Single-Shot Multispectral Mid-Infrared Imaging with Incoherent Light via Adiabatic Upconversion

Abstract

Multispectral mid-infrared (2-5 ${μm}$) imaging is a critical capability across science and technology, offering a window into the vibrational and thermal landscape of matter that is inaccessible to visible sensors. It bridges the microscopic world of molecular interactions with macroscopic sensing technologies, with applications in environmental sensing, defense and molecular diagnostics. However, current mid-IR cameras require cryogenic cooling and exhibit limited pixel resolution, high cost, and restricted spectral access. Optical up-conversion provides a pathway to overcome these limitations, but existing systems typically rely on narrowband phase matching, mechanical scanning, or angular tuning, limiting imaging speed and practicality. Here, we demonstrate the first single-shot, room-temperature multispectral mid-IR imaging of incoherent thermal light enabled by adiabatic sum-frequency conversion. Our system simultaneously converts the entire (2-5 ${μm}$) region into the visible domain, capturing the image on a Silicon detector with spatial resolution below 20 ${μm}$ and high angular tolerance. We validate full-field imaging using a USAF resolution target and demonstrate spectroscopic contrast imaging in dielectric metamaterials by resolving wavelength and polarization dependent scattering resonances, all achieved without scanning, thermal control, or cryogenic operation. This compact and robust approach bridges the gap between laboratory-grade infrared sensors and scalable Silicon-based detection technologies suitable for real-world deployment.

Figures (4)

• Figure 1: Broadband adiabatic up-conversion imaging system for incoherent mid-IR illumination.a Schematic of the single-shot imaging setup. Broadband incoherent (thermal) radiation from a black-body source ($\sim2–5\;\mu m$) illuminates the sample and is relayed through a 4f system. A Q-switched $1064\;nm$ pump beam is combined with the mid-IR image at a dichroic mirror and focused into an adiabatically poled Lithium-Niobate crystal, where sum-frequency generation (SFG) converts the mid-IR spatial information into the visible–near-infrared (VIS–NIR) domain. A second dichroic mirror removes residual mid-IR and pump light, and the up-converted image is recorded on a room-temperature Silicon EMCCD. A VIS–NIR filter wheel enables spectral selection without any mechanical scanning in the mid-IR. b Energy-conservation diagram showing up-conversion of a broad mid-IR spectrum into a narrower VIS–NIR band through interaction with the $1064\; nm$ pump. c Conceptual demonstration of multispectral imaging: band-pass filtering in the VIS–NIR reveals different spectral features of the mid-IR scene from a single captured frame.
• Figure 2: Multispectral mid-IR imaging of a USAF resolution target using visible-band filtering. a Single-shot upconverted mid-IR image of a 1951 USAF resolution test chart, obtained by capturing the entire $\sim 2–5\;\mu m$ band simultaneously. Wavelength-dependent magnification leads to blurring of the finest features in the full-spectrum image. b–d Narrowband VIS–NIR filtering of the up-converted image isolates different regions of the mid-IR spectrum, improving image quality as chromatic dispersion is reduced. Insets show zoomed views of the smallest resolvable features, along with the corresponding portion of the mid-IR illumination spectrum mapped to the filter passband. Effective mid-IR center wavelengths and bandwidths (FWHM) are indicated below each panel. These measurements demonstrate near-diffraction-limited ($<20\;\mu m$) resolution over a wide mid-IR spectral range without mechanical or thermal scanning.
• Figure 3: Multispectral imaging of mid-infrared Mie resonance metamaterials.a Illustration and characterization of the metamaterial sample. Four different designs of nanostructure arrays have been fabricated on a Sapphire subsrate. A fifth array, marked with an additional 'IV' label, is a duplicate of the same design. For a single unit cell, the critical dimensions of each of the designs is presented. These dimensions influence the central wavelength and shape of the mid-IR resonance and are elaborated in the Methods section. Additionally, scanning electron microscope images of the nanostructure array and a single unit cell are also provided. b Narrowband VIS–NIR filtering of the up-converted image demonstrates a strong scattering response from individual nanostructure arrays, in correlation with their typical resonance peaks. For each of the filtered up-converted images, the corresponding spectral region of the illumination is highlighted. This clearly demonstrates the spectroscopic imaging capabilities of the system.
• Figure 4: Polarization-dependent response of mid-infrared Mie-resonant metasurfaces.a Spectrally filtered upconverted images of the nanostructure arrays recorded at $810\; nm$ ($10\; nm$ FWHM) for different sample rotation angles, revealing polarization-dependent scattering contrast. The inset indicates the corresponding effective mid-IR spectral range selected by the visible-domain filtering. b Lumerical FDTD simulations of the polarization-resolved spectral response of the all-dielectric nanostructures (design II), showing a resonance that is strongest for a polarization angle of $0^\circ$ and progressively weakens as the polarization is rotated.