Heterodyne moiré surface profilometry.

In this study, a novel moiré fringe analysis technique is proposed for measuring the surface profile of an object. After applying a relative displacement between two gratings at a constant velocity, every pixel of CMOS camera can capture a heterodyne moiré signal. The precise phase distribution of the moiré fringes can be extracted using a one-dimensional fast Fourier transform (FFT) analysis on every pixel, simultaneously filtering the harmonic noise of the moiré fringes. Finally, the surface profile of the tested objected can be generated by substituting the phase distribution into the relevant equation. The findings demonstrate the feasibility of this measuring method, and the measurement error was approximately 4.3 µm. The proposed method exhibits the merits of the Talbot effect, projection moiré method, FFT analysis, and heterodyne interferometry.

Vortex-assisted liquid-liquid microextraction coupled with derivatization for the fluorometric determination of aliphatic amines.

A new one-step derivatization and microextraction technique was developed for the fluorometric determination of C(1)-C(8) linear aliphatic primary amines in complex sample solutions containing high levels of amino acids. In this method, amines were derivatized with o-phthalaldehyde (OPA) and 2-mercaptoethanol (2-ME) in aqueous solution and extracted simultaneously by vortex-assisted liquid-liquid microextraction (VALLME). Parameters affecting the extraction efficiency were investigated in detail. The optimum conditions were as follows: 50 µL of isooctane as the extractant phase; 2.0 mL aqueous donor samples with 12 mM OPA, 24 mM 2-ME, and 0.1 M borate buffer at pH 10; 1 min vortex extraction time; centrifugation for 4 min at 6000 rpm. After centrifugation, the enriched analytes in the floated extractant phase were determined by HPLC-FL in less than 14 min. Under the optimum conditions, the limits of detection were of the order of 0.09-0.31 nM. The calibration curves showed good linearity over the investigated concentration range between 0.4 and 40 nM. The proposed method has been applied to the determination of aliphatic amines in acidophilus milk, beer, and Cu(II)/amino acid solution.

High-accuracy thickness measurement of a transparent plate with the heterodyne central fringe identification technique.

In a modified Twyman-Green interferometer, the optical path variation is measured with the heterodyne central fringe identification technique, as the light beam is focused by a displaced microscopic objective on the front/rear surface of the test transparent plate. The optical path length variation is then measured similarly after the test plate is removed. The geometrical thickness of the test plate can be calculated under the consideration of dispersion effect. This method has a wide measurable range and a high accuracy in the measurable range.

Alternative method for measuring the full-field refractive index of a gradient-index lens with normal incidence heterodyne interferometry.

A linearly/circularly polarized heterodyne light beam coming from a heterodyne light source with an electro-optic modulator in turn enters a modified Twyman-Green interferometer to measure the surface plane of a GRIN lens. Two groups of periodic sinusoidal segments recorded by a fast complementary metal-oxide semiconductor camera are modified, and their associated phases are derived with the unique technique. The data are substituted into the special equations derived from the Fresnel equations, and the refractive index can be obtained. When the processes are applied to other pixels, the full-field refractive-index distribution can be obtained similarly. Its validity is demonstrated.

Method for gauge block measurement with the heterodyne central fringe identification technique.

In a modified Michelson interferometer, the top face of the wringing platen is first identified using the heterodyne central fringe identification technique. Then the reference mirror located in the other arm is moved by a precision translation stage until the top face of the tested gauge block is also identified with the same technique. The displacement of the mirror is exactly equivalent to the length of the tested gauge block. The measurable range of the interferometer relates to the maximum travel range of the translation stage and its uncertainty depends on the uncertainty of the heterodyne central fringe identification method and the resolution of the translation stage.

Measurement of the pretilt angle and the cell gap of nematic liquid crystal cells by heterodyne interferometry.

This work proposes a simple method, based on the crystal rotation technique and heterodyne interferometry, to simultaneously determine the pretilt angle and cell gap of nematic liquid crystal cells. When heterodyne light passes through a nematic liquid crystal cell, the phase retardation given by the characteristic parameters of the cell can be measured accurately by heterodyne interferometry. This phase retardation relates to the pretilt angle, cell gap, and angle of incidence on the cell. By using the measured phase retardations at two incident angles, the pretilt angle and cell gap of the nematic liquid crystal cell can be estimated by numerical analysis. This method is feasible, requiring only two incident angles and prior knowledge of two characteristic parameters--extraordinary and ordinary refractive indices of the liquid crystal. It is characterized by the advantages of simplicity of installation, ease of operation, high stability, high accuracy, and high resolution.