Mid‐Infrared Single‐Photon Edge Enhanced Imaging Based on Nonlinear Vortex Filtering

Abstract

Edge enhanced imaging via the spiral phase contrast enables to reveal the phase or amplitude gradients of a target, which has been proved useful in feature recognition, machine vision, and object identification. A long quest is to extend the operation wavelength into the mid‐infrared (MIR) region, as highly demanded in various fields including infrared sensing, astronomic observation, and biomedical diagnosis. Here, ultra‐sensitive MIR imaging at the single‐photon level based on nonlinear frequency upconversion is demonstrated, where the spectrally converted replica of the MIR object image at 3070 nm is captured by a silicon electron multiplying charged coupled device. The imaging sensitivity is significantly improved by the coincidence pulsed pumping with a spectro‐temporal optimization. Furthermore, the edge enhancement is realized by imprinting the spiral phase pattern of the pump onto the upconverted field at the Fourier plane within the nonlinear crystal. Such a nonlinear spatial filter not only provides an effective way to implement the required high‐fidelity vortex screening in the edge enhanced detection, but also renders the MIR illumination into a visible image in an efficient and low‐noise fashion. The presented system for MIR edge enhanced imaging might facilitate immediate applications in label‐free histopathological diagnosis and non‐destructive defect inspection.

Mid-infrared single-pixel imaging at the single-photon level

“…The frequency-upconversion detection provides an effective way to realize the MIR single-photon imaging, as manifested in the infrared upconversion imaging systems based on coherent frequency conversion 42,47,48 or quantum spectral correlation 50,51 , which typically needs a FPA based on electron multiplying charge-coupled devices (EMCCDs). In comparison, the proposed single-pixel scheme offers advantages of single-pixel simplicity and low cost by using a silicon avalanche photodiode at room temperature.…”

“…The involved angular frequencies for the signal, pump and SFG fields satisfy the energy conservation as ω up = ω s + ω p . In practice, the conversion efficiency is usually optimized at the phase-matching condition with Δk z = 0, the SFG intensity is thus simply related to the inner product of the signal and pump intensities, as given by I up (x, y) ∝ I s (x, y) × I p (x, y) 41,42 . Such a relation indicates that the pump intensity pattern serves as a spatial transmission mask onto the MIR object image, and the mask filtered pattern is directly linked to the intensity profile of the upconverted field.…”

Optical Phase Contrast Microscopy with Incoherent Vortex Phase

“…Among these imaging methods, the recently demonstrated optical spatial differentiation shows great advantages owing to its two-dimensional (2D) isotropic edgeenhancement, relatively compact optical configuration, [13] and broad operation band ranging from the visible to the mid-infrared. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Optical spatial differentiation is one of the optical analog signal processing technologies, which is high-speed and low-power consumption with respect to its digital counterparts. In 2017, Zhu et.…”

“…Among these imaging methods, the recently demonstrated optical spatial differentiation shows great advantages owing to its two‐dimensional (2D) isotropic edge‐enhancement, relatively compact optical configuration, [ 13 ] and broad operation band ranging from the visible to the mid‐infrared. [ 2–15 ]…”

Near-Infrared 3D Imaging with Upconversion Detection

“…On the other hand, visible detectors have much lower noise and high sensitivity without the need for cryogenic cooling. Instead of the direct IR imaging, the parametric frequency upconversion imaging [23][24][25] plays a critical role for hyper-spectral IR imaging, where the IR signal is frequency upconverted into visible wavelength [20,[26][27][28][29] and detected by a silicon-based detector or camera with high sensitivity and low noise. Many unique nonlinear optical systems have also been developed for 2D imaging, such as noise-less optical parametric amplification imaging [30,31], non-degenerate two-photon absorption [32][33][34], spontaneous parametric down conversion imaging [35,36].…”