Wide-field super-resolution optical sectioning microscopy using a single spatial light modulator

Structured illumination microscopy with partially coherent illumination for phase and fluorescent imaging

This study presents a partially coherent illumination based (PCI-based) SIM apparatus for dual-modality (phase and fluorescent) microscopic imaging. The partially coherent illumination (PCI) is generated by placing a rotating diffuser on a monochromatic laser beam, which suppresses speckle noise in the dual-modality images and endows the apparatus with sound sectioning capability. With this system, label-free quantitative phase and super-resolved/sectioned fluorescent images can be obtained for the same sample. We have demonstrated the superiority of the system in phase imaging of transparent cells with high endogenous contrast and in a quantitative manner. In the meantime, we have also demonstrated fluorescent imaging of fluorescent beads, rat tail crosscut, wheat anther, and hibiscus pollen with super-resolution and optical sectioning. We envisage that the proposed method can be applied to many fields, including but not limited to biomedical, industrial, chemistry fields.

Optogenetics in Brain Research: From a Strategy to Investigate Physiological Function to a Therapeutic Tool

Dissecting the functional roles of neuronal circuits and their interaction is a crucial step in basic neuroscience and in all the biomedical field. Optogenetics is well-suited to this purpose since it allows us to study the functionality of neuronal networks on multiple scales in living organisms. This tool was recently used in a plethora of studies to investigate physiological neuronal circuit function in addition to dysfunctional or pathological conditions. Moreover, optogenetics is emerging as a crucial technique to develop new rehabilitative and therapeutic strategies for many neurodegenerative diseases in pre-clinical models. In this review, we discuss recent applications of optogenetics, starting from fundamental research to pre-clinical applications. Firstly, we described the fundamental components of optogenetics, from light-activated proteins to light delivery systems. Secondly, we showed its applications to study neuronal circuits in physiological or pathological conditions at the cortical and subcortical level, in vivo. Furthermore, the interesting findings achieved using optogenetics as a therapeutic and rehabilitative tool highlighted the potential of this technique for understanding and treating neurological diseases in pre-clinical models. Finally, we showed encouraging results recently obtained by applying optogenetics in human neuronal cells in-vitro.

Accurate surface profilometry using differential optical sectioning microscopy with structured illumination

A differential optical sectioning microscopy with structured-illumination (DOSM-SI) with enhanced axial precision is explored in this paper for three-dimensional (3D) measurement. As the segment of data on the linear region of the contrast depth response curve (CDR) is very sensitive to variation of the height information, the DOSM-SI introduces a new CDR2 with an axial shift to intersect the linear region of the CDR1, which is achieved by using two charge-coupled detectors (CCDs) in the optical path. The CCD1 is located on the imaging plane and the CCD2 is displaced from the imaging plane. The difference between the CDR1 and CDR2 for each pixel is defined as the differential depth response curve (DCDR). Further, the zero-crossing point of the DCDR for each pixel is accurately extracted using the line-fitting technique, and finally, the sample surface can be reconstructed with a high resolution and precision. Since the slope around the zero-crossing point of the DCDR is apparently larger than that of near the focal position, an enhanced resolution and precision can be realized in DOSM-SI. The experiments and theoretical analysis are elaborated to demonstrate the feasibility of DOSM-SI.

Ultrafast z-scanning for high-efficiency laser micro-machining

High-throughput laser micro-machining demands precise control of the laser beam position to achieve optimal efficiency, but existing methods can be both time-consuming and cost-prohibitive. In this paper, we demonstrate a new high-throughput micro-machining technique based on rapidly scanning the laser focal point along the optical axis using an acoustically driven variable focal length lens. Our results show that this scanning method enables higher machining rates over a range of defocus distances and that the effect becomes more significant as the laser energy is increased. In a specific example of silicon, we achieve a nearly threefold increase in the machining rate, while maintaining sharp side walls and a small spot size. This method has great potential for improving the micro-machining efficiency of conventional systems and also opens the door to applying laser machining to workpieces with uneven topography that have been traditionally difficult to process.

Active computational imaging for circumventing resolution limits at macroscopic scales

Macroscopic imagers are subject to constraints imposed by the wave nature of light and the geometry of image formation. The former limits the resolving power while the latter results in a loss of absolute size and shape information. The suite of methods outlined in this work enables macroscopic imagers the unique ability to capture unresolved spatial detail while recovering topographic information. The common thread connecting these methods is the notion of imaging under patterned illumination. The notion is advanced further to develop computational imagers with resolving power that is decoupled from the constraints imposed by the collection optics and the image sensor. These imagers additionally feature support for multiscale reconstruction.

Improvement of Spatial Resolution for Nonlinear Raman Microscopy by Spatial Light Modulation

The development of a stimulated Raman scattering (SRS) microscope with a wavefront modulation unit is presented. In the apparatus, two beams for introducing the SRS process were focused into the sample with an objective lens. In the pathway of the Stokes beam, which is one of the two incident beams, a spatial light modulator (SLM) was located. Using the SLM, the wavefront of the Stokes beam was modulated to make the shape of the focal point a concentric circular pattern. By this spot shaping technique, the area where the SRS signal generates is restricted. The instrument response function (IRF) of the SRS microscope was examined by measuring the SRS intensity while scanning the sample position. From the result, the width of the IRF was reduced by about 15% by the wavefront modulation. It is suggested that the introduction of SLM is a way to improve the IRF of vibrational spectroscopic microscopes.

Wide-field optical nanoprofilometry using structured illumination

We combine the differential height measurement concept with structured illumination microscopy to develop wide-field optical nanoprofilometry. Sub-diffraction-limit lateral resolution and axially sectioning imaging are achieved with structured illumination using a liquid-crystal spatial light modulator. As the sample surface is placed into the linear region of the sectioning axial response curve, the signal change owing to topographic variations provides nanometer depth sensitivity. The lateral resolution and the depth profiling accuracy are about 0.3 wavelengths and 6 nm, respectively. Depth profiling on solid-state specimens and label-free superresolution imaging of living cells are demonstrated.