Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography—all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.

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.

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We present experimental demonstration and modeling of the optimization of a phase-sensitive optical parametric amplifier by tuning the relative position between the pump-and signal-beam waists along the propagation direction. At the optimum position, the pump beam focuses after the signal beam, and this departure from co-located waists increases with increasing pump power. Such optimization leads to more than 3 dB improvement in the measured de-amplification response of the amplifier. c 2017 Optical Society of America OCIS codes: 190.4410, 230.4320, 230.7020. Optical parametric amplifiers (OPAs) are ubiquitous these days both in pure research and in industrial applications. Hence, it is important to adjust these OPA systems for optimum matching with the input signal and detector modes. In squeezing experiments, a matched local-oscillator (LO) that properly extracts the distorted spatiotemporal squeezed mode can optimize the detected amount of squeezing [1]. In the same spirit, we report here on the performance optimization of an OPA-based system by adjusting the longitudinal offset between the waist locations of the pump and signal beams. We find that the optimal offset is significantly different from zero, contrary to conventional wisdom.In Fig. 1 we show the key elements of the experimental setup. Light from a telecom-band (1560 nm) continuouswave (CW) distributed-feedback (DFB) laser is fed into a pulse carver that outputs an 8 MHz train of 160 ps flattop pulses. These pulses are subsequently amplified by a series of erbium-doped fiber amplifiers (EDFAs) to reach peak powers of >2 kW. This pulsed vertically polarized light is then collimated into a free-space beam and focused into a 1-cm-long periodically-poled potassiumtitanyl-phosphate (PPKTP) crystal for second-harmonic generation (SHG). Conversion efficiencies of >65% produce a pulse train at 780 nm with >1 kW peak power that is then used to pump a 3-cm-long PPKTP-based OPA stage. A small signal to be amplified by the OPA is tapped from the main beam prior to the SHG stage, because after the SHG stage the spatiotemporal mode at 1560 nm is severely distorted due to the high conversion efficiency. Both crystals (Raicol Crystals Ltd.) are poled for type-0 interaction (i.e., all fields are copolarized). The OPA stage is operated as a degenerate OPA (DOPA). Each of the crystals is held at the phase-matching temperature with better than 10 mK stability. The pump and signal beams are combined on a dichroic mirror (DM) and are directed into the OPA crystal. The focusing lens of the pump beam is mounted on a micrometer-controlled translation stage, allowing for fine adjustment of the pump-waist location inside the crystal along the propagation direction. A tap is placed before the crystal, which directs both beams to a spatial profiler (DataRay Inc., model BMS2-CM4-IGA) capable of measuring beam waists down to 1 µm with 0.1 µm accuracy and the focal-point positions with ±1 µm repeatability. The profiler is placed near the focal plane and is used to determine t...