We describe a device to measure blood perfusion for the human optic nerve head (ONH) based on laser Doppler flowmetry (LDF) with a flicker stimuli of the fovea region. This device is self-aligned for LDF measurements and includes near-infrared pupil observation, green illumination, and observation of the ONH. The optical system of the flowmeter is based on a Schlieren arrangement which collects only photons that encounter multiple scattering and are back-scattered out of the illumination point. LDF measurements are based on heterodyne detection of Doppler shifted back-scattered light. We also describe an automated analysis of the LDF signals which rejects artifacts and false signals such as blinks. By using a Doppler simulator consisting of a lens and a rotating diffusing wheel, we demonstrate that velocity and flow vary linearly with the speed of the wheel. A cohort of 12 healthy subjects demonstrated that flicker stimulation induces an increase of 17.8% of blood flow in the ONH.
The design and development of the miniaturized interferometer for measurement of the refractive index or concentration
of sub-microliter volume aqueous solution in microfludic chip is presented. It is manifested by a successful measurement
of the refractive index of sugar-water solution, by utilizing a laser diode for light source and the small robust
instrumentation for practical implementation. Theoretically, the measurement principle and the feasibility of the system
are analyzed. Experimental device is constructed with a diode laser, lens, two optical plate and a complementary metal
oxide semiconductor (CMOS). Through measuring the positional changes of the interference fringes, the refractive index
change are retrieved. A refractive index change of 10-4 is inferred from the measured image data. The entire system is
approximately the size of half and a deck of cards and can operate on battery power for long time.
A portable choroidal laser Doppler flowmeter (LDF) with enhanced sensitivity based on a scattering plate is developed. The portable LDF is weighted 2 kg operated at center wavelength of 780 nm, leading to a better penetration into the eye fundus in contrast to the previous LDF operated at center wavelength of 670 nm. Enhancement of number of detected photons that undergo Doppler scattering and improved measured speed of choroidal blood flow are achieved with the use of a scattering plate positioned in front of the eye. The mechanism of detection and sensitivity enhancement is theoretically analyzed. Evaluation of system performance is done by in vivo measurements on ten volunteers. The results demonstrate that an increased percentage of backscattering light at high Doppler shift frequency is collected due to utilization of the scattering plate. However, this kind of light detection influences spatial resolution of the system and decreases the total signal measured. The proposed method for detection and sensitivity enhancement might be useful in a case where the perception of very slight alternation of blood flow is pursued and the spatial resolution is not as critical as that in a choroidal vascular bed.
Dual-wavelength optical low-coherent interferometry is proposed in this paper to measure the oxygen saturation in
human retinal blood vessel. Wavelength consideration is made from the standpoint of eye safety and system
sensitivity. Principle of oxygen saturation measurement based on dual-wavelength low-coherence interferometer is
thoroughly developed. Numerical simulation on interference signal versus oxygen saturation corresponding to the
oxygen sensitive wavelength and the isobestic wavelength is conducted.
A compact laser Doppler flowmeter (35x80x210mm3) for the measurement of subfoveal choroidal blood flow parameters (ChBF) was mounted on a helmet. This device allows the measurement of ChBF during dynamic exercises or in supine position, without the need for pupil dilatation. Its optical system is based on a Schlieren arrangement by which the surface of light collection and that of the illumination are spatially separated by an obscuration. The laser probing beam ((lambda) equals 790 nm, 100 (mu) W at the cornea) is focused at the fovea by having the tested subject look directly at the beam. Computer analysis of the photocurrent produced by the scattered light provides a relative measure of the mean blood velocity, number and flux of the red blood cells in the choriocapillaris. Measurements were performed to assess the reliability of the flow parameters measurements in normal volunteers: reproducibility and sensibility when subjects are sitting or standing; measurement of changes in ChBF in the case of isometric and dynamic exercises. Results demonstrate that this new helmet-mounted device provides data comparable to the conventional device. It allows for the first time, however, the continuous measurement of choroidal hemodynamics in humans during various types of exercises.
The goal of this work is to allow a precise measurement of bar turning pieces. The dimensions of the pieces under study were smaller than 50mm. We have developed an illumination system which is specifically designed for a telecentric objective. Furthermore a special positioning system, which allows an integration of the measurement in a fabrication process, was added to the system. Thanks to this arrangement, it is possible to follow and master the fabrication process with a relative tolerance of the dimension of about 0.07 percent for the process and about 0.014 percent for the final control.
An interactive CAD system for a computer-generated hologram (CGH) is developed to produce many kinds of CGHs in the form of Postscript files, G-code files for NC machines, and HPGL files. These files can later be sent to a laser printer and also a laser beam lithography system. The laser beam lithography system developed has a writing area of 200 mmA approximately 200 mm with 0.5E m positional accuracy. By using the LBL system, some CGHs for optical interconnection and kinoforms are optimized with the simulated annealing algorithm.
We have produced a high efficient phase-only hologram, of which refractive index distribution is
modified by using an ion exchange method. This paper describes an optimum condition of the phase
profile of the hologram. In computer simulation, ion density and phase profile generated by ion
exchanging is calculated. The diffractiion patterns of the gratings are calculated based on phase
distribution data of the gratings. An optimum phase distribution is estimated. The optimum condition is
Petzval curvature plays an important role in the design of a triplet. Its value should be defined at the beginning of the design process, and along with the field of view, it will characterize the type of design. For these reasons, a look at the consequences of choosing various Petzval values is interesting. Different image quality criteria versus the Petzval radius for different glass combinations are studied. It is shown that the natural Petzval radius of a Cooke triplet lies at about - 2.7 times the focal length.