Final Report Summary - REALTIMEIMAGING (Real Time Imaging with Near Field Focusing Plates)
Fast laser scanning systems especially for high-throughput applications that require scanning a large area or many objects in a short period of time are highly desired in many areas ranging from defense, microscopy, surface metrology and micro-manufacturing. Various types of laser scanning technologies such as the galvanometric mirrors which and acousto-optic deflectors (AODs) which provide 2D scan rates of respectively 100 Hz and ~1 kHz have been proposed. Digital micro-mirror device (DMD) providing extremely faster switching speeds (<30μs), higher fill factor of 90%, higher diffraction efficiency of %88, feasibility for wide range of wavelengths (UV to NIR), exceptional stability and excellent controllability over thousands of individual micro mirrors can be used for fast beam steering applications. In this project, we proposed and demonstrated a novel method for 2D spatial disperser by using these MEMS based digital micro-mirror arrays in an amplified time stretched dispersive system. Proposed research and imaging technique relies on space time wavelength mapping technique. In this technique we use chromatic dispersion to map spectral information in time domain such that each temporal position carries the information different colors of the short pulse laser spectra. Here we use a mode locked fiber laser at 1550nm. In the second stage of the experiment we use spatial dispersion such as gratings and prisms to map each colors to different spatial points. As a result information collected by different colors from different spatial points will arrive to the detector at different times which will facilitate time domain analysis in real time. In particular, in our experiment we investigated novel method that can create 2 dimensional scanning by using novel MEMS based digital light mirror arrays. In the first phase of experimental work we demonstrate scanning ~20mm2 with ~20μm lateral and ~25μm vertical resolution that can be controlled by using 1024x768 mirror arrays in the first phase of the project. In the second phase of the research, the PI had proposed development of real time imaging system with subwavelength resolution and investigation of its applications in manufacturing and bio areas.
In our experimental study we use MEMS mirror arrays to create beam steering by means of individually tuning the mirrors angles. We have already illustrated and published an imaging system that can achieve imaging area of 5mmx5mm in 50ns time frame that is limited by the laser repetition rates. We have also illustrated particle tracking without using the light mirrors. Most of the efforts in the second period spent on the development of nano surfaces and its applications. To achieve this goal we have designed and fabricated plasmonic metasurfaces to increase the power efficiency of diffractive optics and also designed and fabricated plasmonic focusing lenses suitable to achieve high resolution imaging. In particular we fabricated a novel single layer metalens design based on Y-shaped nanoantennas capable of focusing and polarization manipulation, simultaneously. The theory and the examples developed here will enable improvement of several devices, such as (i) reflecting or (ii) transmitting focusing lenses, (iii) polarizing lenses, (iv) lenses with dual foci, one for each polarization, and (v) lenses with dual foci one for each wavelength. Moreover we have illustrated how to use such imaging system for real time quality control in micro manufacturing environment. Recently we have completed a new application of the imaging system for bio applications by utilizing optical tweezing properties. These achievements exceed the four objectives of the proposed work.
In dispersive imaging system, wavelength-to-space mapping was usually realized by using spatially dispersive components, such as diffraction grating, digital micro-mirror devices (DMD), acoustic-optical deflectors and virtually imaged phased array. However, low diffraction or power efficiency associated with these devices often poses serious limitations on the performance of the dispersive imaging systems. Alternative mechanisms have to be sought. In this research we have investigated metasurfaces as a means of sub-wavelength phase manipulation for micro/nano-scale light control. Among all types of proposed metasurfaces, metal-backed metasurface, known as gap-plasmon metasurface (GPM), have the advantage of high efficiency and conservation of polarization. In this work, the idea of wavefront manipulating plasmonic metasurfaces has been investigated to improve the power efficiency and diffraction efficiency of conventional diffractive optical components. We designed and fabricated a GPM-based blazed grating operating at 1550nm optical communication band to replace the grating in the dispersive imaging system to improve power efficiency. The fabricated GPM grating consists of an array of unit cells and provides reflection at an angle of ~51º with an angular dispersion of ~0.4º/10nm. The power efficiency of the grating was measured to be as high as 75.6%. By incorporating the GPM-based grating into the dispersive imaging system, we achieved an imaging resolution of <300µm. Sub-wavelength manipulation of wave-front phase at infrared wavelength opens the door to a wide range of telecommunication applications and can be extended to any device based on wavefront engineering. Since the proposed and implemented device is planar, it can be easily integrated with other components, which is a key to future miniaturization of complex systems.
In our experimental study we use MEMS mirror arrays to create beam steering by means of individually tuning the mirrors angles. We have already illustrated and published an imaging system that can achieve imaging area of 5mmx5mm in 50ns time frame that is limited by the laser repetition rates. We have also illustrated particle tracking without using the light mirrors. Most of the efforts in the second period spent on the development of nano surfaces and its applications. To achieve this goal we have designed and fabricated plasmonic metasurfaces to increase the power efficiency of diffractive optics and also designed and fabricated plasmonic focusing lenses suitable to achieve high resolution imaging. In particular we fabricated a novel single layer metalens design based on Y-shaped nanoantennas capable of focusing and polarization manipulation, simultaneously. The theory and the examples developed here will enable improvement of several devices, such as (i) reflecting or (ii) transmitting focusing lenses, (iii) polarizing lenses, (iv) lenses with dual foci, one for each polarization, and (v) lenses with dual foci one for each wavelength. Moreover we have illustrated how to use such imaging system for real time quality control in micro manufacturing environment. Recently we have completed a new application of the imaging system for bio applications by utilizing optical tweezing properties. These achievements exceed the four objectives of the proposed work.
In dispersive imaging system, wavelength-to-space mapping was usually realized by using spatially dispersive components, such as diffraction grating, digital micro-mirror devices (DMD), acoustic-optical deflectors and virtually imaged phased array. However, low diffraction or power efficiency associated with these devices often poses serious limitations on the performance of the dispersive imaging systems. Alternative mechanisms have to be sought. In this research we have investigated metasurfaces as a means of sub-wavelength phase manipulation for micro/nano-scale light control. Among all types of proposed metasurfaces, metal-backed metasurface, known as gap-plasmon metasurface (GPM), have the advantage of high efficiency and conservation of polarization. In this work, the idea of wavefront manipulating plasmonic metasurfaces has been investigated to improve the power efficiency and diffraction efficiency of conventional diffractive optical components. We designed and fabricated a GPM-based blazed grating operating at 1550nm optical communication band to replace the grating in the dispersive imaging system to improve power efficiency. The fabricated GPM grating consists of an array of unit cells and provides reflection at an angle of ~51º with an angular dispersion of ~0.4º/10nm. The power efficiency of the grating was measured to be as high as 75.6%. By incorporating the GPM-based grating into the dispersive imaging system, we achieved an imaging resolution of <300µm. Sub-wavelength manipulation of wave-front phase at infrared wavelength opens the door to a wide range of telecommunication applications and can be extended to any device based on wavefront engineering. Since the proposed and implemented device is planar, it can be easily integrated with other components, which is a key to future miniaturization of complex systems.