Event based coherence scanning interferometry.

Coherence scanning interferometry enables high precision measurements in manifold research and industry applications. In most modern systems, a digital camera (CCD/CMOS) is used to record the interference signals for each pixel. When measuring steep surfaces or using light sources with a broad wavelength spectrum, only a small area of the sensor captures useable interference signals in one frame, so a large fraction of pixels is unused. To overcome this problem and enable measurements with high dynamic range and high scan speeds, we propose the use of an event based image sensor. In these sensors, each pixel independently registers only changes in the signal, which leads to a continuous asynchronous pixel stream of information not based on fixed frame capturing. In this Letter, we show the signal generation, an implementation in a coherence scanning microscope in combination with the nanopositioning and nanometrology machine NPMM-200, and first measurements as promising results for event based interferometry.

Optimum Wavelengths in the Near Infrared for Imaging Photoplethysmography.

OBJECTIVE: The purpose of this contribution is to determine the ideal near infrared wavelength bands for monochromatic and dual-band remote heartbeat detection using imaging photoplethysmography (iPPG) of the forehead. METHODS: Experimental data of 38 healthy volunteers has been recorded and analyzed. For the data acquisition, a fast hyperspectral imager has been used. A new combination approach has been implemented that computes the quotient of the bands and, therefore, reduces motion artifacts. RESULTS: With this dual-band method excellent results (1.67 beats per minute mean deviation from electrocardiogram measurements for 73 recordings) have been obtained using a simple algorithm to analyze images at 799 and 861 nm. CONCLUSION: It can be concluded that excellent imaging photoplethysmography measurements can be performed at low cost using conventional silicon-based image sensors with invisible light in the near infrared region. SIGNIFICANCE: This approach is a contribution to the development of non-contact heart rate measurement systems that can be used for medical diagnosis or other applications.