171 research outputs found
A Search for N2+ in Spectra of Comet C/2002C1 (Ikeya-Zhang)
We report low- and high-resolution spectra of comet C/2002 C1 (Ikeya-Zhang)
from McDonald Observatory. The comet had a well-developed ion tail including
CO+, CO2+, CH+, and H2O+. We used our high-resolution spectra to search for
N2+. None was detected and we placed upper limits on N2+/CO+ of 5.4 times
10^{-4}. N2+ was detected in the low-resolution spectra but we show that this
emission was probably telluric in origin (if cometary, we derive N2+/CO+ = 5.5
times 10^{-3}, still very low). We discuss the implications for the conditions
in the early solar nebula of the non-detection of N2+. These depend on whether
the H2O ice was deposited in the amorphous or crystalline form. If H2O was
deposited in its crystalline form, the detection of CO+ but not N2+ has
implications for H2O/H2 in the early solar nebula.Comment: Accepted for publication in ApJ (Letters) - 10 Sept 200
Demonstration of quantum-enhanced rangefinding robust against classical jamming
In this paper we demonstrate operation of a quantum-enhanced lidar based on a
continuously pumped photon pair source combined with simple detection in
regimes with over 5 orders of magnitude separation between signal and
background levels and target reflectivity down to -52 dB. We characterise the
performance of our detector using a log-likelihood analysis framework, and
crucially demonstrate the robustness of our system to fast and slow classical
jamming, introducing a new protocol to implement dynamic background tracking to
eliminate the impact of slow background changes whilst maintaining immunity to
high frequency fluctuations. Finally, we extend this system to the regime of
rangefinding in the presence of classical jamming to locate a target with an 11
cm spatial resolution limited only by the detector jitter. These results
demonstrate the advantage of exploiting quantum correlations for lidar
applications, providing a clear route to implementation of this system in
real-world scenarios
High-efficiency coupled-cavity optical frequency comb generation
We present a high efficiency source of picosecond pulses derived from a dual cavity optical frequency comb generator. This approach overcomes the limitations of single cavity comb generators that are restricted to efficiencies of a few percent. We achieve picosecond pulses with GHz repetition rates offering over a hundred times higher output efficiency than a single cavity design and demonstrate tuning of pulse width by varying the modulation depth of the intra-cavity electro-optic modulator. These results provide a wavelength-agnostic design with a compact footprint for the development of portable picosecond pulsed laser systems for timing, metrology, and LIDAR applications
Ultra-low noise, bi-polar, programmable current sources
We present the design process and implementation of fully open-source,
ultra-low noise programmable current source systems in two configurations.
Although originally designed as coil drivers for Optically Pumped Magnetometers
(OPMs), the device specifications make them potentially useful in a range of
applications. The devices feature a bi-directional current range of ~10~mA
and ~250~mA respectively on three independent channels with 16-bit
resolution. Both devices feature narrow 1/f noise bandwidth of 1~Hz, enabling
magnetic field manipulation for high-performance OPMs. They exhibit low noise
of 146.3~pA/ and 4114~pA/ which
translates to 14.57~ppb/ and 16.46~ppb/
noise relative to full scale.Comment: 9 pages, 9 figure
Demonstration of quantum-enhanced rangefinding robust against classical jamming
We demonstrate a quantum-enhanced lidar capable of performing confident target detection and rangefinding in the presence of strong, time-varying classical noise whilst operating with over five orders of magnitude separation between signal and background levels and target reflectivities down to -52 dB. We use a log-likelihood-based framework to introduce a new protocol for dynamic background tracking, verifying resilience of our system to both fast- and slow-modulation jamming in regimes where a classical illumination-based system fails to find a target. These results demonstrate the advantage of exploiting quantum correlations for lidar applications, providing a clear route to implementation in real-world scenarios
Free-induction-decay magnetometer with enhanced optical pumping
Spin preparation prior to a free-induction-decay (FID) measurement can be
adversely affected by transverse bias fields, particularly in the geophysical
field range. A strategy that enhances the spin polarization accumulated before
readout is demonstrated, by synchronizing optical pumping with a magnetic field
pulse that supersedes any transverse fields by over two order of magnitude. The
pulsed magnetic field is generated along the optical pumping axis using a
compact electromagnetic coil pair encompassing a micro-electromechanical
systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs)
vapor to the optimal atomic density without spurious magnetic field
contributions as they are rapidly demagnetized to approximately zero field
during spin readout. The demagnetization process is analyzed electronically,
and directly with a FID measurement, to confirm that the residual magnetic
field is minimal during detection. The sensitivity performance of this
technique is compared to existing optical pumping modalities across a wide
magnetic field range. A noise floor sensitivity of
was achieved in a field of approximately , in close
agreement with the Cram\'{e}r-Rao lower bound (CRLB) predicted noise density of
.Comment: 10 pages, 7 figure
Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides
This paper shows how to analyze plasmonic metal-insulator-metal waveguides
using the full modal structure of these guides. The analysis applies to all
frequencies, particularly including the near infrared and visible spectrum, and
to a wide range of sizes, including nanometallic structures. We use the
approach here specifically to analyze waveguide junctions. We show that the
full modal structure of the metal-insulator-metal (MIM) waveguides--which
consists of real and complex discrete eigenvalue spectra, as well as the
continuous spectrum--forms a complete basis set. We provide the derivation of
these modes using the techniques developed for Sturm-Liouville and generalized
eigenvalue equations. We demonstrate the need to include all parts of the
spectrum to have a complete set of basis vectors to describe scattering within
MIM waveguides with the mode-matching technique. We numerically compare the
mode-matching formulation with finite-difference frequency-domain analysis and
find very good agreement between the two for modal scattering at symmetric MIM
waveguide junctions. We touch upon the similarities between the underlying
mathematical structure of the MIM waveguide and the PT symmetric quantum
mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM
waveguide supports forms a canonical example against which other more
complicated geometries can be compared. Our work here encompasses the microwave
results, but extends also to waveguides with real metals even at infrared and
optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed,
figures slightly modifie
Ultra-low noise, bi-polar, programmable current sources
We present the design process and implementation of fully open-source, ultra-low noise programmable current source systems in two configurations. Although originally designed as coil drivers for Optically Pumped Magnetometers (OPMs), the device specifications make them potentially useful in a range of applications. The devices feature a bi-directional current range of ±10 and ±250 mA on three independent channels with 16-bit resolution. Both devices feature a narrow 1/f noise bandwidth of 1 Hz, enabling magnetic field manipulation for high-performance OPMs. They exhibit a low noise of 146 pA/√Hz and 4.1 nA/√Hz, which translates to 15 and 16 ppb/√Hz noise relative to full scale
Optical pumping enhancement of a free-induction-decay magnetometer
Spin preparation prior to a free-induction-decay (FID) measurement can be adversely affected by transverse bias fields, particularly in the geophysical field range. A strategy that enhances the spin polarization accumulated before readout is demonstrated, by synchronizing optical pumping with a magnetic field pulse that supersedes any transverse fields by over two order of magnitude. The pulsed magnetic field is generated along the optical pumping axis using a compact electromagnetic coil pair encompassing a micro-electromechanical systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs) vapor to the optimal atomic density without spurious magnetic field contributions as they are rapidly demagnetized to approximately zero field during spin readout. The demagnetization process is analyzed electronically, and directly with a FID measurement, to confirm that the residual magnetic field is minimal during detection. The sensitivity performance of this technique is compared to existing optical pumping modalities across a wide magnetic field range. A noise floor sensitivity of 238 fT/√Hz was achieved in a field of approximately 50 μT, in close agreement with the Cramér-Rao lower bound (CRLB) predicted noise density of 258 fT/√Hz
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