-comb Fourier transform spectrometer operating in the 2100-to-3700-cm-1 spectral region that allows fast and simultaneous acquisitions of broadband absorption spectra with up to 0.0056 cm-1 resolution. We demonstrate part-per-billion detection limits in 30 seconds of integration time for various important molecules including methane, ethane, isoprene, and nitrous oxide. Our system enables precise concentration measurements even in gas mixtures that exhibit continuous absorption bands, and it allows detection of molecules at levels below the noise floor via simultaneous analysis of multiple spectral features. This system represents a near real-time, high-resolution, high-bandwidth mid-infrared spectrometer which is ready to replace traditional Fourier transform spectrometers for many applications in trace gas detection, atmospheric science, and medical diagnostics.
8781619
Control of four-level quantum coherence via discrete spectral shaping of an optical frequency comb.
We present experiments demonstrating high-resolution and wide-bandwidth coherent control of a four-level atomic system in a diamond configuration. A femtosecond frequency comb is used to excite a specific pair of two-photon transitions in cold 87Rb. The optical-phase-sensitive response of the closed-loop diamond system is studied by controlling the phase of the comb modes with a pulse shaper. Finally, the pulse shape is optimized resulting in a 256% increase in the two-photon transition rate by forcing constructive interference between the mode pairs detuned from an intermediate resonance.
31462099
Precision stabilization of femtosecond lasers to high-finesse optical cavities
We report on direct stabilization of a femtosecond laser by a high-finesse passive optical cavity. Detailed comparison of two distinct stabilization schemes leads to new understanding of the optimum conditions for cavity stabilization and limitations on the ability to transfer the frequency stability of the cavity to the microwave domain. The stability of the frequency comb is explored in both the optical and the radio frequency domain. With an independent, stable cw laser, we verify that the linewidth and stability of the optical comb components, respectively, reach below 300 Hz and 53 10 ˛14 at 1 s averaging time, both limited by the
25651519
New limits on coupling of fundamental constants to gravity using 87Sr optical lattice clocks.
The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu.
53756653
Redundancy or GaAs? Two different approaches to solve the problem of SEU (Single Event Upset) in a digital optical link
The fast digital optical links for the ATLAS Liquid Argon Calorimeter must survive in a high radiation environment with a total fluence of 3x10 neutrons (1MeV Si)/cm and 10 kGy (Si). The links based on Agilent Technologies Glink serializer/deserializer set, show a total dose radiation resistance to neutrons and gammas that would allow for 10 years of operation in the ATLAS detector. We have observed, however, an unacceptable rate of single event upsets (SEU) due to neutrons interacting in the silicon-based serializer. In order to solve this problem, we have developed two link systems. The first one, Dual-Glink, is based on a principle of redundancy: data are sent on two independent links. On the reception side, data are analyzed and error recovery is performed without dead time. The second solution uses a GaAs serializer/deserializer set from TriQuint. We observe a very small number of SEU’s. In addition, high speed of 2.5 Gb/s allows for transmission of the data twice during one event period and for error recovery. The design of the 3 types of links, their performance in the laboratory and the results of the radiation tests are presented for all systems.
120914328
The 120Gbps VCSEL Array Based Optical Transmitter (ATx) development for the High-Luminosity LHC (HL-LHC) experiments
The integration of a Verticle Cavity Surface-Emitting Laser (VCSEL) array and a driving Application-Specific Integrated Circuit (ASIC) in a custom optical array transmitter module (ATx) for operation in the detector front-end is constructed, assembled and tested. The ATx provides 12 parallel channels with each channel operating at 10 Gbps. The optical transmitter eye diagram passes the eye mask and the bit-error rate (BER) less than 10(-12) transmission is achieved at 10 Gbps/ch. The overall insertion loss including the radiation induced attenuation is sufficiently low to meet the proposed link budget requirement.
111270365
The miniature optical transmitter and transceiver for the High-Luminosity LHC (HL-LHC) experiments
We present the design and test results of the Miniature optical Transmitter (MTx) and Transceiver (MTRx) for the high luminosity LHC (HL-LHC) experiments. MTx and MTRx are Transmitter Optical Subassembly (TOSA) and Receiver Optical Subassembly (ROSA) based. There are two major developments: the Vertical Cavity Surface Emitting Laser (VCSEL) driver ASIC LOCld and the mechanical latch that provides the connection to fibers. In this paper, we concentrate on the justification of this work, the design of the latch and the test results of these two modules with a Commercial Off-The-Shelf (COTS) VCSEL driver.
14992394
An Optical Demo-Link for ATLAS Inner Detector Readout Upgrade
The GOL ASIC is a serializer chip developed by CERN based on a 0.25 μm CMOS technology [1]. The GOL operates with two data rates: 800 Mbps and 1.6 Gbps. This ASIC has been evaluated with radiation tolerance requirement for the ATLAS Inner Detector upgrade for the SLHC 1 . A demo-link has been designed and constructed to read out silicon detectors in the test staves through fiber optics. Through this demo-link we plan to study system issues in a giga-bit optical link. This concept will be extended to future serializer ASICs like the GBTx and the LOC when they become available. Experience gained from these demolinks will help us design and build a reliable optical readout system for new ATLAS Inner Detector readout.
18954058
Quality Control of Optical Transmitters for the ATLAS Liquid Argon Calorimeter
A quality control test is performed on nearly 2000 custom optical transmitters for use in the Liquid Argon Calorimeter of the ATLAS detector. More than 90% of these optical transmitters passed the test and have been installed in the calorimeter readout system. The acceptance criteria, measurement procedure, and results of the quality control test are presented in this note.