Plano Convex Research Articles

Micro-optics fabrication using blurred tomography

We demonstrate the fabrication of millimeter-sized optical components using tomographic volumetric additive manufacturing (VAM). By purposely blurring the writing beams through the use of a large etendue source, the layer-like artifacts called striations are eliminated enabling the rapid and direct fabrication of smooth surfaces. We call this method blurred tomography and demonstrate its capability by printing a plano–convex optical lens with comparable imaging performance to that of a commercially available glass lens. Furthermore, due to the intrinsic freeform design nature of VAM, we demonstrate the double-sided fabrication of a biconvex microlens array, and for the first time demonstrate overprinting of a lens onto an optical fiber using this printing modality. This approach to VAM will pave the way for low-cost, rapid prototyping of freeform optical components.

Design and Comparison of three Unconventional Shaped DRAs for 60GHz Application

Shape modification and analysis of a conventional circular dielectric resonating antenna for 60 GHz application has been included in this paper. With The conformist shapes have been modified and a comparative study has been done among the unconventional designs based on scattering parameter, antenna gain and directivity. The circular shaped DRA has been modified as Biconvex, Plano convex and biconcave shaped DRA. With the dimension 20 mm × 20 mm × 1.6 mm, FR4 Epoxy material is used for the substrate. Alumina_92pct material with a dielectric constant of 9.2 has been used for the dielectric resonators. Frequency range from 55 GHz to 65 GHz has been considered and the resonant frequencies have been found as 58.7 GHz, 59.7 GHz and 55.5 GHz for Biconvex DRA, Plano Concave DRA and Biconcave DRA respectively. A comparative study has been done among all these three DRAs to find out the best DRA for 60 GHz WLAN application.

Mid-infrared vortex array generation with a tunable singularity in an Er:YAP laser

Optical vortex arrays are structured light fields with multiple phase singularities that have attracted considerable attention in recent years. Here, we demonstrate the direct generation of an optical vortex array with tunable singularity from a mid-infrared Er: yttrium aluminum perovskite laser under the annular-pumping regime. An axicon combined with a plano–convex lens is used to reshape the pumping beam into an annular one to match the different orders of the Laguerre–Gaussian mode. By adjusting the pump power and the lateral displacement of the gain medium, a tunable vortex array with one to four singularities is obtained in the ∼3-μm mid-infrared wavelength region. The lasing characteristics of the mid-infrared vortex arrays are evaluated and discussed. The experimental results can shed some light on the generation of mid-infrared optical vortex laser arrays and their applications.

A plano-convex thick-lens velocity map imaging apparatus for direct, high resolution 3D momentum measurements of photoelectrons with ion time-of-flight coincidence.

Since their inception, velocity map imaging (VMI) techniques have received continued interest in their expansion from 2D to 3D momentum measurements through either reconstructive or direct methods. Recently, much work has been devoted to the latter of these by relating electron time-of-flight (TOF) to the third momentum component. The challenge is having a timing resolution sufficient to resolve the structure in the narrow (<10ns) electron TOF spread. Here, we build upon the work in VMI lens design and 3D VMI measurement by using a plano-convex thick-lens (PCTL) VMI in conjunction with an event-driven camera (TPX3CAM) providing TOF information for high resolution 3D electron momentum measurements. We perform simulations to show that, with the addition of a mesh electrode to the thick-lens geometry, the resulting plano-convex electrostatic field extends the detectable electron cutoff energy range while retaining the high resolution. This design also extends the electron TOF range, allowing for a better momentum resolution along this axis. We experimentally demonstrate these capabilities by examining above-threshold ionization in xenon, where the apparatus is shown to collect electrons of energy up to ∼7eV with a TOF spread of ∼30ns, both of which are improved compared to a previous work by factors of ∼1.4 and ∼3.75, respectively. Finally, the PCTL-VMI is equipped with a coincident ion TOF spectrometer, which is shown to effectively extract unique 3D momentum distributions for different ionic species in a gas mixture. These techniques have the potential to lend themselves to more advanced measurements involving systems where the electron momentum distributions possess non-trivial symmetries.

Comparison of a high-power 3.75 µm BaGa4Se7 OPO based on a plane-parallel resonator and an unstable resonator with a Gaussian reflectivity mirror.

Using a homemade Nd:YAG laser with a pulse repetition frequency of 300 Hz as a pump source, we demonstrated a tunable BaGa4Se7 (BGSe) optical parametric oscillator (OPO). Wavelength-tuning ranges of 1.42-1.59 µm and 3.21-4.22 µm were realized, and a maximum average output power of 1.03 W at 3746 nm was achieved in a plane-parallel resonator. To date, this is the highest output power at around 4 µm obtained from a BGSe OPO pumped by a 1 µm laser, to our knowledge. Moreover, the BGSe OPO employing a plano-convex Gaussian reflectivity mirror (GRM) as an output coupler (OC) was demonstrated for the first time, to our knowledge. At the same pump power, the corresponding output power and M2 value of the idler at 3746 nm were 0.86 W and 10.2 (x direction) and 11.6 (y direction), respectively. The results indicate that the beam quality factor M2 of the idler has an over 30% improvement in comparison with the BGSe OPO based on a conventional flat OC of a plane-parallel resonator. Limited by the beam quality of the pump source, there is little room for improvement in the beam quality of the BGSe OPO with a GRM OC, which could be improved in the future by optimizing the pump beam.

Tunable laser frequency lock based on a temperature-dependent Fabry-Perot etalon.

A simple method for laser frequency stabilizing by a temperature-tuned Fabry-Perot etalon is reported. The etalon is a plano-convex lens that permits tuning the length and refractive index via controlling the temperature for shifting wavelengths in the region of 852 nm, with a transmission spectral linewidth of ∼72.5MHz and free spectral region of ∼16GHz. Using this scheme, arbitrary frequency locking of a laser with an adjustable frequency resolution of 2.34GHz/∘C is realized, and MHz-level long-term stability is demonstrated.

Meta-objective with sub-micrometer resolution for microendoscopes

Microendoscopes are vital for disease detection and clinical diagnosis. The essential issue for microendoscopes is to achieve minimally invasive and high-resolution observations of soft tissue structures inside deep body cavities. Obviously, the microscope objective is a must with the capabilities of both high lateral resolution in a wide field of view (FOV) and miniaturization in size. Here, we propose a meta-objective, i.e., microscope objective based on cascaded metalenses. The two metalenses, with the optical diameters of 400 μm and 180 μm, respectively, are mounted on both sides of a 500-μm-thick silica film. Sub-micrometer lateral resolution reaches as high as 775 nm in such a naked meta-objective, with monochromatic aberration correction in a 125 μm full FOV and near diffraction limit imaging. Combined with a fiber bundle microscope system, the single cell contour of biological tissue (e.g., water lily leaf) can be clearly observed, compared to the indistinguishable features in other conventional lens-based fiber bundle systems, such as plano–convex and gradient refractive index (GRIN) cases.

Reversible Morphology Switching of Colloidal Particles

A facile method has been discovered that enables switching of non-cross-linked poly(styrene) (Nx-PS) colloidal particle morphologies, including spherical and anisotropic convex–convex, plano–convex, and concave–convex. The anisotropic morphologies can be achieved readily from spherical Nx-PS particles through control of annealing time at elevated temperatures or surfactant concentration. These anisotropic morphologies can be reversed to spherical at lower temperatures, and reversible morphology switching between any pair of anisotropic morphologies also can be attained. This approach to particle morphology switching establishes a straightforward method for the synthesis of designer anisotropic particles using commercially available spherical particles as starting materials.

Dual-band circularly polarized flat antenna with plano convex and concave slots for RFID readers

This article has proposed a circularly polarized dual-band antenna with unidirectional pattern operating at the bandwidth frequencies of 920–925 MHz and 2.40–2.48 GHz for radiofrequency identification (RFID) readers. The proposed antenna structure is of a radiating patch with a single feeder and two pairs of plano convex and concave slots. This work has innovated and utilized the convex and concave slotting technique to generate the circular polarization. The simulated results showed that the dual-band antenna is of circular polarization (CP) and unidirectional radiation pattern with the 3 dB axial ratio and the respective gains of 1.31 and 1.36 dBic for the experimental lower and upper bandwidth frequencies. An antenna prototype was subsequently fabricated and tests performed. The simulated and measured results are in good agreement, rendering the proposed dual-band antenna with plano convex and concave slots suitably applicable to the ultrahigh frequency and microwave RFID readers.

Design of Silicon Plano Convex Lens for Optimized Light Coupling Between Laser Diodes and Single Mode Optical Fiber

Design of Silicon Plano Convex Lens for Optimized Light Coupling Between Laser Diodes and Single Mode Optical Fiber

Experimental Analysis of Desalination Unit Coupled with Solar Water Lens Concentrator

The main problem that the world faces in this scenario is shortage of potable water. Hence this research work rivets to increase the yield of desalination system in an economical way. The integration of solar concentrator and desalination unit can project the desired yield, but the commercially available concentrated solar power technologies (CSP) are not economically viable. So this study proposes a novel method to concentrate ample amount of solar radiation in a cost effective way. Water acting as lens is a highlighted technology initiated in this work, which can be a substitute for CSP systems. And water lens can accelerate the desalination process so as to increase the yield economically. The solar irradiance passing through the water will be concentrated at a focal point, and the concentration depends on curvature of water lens. The experimental analysis of water lens makes use of transparent thin sheet, supported on a metallic structure. The Plano convex shape of water lens is developed by varying the volume of water that is being poured on the transparent thin sheet. From the experimental analysis it is inferred that, as the curvature of water lens increases, solar irradiance can be focused more accurately on to the focus and a higher water temperature is obtained inside the solar still.

Generation of Aspherical Optical Lenses via Arrested Spreading and Pinching of a Cross-Linkable Liquid.

Aspherical optical lenses with spatially varying curvature are desired for capturing high quality, aberration free images in numerous optical applications. Conventionally such lenses are prepared by multistep top-down processes which are expensive, time-consuming, and prone to high failure rate. In this context, an alternate method is presented here based on arrested spreading of a sessile drop of a transparent, cross-linkable polymeric liquid on a solid substrate heated to an elevated temperature. Whereas surface tension driven flow tends to render it spherical, rapid cross-linking arrests such flow so that nonequilibrium aspherical shapes are attained. It is possible to tune also the initial state of the drop via delayed pinching of a liquid cylinder which precedes its release on the substrate. This method has led to the generation of a wide variety of optical lenses, ranging from spherical plano convex to superspherical solid immersion to exotic lenses not achieved via conventional methods.

Development and validation of a laser-induced breakdown spectroscopic method for ultra-trace determination of Cu, Mn, Cd and Pb metals in aqueous droplets after drying

The present study reports a fast and accurate methodology for laser-induced breakdown spectroscopic, LIBS, analysis of aqueous samples for environmental monitoring purposes. This methodology has two important attributes: one is the use of a 300nm oxide coated silicon wafer substrate (Si+SiO2) for the first time for manual injection of 0.5 microliter aqueous metal solutions, and two is the use of high energy laser pulses focused outside the minimum focus position of a plano convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Optimization of instrumental LIBS parameters like detector delay time, gate width and laser energy has been performed to maximize atomic emission signal of target analytes; Cu, Mn, Cd and Pb. Under the optimal conditions, calibration curves were constructed and enhancements in the LIBS emission signal were obtained compared to the results of similar studies given in the literature. The analytical capability of the LIBS technique in liquid analysis has been improved. Absolute detection limits of 1.3pg Cu, 3.3pg Mn, 79pg Cd and 48pg Pb in 0.5 microliter volume of droplets were obtained from single shot analysis of five sequential droplets. The applicability of the proposed methodology to real water samples was tested on the Certified Reference Material, Trace Metals in Drinking Water, CRM-TMDW and on ICP multi-element standard samples. The accuracy of the method was found at a level of minimum 92% with relative standard deviations of at most 20%. Results suggest that 300nm oxide coated silicon wafer has an excellent potential to be used as a substrate for direct analysis of contaminants in water supplies by LIBS and further research, development and engineering will increase the performance and applicability of the methodology.

On Alternative Methods of Determining Radius of Curvature Using Newton’s Rings Set up

It well known that radius of curvature of a plano convex lens can be determined using Newton’s Rings set up making use of Interference by division of amplitude principle. The general method widely used involves measurement of diameter of several circular dark fringes. We propose two alternative methods involving different formulae. It is based on the fact that, the formation of bright and dark interference fringes is a measure of the thickness of the air film at that point. The methods use simpler geometry and the formulae are easier to derive. We present the experimental data. The results from the experiment are in agreement with results obtained through the general method.

On Alternative Methods of Determining Radius of Curvature Using Newton’s Rings Set up

It well known that radius of curvature of a plano convex lens can be determined using Newton’s Rings set up making use of Interference by division of amplitude principle. The general method widely used involves measurement of diameter of several circular dark fringes. We propose two alternative methods involving different formulae. It is based on the fact that, the formation of bright and dark interference fringes is a measure of the thickness of the air film at that point. The methods use simpler geometry and the formulae are easier to derive. We present the experimental data. The results from the experiment are in agreement with results obtained through the general method.

Fabrication of long-focal-length plano-convex microlens array by combining the micro-milling and injection molding processes.

A uniform plano-convex spherical microlens array with a long focal length was fabricated by combining the micromilling and injection molding processes in this work. This paper presents a quantitative study of the injection molding process parameters on the uniformity of the height of the microlenses. The variation of the injection process parameters, i.e., barrel temperature, mold temperature, injection speed, and packing pressure, was found to have a significant effect on the uniformity of the height of the microlenses, especially the barrel temperature. The filling-to-packing switchover point is also critical to the uniformity of the height of the microlenses. The optimal uniformity was achieved when the polymer melts completely filled the mold cavity, or even a little excessively filled the cavity, during the filling stage. In addition, due to the filling resistance, the practical filling-to-packing switchover point can vary with the change of the filling processing conditions and lead to a non-negligible effect on the uniformity of the height of the microlenses. Furthermore, the effect of injection speed on the uniformity of the height of the microlenses was analyzed in detail. The results indicated that the effect of injection speed on the uniformity of the height of the microlenses is mainly attributed to the two functions of injection speed: transferring the filling-to-packing switchover point and affecting the distribution of residual flow stress in the polymer melt.

Magnetic Stopping of Transient Laser Plasmas

We investigated the expansion features of laser- produced Al plasma in the presence of 0.8 T magnetic field. Fast-gated photography was used to record 2-D snapshots of plasma at various moments during its expansion. The slowing down and stopping of the plasmas were observed at all laser irradiance levels used (3-10 GW·cm �2 ), however, increasing con- vexity of the plasma periphery was noticed at higher irradiance levels. C ONTROLLING the parameters of laser-produced plasmas (LPPs) is very important for most of its applications. A magnetic field is capable of providing such control by influencing the dynamic, ionization, and optical properties of a LPP (1), (2). The presence of magnetic field during the expansion of the plume may lead to plasma confinement, ion acceleration, enhanced emission intensity, instabilities, focusing and so on (3), (4). In this paper, we report the dynamics of expanding laser-plasma under a transverse B field studied using fast gated photography. We investigated the changes in the morphology of laser- produced plumes under different irradiation conditions expanding in vacuum into a 0.8 T magnetic field. For plasma-B field interaction experiments, a magnetic trap was fabricated using Nd-based rare-earth magnets. Magnetic circuits closed by magnetic steel provided an approximately uniform field, as well as field strength, in the gap nearly twice as high as the case with an isolated pair of magnetized plates. With this configuration, we obtained a magnetic field ∼0.8 T, measured using a Gauss meter. An Al target was positioned at equi-center between the pole edges of the two magnets. For producing plasmas, the Al target was irradiated using pulses from a Q-switched Nd:YAG laser with 6-ns full width half maximum at 1064 nm and focused using a f/40 plano convex lens to a spot size of ∼1 mm. The laser pulse energy at the target surface was varied using a combination of half wave plate and cube polarizer. All experiments were done in a vacuum chamber with a base pressure ∼10 −5 torr. An intensified CCD (ICCD) camera was used to capture time resolved images of the expanding plasma in the presence and absence of the B field.

Experimental generation of ring-shaped beams with random sources

We have experimentally reproduced ring-shaped beams from the scattered Laguerre-Gaussian and Bessel-Gaussian beams. A rotating ground glass plate is used as a scattering medium, and a plano-convex lens collects the scattered light to generate ring-shaped beams at the Fourier plane. The obtained experimental results are supported with the numerical results and are in good agreement with the theoretical results proposed by Wang et al. [Opt. Express17, 22366 (2009)].

Low-cost micro-lens arrays fabricated by photosensitive sol–gel and multi-beam laser interference

In this paper, we introduce a low-cost approach for fabricating micro-lens arrays that is based on photosensitive sol–gel and multi-beam laser interference. UV photosensitive ZrO2 gel films are prepared with Zr(O(CH2)3CH3)4 and BzAcH as the precursor and chemical modifier, respectively. With UV laser irradiation via different dose, nonlinear photodecomposition occurs in this film. Large scale 2D micro lens arrays with the sizes of 830nm×830nm and 280nm×280nm are fabricated by four-beam laser interference. The surface profile modeling shows that the micro lens is plano convex lens, and the effective focal lengths are 812.0nm and 317.6nm, respectively.

Fabrication of polymer micro-lens array with pneumatically diaphragm-driven drop-on-demand inkjet technology

The paper reports an effective method to fabricate micro-lens arrays with the ultraviolet-curable polymer, using an original pneumatically diaphragm-driven drop-on-demand inkjet system. An array of plano convex micro-lenses can be formed on the glass substrate due to surface tension and hydrophobic effect. The micro-lens arrays have uniform focusing function, smooth and real planar surface. The fabrication process showed good repeatability as well, fifty micro-lenses randomly selected form 9 × 9 miro-lens array with an average diameter of 333.28μm showed 1.1% variations. Also, the focal length, the surface roughness and optical property of the fabricated micro-lenses are measured, analyzed and proved satisfactory. The technique shows great potential for fabricating polymer micro-lens arrays with high flexibility, simple technological process and low production cost.