116 research outputs found
Generation of Ultrastable Microwaves via Optical Frequency Division
There has been increased interest in the use and manipulation of optical
fields to address challenging problems that have traditionally been approached
with microwave electronics. Some examples that benefit from the low
transmission loss, agile modulation and large bandwidths accessible with
coherent optical systems include signal distribution, arbitrary waveform
generation, and novel imaging. We extend these advantages to demonstrate a
microwave generator based on a high-Q optical resonator and a frequency comb
functioning as an optical-to-microwave divider. This provides a 10 GHz
electrical signal with fractional frequency instability <8e-16 at 1 s, a value
comparable to that produced by the best microwave oscillators, but without the
need for cryogenic temperatures. Such a low-noise source can benefit radar
systems, improve the bandwidth and resolution of communications and digital
sampling systems, and be valuable for large baseline interferometry, precision
spectroscopy and the realization of atomic time
Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb
We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.Comment: 18 pages, 4 figure
Precision Optical Measurements and Fundamental Physical Constants
A brief overview is given on precision determinations of values of the
fundamental physical constants and the search for their variation with time by
means of precision spectroscopy in the optical domain
'Designer atoms' for quantum metrology
Entanglement is recognized as a key resource for quantum computation and
quantum cryptography. For quantum metrology, the use of entangled states has
been discussed and demonstrated as a means of improving the signal-to-noise
ratio. In addition, entangled states have been used in experiments for
efficient quantum state detection and for the measurement of scattering
lengths. In quantum information processing, manipulation of individual quantum
bits allows for the tailored design of specific states that are insensitive to
the detrimental influences of an environment. Such 'decoherence-free subspaces'
protect quantum information and yield significantly enhanced coherence times.
Here we use a decoherence-free subspace with specifically designed entangled
states to demonstrate precision spectroscopy of a pair of trapped Ca+ ions; we
obtain the electric quadrupole moment, which is of use for frequency standard
applications. We find that entangled states are not only useful for enhancing
the signal-to-noise ratio in frequency measurements - a suitably designed pair
of atoms also allows clock measurements in the presence of strong technical
noise. Our technique makes explicit use of non-locality as an entanglement
property and provides an approach for 'designed' quantum metrology
Frequency Comb Assisted Diode Laser Spectroscopy for Measurement of Microcavity Dispersion
While being invented for precision measurement of single atomic transitions,
frequency combs have also become a versatile tool for broadband spectroscopy in
the last years. In this paper we present a novel and simple approach for
broadband spectroscopy, combining the accuracy of an optical fiber-laser-based
frequency comb with the ease-of-use of a tunable external cavity diode laser.
This scheme enables broadband and fast spectroscopy of microresonator modes and
allows for precise measurements of their dispersion, which is an important
precondition for broadband optical frequency comb generation that has recently
been demonstrated in these devices. Moreover, we find excellent agreement of
measured microresonator dispersion with predicted values from finite element
simulations and we show that tailoring microresonator dispersion can be
achieved by adjusting their geometrical properties
Searching for Exoplanets Using a Microresonator Astrocomb
Detection of weak radial velocity shifts of host stars induced by orbiting
planets is an important technique for discovering and characterizing planets
beyond our solar system. Optical frequency combs enable calibration of stellar
radial velocity shifts at levels required for detection of Earth analogs. A new
chip-based device, the Kerr soliton microcomb, has properties ideal for
ubiquitous application outside the lab and even in future space-borne
instruments. Moreover, microcomb spectra are ideally suited for astronomical
spectrograph calibration and eliminate filtering steps required by conventional
mode-locked-laser frequency combs. Here, for the calibration of astronomical
spectrographs, we demonstrate an atomic/molecular line-referenced,
near-infrared soliton microcomb. Efforts to search for the known exoplanet HD
187123b were conducted at the Keck-II telescope as a first in-the-field
demonstration of microcombs
Adaptive real-time dual-comb spectroscopy
With the advent of laser frequency combs, coherent light sources that offer
equally-spaced sharp lines over a broad spectral bandwidth have become
available. One decade after revolutionizing optical frequency metrology,
frequency combs hold much promise for significant advances in a growing number
of applications including molecular spectroscopy. Despite its intriguing
potential for the measurement of molecular spectra spanning tens of nanometers
within tens of microseconds at Doppler-limited resolution, the development of
dual-comb spectroscopy is hindered by the extremely demanding high-bandwidth
servo-control conditions of the laser combs. Here we overcome this difficulty.
We experimentally demonstrate a straightforward concept of real-time dual-comb
spectroscopy, which only uses free-running mode-locked lasers without any
phase-lock electronics, a posteriori data-processing, or the need for expertise
in frequency metrology. The resulting simplicity and versatility of our new
technique of adaptive dual-comb spectroscopy offer a powerful transdisciplinary
instrument that may spark off new discoveries in molecular sciences.Comment: 10 pages, 5 figure
Quantum cascade laser based hybrid dual comb spectrometer
Four-wave-mixing-based quantum cascade laser frequency combs (QCL-FC) are a powerful photonic tool, driving a recent revolution in major molecular fingerprint regions, i.e. mid- and far-infrared domains. Their compact and frequency-agile design, together with their high optical power and spectral purity, promise to deliver an all-in-one source for the most challenging spectroscopic applications. Here, we demonstrate a metrological-grade hybrid dual comb spectrometer, combining the advantages of a THz QCL-FC with the accuracy and absolute frequency referencing provided by a free-standing, optically-rectified THz frequency comb. A proof-of-principle application to methanol molecular transitions is presented. The multi-heterodyne molecular spectra retrieved provide state-of-the-art results in line-center determination, achieving the same precision as currently available molecular databases. The devised setup provides a solid platform for a new generation of THz spectrometers, paving the way to more refined and sophisticated systems exploiting full phase control of QCL-FCs, or Doppler-free spectroscopic schemes
Fully Phase Stabilized Quantum Cascade Laser Frequency Comb
The road towards the realization of quantum cascade laser (QCL) frequency combs [1,2] has undoubtedly attracted ubiquitous attention from the scientific community. These devices promise to deliver an all-in-one (i.e. a single, miniature, active device) frequency comb synthesizer in a range as wide as the QCL spectral coverage itself (from about 4 microns to the THz range), with the unique possibility to tailor their spectral emission by band structure engineering. For these reasons, vigorous efforts have been spent to characterize the emission of four-wave-mixing (FWM) multi-frequency QCLs, aiming to seize their comb-like mode-locked operation [3–6]
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