The use of exotic optical modes is becoming increasingly widespread in microscopy. Particularly, propagation-invariant beams, such as Airy and Bessel beams and optical lattices, have been particularly useful in light-sheet fluorescence microscopy (LSFM) as they enable high-resolution imaging over a large field-of-view (FOV), possess a resistance to the deleterious effects of specimen induced light scattering, and can potentially reduce photo-toxicity.
Although these propagation-invariant beams can resist the effects of light scattering to some degree, and there has been some interest in adaptive-optical methods to correct for beam aberrations when they cannot, scattering and absorption of the illuminating light-sheet limit the penetration of LSFM into tissues and results in non-uniform intensity across the FOV.
A new degree of control over the intensity evolution of propagation-invariant beams can overcome beam losses across the FOV, restoring uniform illumination intensity and therefore image quality. This concept is compatible with all types of propagation-invariant beams and is characterised in the context of light-sheet image quality.
Another property to control is the wavelength of light used. Optical transmission through tissue is greatly improved at longer wavelengths into the near-infrared due to reduced Rayleigh scattering and two-photon excitation has proved beneficial for imaging at greater depth in LSFM. Three-photon excitation has already been demonstrated as a powerful tool to increase tissue penetration in deep brain confocal microscopy, and when combined with beam shaping can also be a powerful illumination strategy for LSFM.
Recent progress in shaping optical fields for LSFM will be presented.
Light sheet fluorescent microscopy is able to provide high acquisition speed and high contrast images, as well as the low photo-bleaching and photo-damage brought to the sample. Here we describe a compact setup design optimized for applications in neuroscience, in particular fast imaging of sub-neuronal structures in mammalian brain slices. We report this prototype instrument is capable of rapid imaging wide area of the dendritic or axonal arbor of a dye-filled neuron in hippocampal slice. We also show several applications of this compact light sheet fluorescent microscope, to demonstrate that our approach offers a powerful functionality to the neuroscience community that is not achievable with traditional imaging methods.
Biological research requires high-speed and low-damage imaging techniques for live specimens in areas such as development study in embryos. Light sheet microscopy provides fast imaging speed whilst keeps the photo-damage and photo-blenching to minimum. Conventional sample embedding methods in light sheet imaging involves using agent such as agarose which potentially affects the behavior and the develop pattern of the specimens. Here we demonstrate integrating dual-beam trapping method into light sheet imaging system to confine and translate the specimen whilst light sheet images are taken. Tobacco plant cells as well as <i>Spirobranchus lamarcki </i>larva were trapped solely with optical force and sectional images were acquired. This now approach has the potential to extend the applications of light sheet imaging significantly.
We experimentally demonstrate continuous attraction of macroscopic targets (> 1 cm) towards the source, against a net momentum flux in the system. Use of a simple setup provides an easily understood illustration of the negative radiation pressure concept for tractor beam, and how these are distinct from the gradient
force acting in conventional optical tweezers. Here, we map out regimes over which
negative radiation forces dominate, and (favorably) compare the thresholds observed to those that emerge from simulations. Theoretical explorations of tractor beam action commonly invoke higher-order Bessel beams, and here we make clear that the reason for this is because of the reduction in axial momentum associated with such hollow-core beams, which allows effects associated with off-axis “skew” momentum to become dominant. Ultimately, there is interest in exploring the language used for describing such effects: radiation pressure versus gradient force (which we suggest might be better described in terms of non‐conservative versus conservative forces), and “orbital” angular momentum (which we suggest might be more appropriately termed “topological” angular momentum).
When samples of interest are small enough, even the relatively weak forces and torques associated with
<i>light</i> can be sufficient for mechanical manipulation, can offer extraordinary position control, and can
measure interactions with three orders of magnitude better resolution than atomic force microscopy.
However, as the components of interest grow to slightly larger length scales (which may yet be of interest
for microfluidic, "lab-on-a-chip" technologies and for research involving biomedical imaging), other
approaches gain strength. This paper includes discussion of the angular momentum carried by sonic beams
that we have implemented both to levitate and controllably rotate disks as large as four inches across.
Discussion of such acoustic beams complements the discussion of the angular momentum carried by light
and, by further analogy, how we view stationary states discussed in quantum mechanics. Hence, a primary
use of the sonic screwdriver is as a model system, although these beams are useful for a variety of other
reasons as well (not least for aberration correction for ultrasonic array systems). Methods, including the use
of holographically structured fields, are discussed.