Two spatially and spectrally resolved narrowband absorbers based on 2D grating nanostructures (polymethylmethacrylate (PMMA) grating and gold grating) on metallic films are designed, fabricated, and characterized. For PMMA grating on a metallic film, the measured absorption bandwidth is 12 nm with a nearly 80% absorption at normal incidence. The transverse electric (TE) localized mode shows a calculated 3.5° angular width. The transverse magnetic (TM) resonant mode supports both a localized mode and a lattice mode. The TM lattice mode shows a calculated angular width of 0.75° and exhibits a large wavelength-angle sensitivity of nearly 15 nm per degree and a large absorption-angle sensitivity of 77.5% per degree. For gold grating on a metallic film, the measured absorption bandwidth is 40 nm with a nearly 70% absorption. Such spatially and spectrally resolved 2D nanostructure arrays with large angle sensitivities have potential applications in angle measurement, thermal emitters, optical filters, and biosensors.

Spatially and Spectrally Resolved Narrowband Optical Absorber Based on 2D Grating Nanostructures on Metallic Films

A two-dimensional (2D) angle probe was developed to realize a new scanning multi-probe instrument employing 2D angle probes for flatness measurement of large silicon wafers. Each probe, which utilizes the principle of autocollimation, detects the 2D local slope components of a point on the wafer surface. The 2D local slopes (angles) are obtained through detecting the corresponding 2D positions of the reflected light spot on the focal plane of the object lens using position-sensing devices (PSDs). To make the probe compact in size, it is more effective to improve the sensitivity of angle detection by selecting proper PSDs than using an objective lens with a larger focal distance. Two kinds of photo devices, linear lateral effect PSDs and quadrant photodiodes (QPD), for sensing 2D positions were discussed theoretically and experimentally. It was shown that a QPD is the best for highly sensitive 2D angle detection. In the experiments, a compact prototype angle probe with dimensions 90 (L) mm ×60 (W) mm ×30 (H)  mm employing a QPD as the PSD was confirmed to have a resolution of approximately 0.01 arc-second.

A compact and sensitive two-dimensional angle probe for flatness measurement of large silicon wafers

An optical method for precision small-angle measurement based on CCD-area-based autocollimator is proposed in this article. The autocollimator utilizes CCD area—an interline CCD image sensor in a video camera as its detector. A collimated image is taken by the video camera and captured into the memory of a personal computer by an image board with high performance, then the image is transformed into a digital image and can be further processed by software with special arithmetic. A small angular displacement is magnified twice by the collimator objective with a long focal length and the camera lens of the video camera. By using a cold-light source and special data processing arithmetic, the measuring resolution of the autocollimator has been greatly improved. The method is proved to be reliable by a prototype experiment. Although some inexpensive materials were used in the experiment, two-axis angular displacement can be measured simultaneously and a measuring accuracy of 0.01 arcsec has been achieved. If some expensive materials with lower temperature expansion coefficient are used, a measuring accuracy of about 0.005 arcsec or a much higher measuring accuracy can be achieved. Until now, this has been the highest measuring accuracy.

CCD-area-based autocollimator for precision small-angle measurement

A new development in angle measurement based on the internal-reflection effect (AMIRE) is described in which a pair of right-angle prisms is used to replace the previously used elongated critical-angle prisms, resulting in lower costs and a more compact size. Excellent linearity is achieved through careful alignment of the right-angle prisms. The measurement sensitivity and range can be selected through the use of light sources with different polarization states. Experiments with a prototype sensor demonstrated a measurement range of 1.6°, a resolution of 0.04 arcsec, and a nonlinearity error of ±0.1%. Both analytical and experimental results are presented.

Angle measurement based on the internal-reflection effect and the use of right-angle prisms.

This paper presents a new error separation method for accurate roundness measurement called the orthogonal mixed method. This method uses the information of one displacement probe and one angle probe to separate roundness error from spindle error. This method was developed from the mixed method, which uses the information of two displacement probes and one angle probe to carry out the error separation. In the present paper, the relationship between the characteristics of the mixed method and the probe arrangement is analyzed. Well-balanced harmonic response of the mixed method is verified to be obtainable for the case where the angular distance between the displacement probe and the angle probe is set at 90°. This orthogonal mixed method also had the simplest probe arrangement, because it requires only one displacement probe and one angle probe to realize the error separation. Optical probes were used to construct an experimental measurement system that employs the orthogonal mixed method. The displacement probe and the angle probe both use the principle of the critical angle method of total reflection, and they have stabilities of 1 nm and 0.01 in., respectively. The measurement results show that roundness measurement can be performed with a repeatability on the order of several nanometers.

High-accuracy roundness measurement by a new error separation method

We describe a new method of angle measurement that is based on the internal-reflection effect at an air-glass boundary. The method uses a differential detection scheme to largely reduce the inherent nonlinearity of the reflectance versus the angle of incidence in internal reflection. With nonlinearity reduced, the displacement of the angle of incidence can be determined accurately by measuring the reflectance. The resolution and measurement range are determined by the initial angle of incidence, the polarization state of the light, and the number of reflections. Compared with interferometers and autocollimators, this method has the advantage of a simple sensor design for applications ranging from a wide measurement range to extremely high resolution. Other advantages are compact size, simple structure, and low cost. A theoretical analysis of the method and some experimental results of a prototype sensor are presented. The possible applications of the method are also discussed.

P. S. Huang

Papers

Angle measurement based on the internal-reflection effect: a new method