He-Ne Laser Source Research Articles

Optical gain and large-signal characteristics of illuminated GaAs MESFET's

The illuminated large-signal characteristics of a uniformly doped epitaxial GaAs MESFET have been measured when optically gated with an He-Ne laser source. The dependence of the measured optical gains on the applied electrical biases and optical intensity, position, and spot size indicate that the dominant dc gain mechanisms are transit time photoconductivity combined with an effective photovoltaic change in the pinchoff voltage. The photovoltaic change in the pinchoff voltage dominates for high optical power levels, while the photoconductive response dominates for low power levels. Optical gains in the range of 5-10 were measured for the photoconductive regime, while gains in the range of 50-70 were measured for the photovoltaic regime.

Construction of an optical-carry adder

We have constructed a hybrid electronic/optical digital adder, based on a system suggested by B. Arazi [Proc. IEEE 73,162 (1985)], which uses an optical system for the carry-bits, giving fully parallel operation. Our bulk-optic breadboard system has six acoustooptic modulators as optical switches, with a single He-Ne laser source. It adds two 4-bit words at 10 MHz, with a 500-ns pipeline delay. The optical carry is based on a multistage optical path, with light added or allowed to pass at each stage, according to whether carries are generated or propagated at the corresponding column of the addition. For long addends, the system speed is limited by light loss through the carry path and by size effects.

MAORI : New Apparatus to Measure the Optical Regularity of Printing

Modern printing presses are more and more controled by automatic means such as printed paper on line optical controls for inking. These automatic control means will ask for new techniques for measuring paper properties based on an increased use of optical devices. At present, irrespective of the printing process, the printing quality analysis is made by visual inspection and judgment. Therefore, substituting an optical measuring device to the visual judgment would allow better, quicker and less expensive interpretation of the results. In a study of uniformity analysis on newsprint, we found out that solidcolour analysis could be solved with a micro-photometer, the signal of which, and more especially its variations, is well correlated with visual judgment. Further study of the analytical method induced us to design a new instrument fitted with a He-Ne laser source, and giving a measure of local variations of the light back seattering coefficient of a solid colour. This instrument called MAORI is described. The attention is focussed on two interesting points :-the moving holder of the printed sample, the motion of which is such that each point describes a circle, the sample staying in its own plane and remains parallel to itself-the signal processing which gives a voltage out put proportionnal to the RMS value of the backscattering coefficient.Implementing this method in the case of rotogravure and in the case of offset printing is also described. The extremely good correlation which exists between the MAORI quality index and the visual judgment, in terms of classifying the samples is shown.Commercialisation of the equipment is foreseen.

Fiber gyroscope with nonreciprocally operated, fiber-coupled LiNbO_3 phase shifter

We describe a fiber gyroscope operating at maximum sensitivity that is due to a nonreciprocal pi/2 phase bias effected with a pulsed voltage applied to an electro-optic LiNbO(3) channel waveguide phase shifter. With a He-Ne laser source, the noise was equivalent to a 0.1 degrees /sec rotation, for a 10-Hz bandwidth and 2% reflectivity at each fiber-LiNbO(3) interface. The phase shifters showed polarization-independent behavior that was characterized by measurements in a fiber interferometer. They were flip-chip coupled with single-mode fiber that were cemented to the channel ends to give a stable module.

Polarimetry Applied To Alignment And Angle Measurement

Factors limiting the sensitivity of measurement obtainable with polarimetric instrumentation are discussed, with particular emphasis on modulation methods and the special problems associated with a coherent light source. Under optimum conditions the peak noise level of a Faraday-effect polarimeter with a He-Ne laser source has been found to be as low as ± 0.05 second of arc. The addition of quartz wedge units enables lateral displacements and departures from straightness to be measured and a system is described that possesses low sensitivity to laser beam direction changes and air turbulence. Profile measurements on a silica bar using this polarimetric system and measurements by precise Fizeau interferometry have agreed to better than 0.2 um over the 300 mm length of the bar.

High Density Direct Read after Write (DRAW) Recording

Burning holes into a thin layer of bismuth film is the basis for the development of a large capacity store for DRAW operation (2 × 1010 bits). In 600 Å bismuth films deposited on a rotating disc, storage is achieved at a data rate of 1 Mbit/s using a He-Ne laser source. Reading the record in transmission, an optical contrast ratio of 2–3 was observed. Storage densities close to 108 bits/cm2 are achievable.

Lattice Vibrations of Imidazole Crystals

Abstract Polarized low-frequency Raman spectra of imidazole single crystals were measured with a He-Ne laser source. A new band at 172 cm−1 (Bg) was observed. An assignment for the lattice vibrations of imidazole crystals is proposed on the bases of this Raman data and far-infrared spectral data of Perchard and Novak, as well as the preliminary results calculated from Harada's and Williams' potentials.

Holographic vibration measurement using a tv speckle interferometer with silicon target vidicon

A basic realization of a TV speckle interferometer applying a silicon target vidicon is described. The increased detectivity compared with other vidicons reduces the laser power requirements. This enables stroboscopic operation in a fairly straightforward manner with a He-Ne laser source. Time average- and stroboscopic fringe patterns for a vibrating test object are presented.

Interferometric method of checking parallelism and prism angles

Examples are given of a quick and convenient method of testing optical components: the parallelism of glass blocks; the 90° angle error and pyramidal error of a porroprism; and the error in the 45° angles of a right angle prism. A He-Ne laser source is used and the component to be tested acts as an interferometer.

Three Beam Interferometer for the Observation of Kinetic Cooling in Air

A three beam interferometer, which has recently been used to measure the time constant associated with kinetic cooling, is described in detail. Design features necessitated by operation of the device over a 5-m path are discussed, as well as system response to vibrational noise and drift, and means used for their monitoring and control. The effective working length resolution of the system, dL/L, was 1 part in 2.6 x 10(9) with a He-Ne laser source operating at 0.63 microm.

An Optical Range-Gated Filtering Technique for Mti Radar

Moving targets submerged in clutter can be more readily detected by range-gated filtering techniques. Range-gated filtering is a two-dimensional process in which target Doppler frequency and range are desired output quantities. Optical data processing techniques are inherently multidimentsional. An experimental system using a He-Ne laser source and film transparencies representing radar echoes gave output patterns in agreement with theoretical predictions. Major advantages of an optical filter are simplicity and relatively small size.

Interferometry through the Turbulent Atmosphere at an Optical Path Difference of 354 m

A modified Michelson interferometer with a stable He-Ne laser source has been used to study fluctuations in the mean refractive index over a long path through the turbulent atmosphere. Distinct interference fringes were obtained at mirror separations up to 177 m, corresponding to an optical path difference of 354 m. The spatial stability of the interference fringes was found to decrease with increasing optical path length, indicating an increasing contribution from the atmosphere. Details of the interferometer and the experimental procedure are given as well as a discussion of the fluctuations in the mean refractive index.

The Raman spectrum of gallium phosphide

The first and second-order Raman spectra of gallium phosphide recorded recently by Russell and Hobden using a He-Ne laser source, are discussed in the light of current theories on the dynamics of crystal lattices. The observed spectra of GaP is examined in detail with a calculation of the phonon frequencies from the critical points Γ, L and X, using the Raman supercell modes and their frequency expressions as given by Ramanathan for ZnS lattice. Satisfactory explanations have been given for the observed second-order frequencies in the case of GaP.

The second order Raman spectrum of calcium fluoride

The second-order Raman spectrum of calcium fluoride recorded recently by Russell, using a He-Ne laser source, is discussed in the light of current theories on the dynamics of crystals. The observed spectrum of CaF 2 is examined in detail with a calculation of the frequencies of the supercell modes using the lattice dynamic models of Ramanathan and Ganesan and Srinivasan, with the selection rules for the combinations from the critical points X for CaF 2 structures. Satisfactory explanations have been given for most of the observed second-order frequency shifts.