KEYWORDS: Sensors, Cameras, Microscopy, Light emitting diodes, Photodetectors, Signal to noise ratio, Time metrology, Statistical methods, Optical testing, Single photon
In modern single pixel microscopy techniques, like Nano-Illumination Microscopy, long measurement times can become a major issue, especially when imaging biological tissues with large field of view. Usually, light intensity measurements are performed with CMOS pixels, with typical integration times around tens of milliseconds. In this work, we propose to obtain a light intensity measurement indirectly by applying statistical techniques to the photon arrival times gathered with an SPAD photodetector. We will present how the different statistical measurements can be used to minimize the total acquisition time and minimize also the hardware required. In this work, with captures of 256 SPAD measurements, reducing measurement time from 50ms to 50us. The dynamic range is extended by combining multiple statistical techniques with standard intensity measurements. This paves the way to practical Nano-Illumination Microscopy and other single pixel microscopy techniques.
Nano-Illumination Microscopy (NIM) is a technique that provides compact microscopes but at the present time only setups with limited Field-of-View (FOV) have been presented. Existing NIM setups reconstruct the image by measuring the light intensity that passes through the specimen when switching after one another the light emitting diodes (LEDs) on an array. The resolution of NIM is related to the LEDs pitch, while the FOV to the total area covered by the array. The first prototypes were demonstrated with 10 μm-pitch GaN-based 8x8 LED arrays giving rise to 80x80 μm2 FOV. This work presents the first electronically-activated Scanning Transmission Optical Microscope (eSTOM) built with an Organic LED-on-silicon micro-display with 5 μm LEDs pitch, providing a FOV of 3.6 × 1.28 mm2 . It is combined with a CMOS optical sensor with no other optical or mechanical components. We demonstrate how downscaling of the OLED array by means of optical lenses allows to further reduce the size of the light sources to explore the technique in more detail. Here we show steps towards the utility of NIM as a practical, low-cost and compact microscopy technique for biophotonics and many other applications.
In this work we present a new microscope based on Nano-illumination microscopy (NIM), i.e., an innovative technique based on a 2D array of nano-Light-Emitting Diodes (LEDs) used to illuminate a sample. The key point of this method is that the pitch of the LED array fixes the spatial resolution. So, potentially, with LED pitches lower than the diffraction limit, super resolution could be achieved. While nanometer sized LEDs are not available yet, we present a prototype based on optical downscaling of a single 5µm lateral size LED. Extended Field-of-View (FOV) is obtained by mechanical movement with nanopositioners. Aspects of NIM microscopy such as its size, its flexibility in the sensing hardware or its potential for fluorescence, make it a perfect candidate to enhance emerging sensing applications in different fields, but especially life science (medical imaging, genomics, ...). We demonstrate the possibilities of the NIM technique with patterns as well as with biological samples.
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