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.