Note: development of high speed confocal 3D profilometer.

A high-speed confocal 3D profilometer based on the chromatic confocal technology and spinning Nipkow disk technique has been developed and tested. It can measure a whole surface topography by taking only one image that requires less than 0.3 s. Surface height information is retrieved based on the ratios of red, green, and blue color information. A new vector projection technique has developed to enhance the vertical resolution of the measurement. The measurement accuracy of the prototype system has been verified via different test samples.

Note: real time three-dimensional topography measurement of microfluidic devices with pillar structures using confocal microscope.

Miniature pillars are three-dimensional (3D) features commonly found in microfluidic device. These features are usually employed as filters. Non-confocal profilometers have difficulties in measuring 3D topography of pillar structures in transparent microfluidic devices. Confocal sensors can be used to measure the 3D topography of pillar structures but they are usually time consuming due to the scanning process. We have developed a technique to measure 3D topography using a modified confocal microscope with a spinning Nipkow disk and chromatic confocal technique. Experimental results on a microfluidic device with pillar structures demonstrate the feasibility of the proposed technique. Our technique is suitable for in situ, real time measurement of microfluidic device at production speed since it requires only one confocal image to complete a measurement.

Feasibility study on bonding quality inspection of microfluidic devices by optical coherence tomography.

This paper reports the feasibility of optical coherence tomography (OCT) technology for inspection of bonding quality of microfluidic devices in manufacturing environments. A compact optical-fiber-based OCT is developed and its measurement performance is characterized. A series of microfluidic devices respectively bonded by adhesive tape, thermal method, and oxygen plasma, are inspected. The defects of geometry deformation and sealing completeness are emphasized during measurements. Based on the inspection results, some discoveries related to the production of microfluidic devices are discussed.

Measurement of buried undercut structures in microfluidic devices by laser fluorescent confocal microscopy.

Measuring buried, undercut microstructures is a challenging task in metrology. These structures are usually characterized by measuring their cross sections after physically cutting the samples. This method is destructive and the obtained information is incomplete. The distortion due to cutting also affects the measurement accuracy. In this paper, we first apply the laser fluorescent confocal microscopy and intensity differentiation algorithm to obtain the complete three-dimensional profile of the buried, undercut structures in microfluidic devices, which are made by the soft lithography technique and bonded by the oxygen plasma method. The impact of material wettability and the refractive index (n) mismatch among the liquid, samples, cover layer, and objective on the measurement accuracy are experimentally investigated.

Microvalve thickness and topography measurements in microfluidic devices by white-light confocal microscopy.

A microvalve is a key part in a multilayer microfluidic device to control the fluid flow, and its thickness directly determines its performance. In this paper, a three-dimensional measurement technology using a white-light confocal microscope is developed for measuring both the topography and thickness of microvalves. The impact of system parameters and sample parameters on measurement accuracy is discussed in detail, particularly for measurement with a dry objective. With this technique, the microvalve thicknesses before and after bonding were characterized with submicrometer measurement sensitivity and about 1 microm measurement accuracy.

Three dimensional sidewall measurements by laser fluorescent confocal microscopy.

Precise three dimensional (3D) profile measurements of vertical sidewalls of concave micro-structures are impossible by conventional profiling techniques. This paper introduces a simple technique which can obtain 3D sidewall geometry by means of laser fluorescent confocal microscopy and an intensity gradient algorithm. The measurement principle is: when a concave micro-structure is filled up with fluorescent solution, the position where the maximum intensity variation lays represents the profile of the micro-structure in the fluorescent 3D volume image. The physical essence behind this measurement principle is analyzed in this paper in detail. The strengths and limitations of this technique are studied by experiments or by illustrations. The factors that are able to improve the measurement accuracy are discussed. This technique has demonstrated the capability for measuring of 3D geometry of various concave features, such as vertical, buried and other micro channels with sub-mum (RMS) measurement accuracy and repeatability.

Efficient implementation of a spatial light modulator as a diffractive optical microlens array in a digital Shack-Hartmann wavefront sensor.

A traditional Shack-Hartmann wavefront sensor (SHWS) uses a physical microlens array to sample the incoming wavefront into a number of segments and to measure the phase profile over the cross section of a given light beam. We customized a digital SHWS by encoding a spatial light modulator (SLM) with a diffractive optical lens (DOL) pattern to function as a diffractive optical microlens array. This SHWS can offer great flexibility for various applications. Through fast-Fourier-transform (FFT) analysis and experimental investigation, we studied three sampling methods to generate the digitized DOL pattern, and we compared the results. By analyzing the diffraction efficiency of the DOL and the microstructure of the SLM, we proposed three important strategies for the proper implementation of DOLs and DOL arrays with a SLM. Experiments demonstrated that these design rules were necessary and sufficient for generating an efficient DOL and DOL array with a SLM.