Resolution enhancement in laser scanning microscopy with deconvolution switching laser modes (D-SLAM)

Electrically tunable lens with a non-monotonic wavefront control capability

We describe an electrically tunable liquid crystal lens that can produce a rich variety of wavefronts, including sombrero-type (non-monotonic) phase modulation, enabling the focusing of light into a ring-shaped intensity distribution. The lens can also generate axicons or standard spherical lenses with a bipolar response (providing both positive and negative optical powers). The design of the lens requires only a single-step lithography process, dramatically simplifying its manufacturing. We describe various driving modes of this lens and present the first experimental results and discuss its possible applications in miniature cameras and microscopes. We think that this device can revolutionize the optical design in many areas of photonics.

Modulated pattern scanning microscopy

In confocal microscopy, the effective optical transfer function (OTF_eff) with Gaussian plane wave illumination covers very few high-frequency components, which prohibits further improvement of the resolution. We propose modulated pattern scanning microscopy (MPSM) to achieve super-resolution imaging. In MPSM, the phase of the illumination beam is modulated to reassign the OTF_eff in the Fourier domain. The phase mask is designed using an optimization algorithm to obtain the fluorescence emission pattern with rich high-frequency components. Then, the postprocessing algorithms are adapted to retrieve the super-resolved images from the modulated recordings. Simulation and experiment demonstrate that MPSM increases the resolution approximately 1.3 times better than confocal microscopy. Compared with conventional deconvolution, MPSM exhibits a higher signal-to-noise ratio.

Heterochromatic Nonlinear Optical Responses in Upconversion Nanoparticles for Super-Resolution Nanoscopy

Point spread function (PSF) engineering by an emitter's response can code higher-spatial-frequency information of an image for microscopy to achieve super-resolution. However, complexed excitation optics or repetitive scans are needed, which explains the issues of low speed, poor stability, and operational complexity associated with the current laser scanning microscopy approaches. Here, the diverse emission responses of upconversion nanoparticles (UCNPs) are reported for super-resolution nanoscopy to improve the imaging quality and speed. The method only needs a doughnut-shaped scanning excitation beam at an appropriate power density. By collecting the four-photon emission of single UCNPs, the high-frequency information of a super-resolution image can be resolved through the doughnut-emission PSF. Meanwhile, the two-photon state of the same nanoparticle is oversaturated, so that the complementary lower-frequency information of the super-resolution image can be simultaneously collected by the Gaussian-like emission PSF. This leads to a method of Fourier-domain heterochromatic fusion, which allows the extended capability of the engineered PSFs to cover both low- and high-frequency information to yield optimized image quality. This approach achieves a spatial resolution of 40 nm, 1/24th of the excitation wavelength. This work suggests a new scope for developing nonlinear multi-color emitting probes in super-resolution nanoscopy.

Resolution enhancement in an extended depth of field for volumetric two-photon microscopy

The resolution enhancement over the extended depth of field (DOF) in the volumetric two-photon microscopy (TPM) is demonstrated by utilizing multiple orders of Bessel beams. Here the conventional method of switching laser modes (SLAM) in 2D is introduced to 3D, denoted as the volumetric SLAM (V-SLAM). The equivalent scanning beam in the TPM is a thin needle-like beam, which is generated from the subtraction between the needle-like 0th-order and the straw-like 1st-order Bessel beams. Compared with the 0th-order Bessel beam, the lateral resolution of the V-SLAM is increased by 28.6% and maintains over the axial depth of 56 µm. The V-SLAM performance is evaluated by employing fluorescent beads and a mouse brain slice. The V-SLAM approach provides a promising solution to improve the lateral resolutions for fast volumetric imaging on sparsely distributed samples.

Simultaneous label-free autofluorescence-multiharmonic microscopy and beyond

Without sophisticated data inversion algorithms, nonlinear optical microscopy can acquire images at subcellular resolution and relatively large depth, with plausible endogenous contrasts indicative of authentic biological and pathological states. Although independent contrasts have been derived by sequentially imaging the same sample plane or volume under different and often optimized excitation conditions, new laser source engineering with inputs from key biomolecules surprisingly enable real-time simultaneous acquisition of multiple endogenous molecular contrasts to segment a rich set of cellular and extracellular components. Since this development allows simple single-beam single-shot excitation and simultaneous multicontrast epidirected signal detection, the resulting platform avoids perturbative sample pretreatments such as fluorescent labeling, mechanical sectioning, scarce or interdependent contrast generation, constraints to the sample or imaging geometry, and intraimaging motion artifacts that have limited in vivo nonlinear optical molecular imaging.