High-resolution optical imaging is accompanied by a limited depth of field, making it challenging to obtain non-stitched, high-resolution images of samples with uneven surfaces without performing Z-axis scanning. To solve this problem, we introduced diffractive optical elements into the conventional OCT system and develop a needle-shaped beam OCT system with both long DOF and high resolution, which maintains 8μm lateral resolution over a depth range of 620μm. The system was then employed to perform a 10-day cortical blood perfusion observation after stroke, providing visual and mechanistic insight into stroke, deepening our understanding of the brain response after stroke.
Optical coherence tomography (OCT) has become a promising tool for studying anatomical and functional dynamics of the cerebral cortex, offering advantages such as label-free imaging, high resolution, and non-invasive optical biopsy. However, observing the brains of non-anesthetized and freely moving mice has been a long-standing challenge for OCT. In this study, we designed a wearable OCT probe to observe the vascular morphology of the mouse brain and track short-term vascular changes after thrombosis. We utilized a microelectromechanical system (MEMS) scanning mirror for three-dimensional scanning. Compared to traditional OCT systems, this wearable imaging probe features miniaturization, low cost, portability, and stability, allowing for imaging of the mouse brain in a non-anesthetized and freely moving state. The entire probe weighs 8 g and achieves a lateral resolution of 5.5 μm, a longitudinal resolution of 12 μm, and an effective imaging area of 4 mm × 4 mm. We evaluated the performance of the probe through phantom experiments and imaging of the mouse brain's vascular network, and successfully monitored local vascular morphological changes in the mouse brain shortly after stroke under awake conditions. We believe that the wearable probe can be applied in various fields such as ophthalmology, dermatology, and dentistry, and due to its portability and non-invasiveness, the wearable OCT probe is expected to have wide clinical research applications.
Optical coherence tomography angiography (OCTA) has emerged as a highly competitive technique for visualizing blood perfusion without the need for exogenous contrast agents. However, for high-resolution optical imaging, a tight optical focus is usually needed to achieve the diffraction-limited resolution in optical microscopy, which results in a limited depth of field (DOF), making it challenging to obtain large-scale, non-stitched, high-resolution images of samples with uneven surfaces without performing Z-axis scanning. To solve this problem, we introduce the diffractive optical elements (DOEs) into the conventional Gaussian beam (GB) OCT system and develop a needle-shaped beam (NB) OCT system with both long DOF and high resolution, which maintains 8 μm lateral resolution over a depth range of 620 μm, allowing real-time, non-stitched, large-field imaging of samples with uneven surfaces. OCTA imaging of mouse brains with natural curvature was demonstrated in our work.
Radiation calibration is the core issue of quantitative remote sensing. Polarization spectrum detection can characterize fine structure. In order to improve the accuracy of remote sensing under outdoor lighting conditions, the multi-angle polarized hyperspectral images of the jujube canopy were obtained, and the quality distribution characteristics of the jujube canopy were analyzed by extracting multi-dimensional information features such as angle, polarization and spectrum from hyperspectral images. Secondly, the normalized vegetation index NDVI, With the polarization parameter such as the dolp (degree of linear polarization) and Orient to obtain the polarization parameter images of jujube. To get the other targets with obvious features and clear texture in details. Finally, by performing multi-band fitting and related processing on the hyperspectral characterizing the water content and other quality information of the jujube, a polarized hyperspectral quantitative remote sensing model was established to obtain grayscale images that characterize the spatial distribution of the water content and other qualities. This provides an important reference for the development of digital intelligent agriculture.
The composition and structure of fruit and other natural products are complex. Due to the influence of environmental factors, it is urgent to combine quantitative detection with remote sensing technology to quickly obtain the quality distribution of jujube in large area of jujube orchard. In order to improve the accuracy and efficiency of the outdoor near-surface quality detection model. The jujube is equivalent to a scattering medium with random refractive index distribution. Biological tissue optical parameters were used to describe the quality changes of jujube in different maturity stages. Through simulating different scattering conditions (particle size, the refractive index) light intensity distribution and the change law of polarization, with the hyperspectral polarization experiments of jujube in indoor and outdoor, Through Principal component analysis(PCA), Minimum Noise Fraction (MNF) reduces the dimension of the hyperspectral imageries, we compared the results and found that the polarization direction in principal component characteristics and minimum noise distribution have obvious difference, the polarization dimension difference between high_dimensional information was expressed by the noise distribution, different characteristics through the dimension of the polarization noise distribution. In the high_dimensional space. The jujubes and the leafs of canopy have obvious differences in P0_MNF14 and P45_MNF13.Jujube can be separated from the complex background. The accuracy and efficiency of near_ground remote sensing for the quality of jujube can be improved by extracting multi_dimensional characteristic information of hyperspectral polarization.
Mechanism of the two-port one input mirror-symmetric all-dielectric disk array perfect absorbers is studied by temporal coupled mode theory. The perfect absorption is resulted from the degenerate critical coupling of EH111 and HE111 modes of the dielectric disks. Analytical absorption with parameters extracted from Eigen-frequency analysis matches well with that by Scattering parameter simulations, we also show that the asymmetric total field is due to the different symmetry of the two modes. The effect of the geometric parameters and material loss tangent is also investigated, which can guide the design of such all-dielectric perfect absorbers.
To advance the practical application of optical coherence tomography (OCT) in the field of biomedical imaging, the imaging depth must be extended without sacrificing resolution while maintaining sufficient sensitivity. However, there is an inherent trade-off between lateral resolution and depth of field (DOF) in OCT. To address this shortcoming, this article proposes a multifocal Bessel beam spectral-domain optical coherence tomography (MBSDOCT) capable of increasing the DOF with unchanged lateral resolution and a high signal-to-noise ratio. The proposed technique is demonstrated by simulation and experiment. A three-focal MBSDOCT with an axicon lens theoretically achieved a DOF of ∼6 mm with a lateral resolution of ∼13 μm. In imaging experiments performed on the acinar cells of orange tissue, a measured DOF of ∼4 mm was demonstrated with a sensitivity penalty of ∼18.1 dB, relative to the Gaussian beam spectral-domain OCT, with a 9-mW light source.
We present a single pixel frequency division multiplexing imaging system with two metamaterial spatial light modulators (SLMs) for THz light field imaging. One SLM is used for slicing/modulating the 4D light field from various sub-apertures, while the second one together with a single pixel detector to implement 2D multiplexing measurement. This system is in essential a programming aperture in the frequency domain of carrier signals in our categorization of the traditional light field acquisition systems. We propose a prototype adaption design with available elements for THz imaging. Besides, we present the frequency selection method and reconstruction algorithm for square wave modulation/carrier signals for at most 4096-voxel light field dataset.
The calibration method using high-power halogen tungsten lamp as calibration source is very fit for calibration of high-energy laser energy meters. However, high-power halogen tungsten lamps after power-off still reserves much residual energy and continually radiates energy. The radiation efficiency of the halogen tungsten lamp after power-off can be quantitatively measured by a fast response radiation detector. The results show that the halogen tungsten lamp's radiation efficiency was improved with power-on time, but did not change under constant power-on time/energy. All the tested halogen tungsten lamps reached 89.3% of radiation efficiency at 50 s after power-on. After power-off, the residual energy in the halogen tungsten lamp gradually dropped to less than 10% of the initial radiation power, and the radiation efficiency changed with time. The final total radiation energy was decided by the halogen tungsten lamp's radiation efficiency, the radiation efficiency of residual energy, and the total energy consumption. The measuring uncertainty of total radiation energy was about 2.4% (k=2).
Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere. The concentrations of trace gases can be retrieved by fitting differential absorption spectra with standard differential absorption cross-section using the linear least-square method. The basic principle of DOAS is introduced. The construction of DOAS on-line monitoring system is designed and the retrieval method of trace gases concentration based on the principle of least-squares is discussed. The properties of DOAS system are tested by experiments. The advantages of DOAS system used in atmosphere quality monitoring are shown.
The imaging method by simply putting the object directly on the surface of CCD or CMOS array chip is
experimented. A 4.65*4.65μm pixel size 1024*768 CCD chip is used in the experiments. CCD's optic window is
removed and surrounding lead on chip is covered with some glue to protect the CCD chip from damaged during the
imaging operation. Light emitted or transmitted from object is gathered by the nearest one or several pixels. The
comparative experiment shows, to compare the normal microscope imaging using the optic lens, Sharp image with no
color shift, optic aberration and field distortion is achieved. To compare with a 4x N.A=0.1 lens at the same
magnification, better light couple efficiency and simple optomechanics construction are achieved in our experiment
system. As the key factors effecting the image PSF,MTF, resolution, contrast and couple efficiency, the object distance
and illumination light path are analyzed and experimented. It shows this will be a potential ultra small size, high
efficiency and low cost micro-object imaging and fluorescence imaging system for cell level biology photometry and
imaging.
A simple cw mode-locked solid-state laser, which is end-pumped by a low-power laser diode, was demonstrated by optimizing the laser-mode size inside the gain medium. The optimum ratio between mode and pump spot sizes inside the laser crystal was estimated for a cw mode-locked laser, taking into account the input pump power. Calculation and experiment have shown that the optimum ratio was about 3 when the pump power is 2 W, which is different from the value regularly used in passively mode-locked solid-state lasers. This conclusion is also helpful in increasing the efficiency of high-power ultrashort lasers.
A deep self modulation output in the diode pumped Bi-directional CW Nd:YVO4 ring laser is observed. The self-modulation has multiple styles and in certain style it shows the distinctness sensitive of rotation. The phenomenon in our experiment is reported in detail. There will be a potential application to the rotation sensor or gyroscope.
Re-entrant fiber optic gyro (Re-FOG), using a shorter Sagnac sensitive ring (SSR), makes parts of the two counter-propagandizing lights re-enter the ring before they interference with each other when they reach the photo-detector. Multiple-integrated-optic-chip (MIOC) is one of the most important components of a Re-FOG. In this paper, the principle of the Re-FOG is first reviewed. A method of measuring the half-wave voltage is presented. The thermal induced change of half-wave voltage was tested.
Re-entrant fiber optic gyroscope (Re-FOG), using a shorter Sangnac sensitive ring (SSR), makes the two counter-propagandizing lights re-enter the ring before they interference with each other when they reach the photo-detector. By this means, the Re-FOG gets the same detecting accuracy as the conventional interferometric fiber optic gyroscope (IFOG) that has several times length of the sensitive ring. In this paper, the principle of the Re-FOG is first reviewed. Then the output signal is analyzed. Finally a method of signal detection is presented.
Simultaneous passive Q-Switching and mode locking at low pump power was observed in a Laser Diode (LD) pumped Nd3+:YVO4-Cr4+:YAG laser, detailed studies were experimentally carried out. A fiber-coupled LD with maximum output power of 2 W is used as pump source. In a 50cm long cavity, the repetition rate of obtained mode-locking pulse train is about 300MHz, and the pulse duration was estimated to be at sub-nanosecond level. The repetition rate of the passive Q-Switched pulse train varies from 10kHz~130kHz with the increasing of the pump power. It was found that the threshold of incident pump power to generate mode-lock in such a laser is dependent on the position of Cr4+:YAG crystal inside the cavity. Select proper Cr4+:YAG as saturable absorber and optimize its position, simultaneous Q-Switching and mode-locking occurred in the Nd3+:YVO4 laser at pump power as low as about 200 mW. The experimental result demonstrates the possibility of obtains ultra short optical pulse in a simple and low cost way, which is of great interest in some applications.
KEYWORDS: Near field, Near field optics, Optical storage, Diffraction, Interfaces, Data storage, Solids, Data modeling, Near field scanning optical microscopy, 3D modeling
Near-field optical virtual probe is a kind of virtual probe based on evanescence wave interference and aperture diffraction, which has great potential in near-field optical data storage.
This paper reports an experimental research on the stability of bidirectional outputs and multi-longitudinal mode interference of laser diode end-pumped Nd:YVO4 solid-state ring laser (DPSSL). The bidirectional, multi-longitudinal and TEM00 mode continuous wave outputs are obtained and the output powers are measured and their stabilities are analyzed respectively. The spectral characteristic of the outputs is measured. The interfering pattern of the bidirectional longitudinal mode outputs is obtained and analyzed in the condition of the ring cavity with rotation velocity. The movement of the interfering fringe of the multi-longitudinal modes is very sensitive to the deformation of the setup base and the fluctuation of the intracavity air, but is stationary or
randomly dithers when the stage is rotating.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Optical storage, Optical resolution, Objectives, Nonlinear optics, Diffraction, Solids, Optical properties
Based on theory and method of the near-field optics, optical resolution of near-field scanning optical microscopy (NSOM) is beyond the classical optical diffraction limit and down to tens of nanometer or even less. In this paper, a collection mode NSOM is built to detect and analyze local near-field distribution. The output optical field of a standard 1μm×1μm scale 2D grating has been detected. This NSOM system can also be used to study local near-field distribution of the focused spot of solid immerging lens (SIL) and the result can be directly used to evaluate SIL and compared with the calculation of its theoretical model and as a result, to improve the theoretical model.
KEYWORDS: Near field, Near field optics, Metals, Light sources, Optical storage, Finite-difference time-domain method, Semiconductor lasers, Polarization, Electromagnetism, Data storage
Nanometric light source is one ofthe most important elements in near-field optical system. In this paper the nearfield distribution of nano-aperture lasers (NAL) with square and asymmetrical C aperture are characterized by the method of 3D finite-difference time-domain (FDTD). The simulation results theoretically reveal that the output power peak from the asymmetrical NAL is three or four orders of magnitude higher than that from the normal square or round aperture with the comparable light spot size in the near-field region and power throughput is more than unity. The maximum ofthe field enhancement occurs at the C aperture size corresponding to one third ofwavelength. The effects of configuration, aperture dimension, electric field component, polarization and separation in local near field close to the aperture have been investigated theoretically and numerically. The mechanism of electromagnetic field enhancement is also discussed. The asymmetrical NAL with higher throughput may expand the range of applications possible in near-field optics.
Nowadays laser diode pumped solid-state laser is becoming more and more attractive to numerous applications. In Gyroscope, because of its solid-state, high gains and other merits, Laser Diode Pumped Solid-State Ring Laser (DPSSRL) has gained much attention from researchers. The bi-directional DPSSRL using Nd:YVO4 that is never reported as far as we know has been approved in our experiment. The most obvious application ofthis kind ofDPSSRL is in the gyroscope. But DPSSRL has its natural tendency to operate in multiple-longitudinal-mode that will affect the precision of gyroscopes dramatically. So a novel longitudinalmode analysis and selection of DPSSRL is performed. In this analysis a Fabry-Perot etalon is added to the settings of a bi-directional operation of DPSSRL. And the theoretical result is single longitudinal mode. In this paper the bi-directional DPSSL experiment configuration is presented. The bi-directional singlelongitudinal- mode DPSSRL modal using Nd:YVO4 have been developed. In order to get a good performance in the experiments, the beam size ofthe laser in the cavity with and without the crystal has been calculated.
KEYWORDS: Near field, Near field optics, Diffraction, Interfaces, Polarization, Optical storage, Finite-difference time-domain method, Near field scanning optical microscopy, Solids, Optical imaging
Near-field optical virtual probe (NFOVP) is a kind of immaterial tip based on evanescence wave interference and nano-aperture diffraction, which has great potential in near-field optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation and etc. . In this paper, the characteristics of NFOVP have been revealed through numerical simulation by the method of 3-D Finite-Difference Time-Domain (FDTD) and vector diffraction. The simulation results show that the transmission efficiency is higher than that of nanoaperture metal-coated fiber probe widely used in near-field optical systems. The FWHM of central peak, in other words, the size ofnear-field virtual probe is constant whatever the distance increases in a certain range so that the critical nanoseparation control in near-field optical system can be relaxed. A realization model of NFOVP in solid immersion lens system has been proposed. The influences of some factors of NFOVP, such as the shape and size of aperture, polarization and etc. have been analyzed. And the results also show that sidelobe suppression may depend on optimization ofaperture function and incident beams of NFOVP.
The experimental research on diode-pumped solid-state ring laser (DPSSL) is reported in this paper. The research target is to develop a new style optical gyroscope. The ring cavity is a plane, 8-shape 4-mirror laser resonator. Nd:YVO4 crystal is exploited as a laser media which is longitudinally pumped by a 2w laser diode. An optical delay path attached to the cavity is composed of a beam splitter and a prism. The bidirectional traveling waves partly output from one of the flat mirror and one directional beam interferes with the other on a photo detector with optical delay. The resonator design is discussed; the pump power threshold is about 600mW. We obtain the bidirectional continuous TEM00 mode outputs and their interfering pattern. In the experiment, Sagnac effect is watched, which indicates that the DPSSRL can be used as optical gyroscope.
KEYWORDS: Near field, Near field optics, Radio propagation, Super resolution, Optical storage, Nonlinear optics, Numerical simulations, Diffraction, Computer simulations, Germanium antimony tellurium
High density optical data storage based on near-field optical super resolution is a new t4echnique that attracts great attention in recent years. Super-resolution near-field structure, glass/SiN/Sb/SiN, a promising structure for near field ultrahigh-density optical storage, has been proposed and investigated since 1998. The recording mark size is a few tens of nanometers, far beyond the diffraction limit of the traditional optics. The mechanism of this Super-RENS including the working principle of the non-linear optical layers and the size reduction of the recording marks has not been clearly understood. In this paper, the electromagnetic propagation in Super-RENS is numerically simulated. The results show that the recording mark size is reduced and the peak intensity increased by the Super-RENS. The mechanisms of the phenomenon is discussed.
A new method of absolute measurement of photodetector quantum efficiency based on spontaneous parametric down- conversion (SPDC) biphoton field is discussed. The process of SPDC is studied theoretically. The single photon detection probability and two-photon coincidence probability are derived and the measurement principle of photodetectors is explained. An experimental system has been set up. The quantum efficiency of a photon-counting photomultiplier tube was measured, and the results were compared with that obtained using conventional method.
The configuration of imaging photon-counting intensifier (IPCI) is introduced, and the differences between traditional II generation intensifiers and the IPCI are given. Based on the single channel photon-counting technique, the measurement principle and method of the IPCI's key performances, such as dark count and photon gain are discussed theoretically. The experimental system has been developed. Measurement work of the two performances mentioned above are carried out under the condition of different MCPs operating voltage and temperature. The experimental result and its comparison with traditional II generation intensifiers are presented.
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