A video-rate laser scanning microscope was developed as an imaging engine to integrate with other photonic building
blocks to fulfill various microscopic imaging applications. The system is quipped with diode laser source, resonant
scanner, galvo scanner, control electronic and computer loaded with data acquisition boards and imaging software.
Based on an open frame design, the system can be combined with varies optics to perform the functions of fluorescence
confocal microscopy, multi-photon microscopy and backscattering confocal microscopy. Mounted to the camera port, it
allows a traditional microscope to obtain confocal images at video rate. In this paper, we will describe the design
principle and demonstrate examples of applications.
KEYWORDS: Blood vessels, Skin, Reconstruction algorithms, Radiometry, Temperature metrology, In vivo imaging, Pulsed laser operation, Blood, Solids, Medical laser equipment
We report on application of pulsed photothermal radiometry (PPTR) to determine the depth of port wine stain (PWS) blood vessels in human skin. When blood vessels are deep in the PWS skin (>100 µm), conventional PPTR depth profiling can be used to determine PWS depth with sufficient accuracy. When blood vessels are close or partially overlap the epidermal melanin layer, a modified PPTR technique using two-wavelength (585 and 600 nm) excitation is a superior method to determine PWS depth. A direct difference approach in which PWS depth is determined from a weighted difference of temperature profiles reconstructed independently from two-wavelength excitation is demonstrated to be appropriate for a wider range of PWS patients with various blood volume fractions, blood vessel sizes, and depth distribution. The most superficial PWS depths determined in vivo by PPTR are in good agreement with those measured using optical Doppler tomography (ODT).
KEYWORDS: Polarization, Birefringence, Optical coherence tomography, Skin, Tissue optics, Tissues, In vivo imaging, Modulators, Signal analyzers, Signal processing
A phase-resolved polarization sensitive optical coherence tomography (PS-OCT) system was used to determine the burn depth of in vivo tissue non-invasively. The phase retardation information was obtained by processing the analytical interference fringe signals from two perpendicular polarization-detection channels. From the birefringence images for the four reference polarization states, the birefringence reduction in the rat skin due to thermal damage can be measured. The determined burn depth showed good agreement with histological result.
We describe power optical Doppler tomography (ODT) imaging in phase-resolved optical coherence tomography (OCT) capable of providing the precise location of blood flow in human skin. The power Doppler signal is the squared amplitude of the Doppler signal. By properly setting the intensity threshold and priority displaying Doppler power in phase-resolved OCT, we obtained a Doppler power tomography image of the blood flow in human skin. Power Doppler tomography uses only the amplitude information, so it is not susceptible to aliasing and Doppler flow angle and provides more accurate and smooth imaging of the location of the blood vessels in human skin than Doppler velocimetry. We also modified the phase-resolved algorithm we published before and used it to do Doppler tomography and M-mode Doppler imaging. The dynamic of blood flow in chick chorioallantoic membrane (CAM) was studied using M-mode Doppler imaging.
We describe a phase-resolved polarization sensitive optical coherence tomography system that can obtain the Stokes vectors, polarization diversity intensity, and birefringence images of rat-tail tendon and muscle. The Stokes vectors were obtained by processing the analytical interference fringe signals from two perpendicular polarization-detection channels for the same reference polarization state. From the four Stokes vectors, the birefringence image, which is insensitive to orientation of the optical axis in the sample, and the polarization diversity intensity image, in which speckle noise is greatly reduced, were obtained. The birefringence changes in the rat muscle caused by freezing were investigated using phase-resolved polarization sensitive optical coherence tomography. It was found that freezing degrades birefringence in rat muscle.
We developed an ultrahigh resolution optical coherence tomographic system utilizing broadband continuum generation from a photonic crystal fiber for high axial resolution. Longitudinal resolution of 1.3 μm has been achieved in a biological tissue by use of continuum light from 800 - 1400 nm as the light source. The system employed a dynamic focusing tracking method to maintain high lateral resolution over a large imaging depth. Subcellular imging is demonstrated.
We developed a optical coherence tomographic (OCT) system that utilized broadband continuum generation from a crystal fiber for high axial resolution. Longitudinal resolution of 3 micrometers has been achieved in free space with continuum light from 780 to 1400nm as light source. The system employed a dynamic focusing tracking method to get high lateral resolution. Ultrahigh resolution imaging in onion was demonstrated.
In optical coherence tomography (OCT), axial and lateral resolutions are determined by the source coherence length and numerical aperture of the sampling lens, respectively. While axial resolution can be improved using a broadband light source, there is a trade-off between lateral resolution and focus depth when conventional optical elements are used. In this paper, we report on the incorporation of an axicon lens into the sample arm of the interferometer to overcome this limitation. Using an axicon lens with a top angle of 160 degrees, 10 micrometers or better lateral resolution is maintained over a focus depth of at least 6 mm. In addition to high lateral resolution, the focusing spot intensity is approximately constant over the whole focus depth.
We have developed a novel optical Hilbert transformation for phase-resolved optical Doppler tomographic imaging. Using a resonant scanner in the reference arm of the interferometer and the axial scanning speed of 4 kHz, the frame rate can be as high as 10 Hz for both structural and Doppler blood flow imaging 400 axial scans. The system has high sensitivity for measuring the Doppler frequency shift due to moving red blood cells. Real time images of in vivo blood flow in human skin using this interferometer are presented.
The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved optical Doppler tomography (ODT) is used to image the velocity component transverse to the probing beam. Using a simple geometric optics model, the linear dependence of the Doppler bandwidth on flow velocity is theoretically derived and it is found that the effective numerical aperture (NA) of the optical objective determines the slope of this dependence. Above a certain threshold flow velocity, this linear relationship is in good agreement with experimental data. In the case where the angle between the probing beam and flow direction is within –15 degree to the perpendicular, the Doppler frequency shift is very sensitive to angle position while the Doppler bandwidth is insensitive to flow direction. Linear dependence of the flow velocity on the Doppler bandwidth allows accurate measurement of flow velocity without precise determination of flow direction. In addition, it also extends the dynamic range of the average frequency shift mapping method used in the phase-resolved ODT.
We developed a novel optical coherence tomographic (OCT) system which utilized broadband continuum generation for high axial resolution and a high numeric-aperture (N.A.) Objective for high lateral resolution (<5 micrometers ). The optimal focusing point was dynamically compensated during axial scanning so that it can be kept at the same position as the point that has an equal optical path length as that in the reference arm. This gives us uniform focusing size (<5 mum) at different depths. A new self-adaptive fast Fourier transform (FFT) algorithm was developed to digitally demodulate the interference fringes. The system employed a four-channel detector array for speckle reduction that significantly improved the image's signal-to-noise ratio.
The measurements of refractive index and thickness of various transparent plates and films are very important for quality control. Additionally, the knowledge of refractive index, and thickness is significant in biomedicine for the treatment of many kinds of tumors. In this paper, we propose a new method for noninvasive and simultaneous measurement of refractive indices and physical thickness of specimens, which consist of surrounding and interior components with different refractive indices. In our experiment, we measure the refractive index and the physical thickness of a multimode fiber and a lotus root with a hollow hole, respectively. The experimental results verify the feasibility of this method.
An optical coherence tomography system capable of imaging subsurface objects in turbid media is described and the obtained cross-sectional image of a small region of lotus root by OCT is presented. The deconvolution algorithm with wiener filter was implemented to reconstruct this cross-sectional image. The imaging mechanism of OCT is investigated by Monte Carlo method.
A lattice random walk model based on walkers wandering on discrete lattice of scattering space by discrete spatial and temporal step is presented. The discrete Green's function for infinite homogeneous turbid medium deduced by inductive method from the lattice random walk model is used with the method of images to describe the photon density distribution in two dimensional semi-infinite and finite slab homogenous turbid media such as tissue. The scattering matrix and linking matrix of the lattice random walk are obtained to describe the scattering and absorption processes in homogeneous and inhomogeneous turbid media. All the results obey the principle of causality.
Improvement of beam quality is a major task in most of the laser systems. To optimize the performance of copper vapor laser system, beam propagation in an injection-controlled copper vapor laser system is investigated on account of thermal lens effect. Far-field intensity distribution as well as its temporal evolution of the output from a copper vapor laser oscillator at different operating conditions are measured in detail. Experimental observation has bene performed about the influence of delay time between the oscillator and amplifier on the far-field intensity distribution of the output from the amplifier. The application of a single-pass unfolded amplifier model has been successfully demonstrated to describe beam propagation within the system.
In order to study the feasibility of submicron lithography using second-harmonic light (SHL) at wavelength of 255.3 nm of copper vapor laser (CVL), a 1:1 catadioptric projection lens and an illumination system are designed and constructed. A resolution of 0.7 micrometers line/space patterns is produced in AZ1350J resist, which reveals that the SHL of CVL can be used as an illumination source in submicron lithography.
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