Periyasamy Angamuthu Praveen

A furan derivative, 2-[1,1'-biphenyl]-4-yl-5-(5'-[1,1'-biphenyl]-4-yl-[2,2'-bithiophen]-5-yl)furan (BPFTT), was designed and synthesized and shown to have excellent optical and electronic characteristics. The synthesized compound exhibits a photoluminescence quantum yield (PLQY) of 28%. In addition, a field-effect transistor fabricated using this material in the active layer exhibits ambipolar mobilities of 0.54 (hole) and 0.03 (electron) cm² V^-1 s^-1. Single crystals with their natural crystal edges acting as Fabry-Pérot resonators exhibit dual gain narrowing phenomena with optical pumping thresholds as low as 15 μJ/cm². Introducing planar distributed feedback resonators reduces the threshold to 2.41 μJ/cm², with the Q-factor reaching 1.5 × 10⁴. The full width at half-maximum is measured to be 0.074 nm, which is an excellent value reported to date for any organic single-crystal laser.

We design and synthesise an organic lasing system, 2,5-bis(5-[1,1′-biphenyl]-4-ylthiophen-2-yl)furan, which has advanced optoelectronic properties. Grown as a single crystal, this monoclinic system exhibits typical H-aggregation and has a photoluminescence quantum yield of 29% and ambipolar field effect mobilities of approximately 0.7 (hole) and 0.1 (electron) cm² V⁻¹ s⁻¹. The system is validated for its suitability towards laser development, and it exhibits excellent gain along with dual gain-narrowing emission in the yellow region. It has superior optical and electrical properties compared to its structural counterpart and similar systems. The system can be further developed by incorporating a planar resonator structure and using contact engineering techniques to realise electrically driven semiconductor lasers.

A detailed understanding of charge transport at the interface is necessary to explore the potential of organic field‐effect transistors. This can be realized by adequately analyzing the trap states at the interface. In the present work, rubrene‐based organic field‐effect transistors have been fabricated with three different interfaces. The device properties are used along with a technology computer‐aided design to deduce the interface trap density quantitatively. The transfer characteristics are simulated using a double Gaussian density of states and fitted with experimental data by adding traps to the semiconductor dielectric interface. A typical transistor with SiO₂ interface has shown an interface trap density of about ≈10¹⁶ cm⁻², and it is reduced to 10¹⁴ cm⁻² when poly(methyl)methacrylate or polystyrene is coated on SiO₂ interface, attributed to the surface passivation. This approach provides a simple and accurate way to estimate the interfacial traps and offers the possibility to tune the device architecture and performance.

Pattern recognition techniques form the heart of most, if not all, incoherent linear shift-invariant systems. When an object is recorded using a camera, the object information is sampled by the point spread function (PSF) of the system, replacing every object point with the PSF in the sensor. The PSF is a sharp Kronecker Delta-like function when the numerical aperture (NA) is large with no aberrations. When the NA is small, and the system has aberrations, the PSF appears blurred. In the case of aberrations, if the PSF is known, then the blurred object image can be deblurred by scanning the PSF over the recorded object intensity pattern and looking for pattern matching conditions through a mathematical process called correlation. Deep learning-based image classification for computer vision applications gained attention in recent years. The classification probability is highly dependent on the quality of images as even a minor blur can significantly alter the image classification results. In this study, a recently developed deblurring method, the Lucy-Richardson-Rosen algorithm (LR²A), was implemented to computationally refocus images recorded in the presence of spatio-spectral aberrations. The performance of LR²A was compared against the parent techniques: Lucy-Richardson algorithm and non-linear reconstruction. LR²A exhibited a superior deblurring capability even in extreme cases of spatio-spectral aberrations. Experimental results of deblurring a picture recorded using high-resolution smartphone cameras are presented. LR²A was implemented to significantly improve the performances of the widely used deep convolutional neural networks for image classification.

Pattern recognition techniques form the heart of most, if not all, incoherent linear shift-invariant systems. When an object is recorded using a camera, the object information gets sampled by the point spread function (PSF) of the system, replacing every object point with the PSF in the sensor. The PSF is a sharp Kronecker Delta-like function when the numerical aperture (NA) is large with no aberrations. When the NA is small, and the system has aberrations, the PSF appears blurred. In the above case, if the PSF is known, then the object information can be obtained by scanning the PSF over the recorded object intensity pattern and looking for pattern matching conditions through a mathematical process called correlation. In this study, a recently developed deconvolution method, the Lucy-Richardson-Rosen algorithm (LR2A), has been implemented to computationally refocus images recorded in the presence of spatio-spectral aberrations. The performance of LR2A was compared against the Lucy-Richardson algorithm and non-linear reconstruction. LR2A exhibits a superior deconvolution capability even in extreme cases of spatio-spectral aberrations and blur. Experimental results of deblurring a picture captured using high-resolution smartphone cameras are presented. LR2A was implemented to significantly improve the performances of the widely used deep convolutional neural networks for image classification.

Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints, as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself, imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open. One such method is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large-area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system, but to focus independently on different points within the sensor area. This approach of a Large-Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and a smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element was implemented in indirect imaging mode using non-linear reconstruction and the Lucy–Richardson–Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed improved optical and computational imaging resolutions compared to previous studies.

Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open up. One such methods is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system but to focus independently on different points within the sensor area. This approach of Large Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element has been implemented in indirect imaging mode using non-linear reconstruction and Lucy-Richardson-Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed an improved optical and computational imaging resolutions compared to previous studies.

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction.