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Optical spectrometers have propelled scientific and technological advancements in a wide range of fields. While sophisticated systems with excellent performance metrics are serving well in controlled laboratory environments, many applications require systems that are portable, economical, and robust to optical misalignment. Here, we propose and demonstrate a spectrometer that uses a planar one-dimensional photonic crystal cavity as a dispersive element and a reconstructive computational algorithm to extract spectral information from spatial patterns. The simple fabrication and planar architecture of the photonic crystal cavity render our spectrometry platform economical and robust to optical misalignment. The reconstructive algorithm allows miniaturization and portability. The intensity transmitted by the photonic crystal cavity has a wavelength-dependent spatial profile. We generate the spatial transmittance function of the system using finite-difference time-domain method and also estimate the dispersion relation. The transmittance function serves as a transfer function in our reconstructive algorithm. We show accurate estimation of various kinds of input spectra. We also show that the spectral resolution of the system depends on the cavity linewidth that can be improved by increasing the number of periodic layers in distributed Bragg mirrors. Finally, we experimentally estimate the center wavelength and linewidth of the spectrum of an unknown light emitting diode. The estimated values are in good agreement with the values measured using a commercial spectrometer., 10 pages, 10 main figures, 3 supplementary figures

The mobility sector is heavily reliant on fossil fuels for its operations. Fuel cells have a high energy content and use hydrogen as their major energy base which is renewable. As a result, they’re frequently regarded as excellent for zero-emission vehicle purposes. The control method is designed to efficiently absorb energy from the fuel cell stack. The power infrastructure was created with the functioning of an electric car in mind. An optimum power point monitoring regulator premised on the adaptive neurofuzzy inference system (ANFIS) has been tested for a proton exchange membrane fuel cell (PEMFC) technology that may be utilized in an electric automobile. The suggested controller’s functionality is evaluated in the MATLAB Simulink context amid typical operational circumstances and unexpected changes in the fuel cell.

This article gives classification of micromanufacturing in general and micromachining processes in particular. For different micromachining processes, one can have different kinds of operations through which different features, shapes, accuracy, precision, and dimensions can be achieved. This article as Part I reports an overview of only three processes as diamond turn machining (a class of traditional micromachining processes), electrochemical micromachining, and focused-ion-beam micromachining (a class of advanced micromachining processes). About all these three processes, a brief introduction to the mechanisms of material removal is reported followed by the new developments in each process which are discussed independently. In various sections, some areas where research work needs to be done are identified and very briefly discussed.

A hybrid graphene-gold nanomesh, realized through Au deposition on a patterned graphene nanomesh with a focused ion beam, is introduced and illustrated for enhanced light absorption in the visible spectrum. Numerical studies reveal that the hybrid nanomesh with dual resonances in the visible spectrum exhibit ~50% light absorption and enhancement factor as high as ~1 × 108. The simulations also show that the enhanced optical absorption is associated with the excitation of surface Plasmons. This is confirmed through the localization of electric fields at the resonant wavelengths. Such a hybrid graphene-gold nanomesh exhibiting enhanced light-matter interactions paves the way toward plasmonics, surface-enhanced Raman scattering applications, etc.

In this work, controlled bidirectional deformation of suspended nanostructures by site-specific ion irradiation is presented. Multiscale modeling of the bidirectional deformation of nanostructures by site-specific ion irradiation is presented, incorporating molecular dynamics (MD) simulations together with finite element analysis, to substantiate the bending mechanism. Strain engineering of the free-standing nanostructure is employed for controlled deformation through site-specific kiloelectronvolt ion irradiation experimentally using a focused ion beam. We report the detailed bending mechanism of suspended silicon (Si) nanostructures through ion-induced irradiations. MD simulations are presented to understand the ion-solid interactions, defects formation in the silicon nanowire. The atomic-scale simulations reveal that the ion irradiation-induced bidirectional bending occurs through the development of localized tensile-compressive stresses in the lattice due to defect formation associated with atomic displacements. With an increasing ion dose, the evolution of localized tensile to compressive stress is observed, developing the alternate bending directions calculated through finite element analysis. The findings of multiscale modeling are in excellent agreement with the bidirectional nature of bending observed through the experiments. The developed in situ approach for bidirectional controlled manipulation of nanostructures in this work can be used for nanofabrication of numerous novel three-dimensional configurations and can provide a route toward functional nanostructures and devices.

High index nanostructures lead to unique light-matter interactions and strong optical resonances for potential light trapping applications and improved optical performances. In this work, Gaussian shaped subwavelength 3D nanostructures are introduced and rapid prototyping of these nanostructures is carried out on silicon (Si) in a single-step using focused ion beam (FIB) milling. The tapered geometry of Gaussian pillar structures provided reflection suppression from the smaller tip in contrast to its extended base, enabling trapping of light, confirmed through light reflection calculations and hot spots observed through absorption density distributions. The nature of accelerated ions in a FIB system is directly used and highly ordered Gaussian pillar like subwavelength nanostructures are fabricated in a single-step on Si. Simulations and experiments demonstrate nanostructure evolution from periodically spaced subwavelength nanoholes to Gaussian pillar structures with tuning of beam processing parameters, providing fabrication flexibility. The proposed light management structures, investigated through Finite Difference Time Domain (FDTD) calculations, exhibit 10–20% reflection for a broadband visible wavelength range against planar Si and previously reported Si structures (such as nano-cones, nano-wires, nano-pyramids etc.). Experimental results support theoretical predictions and provide evidence for antireflection properties from the fabricated nanostructures. Considering the rapid fabrication approach and tunable nature of Gaussian shaped nanostructures, exhibiting unique optical properties; this work provides realization of nanoscale light management 3D structures for localized light trapping and antireflection applications.

The evolution of polygonal-shaped nanoholes on the (100) surface of germanium, aided by focused ion beam induced self-organization, is presented. The energetic beam of ions creates a viscous phase which, at a thermodynamical minimum, leads to surface self-organization. A directed viscous-flow along the predefined nanoholes provides well-ordered polygonal nanostructures, ranging from triangles to hexagons and octagons, as desired. The amorphization exhibiting a confined viscous-flow at the walls of nanoholes is attributed to the localized melting zones induced by site-specific thermal spikes during ion irradiation, as revealed by microscopy and molecular dynamics studies. This leads to a local self-organization in the vicinity of each circular nanohole via a viscous-fingering process at the nanoscale. Such controlled self-organization, with the help of a predefined scanning grid, transforms the circular holes into the desired polygonal shape. The present morphology manipulation promises to surmount the barriers concerning the size reduction efforts in the field of nanofabrication.

Sparsely distributed and self-organized gold-nanocones are fabricated by broad argon ion beam sputtering on the gold surface with grazing incident angle. The rotation of the sample with respect to the vertical axis has found to influence the morphology of the obtained nanostructures. Ion beam irradiation of the sample leads to formation of nanoripples when the sample is held stationary, otherwise nanocones are formed if the sample is rotated during irradiation. A hybrid gold-nanocone/graphene/gold-nanohole based surface-enhanced Raman scattering (SERS) sensor is proposed and shown to exhibit an enhancement factor of 109 via finite-difference time-domain (FDTD) simulations.

Site-specific ion-irradiation is a promising tool fostering strain-engineering of freestanding nanostructures to realize 3D-configurations towards various functionalities. We first develop a novel approach of fabricating freestanding 3D silicon nanostructures by low dose ion-implantation followed by chemical-etching. The fabricated nanostructures can then be deformed bidirectionally by varying the local irradiation of kiloelectronvolt gallium ions. By further tuning the ion-dose and energy, various nanostructure configurations can be realized, thus extending its horizon to new functional 3D-nanostructures. It has been revealed that at higher-energies (∼30 kV), the nanostructures can exhibit two-stage bidirectional-bending in contrast to the bending towards the incident-ions at lower-energies (∼16), implying an effective transfer of kinetic-energy. Computational studies show that the spatial-distribution of implanted-ions, dislocated silicon atoms, has potentially contributed to the local development of stresses. Nanocharacterization confirms the formation of two distinguishable ion-irradiated and un-irradiated regions, while the smoothened morphology of the irradiated-surface suggested that the bending is also coupled with sputtering at higher ion-doses. The bending effects associated with local ion irradiation in contrast to global ion irradiation are presented, with the mechanism elucidated. Finally, weaving of nanostructures is demonstrated through strain-engineering for new nanoscale artefacts such as ultra-long fully-bent nanowires, nano-hooks, and nano-meshes. The aligned growth of bacterial-cells is observed on the fabricated nanowires, and a mesh based "bacterial-trap" for site-specific capture of bacterial cells is demonstrated emphasizing the versatile nature of the current approach.

The natural range of distribution, conservation status and pollen morphology of Meistera newmanii (M. Sabu & V.P. Thomas) Skornick. & M.F. Newman, an endemic and threatened wild ginger of Western Ghats is discussed.

Thin film optical elements exhibiting translational invariance, and thus robustness to optical misalignment, are crucial for rapid development of compact and integrated optical devices. In this letter, we experimentally demonstrate a beam-shaping element that generates an annular beam by spatially filtering the fundamental Gaussian mode of a laser beam. The element comprises of a one-dimensional photonic crystal cavity fabricated using sputtered thin films. The planar architecture and in-plane symmetry of the element render our beam-shaping technique translationally invariant. The generated annular beam is sensitive to the polarization direction and the wavelength of the incident laser beam. Using this property of the annular beam, we show simultaneous generation of concentric annular beams of different wavelengths. Our experimental observations show an excellent agreement with simulation results performed using finite-difference time-domain method. Such a beam-shaping element has applications in areas ranging from microscopy and medicine to semiconductor lithography and manufacturing in microelectronics industry., Comment: 5 double-column pages, 4 figures, 3 supplementary figures

With the rapid development of microelectronic industry of data processing, data storage/reading, and various optoelectronic devices, the demand for small-sized optical components and optical systems is increasing. Diffractive optics has a potential to improve optical systems by increasing their reliability, robustness, and functional integration, while reducing their sizes. The present work investigated diffractive optical elements with subwavelength features for near-field focusing and laser cavity. Fresnel zone plates (FZPs) in the visible wavelengths were studied for near-field focusing. In addition, for laser cavity reflectors, 2-dimensional grating based on high-index-contrast materials was investigated. Near-field focusing properties of FZPs were investigated in the visible regime by a 3-dimensional finite-difference time-domain (FDTD) method. It was proposed to use phase zone plate structured on a glass to improve the diffraction efficiency of subwavelength focusing. Furthermore, a simple analytical model was used to show that high numerical aperture phase FZP under the linearly polarized illumination produces a rotationally asymmetric focal spot. With a radially polarized illumination, rotationally symmetric focal spot with a minimum beamwidth of 0.39l is obtained. Focusing behavior of phase FZPs fabricated using Focused ion beam (FIB) was characterized by near-field scanning optical microscope (NSOM) and shown to be in agreement with the simulation results. The use of a 2-dimensional high-index-contrast grating (HCG) with a square periodic lattice is proposed to realize surface-emitting lasers. With a suitable design of the 2-dimensional HCGs, Q factor as high as 1032 was achieved. DOCTOR OF PHILOSOPHY (MAE)

Single crystal diamond (SCD) is the ideal tool material in ultra-precision machining because of its high hardness, wear resistance, chemical stability, and the ability to sharpen the cutting edge in nanometers. The sub-micron level in the cutting edge profile could affect the accuracy of the fabricated surfaces, since cutting edge radii strongly influence the specific cutting energy, cutting forces, cutting temperature, residual stress in the workpiece. Therefore, cutting edge profile of an SCD tool should be checked periodically. The measurements of cutting edge radii of SCD tools are very difficult because of their geometric features (angles, radius... etc) and their dimensions in the nanometric level. This paper deals with various methods of cutting edge characterization of SCD tool by Atomic Force Microscopy (AFM). The change to measurement of the cutting edge radii has been done based on the methodology of the least square circle fit over cutting edge radius with error minimization in the calculation and determined iteratively.

INTRODUCTION Hashimoto’s Thyroiditis is a well-known clinical condition affecting the thyroid gland predominantly in women during 4 th decade & is often under diagnosed due its wide spectrum of clinical features. It could present as a multinodular goitre, diffuse goitre, or as a solitary nodule with features of Hypothyroidism, Hyperthyroidism or Euthyroid state. AIMS 1. To detect HT by FNAC, Antibody titers finally by Histopathology of excised Thyroid gland. 2. To know its various clinical features. 3. To study Sex ratio & Age it affects. 4. Management i.e. by conservative or surgical. 5. Complications & malignant transformation including Lymphomas. MATERIALS & METHODS 60 patients were taken for 2 years’ period from March 2014 to Feb 2016 attending Government General Hospital-Nizamabad; Telangana State. OBSERVATIONS  56 case are females, 4 cases are males; common age is 30-39 yrs., >50 yrs.-2 cases.  All cases presented with swelling in front of neck, only 5 had toxicity, 2 had obstructive symptoms. None had voice change.  36 Cases- 60% had MNG, 18 Cases- 30% diffuse goitre and 6 cases- 10%- solitary nodule.  The Hypothyroid, Euthyroid & Hyperthyroid state here are 48%, 44% & 8% comparative to Fenn et al -44%, 47% and 7%,  FNAC- was positive 90% here where as Lakshman Rao et al study has 77%.  We had 80% Anti Thyroid Antibodies positivity, others shown 63% and 84%. MANAGEMENT All are put on Hormone-Thyroxine replacement or suppression therapy and all patients found to be clinically Euthyroid during follow up. All patients showed decrease in size of gland except those with MNG. 8 patients underwent surgery- Subtotal Thyroidectomy. Of these 6 were Colloid goiters, later on diagnosed as HT by final HPE. One case was operated for cosmetic reason and the other for obstructive symptoms which was noticed to be lymphoma after HPE.

This work presents an optimization of focused ion beam (FIB) milling process for the fabrication of optical elements. Focused ion beam is a nanofabrication tool involving ion–beam material interaction at atomic or molecular levels. The ion–solid interactions have been investigated for the fabrication of desired 3D geometries. Focused ion beam dwell time is an important parameter and determines the final geometry and accuracy of the fabrication. An algorithm has been developed to optimize the ion beam dwell time for the desired geometry fabrication maintaining high accuracy. Binary Fresnel zone plates (FZPs) have been fabricated using the optimized simulation results for demonstration. The algorithm can be used for fabrication of 3D elements and micro/nano-structures for various applications.

A slit type dielectric based phase manipulative plasmonic lens for in-plane focusing of linearly polarized light to a single spot is proposed. Focal spot with full-width at half-maximum of 0.28λ0 is obtained to beat the diffraction limit.

The butterfly-inspired 2D periodic tapered-staggered subwavelength gratings were developed mainly using finite difference time domain (FDTD) method, assisted by using focused ion beam (FIB) nanoscale machining or fabrication. The periodic subwavelength structures along the ridges of the designed gratings may change the electric field intensity distribution and weaken the surface reflection. The performance of the designed SiO2gratings is similar to that of the corresponding Si gratings (the predicted reflectance can be less than around 5% for the bandwidth ranging from 0.15 μm to 1 μm). Further, the antireflection performance of the designedx-unspaced gratings is better than that of the correspondingx-spaced gratings. Based on the FDTD designs and simulated results, the butterfly-inspired grating structure was fabricated on the silicon wafer using FIB milling, reporting the possibility to fabricate these FDTD-designed subwavelength grating structures.

A conical configuration plasmonic zone plate based on Fresnel zones made up of Au thin film slits is proposed for focusing in the free space with visible illumination. The surface plasmons enable propagation of radiating modes to distances equal to several wavelengths of the illumination field. Through numerical simulations, the conical structure found to yield focal spot beating the diffraction barrier encountered by conventional focusing elements. The focal spot size measured as full-width at half-maximum (FWHM) is observed to be as small as 0.31 times the illumination wavelength at the focal distance of 8 wavelength. Moreover, the simple design rules make it possible to predict and control the focal distances accurately.

We introduce and demonstrate highly ordered vertical Gaussian pillar anti-reflective nanostructures on single crystalline silicon. The pillars are fabricated using Focused Ion Beam (FIB) in a single step by adopting a unique approach and overlap of incoming FIB Gaussian profile. These pillars are highly ordered and reproducible in a time effective manner. Using FDTD calculations, we demonstrate the suitability of proposed Gaussian pillars for antireflection properties. The proposed structures exhibit maximum 10% reflection for a broad wavelength range of 400–1000 nm.

BACKGROUND There is an increasing incidence of advanced unresectable gallbladder cancer even in patients who undergo re-exploration and these cases are marked by poor survival even after undergoing curative resection and adjuvant chemotherapy. Lack of suspicion during primary surgery, unavailability of frozen section facilities and delayed referrals are believed to contribute to this high incidence. AIM Our aim was to evaluate the results of re-surgery in incidental gallbladder cancers detected after open or laparoscopic cholecystectomy and to assess the outcome in patients who underwent complete radical cholecystectomy and adjuvant therapy. METHOD We retrospectively analyzed the data from a prospectively maintained computerized database of all patients with incidentally detected gallbladder cancers operated in the Department of Surgical Oncology, from June 2006 to January 2013. RESULTS Forty-two patients with incidental gallbladder cancer were re-explored. The median time of re-exploration after initial surgery was 65 days. Eighteen (43%) patients were found inoperable due to locally advanced unresectable or metastatic disease. Among the 24 (57%) patients who underwent completion radical cholecystectomy, 11 developed recurrence over a median time of 11 months. CONCLUSION Despite the dismal prognosis, more than half of the incidentally detected gallbladder carcinoma patients could receive curative treatment. Identification of patients with incidentally discovered gallbladder cancer and early referral to an oncology center may ensure these patients receive curative resection thereby increasing their chances for long-term disease free survival.

A coupler is proposed to interface a hybrid dielectric-loaded plasmonic waveguide (HDLPW) with a silicon photonic slab waveguide. The HDLPW is firstly designed and optimized to attain the best tradeoff between the mode confinement and the propagation distance. The designed coupler is inspired from the taper configuration and numerically modeled through finite-difference time-domain (FDTD) simulation. The results demonstrate that a high confinement and low loss of the energy is achieved from a silicon photonic slab waveguide into the dielectric slot of area 50×200 nm 2 in the HDLPW. The transmission attained through the coupler with a compact size of 400 nm is found to be as high as 80% (1 dB). Further, the planar nature of taper configuration makes the coupler easy to fabricate using the state-of-the-art CMOS facilities. The proposed coupler is useful in enabling the integration between photonic and hybrid plasmonic waveguides and thus realizing on-chip hybrid integrated circuits.

A nanostructure comprising dielectric/Ag interface with central slit surrounded by grooves is presented for beam focusing and collimating. Desired phase retardations of the beam emerging through slits are manipulated by tuning the depth of grooves. Numerical simulations are performed through a finite-difference time-domain (FDTD) algorithm. Results reveal the suitability of parabolic depth-tuned structure for enhanced transmission and beam collimation. Enhanced transmission and beam collimation are the result of transportation of electromagnetic energy in the form of surface plasmon polariton (SPP) waves.

A high numerical aperture binary phase micro-Fresnel zone plate (FZP) is designed and fabricated on a glass substrate by using a focused ion beam technique. Focusing characteristics of the phase micro-FZP are measured by a near-field scanning optical microscope using linearly polarized light as an illumination source. It is found that an asymmetric spot with subwavelength beam width and elongated depth of focus can be obtained from the phase micro-FZP. Furthermore, the measurement is shown to be consistent with the calculation result. Further, the tolerance in fabrication errors like tilt of side walls on focusing is discussed with numerical simulations.

Characterization issues of plasmonic structures are highlighted and investigated in detail in this paper. Combining with the plasmonic structures functioning for sub-wavelength focusing, optical characterization was carried out using a near-field scanning optical microscope (NSOM) system. Characterization errors that originated from both the nanofabrication using a focused ion beam (FIB) direct milling technique and misalignment of the NSOM system were analyzed in comparison to the theoretical computational results. Our experimental results demonstrated that the focusing function of the structures is in agreement with that of the designed structure. However, the measured beam spot size is larger than the designed value due to the direct measurement error originating from the NSOM and the indirect error from the FIB fabrication process.

Radiation Hardened By Design (RHBD) combinational circuits/primitive gates using 0.18um CMOS Technology is developed for Space application with help of Cogenda TCAD software suite. The proposed combinational cells are investigated for radiation simulation using three dimensional (3D) device structure. Single Event Transient (SET) caused by proton, α particle and heavy ions like C, Ar and Kr is observed on developed Cells and SET pulse width is measured on primitive gates. The proposed C element based radiation hardened Inverter is simulated using α, Ar and proton energetic particle. Proposed NOR and NAND gates are simulated under the radiation of proton, α and Kr and Single Event Transient Pulse Width is measured.

In this paper, we demonstrate enhanced light trapping by self-organized nanoripples on the germanium surface. The enhanced light trapping leading to high absorption of light is confirmed by the experimental studies as well as the numerical simulations using the finite-difference time-domain method. We used gallium ion (Ga+) focused ion beam to enable the formation of the self-organized nanoripples on the germanium (100) surface. During the fabrication, the overlap of the scanning beam is varied from zero to negative value and found to influence the orientation of the nanoripples. Evolution of nanostructures with the variation of beam overlap is investigated. Parallel, perpendicular, and randomly aligned nanoripples with respect to the scanning direction are obtained via manipulation of the scanning beam overlap. 95% broadband absorptance is measured in the visible electromagnetic region for the nanorippled germanium surface. The reported light absorption enhancement can significantly improve the efficiency of germanium-silicon based photovoltaic systems. (c) 2018 Author(s).

The backside nanoslot excited sub-wavelength grating-coupled Cu-strip silica-based plasmonic waveguides were developed using the finite difference time domain (FDTD) simulation method. The performance of the designed waveguides was simulated, and the effects of copper film thickness on plasmonic wave propagation were analyzed for relatively low propagation loss design. The designed waveguides could achieve unidirectional guiding of the excited surface plasmon polaritons (SPPs) with sub-wavelength lateral confinement and acceptable propagation length at microscale, and the recommended design for the sub-wavelength grating-coupled Cu-strip SPP waveguide was given, with the potential applications for the fiber-optic devices or elements. ASTAR (Agency for Sci., Tech. and Research, S’pore)

In a Power plant with a Distributed Control System ( DCS ), process parameters are continuously stored in databases at discrete intervals. The data contained in these databases may not appear to contain valuable relational information but practically such a relation exists. The large number of process parameter values are changing with time in a Power Plant. These parameters are part of rules framed by domain experts for the expert system. With the changes in parameters there is a quite high possibility to form new rules using the dynamics of the process itself. We present an efficient algorithm that generates all significant rules based on the real data. The association based algorithms were compared and the best suited algorithm for this process application was selected. The application for the Learning system is studied in a Power Plant domain. The SCADA interface was developed to acquire online plant data.

We present a case of third coronary artery arising directly from the right aortic sinus of Valsalva in a 60 year old male cadaver. It coursed in the epicardium downward, forward and to left on the sternocostal surface of the right ventricle up to the apex of heart where it anastomosed with left anterior descending artery. During its course it gave small ventricular branches to the right and left ventricles. Clinical importance and embryology of the variation are discussed.

The use of a two-dimensional (2D) high-index-contrast grating (HCG) with square periodic lattice is proposed to realize surface-emitting lasers. This is possible because the use of 2D HCG, in which multiple resonant leaky modes are excited by the 2 orthogonal directions of the grating, causes the high reflective zone to be split into two regions. Hence, a dip of the reflectivity is formed to support the excitation of a resonant cavity-mode inside the 2D HCG. With suitable design on the dimensions of the 2D HCGs, Q factor as high as 1032 can be achieved.

Lasing characteristics of randomly assembled SnO2 backbone nanowires coated with ZnO nanofins are investigated. It is shown that the hierarchical nanostructures can sustain ultraviolet random lasing action even at substrate temperature higher than 700 K and the corresponding characteristic temperature is found to be about 390 K. This is because the presence of ZnO nanofins improves heat transfer from the SnO2 backbone nanowires to the surrounding. Hence, some portion of the hierarchical nanostructures can be cooled down and the corresponding optical gain can be maintained even at high substrate temperature. Published version

An analytical model is developed to study the subwavelength focusing characteristics of a binary phase Fresnel zone plate (FZP). The model shows that high numerical-aperture phase FZP under the illumination of linear polarized light produces rotationally asymmetric focal spot with beamwidth varying from 0.36λ to 0.79λ, where λ is the wavelength. On the other hand, rotationally symmetric focal spot with minimum beamwidth of 0.39λ can be obtained from the illumination of radial polarized light.

Near-field focusing properties of zone plates are investigated in the visible regime by a 3-dimensional finite-difference time-domain method. It is shown that Frensel zone plates (FZPs) with metallic coatings can achieve subwavelength focusing in the visible wavelength. The characteristics of subwavelength focusing are found to be independent of the type of metal coatings used. All the FZPs exhibit similar shift in focal length and depth of focus when compared with classical calculations. These results indicate that plasmonic waves do not contribute to subwavelength focusing. Instead the subwavelength focusing characteristic is attributed to the interference of diffracted evanescent waves from a large numerical aperture. It is found that the near-field focusing of FZPs suppresses higher order foci such that the corresponding diffraction efficiency is improved. The use of phase zone plate structured on glass without opaque coating is proposed to improve the diffraction efficiency of subwavelength focusing.