Principle of Tomographic Spectrometer

A tomographic spectrometer captures spatial and spectral information simultaneously by projecting a scene through a dispersive element and reconstructing a 3D hyperspectral datacube from multiple projections.

Basic Concept

A tomographic spectrometer, such as a Computed Tomography Imaging Spectrometer (CTIS), combines the principles of tomography and spectroscopy to obtain a three-dimensional hyperspectral datacube of a scene, where two dimensions represent spatial information and the third represents spectral information . Unlike conventional spectrometers that scan sequentially, CTIS captures all spectral and spatial data in a single snapshot, enabling fast imaging of dynamic scenes.

Optical Layout

The optical system typically consists of:

• Objective lens: Forms an image of the scene.
• Field stop: Limits the field of view to reduce overlapping spectral information.
• Collimating lens: Converts the diverging light from the field stop into parallel rays.
• Dispersive element (grating or prism): Diffracts light into multiple spectral orders, creating projections of the scene at different wavelengths on the detector . The detector records a superimposed pattern of spatial and spectral projections, which can be mathematically interpreted as multiple “mechanical projections” of the theoretical datacube.

Data Acquisition and Reconstruction

The principle of tomography is applied to the spectral data: the recorded projections are analogous to X-ray projections in computed tomography . Each pixel on the detector represents an integral of light intensity along a specific path through the datacube. Using tomographic reconstruction algorithms, such as filtered back projection (FBP) or iterative reconstruction (IR), the system reconstructs the full 3D hyperspectral datacube, resolving both spatial and spectral information .

Applications

Tomographic spectrometers are used in fields requiring high-resolution spectral imaging, including:

• Astronomy: Mapping spectral features of celestial objects.
• Ophthalmology: Imaging retinal structures with spectral contrast.
• Molecular biology: Observing dynamic biochemical processes.
• Military and remote sensing: Detecting materials or chemical signatures .

Summary

The principle of a tomographic spectrometer relies on capturing multiple spectral projections of a scene in a single snapshot and applying tomographic reconstruction to retrieve the full hyperspectral datacube. This approach allows simultaneous acquisition of spatial and spectral information, enabling rapid, non-invasive, and high-resolution imaging across diverse scientific and industrial applications.