Low-quality Optics Research Articles

Single-path interferometer for measuring fluid flows in real time with low-quality optics

An interferometric concept based on a modified version of the Fabry–Perot interferometry is proposed for measuring flow fields in real-time and some results are presented for demonstration. Being based on a single-path configuration of interfering beams, it is very convenient to build a simple compact measurement system. While allowing the deployment of low-quality optics including test-section windows through compensation of system errors, it is also immune to external vibration. In addition, it can easily allow large aperture and long pathlength of probing beams with good precision. These aforementioned features are very appropriate for measuring large flow fields including wind tunnel testing as well as conducting laboratory experiments without elaborate equipment.

Practical common-path interferometry for real-time thermal/fluid flow measurements

Interferometric technique can be a useful gross-field diagnostic tool for quantitative and qualitative evaluation of thermal/fluid flow phenomena. Here, we present a practical interferometric approach based on a common-path configuration of the interfering beams with some results for demonstration. It incorporates advances in the modern optical technology to fully exploit the potential of interferometric techniques for on-site applications. The results of the initial testing are encouraging. The approach can allow one to build a simple and compact system insensitive to external disturbances for real-time monitoring with good measurement accuracy. The system errors contributed by low-quality optics can be eliminated by employing a moire technique. The approach based on the numerical moire, which utilizes the images directly captured by a solid-state camera to avoid wet chemical processing, appears to be promising.

Moire interferometry for out-of-plane displacement measurement

A high sensitivity technique for out-of-plane displacement is demonstrated. A 600 lines mm phase grating is used in conjunction with a specularly reflecting (in some cases mirrored) object, to obtain contours of out-of-plane displacement. Initial patterns due to low quality optics are eliminated by a double exposure technique employing carrier (or mismatch) fringes. Beams with cracks are used to experimentally demonstrate this technique.