
Spectroscopy techniques for non-invasive imaging, such as in medical or archaeological applications.Non-destructive imaging spectroscopy combines spectroscopy with imaging to create detailed maps of a sample's composition and properties without damaging it. This is crucial in medicine, archaeology, and materials science, where the object of interest is valuable or fragile. The technique uses light of different wavelengths to probe the sample, and the resulting spectral information is used to construct an image that reveals hidden structures, chemical gradients, or defects.
The concept dates back to the early 20th century with the development of X-ray spectroscopy, but non-destructive imaging spectroscopy became practical with the advent of digital detectors and computers in the 1970s and 1980s. The use of quantum-correlated light for imaging is a recent development from the 2010s.
The approach typically involves illuminating the sample with light (or other radiation) and measuring the reflected, transmitted, or emitted spectrum at each point. For example, in near-infrared spectroscopy, light penetrates tissue and is absorbed differently by bone, fat, and water, allowing a 3D map of bone density to be built. In X-ray fluorescence, the characteristic X-rays emitted by different elements are used to map their distribution in an artifact. Advanced methods, like quantum-correlated spectroscopy, use entangled photons to enhance sensitivity, allowing detection of tiny amounts of material, such as microplastics in water, without altering the sample.
Used in medical diagnostics to assess bone fragility, in archaeology to analyze pigments in ancient artifacts without sampling, and in environmental science to detect microplastics in water.
A technique called 'photoacoustic imaging' uses a short laser pulse to heat tissue, which then emits ultrasound waves — the resulting image can show blood vessels in real time, and the same principle is used to detect tumors.
| B | variable | Bispectrum of curvature perturbations — bispectrum |
| k_1, k_2, k_3 | variable | Wavenumbers of three modes — wavenumber reciprocal metre |
| f_{NL} | variable | Nonlinearity parameter — nonlinearity parameter |
| P | variable | Power spectrum of curvature perturbations — power spectrum |








