Dual-axes differential confocal microscopy with high axial resolution and long working distance

We discover that the slight transverse offset of a point detector results in a shift of the axial intensity response curve in a dual-axes confocal microscopy (DCM). Based on this, we propose a new dual-axes differential confocal microscopy (DDCM) with high axial resolution and long working distance, in which two point detectors are placed symmetrically about the collection axis. And a signal is obtained through the differential subtraction of two signals received simultaneously by the two point detectors. Theoretical analyses and preliminary experiments indicate that DDCM is feasible and suitable for the high precision tracing measurement of microstructures and surface contours.     

Retinal cone mosaic imaged with transverse scanning optical coherence tomography

We improved our recently reported retinal OCT system based on transverse priority scanning to achieve high resolution in both the transverse and the axial directions. The implementation of an additional SLO channel enables precise on-line focusing. The system enables imaging of the human retinal cone mosaic off the foveal center without adaptive optics. We demonstrate, for what is believed to be the first time, cone mosaic imaging simultaneously in the scanning laser ophthalmoscope and optical coherence tomography (OCT) channels. OCT B-scan images demonstrate that the cone mosaic is observable in two adjacent layers. Furthermore, we present what are believed to be the first C-scan OCT images of the cone mosaic and show that the major part of light backscattered from below the photoreceptor layer is not guided back toward the pupil by the photoreceptors.     

Extended focus depth for Fourier domain optical coherence microscopy

We report on a new detection scheme for Fourier domain optical coherence microscopy that exhibits high transverse resolution along an axially extended focal range. Nearly constant transverse resolution of approximately 1.5 microm along a focal range of 200 microm is experimentally verified with a maximum sensitivity of 105 dB. A broad-bandwidth Ti:sapphire laser allowed for an axial resolution of 3 microm in air.     

Effect of an annular pupil filter on differential confocal microscopy

Combining differential confocal microscopy and an annular pupil filter, we obtained the normalized axial intensity distribution curve of an optical system. We used the sharp slopes of the axial response curve of the optical system to measure the surface profile of a reflection grating. Experimental results prove that this method can extend the axial dynamic range and improve the transverse resolution of three-dimensional profilometry by sacrificing axial resolution.     

MEMS-based adaptive optics scanning laser ophthalmoscopy

We have developed a compact, robust adaptive optics (AO) scanning laser ophthalmoscope using a microelectromechanical (MEMS) deformable mirror (DM). Facilitated with a Shack-Hartmann wavefront sensor, the MEMS-DM-based AO operates a closed-loop modal wave aberration correction for the human eye and reduces wave aberrations in most eyes to below 0.1 microm rms. Lateral resolution is enhanced, and images reveal a clear cone mosaic near the foveal center. The significant increase in throughput allows for a confocal pinhole whose diameter is less than the Airy disc of the collection lens, thereby fully exploiting the axial resolution capabilities of the system.     

光声信号的声透镜层析成像研究

提出了一种用声透镜实现光声层析成像的新模式。从理论上计算出了声透镜的响应，测出了已知声场中标准物像面处的声场分布。考虑到圆形活塞振源的指向性，对代表物成像进行了理论修正，并与实验结果做了对比分析。研究表明，利用声透镜可以实现光声层析成像，并经图像重构得到了生物组织中异物的光声图像，横向、纵向分辨力较高。     

改善共焦系统轴向分辨率的位相型光瞳滤波器

利用约束全局优化算法———CGO算法,设计了两种用于共焦系统的三区位相型光瞳滤波器.第一种滤波器在不改变系统的横向分辨率的同时,可以大幅度地提高轴向分辨率,提高了系统的层析能力.第二种滤波器在提高系统轴向分辨率的同时,又能提高其横向分辨率,适用于系统的三维成像. 关键词： CGO算法 光瞳滤波器 超分辨     

Transverse superresolution with the radial continuous transmittance filter

The radial continuous transmittance filter is presented to realize transverse superresolution. It consists of two parallel polarizers and a radial birefringent element sandwiched between of them. By adjusting the angle between optical axis of the radial birefringent element and the polarization direction of the polarizers, transverse superresolution can be realized. But transverse superresolution is obtained at the cost of the axial resolution and the increase of the side-lobes in strength. So we then mend such filter, with it not only enhance the transverse resolution but also suppress the influence of the side-lobes and the reduction of the axial resolution. At the same time, the Strehl ratio increases. The advantage of such a filter used in superresolution technique is that it is easy to fabricate because its fabrication does not deal with the variation of the phase.     

T-ray topography by time-domain polarimetry

We demonstrate a method for substantially improving the axial resolution of terahertz time-of-flight measurements by analyzing the time-dependent polarization direction of an elliptically polarized single-cycle terahertz electromagnetic (T-ray) pulse. We show that, at its most sensitive, the technique has an axial resolution of ～λ/1000 (<1 μm) with a subsecond measurement time, and very clear T-ray topographic images are obtained. Such a very high axial resolution of the T-ray topography opens the way for novel industrial and biomedical applications such as fine metalworking and corneal inspection in a safe manner.     

Improved sectioning in a slit scanning confocal microscope

We describe a simple implementation of a slit scanning confocal microscope to obtain an axial resolution better than that of a point-scanning confocal microscope. Under slit illumination, images of a fluorescent object are captured using an array detector instead of a line detector so that out-of-focus light is recorded and then subtracted from the adjacent images. Axial resolution after background subtraction is 2.2 times better than the slit confocal resolution, and out-of-focus image suppression is calculated to attenuate with defocus faster by 1 order of magnitude than in the point confocal case.     

Parallel optical coherence tomography using a CCD camera

Parallel optical coherence tomography is demonstrated using a 12-bit scientific-grade charge-coupled device array.A superluminescent diode in combination with a free-space Michelson interferometer was employed to achieve 10-μm axial resolution and 1.1-μm transverse resolution on a 902×575 μm2 field of view.We imaged a test mirror and bovine retinal tissue using a four-step phase shift method.     

Imaging sclera with hard X-ray microscopy

In this study, the organization of collagen fibrils within the sclera of the eye was investigated using the 7 keV hard X-ray microscope of the Pohang light source and compared to images from electron and atomic force microscopy. From the captured X-ray images, individual collagen fibrils were observed clearly in a spatial resolution much better than 100 nm, both in longitudinal sections and in transverse sections. Some of the collagen fibrils showed evidence of axial periodicity. In some regions of the samples, we could see cross-bridge like structures between adjacent collagen fibrils. The X-ray microscope also allowed the observation of keratocytes and the lamella structure of the scleral stroma. The X-ray microscope has some unique advantages in the nano-scale imaging of bio-samples relative to other established imaging techniques.     

共焦扫描光声层析成像技术的研究

报道了一种新的光声层析成像技术－光声傅里叶变换共焦扫描成像技术，并用该技术获得了强散射物质（生物组织）的层析图像，纵向分辨能力小于0．1mm，横向分辨率小于4mm。     

三环位相型光瞳滤波器的横向超分辨与轴向焦深扩展

用矢量衍射方法分析了线偏振光入射到带有三环位相型光瞳滤波器的高数值孔径物镜时,焦点的轴向和横向光强分布.数值模拟结果表明,高数值孔径物镜聚焦时需同时考虑光强的轴向和横向分布.通过加入三环位相光瞳滤波器,在实现横向超分辨的同时实现了光学系统轴向焦深扩展和轴向光强分布平坦化,并且位相调制深度变化时,会出现轴向焦移现象.对三环位相光瞳滤波器结构进行了优化,得出了优化结果. 关键词： 光学超分辨 扩展焦深 位相型光瞳滤波器 矢量衍射方法     

振动声成像系统分辨率研究

本文从振动声成像的基本原理出发，通过引入点扩展函数PSF和定义轴向响应函数ARF，研究了由凹球面聚焦换能器分割而成的一种典型共焦换能器参数对振动声成像系统侧向分辨率和轴向分辨率的影响。计算研究表明：增大凹球面换能器的口径、减小几何焦距和提高中心频率均可以提高系统的侧向分辨率和轴向分辨率；但改变凹球面换能器的分割比例对两种分辨率影响不尽相同。综合考虑超声换能器激励、聚焦性能以及产生的辐射力效果等因素，则换能器应按等辐射面积原则分割为宜。文中还分析了介质的声衰减系数对实际轴向分辨率的影响。     

Stroboscopic ultrahigh-resolution full-field optical coherence tomography

We present a new technique that produces en face tomographic images with a 10-micros acquisition time per image. The setup consists of an interference microscope with stroboscopic illumination provided by a xenon arc flash lamp (10-micros flashes at 15 Hz). The tomographic images are obtained from two phase-opposed interferometric images recorded simultaneously by two synchronized CCD cameras. Transverse resolution better than 1.0 microm is achieved by use of high-numerical-aperture microscope objectives. The short coherence length of the source yields an axial resolution of 0.9 microm. 3 x 3 pixel binning leads to a detection sensitivity of 71 dB. Our system is suitable for various applications, particularly in biology for in vivo cellular-level imaging.     

Dual-axes confocal microscopy with post-objective scanning and low-coherence heterodyne detection

We present a dual-axes confocal microscope that employs postobjective scanning and low-coherence heterodyne detection to collect vertical cross-sectional images from biological tissue with high axial resolution, reduced noise from scattered light, deep tissue penetration, and a large dynamic range. This architecture can be scaled down to millimeter dimensions with microelectromechanical systems technology for performance of in vivo optical biopsy.     

Designing superresolution optical pupil filter with constrained global optimization algorithm

In this paper, a new method for designing three-zone optical pupil filter is presented. The phase-only optical pupil filter and the amplitude-only optical pupil filters were designed. The first kind of pupil for optical data storage can increase the transverse resolution. The second kind of pupil filter can increase the axial and transverse resolution at the same time, which is applicable in three-dimension imaging in confocal microscopy.     

Adaptive-optics ultrahigh-resolution optical coherence tomography

Merging of ultrahigh-resolution optical coherence tomography (UHR OCT) and adaptive optics (AO), resulting in high axial (3 microm) and improved transverse resolution (5-10 microm) is demonstrated for the first time to our knowledge in in vivo retinal imaging. A compact (300 mm x 300 mm) closed-loop AO system, based on a real-time Hartmann-Shack wave-front sensor operating at 30 Hz and a 37-actuator membrane deformable mirror, is interfaced to an UHR OCT system, based on a commercial OCT instrument, employing a compact Ti:sapphire laser with 130-nm bandwidth. Closed-loop correction of both ocular and system aberrations results in a residual uncorrected wave-front rms of 0.1 microm for a 3.68-mm pupil diameter. When this level of correction is achieved, OCT images are obtained under a static mirror configuration. By use of AO, an improvement of the transverse resolution of two to three times, compared with UHR OCT systems used so far, is obtained. A significant signal-to-noise ratio improvement of up to 9 dB in corrected compared with uncorrected OCT tomograms is also achieved.     

Video rate depth-resolved two-dimensional imaging through turbid media by femtosecond parametric amplification

We report two-dimensional imaging through a liquid scattering medium by noncollinear femtosecond parametric amplification in a reflection configuration. The experiment presented permits direct observation at video rate of two-dimensional images with 24-mum depth resolution and 90-mum transverse resolution for an area with a 2.5-mm diameter on the object. These resolutions are achievable through a turbid phantom with a depth near 12 scattering mean free paths in double pass.