Spontaneous parametric down-conversion can produce pairs of entangled photons with very different wavelengths. Using SPDC, the scheme of Imaging with Undetected Photons promises to be a versatile tool to facilitate imaging in various spectral ranges and various interferometer designs and geometries. Here, we tackle the task of Imaging with Undetected Photons with a Mach-Zehnder-type Interferometer in MIR. With imaging achieved in a preliminary setup, we investigate the limitations set by nonlinear conversion efficiencies, optical resolution, laser power, and fluorescence of optics on our way to Imaging with Undetected Photons in MIR.
Spontaneous parametric down-conversion can produce pairs of entangled photons with very different wavelengths. Using SPDC, the scheme of Imaging with Undetected Photons promises to be a versatile tool to facilitate imaging in various spectral ranges and various interferometer designs and geometries. Here, we tackle the task of Imaging with Undetected Photons with a Mach-Zehnder-type Interferometer in MIR. With imaging achieved in a preliminary setup, we investigate the limitations set by nonlinear conversion efficiencies, optical resolution, laser power, and fluorescence of optics on our way to Imaging with Undetected Photons in MIR.
Sensing applications in the mid-infrared (MIR) spectral range are challenging due to the high cost and low performance of the available light sources and detectors. This issue can be bypassed by utilizing the process of spontaneous parametric down-conversion (SPDC) to generate tailored MIR-NIR photon-pairs. The nature of SPDC enforces the generation of frequency-entanglement between these paired photons which can be used for spectroscopy: Within a nonlinear interferometric configuration, the MIR radiation is employed for the illumination of a specific material, whereas the NIR radiation is analyzed using a conventional spectrometer. This technique, which is referred to as sensing with ”undetected photons”, so far relied on a breadboard optical setup that is both space-consuming, heavy and complex. Here we present the design, manufacturing and application of a miniaturized quantum light module, with a footprint of less than 80 x 60 mm², which is powered by a direct emitting diode laser at 720 nm. The module contains the nonlinear crystal as the quantum light source, the optical path for the NIR beam, and mechanical connectors leading to the MIR sensing arm. It also provides an interconnection to a spectrometer for the information-carrying NIR photons. This study presents insights into the optical design of the module, its manufacturing and the nonlinear optics quantum light source. The module emits a MIR-NIR photon-pair rate of 1.7 × 109 s−1 W−1, which allows for the implementation of time-efficient sensing applications. The design is optimized for a first application - the detection of synthetic polymers in aqueous solutions, which will be illustrated by concepts for the detection of micro-plastics in wastewater in the field with a mobile device. The potential for integrating a sophisticated, non-linear optical interference configuration into a user-friendly micro-module paves the way for the development of industry-ready setups. This enables a variety of other applications, which are covered by sensing with undetected photons.
We present principles of quantum imaging with undetected photons (QIUP) and show modifications we made to the nonlinear interferometer for QUIP in order to use off-axes holography for faster image reconstruction. We present images made by off-axes quantum holography (OAQH) and discuss image capabilities of the system. In this work we use a pair of quantum correlated photons, generated by spontaneous parametric down-conversion in a non-linear crystal; one photon form a pair interacts with object, and another is detected. In our system both photons are in near infra-red, but by slight modifications they will be in different spectral regions, interacting photons in mid infra-red, detected photons in visible or near infra-ed. This opens very useful applications of QIUP for imaging and sensing in MIR.
Quantum sensing in the infrared regime often demands the use of expensive and cryogenically operated detectors. Nonlinear interferometry has paved the way for information transfer from the infrared to the near--infrared or visible regime in various quantum technologies. A particularly interesting application of these interferometers involves spectrally--resolved quantum imaging using undetected photons, enabled by the use of temperature--tunable parametric amplifiers. In this work, we demonstrate spectrally resolved transmission imaging with undetected photons around 1550 nm using a spontaneous parametric down conversion based folded nonlinear interferometric scheme, registering the attenuation of a zebrafish larva as a biological feasibility test. We characterize and calibrate the interferometer, having achieved spectrally resolved interference fringes with a maximum baseline visibility of ∼74% in the near--infrared regime. Phase--stepped readout of a grating spectrometer gives a resolving power of ∼1460 (from the spectrometer's point spread function) at 1550 nm, and ∼730 from the coherence length, the finest reported for imaging with undetected photons, over an instantaneous spectral window of ≈51 cm−1.
Metrology with undetected photons is an emerging technique that leverages quantum effects and photon correlations (entanglement) to retrieve valuable information in a target spectral range (e.g., mid-infrared, mid-IR) using measurements in an easily accessible domain (e.g., visible, near-IR). The underlying quantum process of spontaneous parametric down-conversion (SPDC) is utilized to generate non-degenerate correlated signal and idler photons to serve as detection and probing photons, respectively. Sensing with undetected photons enables important advantages, such as ultra-low probe powers, room-temperature operation, and shot-noise-limited detection. In this contribution, we apply a quantum nonlinear interferometer based on an SPDC source to perform applied mid-IR spectroscopy, mid-IR microscopy, and mid-IR optical coherence tomography (OCT) as among the most promising techniques for quantum-based routine non-destructive testing. Moreover, we characterize the system, benchmark it against classical systems, and provide a prospective outlook for this new technology.
Quantum imaging with undetected photons allows for imaging an object by detecting photons that never interacted with it, using the correlation between photon pairs generated in the process of spontaneous parametric down conversion (SPDC) [1] . Through SPDC in a χ (2) material, a pump (P) photon of wavelength λ P can split into a pair of signal (S) and idler (I) photons, such that 1/ λ P = 1/ λ S + 1/ λ I . In such imaging schemes, the object’s optical properties at λ I , such as its absorption profile, can be inferred by only imaging the signal photons. Thus, one can image in challenging spectral ranges, such as mid-IR for λ I , using detectors in the visible for λ S [1] . In this scheme, the resolution is fundamentally diffraction-limited to the wavelength that interacts with the object, λ I [2] . We show that one can go beyond this diffraction limit by placing the object in the near-field of a subwavelength thin SPDC source, as shown schematically in Fig. 1(a) , through transferring the near-field information at λ I into propagating modes at λ S that can be detected in the far field. In this scheme, the resolution of imaging the object at λ I is determined by the detected signal wavelength λ S . As an application, we numerically demonstrate how two closely-spaced small scatterers at mid-IR can be resolved with a visible-range resolution.
Imaging via nonlinear interferometers make use of induced coherence and take advantage of photon pair correlations to image an object without detecting the photons that illuminate the object [1]. The object's information is transferred from the photon that illuminates the object to the interference pattern of its partner photon, which is detected [2]. Spontaneous parametric down conversion allows to utilize photon pairs with large spectral separation. This fact becomes relevant if we need to image at wavelengths with detection constraints, e.g., mid-infrared, hyperspectral, or terahertz wavelengths [3], [4].