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Distance-Resolving Raman Radar Based on a Time-Correlated CMOS Single-Photon Avalanche Diode Line Sensor
摘要： Remote Raman spectroscopy is widely used to detect minerals, explosives and air pollution, for example. One of its main problems, however, is background radiation that is caused by ambient light and sample fluorescence. We present here, to the best of our knowledge, the first time a distance-resolving Raman radar device that is based on an adjustable, time-correlated complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode line sensor which can measure the location of the target sample simultaneously with the normal stand-off spectrometer operation and suppress the background radiation dramatically by means of sub-nanosecond time gating. A distance resolution of 3.75 cm could be verified simultaneously during normal spectrometer operation and Raman spectra of titanium dioxide were distinguished by this system at distances of 250 cm and 100 cm with illumination intensities of the background of 250 lux and 7600 lux, respectively. In addition, the major Raman peaks of olive oil, which has a fluorescence-to-Raman signal ratio of 33 and a fluorescence lifetime of 2.5 ns, were distinguished at a distance of 30 cm with a 250 lux background illumination intensity. We believe that this kind of time-correlated CMOS single-photon avalanche diode sensor could pave the way for new compact distance-resolving Raman radars for application where distance information within a range of several metres is needed at the same time as a Raman spectrum.
关键词： time-correlated single photon counting (TCSPC),remote Raman spectroscopy,CMOS single-photon avalanche diode (SPAD),time interval measurement,distance-resolving Raman radar,stand-off Raman spectrometer
更新于2025-09-23 15:21:21
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0.16 μm–BCD Silicon Photomultipliers with Sharp Timing Response and Reduced Correlated Noise
摘要： Silicon photomultipliers (SiPMs) have improved significantly over the last years and now are widely employed in many different applications. However, the custom fabrication technologies exploited for commercial SiPMs do not allow the integration of any additional electronics, e.g., on-chip readout and analog (or digital) processing circuitry. In this paper, we present the design and characterization of two microelectronics-compatible SiPMs fabricated in a 0.16 μm–BCD (Bipolar-CMOS-DMOS) technology, with 0.67 mm × 0.67 mm total area, 10 × 10 square pixels and 53% fill-factor (FF). The photon detection efficiency (PDE) surpasses 33% (FF included), with a dark-count rate (DCR) of 330 kcps. Although DCR density is worse than that of state-of-the-art SiPMs, the proposed fabrication technology enables the development of cost-effective systems-on-chip (SoC) based on SiPM detectors. Furthermore, correlated noise components, i.e., afterpulsing and optical crosstalk, and photon timing response are comparable to those of best-in-class commercial SiPMs.
关键词： Silicon photomultiplier (SiPM),photon counting,photon number resolution,optical crosstalk,time-correlated single-photon counting (TCSPC),afterpulsing
更新于2025-09-23 15:21:01
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Characterization of a Time-Resolved Diffuse Optical Spectroscopy Prototype Using Low-Cost, Compact Single Photon Avalanche Detectors for Tissue Optics Applications
摘要： Time-resolved diffuse optical spectroscopy (TR-DOS) is an increasingly used method to determine the optical properties of diffusive media, particularly for medical applications including functional brain, breast and muscle measurements. For medical imaging applications, important features of new generation TR-DOS systems are low-cost, small size and efficient inverse modeling. To address the issues of low-cost, compact size and high integration capabilities, we have developed free-running (FR) single-photon avalanche diodes (SPADs) using 130 nm silicon complementary metal-oxide-semiconductor (CMOS) technology and used it in a TR-DOS prototype. This prototype was validated using assessments from two known protocols for evaluating TR-DOS systems for tissue optics applications. Following the basic instrumental performance protocol, our prototype had sub-nanosecond total instrument response function and low differential non-linearity of a few percent. Also, using light with optical power lower than the maximum permissible exposure for human skin, this prototype can acquire raw data in reflectance geometry for phantoms with optical properties similar to human tissues. Following the MEDPHOT protocol, the absolute values of the optical properties for several homogeneous phantoms were retrieved with good accuracy and linearity using a best-fitting model based on the Levenberg-Marquardt method. Overall, the results of this study show that our silicon CMOS-based SPAD detectors can be used to build a multichannel TR-DOS prototype. Also, real-time functional monitoring of human tissue such as muscles, breasts and newborn heads will be possible by integrating this detector with a time-to-digital converter (TDC).
关键词： diffuse optical spectroscopy,time-resolved spectroscopy,tissue optics,single-photon avalanche diode,silicon photodetectors,time-correlated single-photon counting
更新于2025-09-23 15:21:01
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Resolution and contrast enhancement of laser-scanning multiphoton microscopy using thulium-doped upconversion nanoparticles
摘要： High-contrast optical imaging is achievable using phosphorescent labels to suppress the short-lived background due to the optical backscatter and autofluorescence. However, the long-lived phosphorescence is generally incompatible with high-speed laser-scanning imaging modalities. Here, we show that upconversion nanoparticles of structure NaYF4:Yb co-doped with 8% Tm (8T-UCNP) in combination with a commercial laser-scanning multiphoton microscopy are uniquely suited for labeling biological systems to acquire high-resolution images with the enhanced contrast. In comparison with many phosphorescent labels, the 8T-UCNP emission lifetime of ~ 15 μs affords rapid image acquisition. The high-order optical nonlinearity of the 8T-UCNP (n ≈ 4, as confirmed experimentally and theoretically) afforded pushing the resolution limit attainable with UCNPs to the diffraction-limit. The contrast enhancement was achieved by suppressing the background using (i) bandpass spectral filtering of the narrow emission peak of 8T-UCNP at 455-nm, and (ii) time-gating implemented with a time-correlated single-photon counting system that demonstrated the contrast enhancement of > 2.5-fold of polyethyleneimine-coated 8T-UCNPs taken up by human breast adenocarcinoma cells SK-BR-3. As a result, discrete 8T-UCNP nanoparticles became clearly observable in the freshly excised spleen tissue of laboratory mice 15-min post intravenous injection of an 8T-UCNP solution. The demonstrated approach paves the way for high-contrast, high-resolution, and high-speed multiphoton microscopy in challenging environments of intense autofluorescence, exogenous staining, and turbidity, as typically occur in intravital imaging.
关键词： time-correlated single photon counting,time-gated imaging,scanning microscopy,autofluorescence,upconversion nanoparticles
更新于2025-09-19 17:13:59