3 Minutes
Ancient pinhole idea, modern laser optics
Researchers at East China Normal University have reworked a centuries-old imaging concept into a high-performance, lensless mid‑infrared (mid‑IR) camera capable of producing sharp 2D and 3D images across a wide depth range. Instead of glass optics, the system uses a focused laser to create an "optical pinhole" inside a nonlinear crystal and simultaneously upconverts mid‑IR light into visible wavelengths that standard silicon sensors can read.
Why this matters
Mid‑infrared wavelengths carry valuable information — thermal signatures, molecular absorption features and other cues that are hard to see in visible light. Yet conventional mid‑IR cameras are often bulky, noisy, expensive, or require cryogenic cooling. The new lensless approach promises a simpler optical path, large depth of field and reduced noise through upconversion detection, which could lower cost and power needs over time.
"We developed a high‑sensitivity, lens‑free approach that delivers a much larger depth of field and field of view than other systems," says team lead Heping Zeng. Colleague Kun Huang adds that the technique could be extended to far‑IR or terahertz ranges where traditional lenses are challenging to make.
How it works
A synchronized ultrafast laser pulse forms a tiny effective aperture — an "optical pinhole" roughly 0.20 mm in radius — inside a specially engineered nonlinear crystal. That crystal performs frequency upconversion: it mixes the incoming mid‑IR scene with the laser pulse so the mid‑IR image is converted into visible light. Because the crystal is manufactured with a chirped periodic structure, it accepts light from a wide range of angles, producing a broad field of view and enabling distortion‑free imaging.
Key experimental highlights:
- Sharp mid‑IR images at a wavelength of 3.07 μm
- Depth of field maintained beyond 35 cm
- Field of view exceeding 6 cm
- Effective imaging with input as low as ~1.5 photons per pulse after denoising
3D imaging modes
The researchers demonstrated two 3D methods: time‑of‑flight reconstruction using ultrashort pulse gating to achieve micron‑level axial precision, and a simpler two‑snapshot depth measurement that infers depth from images taken at slightly different object distances. Both techniques work without conventional lenses and require relatively few photons.
Use cases, advantages and limits
Potential applications include night‑time surveillance, industrial inspection, and environmental monitoring where mid‑IR contrast matters. Advantages include low distortion, wide depth of field, compatibility with standard silicon detectors, and intrinsic noise suppression via upconversion.
Limitations remain: current setups use bulky synchronized lasers and lab‑grade nonlinear crystals, so the system is still a proof‑of‑concept. The team is working on higher conversion efficiency, dynamic control of the optical aperture, and more compact integrated light sources that could make commercial deployment more practical.
Ultimately, the method points to a path where lensless mid‑IR and terahertz imaging become more accessible, opening new options for portable, energy‑efficient sensors in security, manufacturing and remote sensing.
Source: scitechdaily
Comments