We investigate the performance of phase-sensitive versus phase-insensitive pre-amplification in optical resolution
enhancement with a binary hypothesis test. Phase-sensitive pre-amplification is shown to outperform phaseinsensitive
pre-amplification by more than 2 dB.
KEYWORDS: LIDAR, Sensors, Speckle, Homodyne detection, Reflectivity, Ranging, Signal to noise ratio, Photodetectors, Target detection, Monte Carlo methods
Theory has shown [1] that the quantum enhancements afforded by squeezed-vacuum injection (SVI) and phasesensitive
amplification (PSA) can improve the spatial resolution of a soft-aperture, homodyne-detection laserradar
(ladar) system. Here we show they can improve the range resolution of such a ladar system. In particular,
because an experimental PSA-enhanced system is being built whose slow photodetectors imply multi-pulse
integration, we develop range-measurement theory that encompasses its processing architecture. We allow the
target to have an arbitrary mixture of specular and speckle components, and present computer simulation results
demonstrating the range-resolution improvement that accrues from quantum enhancement with PSA.
We demonstrate a balanced-homodyne LADAR receiver employing a phase-sensitive amplifier (PSA) to raise the
effective photon detection efficiency (PDE) to nearly 100%. Since typical LADAR receivers suffer from losses in the
receive optical train that routinely limit overall PDE to less than 50% thus degrading SNR, PSA can provide significant
improvement through amplification with noise figure near 0 dB. Receiver inefficiencies arise from sub-unity quantum
efficiency, array fill factors, signal-local oscillator mixing efficiency (in coherent receivers), etc. The quantum-enhanced
LADAR receiver described herein is employed in target discrimination scenarios as well as in imaging applications. We
present results showing the improvement in detection performance achieved with a PSA, and discuss the performance
advantage when compared to the use of a phase-insensitive amplifier, which cannot amplify noiselessly.
Phase-sensitive amplification (PSA) can enhance the signal-to-noise ratio (SNR) of an optical measurement suffering
from detection inefficiency. Previously, we showed that this increased SNR improves LADAR-imaging
spatial resolution when infinite spatial-bandwidth PSA is employed. Here, we evaluate the resolution enhancement
for realistic, finite spatial-bandwidth amplification. PSA spatial bandwidth is characterized by numerically
calculating the input and output spatial modes and their associated phase-sensitive gains under focused-beam
pumping. We then compare the spatial resolution of a baseline homodyne-detection LADAR system with homodyne
LADAR systems that have been augmented by pre-detection PSA with infinite or finite spatial bandwidth.
The spatial resolution of each system is quantified by its ability to distinguish between the presence of 1 point
target versus 2 closely-spaced point targets when minimum error-probability decisions are made from quantum
limited measurements. At low (5-10 dB) SNR, we find that a PSA system with a 2.5kWatts pump focused to
25μm × 400μm achieves the same spatial resolution as a baseline system having 5.5 dB higher SNR. This SNR
gain is very close to the 6 dB SNR improvement possible with ideal (infinite bandwidth, infinite gain) PSA at
our simulated system detection efficiency (0.25). At higher SNRs, we have identified a novel regime in which
finite spatial-bandwidth PSA outperforms its infinite spatial-bandwidth counterpart. We show that this performance
crossover is due to the focused pump system's input-to-output spatial-mode transformation converting
the LADAR measurement statistics from homodyne to heterodyne performance.
Application of slow light linear delay to squint-free (true-time delay) steering of phased array radar antennae
is discussed. Theoretical analysis is provided on true-time delay radar requirements, including delay precision,
amplitude precision, and bandwidth. We also discuss an improvement to the slow light technique based on
stimulated Brillouin scattering by using a Faraday rotator mirror that provides temporally stable, linear (with
pump power) delay, applicable to practical implementations. Future directions are considered.
We demonstrate an experimental technique for manipulating atom clouds with high-speed and high resolution. By
combining holographically engineered laser beams from a spatial light modulator with acousto-optic deflection, we
manipulate the spatial locations of multiple cold atom clouds held in dark optical traps with individual site control.
Additionally, we demonstrate smooth 2-dimensional motion of atomic ensembles.
We demonstrate the generation of single-beam dark toroidal optical intensity distributions, which are of interest for
neutral atom storage and atom interferometry. We demonstrate experimentally and numerically optical potentials that
contain a ring-shaped intensity minimum, bounded in all directions by higher intensity. We use a spatial light modulator
to alter the phase of an incident laser beam, and analyze the resulting optical propagation characteristics. For small
toroidal traps (< 50 &mgr;m diameter), we find an optimal superposition of Laguerre-Gaussian modes that allows the
formation of single-beam toroidal traps. We generate larger toroidal bottle traps by focusing hollow beams with toroidal
lenses imprinted onto the spatial light modulator.
Reduced density matrix descriptions are developed for linear and non-linear electromagnetic interactions of
moving atomic systems, taking into account applied magnetic fields. Atomic collision processes are treated as
environmental interactions. Applications of interest include electromagnetically induced transparency and related pump-probe
optical phenomena in atomic vapors. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator)
formulations are developed in a unified manner. The standard Born (lowest-order perturbation-theory) and
Markov (short-memory-time) approximations are systematically introduced within the framework of the general nonperturbative
and non-Markovian formulations. A preliminary semiclassical treatment of the electromagnetic interaction
is introduced. However, the need for a fully quantum mechanical approach is emphasized. Compact Liouville-space
operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors
occurring in a perturbation-theory treatment of the electromagnetic interaction. These expressions can be evaluated for
coherent initial atomic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator
representing the environmental interactions in the Markov approximation. Intense-field electromagnetic interactions can
be treated by means of an alternative method, which is based on a Liouville-space Floquet representation of the reduced
density operator. Collisional interactions between atoms in a vapor can be treated in various approximations for the self-energy
operator and the influence of Zeeman coherences on the electromagnetic response can be incorporated.
Liouville-space (reduced-density-operator) descriptions are developed for resonant and coherent electromagnetic interactions of quantized electronic systems, taking into account environmental decoherence and relaxation phenomena. Applications of interest include electromagnetically-induced transparency and related pump-probe optical phenomena in many-electron atomic systems (in electron-ion beam interactions, gases, and high-temperature plasmas) and
semiconductor materials (bulk crystals and nanostructures). Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. The standard Born (lowest-order perturbationtheory) and Markov (short-memory-time) approximations are systematically introduced within the framework of the general non-perturbative and non-Markovian formulations. A preliminary semiclassical description of the entire electromagnetic interaction is introduced. Compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors occurring in a perturbation-theory treatment of the semiclassical electromagnetic interaction. These expressions can be evaluated for coherent initial electronic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator representing the environmental interactions in the Markov approximation. Intense-field electromagnetic interactions are treated by means of an alternative, non-perturbative method, which is based on a Liouville-space Floquet-Fourier representation of the reduced density operator. Electron-electron quantum correlations are treated by the introduction of a cluster decomposition of the reduced density operator and a coupled hierarchy of reduced-density-operator equations.
We propose a "channelization" architecture to achieve wide-band
electromagnetically induced transparency (EIT) and ultra-slow light
propagation in atomic Rb-87 vapors. EIT and slow light are achieved
by shining a strong, resonant "pump" laser on the atomic medium,
which allows slow and unattenuated propagation of a weaker "signal"
beam, but only when a two-photon resonance condition is satisfied.
Our wideband architecture is accomplished by dispersing a wideband
signal spatially, transverse to the propagation direction, prior to
entering the atomic cell. When particular Zeeman sub-levels are used
in the EIT system, then one can introduce a magnetic field with a
linear gradient such that the two-photon resonance condition is
satisfied for each individual frequency component. Because slow
light is a group velocity effect, utilizing differential phase
shifts across the spectrum of a light pulse, one must then introduce
a slight mismatch from perfect resonance to induce a delay. We
present a model which accounts for diffusion of the atoms in the
varying magnetic field as well as interaction with levels outside
the ideal three-level system on which EIT is based. We find the
maximum delay-bandwidth product decreases with bandwidth, and that
delay-bandwidth product 1 should be achievable with bandwidth 50 MHz
(5 ns delay). This is a large improvement over the 1 MHz bandwidths
in conventional slow light systems and could be of use in signal
processing applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.