Tom Vettenburg

Light-sheet microscopy using an Airy beam

Light-sheet microscopy facilitates rapid, high-contrast, volumetric imaging with minimal sample exposure. However, the rapid divergence of a traditional Gaussian light sheet restricts the field of view (FOV) that provides innate subcellular resolution. We show that the Airy beam innately yields high contrast and resolution up to a tenfold larger FOV. In contrast to the Bessel beam, which also provides an increased FOV, the Airy beams characteristic asymmetric excitation pattern results in all fluorescence contributing positively to the contrast, enabling a step change for light-sheet microscopy.

Simultaneous determination of the constituent azimuthal and radial mode indices for light fields possessing orbital angular momentum

A wide array of diffractive structures such as arrays of pinholes, triangular apertures, slits, and holograms have all recently been used to measure the azimuthal index of individual Laguerre-Gaussian beams. Here, we demonstrate a powerful approach to simultaneously measure both the radial and azimuthal indices of pure Laguerre-Gaussian light fields using the method of principal component analysis. We find that the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is training any diffracting optical system and transforming the observed pattern into uncorrelated variables. The method is generic and may be extended to other families of light fields such as Bessel or Hermite-Gaussian beams.

A compact Airy beam light sheet microscope with a tilted cylindrical lens

Light-sheet imaging is rapidly gaining importance for imaging intact biological specimens. Many of the latest innovations rely on the propagation-invariant Bessel or Airy beams to form an extended light sheet to provide high resolution across a large field of view. Shaping light to realize propagation-invariant beams often relies on complex programming of spatial light modulators or specialized, custom made, optical elements. Here we present a straightforward and low-cost modification to the traditional light-sheet setup, based on the open-access light-sheet microscope OpenSPIM, to achieve Airy light-sheet illumination. This brings wide field single-photon light-sheet imaging to a broader range of endusers. Fluorescent microspheres embedded in agarose and a zebrafish larva were imaged to demonstrate how such a microscope can have a minimal footprint and cost without compromising on imaging quality.

Wavefront corrected light sheet microscopy in turbid media

Light sheet microscopy is a powerful method for three-dimensional imaging of large biological specimens. However, its imaging ability is greatly diminished by sample scattering and aberrations. Optical clearing, Bessel light modes, and background rejection have been employed in attempts to circumvent these deleterious effects. We present an in situ wavefront correction that offers a major advance by creating an “optimal” light sheet within a turbid sample. Crucially, we show that no tissue clearing or specialized sample preparation is required, and clear improvements in image quality and depth resolution are demonstrated both in Gaussian and Bessel beam-based light sheet modalities.

Fidelity optimization for aberration-tolerant hybrid imaging systems

Several phase-modulation functions have been reported to decrease the aberration variance of the modulation-transfer-function (MTF) in aberration-tolerant hybrid imaging systems. The choice of this phase-modulation function is crucial for optimization of the overall system performance. To prevent a significant loss in signal-to-noise ratio, it is common to enforce restorability constraints on the MTF, requiring trade of aberration-tolerance and noise-gain. Instead of optimizing specific MTF characteristics, we directly minimize the expected imaging-error of the joint design. This method is used to compare commonly used phase-modulation functions: the antisymmetric generalized cubic polynomial and fourth-degree rotational symmetric phase-modulation. The analysis shows how optimal imaging performance is obtained using moderate phase-modulation, and more importantly, the relative merits of the above functions.

Random super-prism wavelength meter.

The speckle pattern arising from a thin random, disordered scatterer may be used to detect the transversal mode of an incident beam. On the other hand, speckle patterns originating from meter-long multimode fibers can be used to detect different wavelengths. Combining these approaches, we develop a method that uses a thin random scattering medium to measure the wavelength of a near-infrared laser beam with picometer resolution. The method is based on the application of principal component analysis, which is used for pattern recognition and is applied here to the case of speckle pattern categorization.

Rotation of two trapped microparticles in vacuum: observation of optically mediated parametric resonances

We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial-light-modulator-based approach to trap more than one particle, induce controlled rotation of individual particles, and mediate interparticle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.

Enhanced cell transfection using subwavelength focused optical eigenmode beams [Invited]

We show that superoscillating light fields, created using the method of optical eigenmodes, enable more efficient multiphoton-mediated cell transfection. Chinese hamster ovary cells are transfected with a plasmid and exhibit expression of DsRed-Mito in the mitochondria. We demonstrate an efficiency improvement of 35% compared to the diffraction-limited spot. This opens up new vistas for nanoscale localized cell transfection.

Holistic optical-digital hybrid-imaging design:wide-field reflective imaging

Reflective imaging systems are typically limited to small field angles in order to avoid overly large obscurations or off-axis aberrations. Reflective optics are often preferred in astronomy due to the associated lower weight and cost, as well as the absence of chromatic aberrations. Although these advantages are compelling, off-axis aberrations typically limit the field of view to a few degrees, while many imaging applications require a considerably larger useful field of view. A hybrid optical-digital design could alleviate the issues associated with wide-field reflective optics by exploiting the larger design freedom inherent in such systems. In this paper we demonstrate how a holistic design approach can enable reflective imaging systems with a consistently sharp image across a wide field of view.

Correction of optical phase aberrations using binary-amplitude modulation

We show that phase aberrations in an imaging system can be mitigated using binary-amplitude masks that reduce destructive interference in the image spatial frequency domain. Appropriately designed masks increase the magnitude of the optical transfer function and prevent nulls. This offers a low-cost, transmission-mode alternative to phase correction as used in active and adaptive optics, without a restriction on the waveband of operation.