Anzhi He

Experimental measurement of the refractive index of biological tissues by total internal reflection

We discuss the refractive-index measurement of biological tissues by total internal reflection. The methodology of the measurement is illuminated comprehensively, and an experimental setup, combined with a data processing program, is developed correspondingly. Refractive indices of typical tissue samples are measured by use of the developed methodology. The agreement of our measurements with the reported results shows the validity of our scheme, which has the potential for being a simple, quick, and low-cost practical means for determining the refractive index of a turbid medium. Moreover, an empirical formula for evaluating the refractive index of Intralipid suspensions with different concentrations is also presented according to experimental measurements.

New method of asymmetric flow field measurement in hypersonic shock tunnel

In this paper a method of large aperture (?500 mm) high sensitivity moire deflectometry is used to obtain multidirectional deflectograms of the asymmetric flow field in hypersonic (M = 10.29) shock tunnel. At the same time, a 3-D reconstructive method of the asymmetric flow field is presented which is based on the integration of the moire deflective angle and the double-cubic many-knot interpolating splines; it is used to calculate the 3-D density distribution of the asymmetric flow field.

MEASUREMENT OF THREE-DIMENSIONAL TEMPERATURE FIELDS WITH INTERFEROMETRIC TOMOGRAPHY

Optical computerized tomography (OCT) technology is used to reconstruct the asymmetric three-dimensional temperature field generated by radiators and electronic chips. First, the OCT method is described. Second, the reconstructed results are tested by a double-cylinder radiator model. Finally, OCT is applied to reconstruction of the temperature field above the surface of a CPU. The air-temperature field above a CPU circuit can be imaged with an OCT system that reflects whether the heat production from different parts of the CPU is even; therefore possibly the technique can be used to determine whether the integrated-circuit design in the CPU is smart.

Multi-directional 3D flame chemiluminescence tomography based on lens imaging

Flame chemiluminescence tomography (FCT) has been widely used in flame diagnostics for three-dimensional (3D), spatially resolved measurements of instantaneous flame geometry and, to some extent, of species concentrations. However, in most studies, tomographic reconstructions are based on a traditional parallel projection model. Due to the light collection characteristics of a lens, a parallel projection model is not appropriate for the practical optical setups that are used for emission imaging, particularly at small F-numbers. Taking the light collection effect of the lens into account, this Letter establishes a complete and novel tomographic theory for a multi-directional tomography system consisting of a lens and CCD cameras. A modified camera calibration method is presented first. It determines the exact spatial locations and intrinsic parameters of the cameras. A 3D projection model based on the lens imaging theory is then proposed and integrated into the multiplicative algebraic reconstruction technique (MART). The new approach is demonstrated with a 12-camera system that is used to reconstruct the emission field of a propane flame, thereby resolving space and time.

Complex refractive index measurement of biological tissues by attenuated total reflection ellipsometry

To apply reflection ellipsometry to determine the real and imaginary parts of the refractive index of biological tissues simultaneously, we combine reflection ellipsometry with total internal reflection to warrant minimal influences by the strong scattering and absorption of biological tissues. A K9 glass prism with refractive index 1.51468 at wavelength 632.8 nm and a Glan prism polarizer with an angular sampling interval of 0.1 degrees were used in our experimental setup. Using the setup, the complex refractive indices of some typical mammalian tissues were measured under the wavelength of 632.8 nm. The results show that the indices of porcine muscle, liver, pancreas, and dermis tissues were 1.3713+0.062i, 1.3791+0.0087i, 1.3517+0.0113i, and 1.3818+0.0049i, respectively.

The study of laser-produced plasma on dielectric thin films

Abstract Time-resolved multi-frame interference records for the plasma that a YAG laser produced on dielectric thin films are made by using a Mach-Zehnder interferometer and an optical delaying system. The speed of two plasma shock and electron density are calculated according to a series of interferograms, and relevant results for a 15 ns pulse width (fwhm) 1.06 μm laser acting on the dielectric thin films within 150 ns are obtained.

Two-step spatial phase-shifting radial shearing interferometery with circular gratings

This Letter presents a simple radial shearing interferometery with circular gratings to measure the radial first-order derivative of arbitrary wavefront phase. Two spatial phase-shifted radial shearing interferograms can be simultaneously obtained by the system, and a two-step phase-shifting algorithm with arbitrary phase-shift value is proposed for phase retrieval. The measurement for spherical wave has shown the feasibility and validity, and the optical system is used to measure the radial first-order derivative of projection wavefront phase of a propane flame with plane incident wave.

Volume moiré tomography based on double cross gratings for real three-dimensional flow field diagnosis

Since the advantages of noncontact, strong antidisturbing capability and wide measurement range, moiré tomography has been considered a powerful diagnostic tool for flow fields. In this paper, the volume computerized tomography is introduced to obtain the real three-dimensional reconstruction based on moiré deflectometry. In order to realize volume moiré tomography (VMT), double cross gratings are applied in the moiré deflected system to gain the shearing phase distribution of the moiré deflected projection in two mutually perpendicular directions simultaneously. Thus, the scalar diffraction theory is used for analyzing the imaging process of VMT based on double cross gratings to achieve the explicit form of shearing phase. Finally, the real temperature distribution of a propane flame is reconstructed, which can confirm the VMT method.

Spatial phase-shifting characteristic of double grating interferometer

Double grating interferometer is usually used to achieve phase information from distorted wave front by its temporal phase-shifting characteristic. In this paper, the spatial phase-shifting characteristic of double grating interferometer is presented. The explicit intensity distributions of interferograms produced by double gratings are derived with the scalar diffraction theory, and the stable phase shift is found between plus-first, zero and minus-first order interferograms. Results indicate that the phase shift only depends on the grating period and the distance between two gratings if no phase object exists. If phase object exists, it varies on the interferograms. But the phase shifts are equal at any special point of interferograms. In particular, the triple grating interferometer is presented to generate at least four phase shift interferograms simultaneously with the similar method.

New reconstruction algorithm for moiré tomography in flow field measurements

A new iterative reconstruction algorithm is developed and applied to moire deflection tomography for flow field measurements. The algorithm is derived from the basic deflection formula and based on a modified algebraic reconstruction technique. The precision and convergence of the algorithm are analyzed through a numerical simulation. To capture multidirectional projection data, a rotatable deflectometric system is developed. The efficacy of the new algorithm is assessed by reconstructing an asymmetric temperature field. Furthermore, the algorithm is employed to investigate the image of a cross section of a free jet containing steep gradients and to reconstruct the density field of the rocket exhausted jet.