A Method to Correct the Temporal Drift of Single-Photon Detectors Based on Asynchronous Quantum Ghost Imaging.

Single-photon detection and timing has attracted increasing interest in recent years due to their necessity in the field of quantum sensing and the advantages of single-quanta detection in the field of low-level light imaging. While simple bucket detectors are mature enough for commercial applications, more complex imaging detectors are still a field of research comprising mostly prototype-level detectors. A major problem in these detectors is the implementation of in-pixel timing circuitry, especially for two-dimensional imagers. One of the most promising approaches is the use of voltage-controlled ring resonators in every pixel. Each of these runs independently based on a voltage supplied by a global reference. However, this yields the problem that the supply voltage can change across the chip which, in turn, changes the period of the ring resonator. Due to additional parasitic effects, this problem can worsen with increasing measurement time, leading to drift in the timing information. We present here a method to identify and correct such temporal drifts in single-photon detectors based on asynchronous quantum ghost imaging. We also show the effect of this correction on recent quantum ghost imaging (QGI) measurement from our group.

3D quantum ghost imaging.

We present current results of a novel, to the best of our knowledge, type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors, first presented in [Appl. Opt.60, F66 (2021)APOPAI0003-693510.1364/AO.423634]. The scheme enables photon pairing without fixed delays and, thus, overcomes some limitations of the widely used heralded setups for quantum ghost imaging [Nat. Commun.6, 5913 (2015)NCAOBW2041-172310.1038/ncomms6913]. It especially allows three-dimensional (3D) imaging by direct time of flight methods, the first demonstration of which will be shown here. To our knowledge, it is also the first demonstration of 3D quantum ghost imaging at all.

Using Multi-Dimensional Dynamic Time Warping to Identify Time-Varying Lead-Lag Relationships.

This paper develops a multi-dimensional Dynamic Time Warping (DTW) algorithm to identify varying lead-lag relationships between two different time series. Specifically, this manuscript contributes to the literature by improving upon the use towards lead-lag estimation. Our two-step procedure computes the multi-dimensional DTW alignment with the aid of shapeDTW and then utilises the output to extract the estimated time-varying lead-lag relationship between the original time series. Next, our extensive simulation study analyses the performance of the algorithm compared to the state-of-the-art methods Thermal Optimal Path (TOP), Symmetric Thermal Optimal Path (TOPS), Rolling Cross-Correlation (RCC), Dynamic Time Warping (DTW), and Derivative Dynamic Time Warping (DDTW). We observe a strong outperformance of the algorithm regarding efficiency, robustness, and feasibility.

Formation of spiraling infrared emission patterns by controlled interaction of optical filaments.

We analyzed the formation of mid-infrared conical emission patterns possessing spiral and half-ring shaped wavelength contours from a beam of a few optical filaments. The complex patterns were generated and modified experimentally by adaptive wavefront shaping of the femtosecond laser pulse. Mutual interactions between co-propagating filaments can induce curvature in their paths, and the spiral and half-ring emissions were shown to be a direct consequence of this angular deflection. Based on our experimental and computational results, the spirals form in the far-field due to self-interference of conical emission from a helically moving filament. The presented findings will advance the tailoring of spatial conical emission patterns potentially beneficial for spectroscopic applications and terahertz generation.

Quantum ghost imaging using asynchronous detection.

We present first results of a novel type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors. This scheme enables photon pairing with arbitrary path length difference and does, therefore, obviate the dependence on optical delay lines of current quantum ghost imaging setups [Nat. Commun.6, 5913 (2015)NCAOBW2041-172310.1038/ncomms6913]. It is also, to our knowledge, the first quantum ghost imaging setup to allow three-dimensional imaging.

Emissions from single filaments in air triggered by tailored background energy flows.

We investigated emission patterns from single or few filaments in air created by femtosecond laser pulses with spatially modulated wavefronts. For 800 nm filaments, spiral emissions can be obtained in the infrared. Time-resolved analysis of the corresponding dynamics of the energy surrounding the filament reveals stable energy flows with angular momentum that interact with the filament and with each other. Changing this energy distribution by modulation of the wavefront of the initial laser pulse directly affects the emission behavior of the filament.

Emission of spiral patterns from filaments in the infrared.

We investigated the spectral and spatial properties of the supercontinuum emission of single filaments in air in the infrared (1.5 µm-5.3 µm). The infrared emission of the filament was controlled by modulating the spatial phase of the femtosecond driver pulse with a deformable mirror. Filaments with a characteristic spiral emission pattern in the infrared were generated for a variety of different wavefront profiles of the femtosecond pulse. The properties of this novel class of emission were analyzed more closely. Further understanding of the corresponding emission dynamics of the filament will help to refine current models of filament propagation.

Towards optimal control with shaped soft-x-ray light.

We demonstrate the first example of a closed-loop adaptive control experiment in the soft-x-ray spectral region. The branching ratio of the dissociative photoionization of sulfur hexafluoride (SF(6)) can be maximized and minimized by applying tailored soft-x-ray femtosecond light fields. The spectrally shaped coherent soft-x-ray pulses are produced by high-harmonic generation driven by phase-shaped femtosecond laser pulses. The stability of the shaped high-harmonic output is high enough to perform adaptive control experiments, albeit its strong nonlinear dependence on the driving laser pulse shape. This experiment opens the door to the application of pulse-shaping and coherent-control techniques in the soft-x-ray range.

Spatial control of high-harmonic generation in hollow fibers.

We demonstrate the control of high-harmonic generation in a hollow fiber by shaping the spatial structure of the generating laser pulse. We use a liquid-crystal-based two-dimensional spatial light modulator to control the spatial phase of the driver pulse. An evolutionary algorithm finds the spatial laser phase distribution that is optimal for reaching maximum total harmonic yield and for selectively enhancing the cutoff region of the spectrum. We show that enhacement of harmonic generation is related to coupling into a single fiber mode. Our results directly show that spatial properties of the laser are important parameters in fully controlling the high-harmonic spectrum. It is thus not possible to derive the controllability of the high-harmonic generation from the single-atom response only.