Photoacoustic microscopy (PAM) is a biological visualization technique that can provide high spatial resolution and high contrast images of deep structures in living tissues. However, because of the spherical aberration of the objective lens and the wavefront distortion due to the surface shape and light scattering of the specimen, obtained photoacoustic images in deep tissues are sometimes blurred or distorted. In order to solve this problem, we have developed a PAM using a transmissive liquid-crystal adaptive optics (AO) element. The transmissive and thin structure of the AO element can be easily installed in the PAM system. Using photoacoustic images of a USAF 1951 resolution test target measured through the glass substrate (thickness; 1.5-mm), the lateral resolutions in PAM were estimated with and without the AO element, when a flashlamp-pumped nanosecond pulse laser (pulse width, 5-ns; wavelength, 500-nm) and water-immersion objective lens (NA = 0.8) were employed. The lateral resolution of PAM at the depth of 1.5-mm was improved from 1.04 ± 0.04 μm to 0.53 ± 0.10 μm by optimizing AO corrections. We have also visualized small blood vessels in mouse ear in vivo by PAM with AO correction. Thus, by optimizing the AO correction according to the imaging depth, our proposed PAM improves the spatial resolution in biological tissues.
Photoacoustic microscopy (PAM) is a biological visualization technique that can provide high spatial resolution and high contrast images of deep structures in living tissues. In PAM, the lateral resolution is determined by the size of the focus spot. Generally, because the wavefront aberration, due to the difference of refractive index between samples and air (water) and the shape of samples, enlarges the focus spot, obtained deep images are blurred or distorted. In order to solve this problem, we corrected the wavefront aberration occurring in samples using a transmissive liquid-crystal adaptive optics (AO) element. Our AO element consists of three liquid-crystal layers which have different ITO (indium tin oxide) patterns and are controlled independently. Their patterns are designed to correct the wavefront aberration suitable for a 40X waterimmersion objective lens. The AO element with transmissive and thin structure is easily installed in the PAM system. Also, our AO element is inexpensive and has low power consumption. In this study, we compared photoacoustic images obtained without and with the AO element for a USAF test target, polystyrene beads diffused in glycerol and various tissue specimens. As a result, we found that the use of transmissive AO element improves the lateral resolution and signal-tonoise ratio in PAM.
In this work we report on our achievements in generating switchable and arbitrary vector beams by means of q-plates. Two kind of q-plates are considered: i) a physical prototype from Citizen Co. and ii) a virtual device that is encoded onto a spatial light modulator (SLM). In both cases experimental and analytical results within the Jones formalism are shown. The performance of a segmented and tunable liquid crystal q-plate prototype is characterized at visible and telecommunications wavelengths, and the generation of first-order vector beams is probed. By using a reflective geometry and tuning the q-plate at half-wave or at quarter-wave retardance, it is shown how the device can operate either as a q-plate with double order. Finally, we show the generation of arbitrary programmable integer and fractional vector beams by encoding a q-plate onto a SLM based system. The system is based on a double-pass configuration that consecutively modulates the vertical and the horizontal polarization components of light using a transmissive LCoS display. Therefore, new and exotic q-plate designs can be analyzed prior to their fabrication.
All aberrations produced inside a biospecimen can degrade the quality of a three-dimensional image in two-photon excitation laser scanning microscopy. Previously, we developed a transmissive liquid-crystal device to correct spherical aberrations that improved the image quality of a fixed-mouse-brain slice treated with an optical clearing reagent. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism. The motivation for this study is that asymmetric aberration can be induced by the shape of a biospecimen and/or by a complicated refractive-index distribution in a sample; this can considerably degrade optical performance even near the sample surface. The device’s performance was evaluated by observing fluorescence beads. The device was inserted between the objective lens and microscope revolver and succeeded in improving the spatial resolution and fluorescence signal of a bead image that was originally degraded by asymmetric aberration. Finally, we implemented the device for observing a fixed whole mouse brain with a sloping surface shape and complicated internal refractive-index distribution. The correction with the device improved the spatial resolution and increased the fluorescence signal by ∼2.4×. The device can provide a simple approach to acquiring higher-quality images of biospecimens.
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.
Effect of scintillations is serious problems in optical systems which require the atmospheric propagation, the optimization of optical system to minimize the effects of scintillation have been examined using the simulation of propagation in atmospheric turbulence. The analytic studies of scintillation index of LG beams show that LG beams have less scintillation than Gaussian beams. However, in these researches, the diameter of receiving aperture was set as point receiver without considering the effects of aperture averaging, which is phenomenon that reduced scintillations over finite aperture. In this paper, considering size of a receiving aperture, the propagation losses and the scintillation index of LG beams are simulated. Also, for practical applications, propagation properties of "quantized" LG(5,1) beams simulated. As a result of the examination, the propagation losses and the scintillation index of LG beams is smaller than those of Gaussian beams. By applying LG beams for optical wireless communications, it is expected to improve better the effect of scintillations than using Gaussian beams. The result is that the scintillation index of quantized LG beams is equal to those of LG beams, and it suggested that quantized LG beams can be treat the quantized LG beams the same as LG beams.
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 device's 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.
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.
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.
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.
We propose a technique that employs single fluorescent molecules for visualizing the distribution of strain induced in
microstructures. We sprayed single-molecule tracers on microstructures by ultrasonic atomization and traced the position
and orientation of the tracers by a single-molecule detection technique with a three-dimensional (3D) orientation
microscope, which consists of a conventional fluorescent microscope and a polarization-mode converter. By using 3D
spline interpolation, we visualized the surface geometry of a microelectromechanical (MEMS) device. We tracked the
3D position and orientation of tracers attached to a supporting beam of the MEMS mirror. The surface declination angles
calculated from the orientation of the tracers were in agreement with the tilt angle obtained from the 3D position of the
tracers.
We report laboratory demonstrations of an eight-octant phase-mask (EOPM) coronagraph for direct detection of
exoplanets. The EOPM coronagraph is a family of a four-quadrant phase-mask (FQPM) one, and shows better
coronagraphic performance for partially resolved stars. We manufactured an eight-octant ferroelectric liquid-crystal
(FLC) mask. The FLC mask is composed of eight-segmented half-wave plates whose principal axes are different
between adjacent segments. The mask operates as a fully achromatic EOPM when the FLC mask is placed between
crossed polarizers. We carried out laboratory experiments on the EOPM coronagraph by using partially resolved whitelight
source, and compared the performance with that of the FQPM one. As a result, we confirmed that the EOPM shows
higher contrast than the FQPM. A drawback of the proposed method is that the FLC mask can be used only for one
component of polarization of incoming light because it is necessary to use the polarizer in front of the FLC mask. To
solve this problem, a two-channel coronagraph, based on two polarizing beam splitters instead of the polarizers, is
proposed. Observational efficiency can significantly be improved because the two-channel coronagraph enables us to
detect both components of polarizations from exoplanets. We also report preliminary experimental results of laboratory
demonstrations of the two-channel coronagraph.
Liquid crystal devices are suitable for spatial light modulators, since their half-wave voltage is only a few volts and can
be driven directly by CMOS ICs. In this paper, we describe liquid crystal GRIN lens with segmented ITO patterns. So
ITO patterns are like zone plates. ITO segments are connected with smaller, highly resistive ITO links that produce
voltage drops between the larger ITO segments. The voltage distribution causes a phase distribution across the modulator
that can be generated by a simple 3-terminal input. Variable focus range of from plus-minus 150mm to infinity with
1.64mm diameter and good image quality is achieved.
Liquid crystal devices are one of the suitable devices for wave-front modulation since its extra low operating voltages
such as 1~3Vrms. In this paper, we will present about liquid crystal active prisms for laser beam steering and its
characteristics to the temperature change which causes an undesired optical power. Further more, we will present a
recent result of a variable focus lens using quantized GRIN lens technology.
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