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We introduce the scalar average similarity of an ensemble of randomly polarized states. This global measure is based on the complex degree of mutual polarization between any pair of vector fields in the ensemble. We show that, in the case of fully correlated and globally unpolarized fields, the variation of this parameter is bounded, and its value can effectively discriminate between different configurations of pure states.The phase evolution of terahertz (THz) radiation from single-color femotsecond laser-induced air plasma controlled by a DC-bias is investigated experimentally. When the DC-bias is moved from the end to the beginning of the laser plasma filament, the produced THz waveform is advanced temporally, and its carrier-envelope phase is changed. Our phase spectrum analysis suggests that the slope and the intercept of the phase spectrum, respectively, determine the temporal shift and the carrier-envelope phase of the THz waveform. Therefore, the observed THz waveform evolution is mainly due to the THz propagation effect in plasma filament and the Gouy phase shift associated with the detection scheme. This Letter also illustrates explicitly the temporal order of THz radiation from different parts of a filament.Multimode interference (MMI) and self-imaging are important phenomena of diffractive optics with major applications in signal processing, beam shaping, and optical sensing. Such phenomena generally arise from interference of normal modes in lossless dielectric guiding structures; however, the impact of spatially inhomogeneous optical gain and loss, which break mode orthogonality and symmetries, has been overlooked. Here we consider MMI in non-Hermitian optical systems, either graded-index or coupled optical waveguide structures, and reveal distinctive features, such as the absence of mirror images and strong sensitivity of self-imaging to perturbations, making MMI in non-Hermitian waveguides of interest in optical sensing.The availability of nonlinear parametric processes, such as frequency conversion in photonic integrated circuits is essential. In this contribution, we demonstrate a highly tunable second-harmonic generation in a fully complementary metal-oxide-semiconductor (CMOS)-fabrication-compatible silicon nitride integrated photonic platform. We induce the second-order nonlinearity using an all-optical poling technique with the second-harmonic light generated in the fundamental mode, and a narrow quasi-phase matching (QPM) spectrum by avoiding higher-order mode mixing. We are then able to broadly tune the phase-matched pump wavelength over the entire C-band (1540 nm to 1560 nm) by varying the poling conditions. Fine-tuning of QPM is enabled by thermo-optic effect with the tuning slope Δλ/ΔT in our device being 113.8 pm/°C. In addition, we exploit the measurable variation of the 3 dB QPM bandwidth to confirm how the length of the all-optically inscribed grating varies with exposure time.High harmonic spectroscopy utilizes the extremely nonlinear optical process of high-order harmonic generation (HHG) to measure complex attosecond-scale dynamics within the emitting atom or molecule subject to a strong laser field. However, it can be difficult to compare theory and experiment, since the dynamics under investigation are often very sensitive to the laser intensity, which inevitably varies over the Gaussian profile of a typical laser beam. This discrepancy would usually be resolved by so-called macroscopic HHG simulations, but such methods almost always use a simplified model of the internal dynamics of the molecule, which is not necessarily applicable for high harmonic spectroscopy. In this Letter, we extend the existing framework of macroscopic HHG so that high-accuracy ab initio calculations can be used as the microscopic input. This new (to the best of our knowledge) approach is applied to a recent theoretical prediction involving the HHG spectra of open-shell molecules undergoing nonadiabatic dynamics. We demonstrate that the predicted features in the HHG spectrum unambiguously survive macroscopic response calculations, and furthermore they exhibit a nontrivial angular pattern in the far field.Phase-shift-amplified interferometry (PAI) is demonstrated using a heterodyne detection scheme. We demonstrate a sensitivity amplification factor of 35, giving $7.9 \cdot 10^ – 4$7.9⋅10-4 rad, or 40 pm displacement, resolution. This was achieved due to the improved immunity of PAI to the total relative intensity noise (RIN) of the system. In addition, we predict a factor of $\sqrt 2 $2 fundamental improvement to shot-noise-limited phase-shift sensitivity as compared to a regular heterodyne Mach-Zehnder interferometer.Electric-field-induced second-harmonic generation, or E-FISH, has received renewed interest as a nonintrusive tool for probing electric fields in gas discharges and plasmas using ultrashort laser pulses. An important contribution of this work lies in establishing that the E-FISH method works effectively in the nanosecond regime, yielding field sensitivities of about a kV/cm at atmospheric pressure from a 16 ns pulse. This is expected to broaden its applicability within the plasma community, given the wider access to conventional nanosecond laser sources. A Pockels-cell-based pulse-slicing scheme, which may be readily integrated with such nanosecond laser systems, is shown to be a complementary and cost-effective option for improving the time resolution of the electric field measurement. Mizagliflozin price Using this scheme, a time resolution of ∼3  ns is achieved, without any detriment to the signal sensitivity. This could prove invaluable for nonequilibrium plasma applications, where time resolution of a few nanoseconds or less is often critical. Finally, we take advantage of the field vector sensitivity of the E-FISH signal to demonstrate simultaneous measurements of both the horizontal and vertical components of the electric field.In this Letter, we demonstrate a high pulse energy and linearly polarized mid-infrared Raman fiber laser targeting the strongest absorption line of $\rm CO_2$CO2 at $\sim4.2\;\unicode x00B5 \rm m$∼4.2µm. This laser was generated from a hydrogen ($\rm H_2$H2)-filled antiresonant hollow-core fiber, pumped by a custom-made 1532.8 nm Er-doped fiber laser delivering 6.9 ns pulses and 11.6 kW peak power. A quantum efficiency as high as 74% was achieved, to yield 17.6 µJ pulse energy at 4.22 µm. Less than 20 bar $\rm H_2$H2 pressure was required to maximize the pulse energy since the transient Raman regime was efficiently suppressed by the long pump pulses.