RamaGopal V Sarepaka

• M Sc (Physics), M.Tech (Applied Optics) PhD (Optical System Design)
• CEO at Optics & Allied Engg.Pvt.Ltd (OPTICA), Bengaluru

Single Point Diamond Turning (SPDT) is a popular and deterministic option to develop optical aspheric surfaces with desired optical quality for use in advanced optical systems. Several critical issues of SPDT determine the outcome of the SPDT exercise. These issues include properties of the substrate materials, machining matters, tool geometry and...

Characterization of Precision Diamond tools for Single Point Diamond Turning

In multiple applications of advanced instrumentation, single-point diamond turning (SPDT) is a popular and effective process to generate novel surfaces with nanometric surface roughness and sub-micron surface irregularities, albeit at a high cost. In SPDT, precision diamond tooling contributes significantly to the process cost escalation. Hence, fo...

Germanium lenses are widely used in various scientific and technological applications mainly infrared optical components. The performance of these lenses depends upon the surface finish, which is challenging to achieve during ductile-regime machining. It is crucial to provide the optimum parameters to ensure the high-quality surface, without surfac...

In the fabrication of precision optical and opto-mechanical components by machining, the micro-crack structure generated under the surface is referred to as Subsurface Damage (SSD). SSD severely affects the quality and strength of an optical component thus reducing its life. One of the most prominent technique by which SSD can be eliminated or redu...

The goal of this book is to familiarize professionals, researchers, and students with the basics of the Diamond Turn Machining Technology and the various issues involved. The book provides a comprehensive knowledge about various aspects of the technology including the background, components of the machine, mechanism of material removal, application...

Single Point Diamond Turning is one of the ultra precision methods to generate surface finish with highest possible dimensional accuracies. It involves material removal by shearing mechanism using a diamond tool tip, shearing of material results in generation of thermal energy which causes adverse impact on the tool wear, dimensional accuracy, and...

In this paper, the results of an experimental study conducted for precision machining of chromium zirconium copper alloy C18150 have been reported. The input parameters include tool overhang, tool nose radius, feed rate, spindle speed and depth of cut. A flat profile is generated on a disc of chromium zirconium copper alloy C18150 with three perfor...

Polymethyl Methacrylate is widely used as substrate material for optical fabrication in infrared and visual applications. The single point diamond turning being one of the deterministic precision machining technologies needs to be explored for the manufacturing of the optical components as it is capable of providing the required characteristics suc...

It has been a challenge to finish optical glass surface due to their hard and brittle nature. Moreover tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of BK7 glass are polished using...

Multi-layer reflective thin film filters optimized for oblique incidence angles were deposited on glass substrates using Electron Beam evaporation technique with in situ thickness monitoring. The present study involves deposition and optical characterization of 5 layered multi-layer structures of TiO2-Al2O3 and TiO2-SiO2 having different thicknesse...

In the fabrication of precision optical and opto-mechanical components by machining, the micro-crack structure generated under the surface is referred to as Sub-Surface Damage (SSD). SSD severely affects the quality and strength of an optical component thus reducing its life. One of the most prominent technique by which SSD can be eliminated or red...

Silicon is widely used in IR optics, X-Ray optics and electronics applications. These applications require Silicon of optical quality surface as well as good form accuracy. To get the desired finish and dimensional accuracy, diamond turning is preferable. Taylor-Hobson Nanoform-250 diamond turning equipment is used to machine flat Silicon mirror. N...

Single point diamond turning is one of the ultraprecision methods to generate high quality surfaces with highest possible profile accuracies. However, diamond turning process also introduces some unique errors which affect the surface finish. Some of these errors are controllable, while some are noncontrollable. Controllable parameters need proper...

In this paper the results of an experimental study conducted for precision machining of mono-crystalline germanium with single point diamond turning (SPDT) have been reported. The input parameters include the top rake angle, tool overhang, depth of cut, tool feed rate, and rotational speed of the workpiece. The flat profile is generated on a disk o...

Oxygen Free High Conducting Copper (OFHC) is one of the suitable materials for many precision optical applications due to its high thermal conductivity, good machinability, and good strength. Optical components like reflecting mirrors and molds require good surface finish for the better performance of the optical system. Single Point Diamond Turnin...

The objective of this work is to estimate the volumetric heat diffusivity and volumetric heat transfer at localized points, during precision machining. This enables the calculation of heat transmission at different points on work piece during the machining operations. Volumetric heat transfer is computed by assuming an infinitesimally small point o...

In precision machining leading to nano-metric surface finish, selection of the suitable machining parameters is a critical task. To ensure the desired surface quality, one needs to optimally select the machining parametric matrix. Towards this effort, this paper adds another critical parameter in terms of tool overhang. A well-defined set of machin...

Nickel–silicon–chromium–copper (C18000) alloy is widely used for many precision applications due to its high thermal conductivity, hardness, and moderate strength in fabrication of parts of molds. This study was carried out on this material for achieving mirror finish and minimizing profile error. Four machine and tool parameters were varied at dif...

A stable optical resonator comprising a spherical rear mirror with a phase step of λ∕2 at its center and a flat output coupler promises to produce a beam with very low diffraction. Based on this premise, a phase step mirror is fabricated on oxygen-free high-conductivity copper substrate using single-point diamond turning method for use in kilowatt-...

This article presents the use of Fiber Bragg Grating (FBG) sensor to measure the temperature induced at the tip of the tool, while micro-face turning of optical surfaces. FBG sensor of 120 μm diameter was mounted near the tip of the tool and the shift in Bragg wavelength due to induced temperature was acquired with the help of an interrogator. The...

Precision surface quality is required for the optical components used in military and aerospace applications. Optical polishing process is one of the critical steps in fabrication of optical components. Final surface quality of the optical surfaces defines the life and performance of the system. Final surface figure and finish of the optical surfac...

During this work, the effects of various machining parameters such as feed rate, cutting speed and depth of cut on surface roughness were experimentally observed during dry turning process using CNMG inserts. Aluminium 6061 alloy is machined using CNMG 120408 EN-TM (H20TI) CNC turning inserts. Response Surface Methodology (RSM) is used to design th...

Magneto-rheological materials are a class of smart materials whose rheological properties can be rapidly varied by applying a magnetic field. Magneto-rheological finishing utilizes magneto-rheological fluid, which consists of magnetic particles, non-magnetic abrasives and some additives in water or other carrier to polish the materials. Single-poin...

Optical grade plastics are increasingly being used as magnifiers in Ophthalmic Optical Instrumentation applications. In its effort to develop indigenously aspheric technology-based Ophthalmic Optical aids, the Aspheric Group at CSIO has studied the machining and surface characteristics of optical grade plastics. Generally, PMMA and polycarbonate co...

In the present study investigation was done to analyze the tool life by analyzing the change in surface rough- ness with time during machining of silicon (infrared crystal) at optimized parameters with a single crystal diamond tool. Silicon has low mass density, low cost & low coefficient of thermal expansion. Due to these properties it is used in...

Plastics are very common materials that can be diamond turned and widely used in optics and our ultra pre- cise applications. Surface texture parameters (Roughness and waviness) are very important considerations in these applications. In this experiment single point diamond turning is done on polycarbonate for about 200Kms length of machining. Surf...

Power spectral density (PSD) distribution provides an accurate measure of roughness of an optical surface. This article presents an analysis of optical surface roughness generated by single point diamond turning (SPDT) using PSD. For this study, flat 60 mm diameter aluminium-6061 samples are machined for varying tool feed rates, while keeping the o...

During single point diamond turning, the effects of tool feed rate on surface figure and finish of aluminium-6061 alloy are evaluated. The studies are conducted on 60 mm diameter optical flat surfaces. Twenty-six specimens are diamond turned for varying tool feed rates (0.3 μm/rev to 30.0 μm/rev) keeping all the other machining parameters constant....

The development of modern optical instruments has evolved into a complex multi-disciplinary activity with the explosion of sophisticated applications. For specialized optical systems, the development of even a prototype has become a costly exercise. This paper presents a new concept of virtual prototyping for optical systems to minimize the develop...

A ground-based three-mirror zero-obscuration astronomical telescope is conceived, designed, and analyzed initially for use as a spectrographic camera covering near UV to near IR (320 - 900 nm) wavelength region in a fiber-fed instrument operating at McDonald Observatory of the University of Texas at Austin. The design is a modified configuration of...

There is a growing demand for a larger field coverage for scanning in IR instrumentation. We have explored the possibility of using the microlens arrays (MLAs) for this purpose, and have developed a generic IR imaging scanner. The application of MLAs in the wide-field IR imagers is presented, along with their advantages and limitations. A series of...

An advanced polarized infra-red imaging sensor (APIRIS) has been designed and prototyped to acquire the polarization signature of targets in the far IR (8 - 12 microns) region with a field of view 4 degree(s) X 3 degree(s). The design (optical and optomechanical), fabrication and assembly issues of the scanning telescope for the APIRIS are discusse...

The ultimate goal of optical instrumentation is to achieve the desired image quality in a given application. This requires a homogenous blend of optical and mechanical design, fabrication, system integration and testing tasks. The space optical systems generally require near theoretical performances in hostile environments within size, weight and c...

The ultimate goal of optical instrumentation is to achieve the desired image quality in a given application. This requires a homogenous blend of optical and mechanical design, fabrication, system integration and testing tasks. The space optical systems generally require near theoretical performances in hostile environments within size, weight and c...

Importance of a proper choice of the ratio of the powers of the individual lenses in the rear doublet and Petzval curvature. Design of five lines Tessar systems (for five different values of the ratio). Comparing these five ranges according to their aberration correction.

An example of doublet design using the double-graph technique as described by Kingslake is given. The potential of the double-graph technique is evaluated by applying it to three different cases of doublet design. The technique in its present form is found to give a solution only in one case. In the other two cases the solution can be obtained only...

The significance of proper selection of Petzval curvature P in the Cooke triplet design has been investigated. Seven triplet systems at 100 mm, f/5.0 for a 35-mm camera, have been designed for seven different values of P (0.0037−0.0002−0.0049), and their performances are evaluated and compared. It is observed that the performance of the triplet doe...