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Near Infra-Red Surface Enhanced Raman Spectroscopy (NIR SERS) has gained huge attention in recent years as the conventional visible SERS suffers from overwhelming fluorescence background from the fluorophore resulting in the masking of Raman signals. In this paper, we propose a novel multi-layered SERS substrate- (Cu2O - Au) - Graphene - Au - for efficient NIR SERS applications. The proposed structure has a monolayer of Cu2O - Au core-shell particles on a Au substrate with 1 nm thick graphene spacer layer. Mie simulations are used to optimize the aspect ratios of core-shell particles to shift their plasmon resonances to NIR region using MieLab software. Further, Finite Difference Time Domain (FDTD) simulations using Lumerical software are used for the design of the multiparticle layered SERS substrate as MieLab software works only for single particle systems. Designed structure is shown to provide high field enhancement factor of the order of 108 at an excitation of 1064 nm thus ensuring the possibility of using the proposed structure as efficient NIR SERS substrate which could probably be used for various NIR sensing applications. Economic Development Board (EDB) Ministry of Education (MOE) Published version The authors acknowledge NTU, COLE-EDB and Ministry of Education, MoE Singapore (RG 192/17) for the financial support.

Additive manufacturing provides flexibility in making structures according to specific geometry requirements. Advances in this technology, including sophisticated laser-based stereolithography (SLA) technique, have paved the way to fabricate structures with layer resolutions up to 25 μm. Although the feasibility of random lasing is shown in 3D-printed structures, a study on varying lasing properties using SLA printing technique with continuous wave laser pumping is not studied yet in depth. Herein, SLA is used to fabricate structures conducive for random lasing. Randomly distributed vertical cylindrical microchannels are fabricated on a 1 cm × 1 cm photoresin chip of thickness 2 mm. The geometry of structures makes it viable for liquid optical gain media to be injected into the cylindrical channels. The random lasing characteristics are demonstrated including threshold and linewidths. Tunability in peak lasing wavelength, required threshold, and minimum achievable linewidth are demonstrated by changing the diameter of the microchannels. Further, it is shown that by changing the hole diameter from 260 to 470 μm, a wavelength tunability of approximately 22 nm is achieved. This structure expects to significantly contribute for its use as an on-chip photonic sensor, wherein liquid analytes achieved can be injected and sensed using optical parameters, and for on-chip spectroscopy applications. Ministry of Education (MOE) Submitted/Accepted version The authors acknowledge the financial support received through COLE funding and MOE-AcRF Tier 1 (No.: RG119/21), Ministry of Education, Singapore.

Hybrid optical elements, which combine refractive and diffractive optical components to enhance optical performance by taking advantage of the optical characteristics of the individual components, have enormous potential for next-generation optical devices. However, there have not been many reports on the simulation methodology to characterize such hybrid optical systems. Here, we present a method for simulating a hybrid optical element realized by attaching an ultra-thin, flexible diffractive optics array onto a refractive optical element. The ultra-thin diffractive optical element is fabricated by direct-laser-writing using a femtosecond pulsed laser as the light source. A systematic investigation of the proposed simulation method, which does not require extensive hardware resources or computational time, but retains resolution and accuracy, is presented. The proposed scheme is validated by comparing simulation and experimental results. The simulation and experimental results on the spot size and focal length for the diffractive Fresnel zone plate (FZP) match well, with typical errors of less than 6%. The aspect ratio of the focal spot sizes at the compound and FZP focal planes of the hybrid optical system from the simulation and experiment also match quite well, with typical errors below 7%. This simulation scheme will expedite the designs for novel hybrid optical systems with optimal optical performances for specific applications, such as microfluidics and aberration-controlled optics. Nanyang Technological University This work was financially supported by a research collaboration agreement by Panasonic Factory Solutions Asia Pacific (PFSAP) and Singapore Centre for 3D Printing (RCA15/027); National Research Foundation of the Republic of Korea (NRF-2012R1A3A1050386, 2020R1A2C2102338, 2021R1A4A1031660); Korea Forest Service (Korea Forestry Promotion Institute) through the R & D Program for Forest Science Technology (2020229C10-2022-AC01); and Basic Research Program funded by the Korea Institute of Machinery and Materials (NK224C).

Corneal diseases, along with glaucoma and cataract, are the leading causes of blindness worldwide. While corneal surgery offers good success rates, early diagnosis and disease prevention is the preferred choice over expensive and complex surgical procedures. Non-contact, high-resolution imaging modalities for imaging the corneal structures are highly desirable for clinical examinations for early diagnosis of corneal diseases. The currently used clinical standard is the in vivo confocal laser scanning microscopy, which is a contact based method. In this context, an in-house developed, non-contact, Gaussian epi-illumination based imaging system was used to image corneal injury in preclinical animal models in vivo. New Zealand white rabbits and Wistar rats were used as the preclinical models for the investigations. The lateral resolution of the developed system is 1.1 μm. The images obtained with the developed system, as well as the dimensional information of the corneal structures, are in good agreement with the data previously reported using standard methods. The proposed system offers a simple, easy operable, real-time, non-contact imaging modality for the evaluation of corneal structures in high-resolution. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University National Medical Research Council (NMRC) The authors acknowledge financial support received through A*STAR-MIG project (BMRC1619077002), SERI-NTU ADVANCED OCULAR ENGINEERING (STANCE) Program Fund, NMRC Singapore Translational Research Investigator Award (NMRC/STaR/0023/2014), NMRC Transition Award (NMRC/TA/0040/2015), and NMRC Transition Award (NMRC/TA/0057/2017) for pursuing parts of the contents presented in this paper, and the research manpower and facilities provided through funding at COLE, NTU.

Malfunctions in printed circuit boards (PCBs) are often caused by damaged copper traces. Printing materials such as metal nanoparticles, conductive polymers, and graphene along with novel printing methods are being actively explored for repairing the conductive connections in PCBs. Because of its high-resolution capability, direct writing of conductive traces gets significant attention, especially with the widespread use of flexible PCBs. Graphene is an ideal material for such applications due to its excellent electrical and mechanical properties. However, there have been limited reports on graphene-based methods for the facile fabrication of conductive traces. A novel method of femtosecond laser direct writing of graphene traces by the photoreduction of graphene oxide (GO) to conductive reduced GO (rGO) for repair and modification of legacy PCBs is reported. A trace-width resolution of 28.4 μm is achieved over a large patterning area of 100 mm × 100 mm. The rGO thickness is found to be tunable from 0.6 to 4.4 μm, while the sheet resistance is minimized to 100 Ω sq−1. The system capability is demonstrated by printing conductive traces on top of a flexible substrate to form a closed path for turning on a light-emitting diode, as well as, by repairing a commercial PCB. The authors acknowledge funding received from research collaboration agreement by Panasonic Factory Solutions Asia Pacific (PFSAP) and Singapore Centre for 3D Printing (RCA-15/027). Y.-J.K. acknowledges funding from National Research Foundation of the Republic of Korea (NRF-2012R1A3A1050386, NRF-2020R1A2C2102338, NRF2021R1A4A1031660), Korea Forest Service (Korea Forestry Promotion Institute) through the R&D Program for Forest Science Technology (2020229C10-2022-AC01), KAIST UP Program, and Basic Research Program (NK224C) funded by the Korea Institute of Machinery and Materials.

Purpose High-resolution imaging of the critical anatomic structures of the eye, especially of the anterior chamber, in vivo, remains a challenge, even with currently available state-of-the-art medical imaging techniques. This study aims for the noninvasive and noncontact sequential imaging of the iridocorneal angle, especially the trabecular meshwork (TM) and the cornea of the eye in high-resolution using a newly developed imaging platform. Methods Bessel beam scanned light sheet fluorescence microscopy is used to attain high-resolution images of the TM. The ability of the Bessel beam to self-reconstruct around obstacles increases the image contrast at the TM region inside eye by reducing scattering and shadow artifacts. With minimal modifications, the excitation arm of the developed imaging system is adapted for noncontact, high-resolution corneal imaging. Results High-resolution images of the TM structures and cellular-level corneal structures are obtained in ex vivo porcine eyes, and subsequently in New Zealand white rabbit, in vivo. The spatial resolution of the developed system is 2.19 µm and has a noncontact working distance of 20 mm. Conclusions A high-resolution imaging platform for noncontact sequential imaging of the TM and the cornea of the eye is developed. This imaging system is expected to be of potential interest in the evaluation and diagnosis of glaucoma and corneal diseases. Translational Relevance The developed prototype offers the plausibility of in vivo, noncontact, and high-resolution imaging of the iridocorneal angle and cornea of the eye that will aid clinicians in diagnosing open-angle glaucoma and corneal diseases better.

For powering wearable electronics, extensive research has been directed toward microscale flexible and stretchable energy-storage devices. Microsupercapacitors, though promising candidates, remain limited in terms of design flexibility, scalability, reusability, and compatibility with general substrates. This paper reports a high-performance sticker-type flexible microsupercapacitor using highly swollen reduced-graphene-oxide electrodes fabricated by an ultrashort-pulse laser to promote full active-site and durability of the electrodes. Our sticker-type flexible micropseudocapacitor provides a comparable volumetric energy density of 1.08 mWh cm−3 and 13 times higher volumetric power density of 83.5 mW cm−3 compared to conventional lithium thin-film batteries. Bio-inspired surface modifications are additionally applied to the reduced-graphene-oxide electrodes, which provides a six-fold increase (10.38 mF cm−2) of the areal capacitance. A 6 × 2 micropseudocapacitor array embedded in a sub-millimeter thin PDMS film adheres to safety goggles and successfully powers a μ-LED. The total capacitance of the array is maintained at ~97% of its original value after 200 repetitive attachments and detachments showing good durability. In addition, the sticker-type micropseudocapacitor array shows a stable performance under repeated deformation, and up to ~99% of capacitance retention after 200 bending cycles. This novel re-attachable flexible micropseudocapacitor will expedite the widespread use of flexible and wearable devices. National Research Foundation (NRF) Accepted version This work was supported by the Research and Development Program of the Korea Institute of Energy Research (KIER) [grant number B9-2461-02, B9-2434-01, B9-2434-03) (to H. Y.); and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1C1B5085456) (to Y. C.). Y.-J. Kim acknowledges financial support by an NRF Fellowship (NRF-NRFF2015-02) from the Singapore National Research Foundation and by a research collaboration agreement by Panasonic Factory Solutions Asia Pacific (PFSAP) and Singapore Centre for 3D Printing (RCA-15/027). S. K. acknowledges financial support from the Creative Materials Discovery Program (NRF-2017M3D1A1039287) and the Basic Research Lab Program (NRF-2018R1A4A1025623) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning.

Breaking the diffraction limit in imaging microscopes with far-field imaging options has always been the thrust challenge for optical engineers and biologists over the years. Although structured illumination microscopy and Bessel beam assisted imaging has shown the capability of imaging with sub-diffraction resolutions, they rely on the use of objective lenses with large numerical apertures (NA). Hence, they fail to sustain resolutions at larger working distances. In this context, we demonstrate a method for nanoscale resolution imaging at longer working distances, named as Structured Illumination Bessel Microscopy (SIBM). The proposed method is envisaged for both biological and engineering applications that necessitate high imaging resolutions at large working distances. EDB (Economic Devt. Board, S’pore) MOE (Min. of Education, S’pore) Published version

The use of carbon fiber-reinforced polymer (CFRP) composite materials in the aerospace industry have far improved the load carrying properties and the design flexibility of aircraft structures. A high strength to weight ratio, low thermal conductivity, and a low thermal expansion coefficient gives it an edge for applications demanding stringent loading conditions. Specifically, this paper focuses on the behavior of CFRP composites under stringent thermal loads. The properties of composites are largely affected by external thermal loads, especially when the loads are beyond the glass temperature, Tg, of the composite. Beyond this, the composites are subject to prominent changes in mechanical and thermal properties which may further lead to material decomposition. Furthermore, thermal damage formation being chaotic, a strict dimension cannot be associated with the formed damage. In this context, this paper focuses on comparing multiple speckle image analysis algorithms to effectively characterize the formed thermal damages on the CFRP specimen. This would provide us with a fast method for quantifying the extent of heat damage in carbon composites, thus reducing the required time for inspection. The image analysis methods used for the comparison include fractal dimensional analysis of the formed speckle pattern and analysis of number and size of various connecting elements in the binary image. NRF (Natl Research Foundation, S’pore) Published version

Time averaged imaging is one of the widely used methods to achieve improved image quality, used in different types of microscopic methods. Time averaged imaging refers to adjusting the exposure time of the imaging system to obtain optimal images. In state of the art microscopes, the region of interest (ROI) of illumination beam for time averaged imaging can be selected to be of regular shapes such as circle or rectangle. This forces smallest possible ROI to be larger than the actual sample’s ROI which can be of a specific shape with complex contours. In this context, we present a flexible fiber bundle based illumination probe capable of illuminating samples of irregular shapes for time averaged imaging. Further, this probe is capable of multi-wavelength illumination, hence can be used for multi-fluorescence imaging. The fiber probe with features such as region selective and multi- wavelength illumination allows it to be used for optimal imaging of multi-fluorescence sample. MOE (Min. of Education, S’pore) Published version

It is well known for structured illumination microscopy (SIM) that the lateral resolution by a factor of two beyond the classical diffraction limit is achieved using spatially structured illumination in wide-field fluorescence microscope. In the state of art SIM systems, grating patterns are generally generated by physical gratings or by spatial light modulators such as digital micro mirrors (DMD), liquid crystal displays (LCD). In this study, using a combination of LCD and ground glasses, size controlled randomized speckle patterns are generated as an illumination source for the microscope. Proof of concept of using speckle illumination in SIM configuration is tested by imaging fixed BPAE cells. MOE (Min. of Education, S’pore) Published version

Hyperspectral imaging was first used in remote sensing and since then, it has been used in many other applications such as cancer diagnosis, precision farming and assessment of the level of flaking in ancient murals. In order to make hyperspectral imaging available for a wide variety of applications, its imagers can be made to operate using different methods and developed into different configurations. This leads to each variant having a set of specifications suitable for certain applications. The many variants of hyperspectral imager produce a set of three-dimensional spatial spatialspectral datacube, which is made up of hundreds of spectral images of one scene. A snapshot hyperspectral imaging probe has recently been developed by integrating a fiber bundle, which is made up of specially-arranged optical fibers, with a spectrograph-based hyperspectral imager. The snapshot method is able to produce a datacube using the information from each scan. The fiber bundle has 100 fiberlets which are arranged in a row in the one-dimensional proximal end, and are rearranged into a 10×10 hexagonal array in the two-dimensional distal end. The image captured by the two-dimensional end of the fiber bundle is reduced from two to one spatial dimension at the one-dimensional end. The raw data acquired from each scan has to be remapped into a datacube with the correct representation of the spectral and spatial features of the captured scene. This paper reports the spatial calibrations of both ends of the fiber bundle and image processing that have to be performed for such a remapping. MOE (Min. of Education, S’pore) Published version

Angle closure glaucoma accounts for majority of the bilateral blindness in Asian countries such as Singapore, China, and India. Abnormalities in the optic nerve and aqueous outflow system are the most indicative clinical hallmarks for glaucoma of this clinical subtype. Traditional photographic imaging techniques to assess the drainage angle are contact based, and may expose patients to risk of corneal abrasion and infections. In addition, these procedures require the use of viscous ophthalmic gels as coupling medium to overcome the phenomenon of total internal reflection at the tear-air interface. In this paper, we propose an integrated flexible handheld probe consisting of a micro color CCD video camera and white light LEDs. The handheld probe is able to capture images of the fundus and opposite iridocorneal angle when placed at the central cornea or limbus respectively. Here, we propose the use of hydrogel contact lens as an index matching medium and better protective barrier, as an alternative to conventional ophthalmic gels. The proposed imaging system and methodology has been successfully tested on porcine eye samples, ex vivo. With its high repeatability, reproducibility, and a good safety profile, it is believed that the proposed imaging system and methodology will complement existing imaging modalities in the diagnosis and management of glaucoma. NRF (Natl Research Foundation, S’pore) Published version

Surface characterization of the working components has always been a subject of interest among researchers and industry specialists. Especially in the aerospace industry where the aerodynamic capabilities are largely altered by the surface quality of the component of interest, there remains an extensive need for developing systems for effectively characterizing the surface quality. To realize an optical based non-contact and an in-line surface roughness measurement system, it is essential to understand the relationship between the quality of the surface and statistical parameter of the reflected speckles. The range of the measurement system being proportional to the wavelength of light used makes the analysis fundamentally important in order to understand the properties of speckles at a different wavelength. In this context, this paper examines the nature of the formed IR speckles from three different diffusers by analyzing their raw structure. Image processing algorithms that are developed study the different parameters of the 8-bit binary speckles, namely, the fractal property and number of connecting components. The paper also discusses the future work direction on relating the proposed analysis to derive the algorithm required for evaluating the surface finish parameters. NRF (Natl Research Foundation, S’pore) Published version

Gradient-Index (GRIN) lenses are characterized by its small diameter and length, enabling them to be an effective lens for an integrated probe based imaging system. For a speckle-based surface metrology system, the imaging lens plays an important role in deciding the statistical dimensions of the speckles. In such cases, the design and simulation of the lens system would be a key process to better the performance of the lensed imaging fiber probe. In this context, this paper focuses on the design of lensed fiber probes for a speckle-based surface metrological imaging system that can find intra cavity interrogation applications. Different optical properties of GRIN lenses and imaging fibers are considered while designing the final probe distal end to meet the targeted specifications. Singlet GRIN lens configuration is analyzed for a front view configuration and a parameter optimization has been carried out to obtain the specifications including the field-of-view, resolution, working distance and magnification. NRF (Natl Research Foundation, S’pore) Published version

Surface defect or damage is one of the critical factors leading to the failure of engineering materials and structures. The methodologies for the measurement of surface shape and feature or defect have been extensively explored and developed over the past few decades, including both contact and non-contact methods. Speckle pattern interferometry, as a non-contact optical method, has been demonstrated to effectively contour the surface shape through adjusting the illumination vector. However, few studies have been made to investigate the effect of the initial position of the illumination source as well as the source translation direction. In this paper, we report to carry out a study of measuring the surface form and feature using digital speckle pattern interferometry system via a slight translation of illumination source. Through theoretically analyzing the sensitivity factor along with the experimental validation, it is shown that the contouring fringe is more sensitive to the surface height with an off-axis illumination than the paraxial illumination. It is also found that translating the source along axial and lateral direction can be both used for the surface shape re-construction. NRF (Natl Research Foundation, S’pore) Published version

Laser speckle pattern is a granular structure formed due to random coherent wavelet interference and generally considered as noise in optical systems including photolithography. Contrary to this, in this paper, we use the speckle pattern to generate predictable and controlled Gaussian random structures and quasi-random structures photo-lithographically. The random structures made using this proposed speckle lithography technique are quantified based on speckle statistics, radial distribution function (RDF) and fast Fourier transform (FFT). The control over the speckle size, density and speckle clustering facilitates the successful fabrication of black silicon with different surface structures. The controllability and tunability of randomness makes this technique a robust method for fabricating predictable 2D Gaussian random structures and black silicon structures. These structures can enhance the light trapping significantly in solar cells and hence enable improved energy harvesting. Further, this technique can enable efficient fabrication of disordered photonic structures and random media based devices.

Non-contact imaging techniques are preferred in ophthalmology. Corneal disease is one of the leading causes of blindness worldwide, and a possible way of detection is by analyzing the shape and optical quality of the cornea. Here, a simple and cost-effective, non-contact optical probe system is proposed and illustrated. The probe possesses high spatial resolutions and is non-dependent on coupling medium, which are significant for a clinician and patient friendly investigation. These parameters are crucial, when considering an imaging system for the objective diagnosis and management of corneal diseases. The imaging of the cornea is performed on ex vivo porcine samples and subsequently on small laboratory animals, in vivo. The clinical significance of the proposed study is validated by performing imaging of the New Zealand white rabbit’s cornea infected with Pseudomonas. Published version

Medical diagnostics in the recent past has seen the challenging trend to come up with dual and multi-modality imaging for implementing better diagnostic procedures. The changes in tissues in the early disease stages are often subtle and can occur beneath the tissue surface. In most of these cases, conventional types of medical imaging using optics may not be able to detect these changes easily due to its penetration depth of the orders of 1 mm. Each imaging modality has its own advantages and limitations, and the use of a single modality is not suitable for every diagnostic applications. Therefore the need for multi or hybrid-modality imaging arises. Combining more than one imaging modalities overcomes the limitation of individual imaging method and integrates the respective advantages into a single setting. In this context, this paper will be focusing on the research and development of two multi-modality imaging platforms. The first platform combines ultrasound and photoacoustic imaging for diagnostic applications in the eye. The second platform consists of optical hyperspectral and photoacoustic imaging for diagnostic applications in the colon. Photoacoustic imaging is used as one of the modalities in both platforms as it can offer deeper penetration depth compared to optical imaging. The optical engineering and research challenges in developing the dual/multi-modality platforms will be discussed, followed by initial results validating the proposed scheme. The proposed schemes offer high spatial and spectral resolution imaging and sensing, and is expected to offer potential biomedical imaging solutions in the near future. Published version

This article reviews different waveguide based architectures forlabel-free detection of biomolecules. Working principles of various configurationsare discussed with an emphasis on their sensing principle and sensitivity. Later part of the article demonstrates a silicon waveguide Bragg grating resonator array as a highly sensitive refractive index sensor device for multiplexed detection of multi-analytes. Main features of the sensor element are discussed through numerical simulation, and proof-of concept device is demonstrated through micro fabrication. The proposed configuration of silicon waveguide based sensor array is expected to find potential application in portable chip based devices as highly sensitive multiplexed biosensors. Published version

Noninvasive medical imaging techniques have high potential in the field of ocular imaging research. Angle closure glaucoma is a major disease causing blindness and a possible way of detection is the examination of the anterior chamber angle in eyes. Here, a simple optical method for the evaluation of angle-closure glaucoma is proposed and illustrated. The light propagation from the region associated with the iridocorneal angle to the exterior of eye is considered analytically. The design of the gel assisted probe prototype is carried out and the imaging of iridocorneal angle is performed on an eye model. Published version

Visual access to physically inaccessible parts has become the forefront of research and development in medical diagnostics tools and procedures. Flexible and thin endoscopes with fiber bundle as an image conduit serves this purpose. However, when the light passes through the core of the fiberlet, it is blocked by the inter fiberlet gap. This structural limitation creates special honeycomb like pattern overlaying the image captured with the image fiber assisted probes, known as the comb structure or fiber pixelation. It obstructs the perception of the original image sacrificing resolution and contrast and inhibits the use of object recognition and tracking algorithms. Generally, comb structure removal or depixelation methods are employed to remove honeycomb pattern from an image. In the recent past, several depixelation techniques have been proposed albeit using different set of pixilated images by different researchers. It is quite difficult to make a comparison of their performances based on such images, as they adopt different images for different particular framework of their study. In this context, a basic database of such images is the need of the hour to meet the growing diagnostic needs in the medical and industrial arena. This paper in this context proposes and details a Comb Structure Affected Image database (CSAI) to meet the objective. Images are generated considering the image fiber specifications and the characteristics at different targeted optical imaging modalities delineated by resolution scales. The proposed database is designed to have a set of synthetically generated pixelated images of test patterns of different scales, sizes and shapes. Published version

In this paper, we report a methodology to fabricate high resolution periodic grating features using high index prism based interferometer and i-line laser source. Features with sub-60 nm half pitch size were fabricated on i-line resist in an immersion medium using a prism of high index 1.939.

We demonstrate a novel multifunctional optical system that is capable of trapping, imaging, position sensing, and fluorescence detection of micrometer-sized fluorescent test particles using hollow-core photonic crystal fiber (HC-PCF). This multifunctional optical system for trapping, position sensing, and fluorescent detection is designed such that a near-IR laser light is used to create an optical trap across a liquid-filled HC-PCF, and a 473 nm laser is employed as a source for fluorescence excitation. This proposed system and the obtained results are expected to significantly enable an efficient integrated trapping platform employing HC-PCF for diagnostic biomedical applications. Published version

In this paper, we report a novel concept and methodology to fabricate high resolution periodic features using i-line laser source and multiple converging lenses. This configuration reduces the number of optical elements by employing a converging two-lens system to direct the beams on to the sample instead of conventional multiple mirror assembly that is normally associated with multiple beam interference configurations. A simple optical configuration using a 60° prism, 364 nm laser source and two converging lenses are employed to implement immersion lithography concept to achieve four beam interference. Square lattice patterns with pitch size of 210±8 and 240±6 nm are recorded on a positive photo resist using this technique.

A double shear TV holographic system is proposed to obtain curvature fringes. TV shearography is applied with the incorporation of phase shifting techniques to obtain curvature information of a deformed objects. The optical configuration is used to get fringes corresponding to slope changes in real-time on a TV monitor. Subsequent incorporation techniques yield curvature information on a TV monitor.

In this work we propose to fabricate nano-scale square lattice features using the principle of four wavefront interference employing a pyramidal prism. A UV laser of 266 nm wavelength was used to pattern features on thinned positive tone resist AZ 7220 using single exposure technique. It was demonstrated that features with sub 500 nm pitch size could be recorded using a pyramidal prism with edge angle of 30.4°. Holes with diameter around 187 nm in square symmetry with pitch of 414 nm were fabricated. The proposed setup is relatively simple, requiring minimum number of components.