D. V. Udupa

Simple Method for Measuring Long Radius of Curvature of Metal Cylindrical Surface

This paper describes a simple method of measuring long radius of curvature of a cylindrical surface made of metal. The method is useful for measuring the radius of curvature of both convex and concave surfaces. The basic element is a strip of plane mirror mounted on three balls. The source of light is a low power He-Ne laser. The conditions are derived to obtain the best possible accuracy using this set-up. The accuracy achieved in the radius of curvature measurement is ± 0.3% for a metal cylindrical plate of radius of curvature 3228 mm and size 295 mm × 30 mm × 30 mm.

Design of narrow band notch filter based on guided mode resonance effect in thin film layers

Narrow band notch filters based on grating waveguide structure have been studied using rigorous coupled wave approximations (RCWA). It has been shown that ultra-narrow bandwidth (0.0042 nm) can be achieved with sinusoidal grating profile.

Characterization of photoresist thin films for surface relief holographic gratings

Depositions of highly uniform thin films of positive photoresist AR-P 3120 were carried out on glass substrates using spin coating technique. Spectroscopic ellipsometry has been used to determine the thickness uniformity of the films. Formation of the surface relief gratings in photoresist and study of their surface profiles have also been described.

THEORY OF A HOLOGRAPHIC LENS WITH A HIGH EFFICIENCY

A two element holographic lens is proposed for obtaining high efficiency in a holographic lens. The two element holographic lens is made up of an off-axis holographic lens and a plane holographic grating. The proposed holographic lens can be used for the correction of chromatic aberration in an achromatic doublet. The theory of the holographic lens and the V-value of the holographic lens are given. The formulae for longitudinal chromatic aberration, transverse chromatic aberration present in a simple holographic lens and a two element holographic lens are derived. It is observed that the expressions for longitudinal chromatic aberration is the same for both the conventional holographic lens and the two element holographic lens proposed in this paper. It is also observed that the expression for the transverse chromatic aberration is the same for both the conventional holographic lens and the two element holographic lens. The two element holographic lens may find application for designing large size achromatic doublet in combination with a glass lens for magnifying purpose.

Measurement of Radius of Curvature of Cylindrical Surfaces

Methods for measuring radius of curvature of a cylindrical surface are described. Based on the above methods a cylindrometer has been designed, fabricated and used for measuring radius of curvature of cylindrical surfaces. The cylindrometer is found to be useful for checking radius of curvature of Rowland circle mounts fabricated in mechanical workshops in addition to glass tubes, metal cylinders and other cylindrical surfaces.

Instrumentation and signal processing for the detection of heavy water using off axis–integrated cavity output spectroscopy technique

An experimental setup is developed for the trace level detection of heavy water (HDO) using the off axis-integrated cavity output spectroscopy technique. The absorption spectrum of water samples is recorded in the spectral range of 7190.7 cm-1-7191.5 cm-1 with the diode laser as the light source. From the recorded water vapor absorption spectrum, the heavy water concentration is determined from the HDO and water line. The effect of cavity gain nonlinearity with per pass absorption is studied. The signal processing and data fitting procedure is devised to obtain linear calibration curves by including nonlinear cavity gain effects into the calculation. Initial calibration of mirror reflectivity is performed by measurements on the natural water sample. The signal processing and data fitting method has been validated by the measurement of the HDO concentration in water samples over a wide range from 20 ppm to 2280 ppm showing a linear calibration curve. The average measurement time is about 30 s. The experimental technique presented in this paper could be applied for the development of a portable instrument for the fast measurement of water isotopic composition in heavy water plants and for the detection of heavy water leak in pressurized heavy water reactors.

Noncontact three-dimensional quantitative profiling of fast aspheric lenses by optical coherence tomography

Abstract The use of optical coherence tomography (OCT) for noncontact three-dimensional aspheric lens profiling and retrieval of aspheric surface parameters is demonstrated. Two commercially available aspheric lenses with different focal length-to-diameter ratio have been imaged using OCT, and the measured optical path length distribution has been least square fitted with the aspheric lens surface retrieving the radius of curvature, aspheric constant, and conic constants. The refractive index of these lenses has also been measured referencing with a standard Zerodur glass flat. The fitted aspheric surface coefficients of the lenses are in close agreement with the manufacturer’s values, thus, envisaging the potential of OCT in rapid screening, testing of aspheric lenses, and other micro-optical components such as those used in illumination optics.

Mixed Phase Gratings: Contribution of Refractive Index Modulations to Diffraction Efficiency

The phase gratings have been recorded in silver halide emulsion (Slavich PFG-01) by utilizing a two-beam laser interferometric technique and Kodak DA-163 as a developer. Such gratings are observed to conform to both the surface relief and refractive index modulations. In the present work, we have studied the contribution of refractive index modulations to diffraction efficiency of the phase gratings for a broad range of exposure time (30-180 s) of recording. It has been observed that contribution of index modulation to diffraction efficiency of the gratings increases with increasing time of exposure in the range of 30-90 s and then saturates. Contribution of relief modulation to diffraction efficiency is also discussed.

High Resolution VUV Spectrometer at the INDUS-1 Synchrotron Source

An indigenously developed high‐resolution vacuum ultraviolet (VUV) spectrometer has recently been commissioned at the INDUS‐1 Synchrotron Source, Indore, India for carrying out spectroscopic research of atomic and molecular gases. The spectrometer uses a 6.65‐meter concave grating in off‐plane Eagle mounting and a photomultiplier tube (PMT) for recording the intensity profile of various spectral lines. Experimental performance of the spectrometer has been tested using laboratory sources and 1200 grooves/mm and 4800 grooves/mm concave gratings. Wavelength resolutions of 0.08 A and 0.01 A have been achieved when 1200 grooves/mm and 4800 grooves/mm concave gratings have been mounted successfully in the spectrometer. The instrument has been integrated with the high resolution VUV beamline at INDUS‐1 and its performance is being evaluated with synchrotron radiation.

Testing of Concave Cylindrical Mirrors, Positive Cylindrical Lenses and Elliptical Cylinder Using a Low Frequency Linear Grating

An application of equidistant low frequency grating for testing of concave cylindrical mirrors and positive cylindrical lenses is described in this paper. The equipments needed for the testing of cylindrical mirrors are visible He-Ne laser, microscope objective, well corrected collimating lens and low frequency grating. The method is found to be useful for revealing the hills, valleys and zonal errors of cylindrical surfaces of medium radius of curvature. The method is useful for estimating the uniformity of cylindrical wavefront emerging out of a cylindrical lens. A method for testing elliptical cylinder surface has also been proposed in this paper.