Editorial Feature

Spectroscopic Methods for Advanced Imaging Techniques

Volumetric three-dimensional displays are known to offer a spatial accuracy that can represent images with 360° view. However, despite their potential, they have been notoriously difficult to implement due to a complex fabrication process. A Research team from Texas, USA, have now developed a chemically enabled volumetric 3D digital light photoactivatable dye display (3D Light PAD), which is not only efficient, but can be easily fabricated.

Advanced imaging techniques now have the ability to capture high-resolution biological imaging data in 3D. However, digital methods to display said data are currently restricted to 2-dimensions.

The entertainment industry uses three-dimensional (3D) stereoscopic movies, but other sectors, including the sciences, have found little uses for these methods, namely because the image outputs are actually two dimensional (2D) and rely on binocular disparity to trick the brain into seeing a 3D image.

Volumetric 3D displays on the other hand, are a true and spatially accurate 3D platform which is currently expanding through the medical, engineering, architectural, educational and military sectors. Volumetric 3D displays are known to structure light in 3D with a full integration of physical depth cues, inclusive of the accommodation, convergence, motion parallax and binocular disparity cues.

The Texas-based Researchers have created a 3D light pad which uses a special combination of photoactivatable molecules and digital light processing (DLP) technology in order to generate light which is structured in three-dimensions.

The device was fabricated using a photoactivatable (fluorescent switchable) N-phenyl spirolactam rhodamine B dye, a picoprojector, an ultraviolet projector and a custom quartz imaging chamber. The Researchers used a Hitachi F-7000 Spectrophotometer to measure the fluorescence emission of the pad.

The Researchers operated the 3D light pad using small photoactivatable molecules with certain optical properties, whereby they became reversibly fluorescent under ultraviolet (UV) light. These were namely through a non-fluorescent ‘off’ state and fluorescent (or visibly absorbing) ‘on’ state, and were decided through the illumination of a wavelength outside of the visible absorbance spectrum, a fast photoactivation rate and the ability to quickly deactivate into the ‘off’ state.

The tuning of the kinetic and emission wavelengths enabled the Researchers to generate a spatial pattern at the intersection of two structured light beams. The Researchers used the 3D pad to simultaneously activate the fluorophores into an excited state, to produce a spatial pattern by DLP and generate a volumetric 3D image which is both viewable and spatially accurate.

The display pad produced a fast photoactivation, a 415 fold increase with respect to the fluorescence emission a minimum voxel (volume + pixel) size of 0.68 mm3, 200 mm resolution, a high stability throughout multiple ‘on-off’ cycles and a relatively low fabrication cost of under $5000 (for the first-generation prototype).

The pad can be used to project high-resolution images at designated points in a 3D space. Utilizing this, a significant number of objects were rendered by the Researchers, including the 3D structure of the N-phenyl spirolactam rhodamine B dye used in the display.

The Researchers employed an optical slicing strategy to overcome issues surrounding ‘ghost’ voxels (a projected image at a different depth to the actual voxel) and it has been thought that the implementation of improved photoactivatable dyes and DLP projector technologies will increase the impact of this mechanism.

3D animations were produced by projecting a dynamic green light onto a static UV photoactivated pattern. This system was found to have a high refresh rate, no moving parts, use low-power light sources, be inexpensive and have an easy implementation. The properties exhibited in this display show significant advances compare to existing volumetric 3D display technologies.

The 3D Light PAD was found to address a larger number of voxels, with a smaller voxel size, when compared to other recently developed static volume volumetric 3D displays. The pad is also favorable in terms of its voxel size against leading swept-volume rotating screen displays.

The Researchers believe that the future development of these device will allow the scaling up of the internal system itself, with results likely to include a higher number of voxels without the need for high-speed projectors or moving parts.

It is anticipated that this device type, and its associated strategy will be included and applied to the growing number of photoactivatable molecules and DLP chip sets, whilst providing a new avenue for the development and commercialization of readily accessible volumetric 3D displays.


“A volumetric three-dimensional digital light photoactivatable dye display”- Patel S. K., et al, Nature Communications, 2017, DOI: 10.1038/ncomms15239

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