Ayano Tanabe

In-line FINCH super resolution digital holographic fluorescence microscopy using a high efficiency transmission liquid crystal GRIN lens

We report a new optical arrangement that creates high-efficiency, high-quality Fresnel incoherent correlation holography (FINCH) holograms using polarization sensitive transmission liquid crystal gradient index (TLCGRIN) diffractive lenses. In contrast, current universal practice in the field employs a reflective spatial light modulator (SLM) to separate sample and reference beams. Polarization sensitive TLCGRIN lenses enable a straight optical path, have >90% transmission efficiency, are not pixilated, and are free of many limitations of reflective SLM devices. For each sample point, two spherical beams created by a glass lens in combination with a polarization sensitive TLCGRIN lens interfere and create a hologram and resultant super resolution image.

Performance of a q-plate tunable retarder in reflection for the switchable generation of both first- and second-order vector beams

We examine the performance of a tunable liquid crystal q-plate in a reflective geometry. When the device is tuned to a half-wave retardance, it operates as a q-plate with twice the value (2q) by adding a quarter-wave retarder between the mirror and the q-plate. However, when the device is tuned to a quarter-wave retardance, it acts as the original q-plate without the retarder. Experimental results are shown. Using an input tunable polarization state generator, the system allows the switchable production of all states on both the first- and second-order Poincaré spheres.

Correcting spherical aberrations in a biospecimen using a transmissive liquid crystal device in two-photon excitation laser scanning microscopy

Abstract. Two-photon excitation laser scanning microscopy has enabled the visualization of deep regions in a biospecimen. However, refractive-index mismatches in the optical path cause spherical aberrations that degrade spatial resolution and the fluorescence signal, especially during observation at deeper regions. Recently, we developed transmissive liquid-crystal devices for correcting spherical aberration without changing the basic design of the optical path in a conventional laser scanning microscope. In this study, the device was inserted in front of the objective lens and supplied with the appropriate voltage according to the observation depth. First, we evaluated the device by observing fluorescent beads in single- and two-photon excitation laser scanning microscopes. Using a 25× water-immersion objective lens with a numerical aperture of 1.1 and a sample with a refractive index of 1.38, the device recovered the spatial resolution and the fluorescence signal degraded within a depth of ±0.6  mm. Finally, we implemented the device for observation of a mouse brain slice in a two-photon excitation laser scanning microscope. An optical clearing reagent with a refractive index of 1.42 rendered the fixed mouse brain transparent. The device improved the spatial resolution and the yellow fluorescent protein signal within a depth of 0–0.54 mm.

Generation of vector beams at 1550 nm telecommunications wavelength using a segmented q-plate

We present the use of a q -plate device operating at the 1550 nm telecommunications wavelength. A prototype liquid-crystal device from Citizen Holdings Co. is demonstrated to be useful for the generation of vector beams and orbital angular momentum transfer at this important wavelength.

Observation of PDLCs by SHG laser scanning microscopy using a liquid crystal vector beam generator

We have succeeded in observing the structure of the polymer-dispersed liquid crystal cell using SHG laser scanning microscopy combined with the Z polarization generator we have developed. The SHG phenomenon should occur in the boundary between LC molecules and the polymer surface where the inversion symmetry of LC molecules is lost. This method has the advantage of non-destructive measurement compared with the SEM imaging method.

Optical coherence tomography with a 2.8-mm beam diameter and sensorless defocus and astigmatism correction

Abstract. An optical coherence tomography (OCT) system with a 2.8-mm beam diameter is presented. Sensorless defocus correction can be performed with a Badal optometer and astigmatism correction with a liquid crystal device. OCT B-scans were used in an image-based optimization algorithm for aberration correction. Defocus can be corrected from −4.3  D to +4.3  D and vertical and oblique astigmatism from −2.5  D to +2.5  D. A contrast gain of 6.9 times was measured after aberration correction. In comparison with a 1.3-mm beam diameter OCT system, this concept achieved a 3.7-dB gain in dynamic range on a model retina. Both systems were used to image the retina of a human subject. As the correction of the liquid crystal device can take more than 60 s, the subject’s spectacle prescription was adopted instead. This resulted in a 2.5 times smaller speckle size compared with the standard OCT system. The liquid crystal device for astigmatism correction does not need a high-voltage amplifier and can be operated at 5 V. The correction device is small (9  mm×30  mm×38  mm) and can easily be implemented in existing designs for OCT.

Transmissive liquid-crystal device correcting primary coma aberration and astigmatism in laser scanning microscopy

Laser scanning microscopy allows 3D cross-sectional imaging inside biospecimens. However, certain aberrations produced can degrade the quality of the resulting images. We previously reported a transmissive liquid-crystal device that could compensate for the predominant spherical aberrations during the observations, particularly in deep regions of the samples. The device, inserted between the objective lens and the microscope revolver, improved the image quality of fixed-mouse-brain slices that were observed using two-photon excitation laser scanning microscopy, which was originally degraded by spherical aberration. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism, motivated by the fact that these asymmetric aberrations can also often considerably deteriorate image quality, even near the sample surface. The devices performance was evaluated by observing fluorescent beads using single-photon excitation laser scanning microscopy. The fluorescence intensity in the image of the bead under a cover slip tilted in the y-direction was increased by 1.5 times after correction by the device. Furthermore, the y- and z-widths of the imaged bead were reduced to 66% and 65%, respectively. On the other hand, for the imaged bead sucked into a glass capillary in the longitudinal x-direction, correction with the device increased the fluorescence intensity by 2.2 times compared to that of the aberrated image. In addition, the x-, y-, and z-widths of the bead image were reduced to 75%, 53%, and 40%, respectively. Our device successfully corrected several asymmetric aberrations to improve the fluorescent signal and spatial resolution, and might be useful for observing various biospecimens.

Transmissive liquid crystal device correcting the spherical aberrations in laser scanning microscopy

Two-photon excitation laser scanning microscopy has enabled us to visualize deep regions in a biospecimen. However, refractive-index mismatches in the optical path cause spherical aberrations, which degrade the spatial resolution and the fluorescent signal during observation, especially at deeper regions. Recently, we developed transmissive liquid crystal devices for correcting a certain spherical aberration without changing the basic design of the optical path in a conventional laser scanning microscope. The devices were inserted in front of the objective lens and supplied with appropriate voltages according to the observation depth. In our previous study, while the devices actually recovered the axial resolution and the fluorescent signal, which were degraded by artificially induced aberrations, those performances were not sufficient for practical use. In this paper, in order to improve the imaging performance of the devices and the objective lens, we first performed more precise numerical calculations. Next, we modified the design of the devices and evaluated these performances by observing fluorescent beads in a single-photon excitation laser scanning microscope. For a 25x water-immersion objective lens with a numerical aperture of 1.1 and a sample with a refractive index of 1.38, these modifications recovered the spatial resolution, and the fluorescent signal degraded within ±0.6 mm depth. Finally, we introduced these modified devices to a conventional two-photon excitation laser scanning microscope and succeeded in improving the spatial resolution; additionally, the fluorescent signal degraded in the same region. Therefore, our devices are expected to be useful for observing much deeper regions within a biospecimen.

Birefringence Bragg Binary (3B) grating, quasi-Bragg grating and immersion gratings

A volume phase holographic (VPH) grating achieves high angular dispersion and very high diffraction efficiency for the first diffraction order and for S or P polarization. However the VPH grating could not achieve high diffraction efficiency for non-polarized light at a large diffraction angle because properties of diffraction efficiencies for S and P polarizations are different. Furthermore diffraction efficiency of the VPH grating extinguishes toward a higher diffraction order. A birefringence binary Bragg (3B) grating is a thick transmission grating with optically anisotropic material such as lithium niobate or liquid crystal. The 3B grating achieves diffraction efficiency up to 100% for non-polarized light by tuning of refractive indices for S and P polarizations, even in higher diffraction orders. We fabricated 3B grating with liquid crystal and evaluated the performance of the liquid crystal grating. A quasi-Bragg (QB) grating, which consists long rectangle mirrors aligned in parallel precisely such as a window shade, also achieves high diffraction efficiency toward higher orders. We fabricated QB grating by laminating of silica glass substrates and glued by pressure fusion of gold films. A quasi-Bragg immersion (QBI) grating has smooth mirror hypotenuse and reflector array inside the hypotenuse, instead of step-like grooves of a conventional immersion grating. An incident beam of the QBI grating reflects obliquely at a reflector, then reflects vertically at the mirror surface and reflects again at the same reflector. We are going to fabricate QBI gratings by laminating of mirror plates as similar to fabrication of the QB grating. We will also fabricate silicon and germanium immersion gratings with conventional step-like grooves by means of the latest diamond machining methods. We introduce characteristics and performance of these gratings.

Simple adaptive optic device for confocal laser scanning microscopy using liquid crystals

We have developed adaptive optic devices for CLSMs using liquid crystals. This device corrects aberration occurs due to thickness error of cover glasses or deep observations. We will report the design of the devices and experimental results.