Showing papers in "Applied Optics in 1977"
TL;DR: The effective index method for calculating waveguide mode dispersion is reviewed and applied to uniform rectangular optical waveguides with both small and large index differences and is shown to be at least as accurate as other approximate techniques.
Abstract: The effective index method for calculating waveguide mode dispersion is reviewed and applied to uniform rectangular optical waveguides with both small and large index differences. The results are shown to be at least as accurate as other approximate techniques. The effective index method is then applied to channel waveguides assuming 1-D and 2-D diffusion. Channel waveguides without sideways diffusion are shown to be described by the method using a normalized notation and previously published universal dispersion curves. Two-dimensional diffusion theory is applied to treat the case of isotropic sideways diffusion. A new, normalized, 1-D universal chart is obtained which in conjunction with previous results defines waveguide mode dispersion in isotropically diffused 2-D channels.
457 citations
TL;DR: A measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters which can be fully automated incorporates a monochromator and single photon counting detection and can be applied over a large wavelength range for very weak optical signals.
Abstract: We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.
293 citations
TL;DR: In this paper, a new measurement technique which allows displaying the length dependence of the fiber attenuation by analyzing backscattered light has been developed by using an optical time domain reflectometer.
Abstract: By using an optical time domain reflectometer a new measurement technique which allows displaying the length dependence of the fiber attenuation by analyzing backscattered light has been developed. This paper compares the backscatter and insertion-loss techniques. In addition, results of several experiments which illustrate the versatility of an optical time domain reflectometer are described.
260 citations
TL;DR: A new type of moiré and its application to topography are discussed and the fact that a contour line system and a sectional shape of the object are automatically reconstructed and displayed on a color TV monitor is very significant.
Abstract: A new type of moire and its application to topography are discussed. moire fringes are generated by observing a grating projected on an object under test with a scanning imaging device. The general equations of the projection-type moire topography are given. By controlling the phase, the pitch, or the direction of the virtual grating corresponding to the scanning lines of the imaging device, the automatic sign determination of the contour lines is accomplished. By the use of a high precision flying spot scanner with CRT(DD-tube) and a minicomputer system, an experimental measurement system is developed. Very significant is the fact that a contour line system and a sectional shape of the object are automatically reconstructed and displayed on a color TV monitor.
253 citations
TL;DR: In order to assist designers of spectrometric systems, a complete range of blaze angles for triangular grooves and modulations for sinusoidal groove shape in first and second orders is covered.
Abstract: Recently developed rigorous theories have been used to investigate the diffraction efficiency behavior of both blazed and holographic gratings. In order to assist designers of spectrometric systems we have covered a complete range of blaze angles for triangular grooves and modulations for sinusoidal groove shape in first and second orders. Several types of mountings are included together with the role played by finite conductivity of aluminum. Useful classifications of both types of gratings are given, as they apply from the near uv to ir regions. Comparisons showing the close agreement between theory and experiment are presented.
239 citations
TL;DR: In this article, a computer controlled polisher is used for fast figuring of aspheric surfaces for lightweighted workpieces using a small, rotating tool which travels over the workpiece surface.
Abstract: The computer controlled polisher uses a small, rotating tool which travels over the workpiece surface. By accurately controlling the velocity of the tool, a prescribed amount of material may be removed at each point on the surface. The use of a small tool permits rapid figuring of aspheric surfaces for lightweighted workpieces. The computer controlled polisher was optimized with regard to tool configurations, dwell times, scanning paths, and operating parameters. The unit has successfully fabricated several different workpieces including a mirror with a 1/80-wave rms departure, where a wave is 0.6328 μm.
218 citations
TL;DR: Findings suggested that photographic ir sensors were more suited to remote sensing of moderate to high biomass levels or vegetational density in a grass canopy than were sensors operating in regions of the spectrum where strong absorption occurred.
Abstract: The asymptotic nature of grass canopy spectral reflectance has been evaluated from field experimental data collected over the wavelength region of 0.500–1.000 μm at 0.005-μm intervals. The spectral reflectance of green vegetation against a soil background decreases in regions of absorption and increases in regions of minimal or no absorption as the vegetational density increases until a stable or unchanging spectral reflectance, called the asymptotic spectral reflectance, is reached. Results indicated spectral reflectance asymptotes occurred at significantly lower levels of total wet biomass, total dry biomass, dry green biomass, chlorophyll content, and leaf water content in regions of strong pigment absorption (low detectability threshold) than in the photographic ir region where absorption was at a minimum (high detectability threshold). These findings suggested that photographic ir sensors were more suited to remote sensing of moderate to high biomass levels or vegetational density in a grass canopy than were sensors operating in regions of the spectrum where strong absorption occurred.
213 citations
TL;DR: The low loss access coupler includes two multimode optic fibers, each having a biconical taper section, which are fused together to provide optical coupling between the fibers.
Abstract: The low loss access coupler includes two multimode optic fibers, each having a biconical taper section. The biconical taper sections of the fibers are fused together to provide optical coupling between the fibers. The fused fibers may also be twisted around one another to enhance mode mixing. The access couplers may be produced by fusing two fibers together along a small length, then heating the fused length and pulling the fibers to form the biconical tapers; or by twisting a portion of each of the fibers around one another, applying a tensile force to the twisted portions of the fibers and heating a region of the twisted fibers to soften and fuse a predetermined length of twisted fibers. If the fibers already have biconical taper sections, the access coupler may be produced by twisting the fibers together along their taper sections and heating a region of the taper sections to fuse them together.
208 citations
TL;DR: Subnanosecond pulses in the 1120-1550-nm region are generated by multiple-order stimulated Raman scattering in a small core single-mode silica fiber pumped by a Q-switched and mode-locked Nd:YAG laser.
Abstract: Subnanosecond pulses in the 1120-1550-nm region are generated by multiple-order stimulated Raman scattering in a small core single-mode silica fiber pumped by a Q-switched and mode-locked Nd:YAG laser at 1064 nm. These near ir pulses are injected into various km long test fibers, and relative time delay changes between different wavelengths are used to determine dispersion in a region where fiber material dispersion is small. Zero material dispersion has been observed in germanium and boron-doped single-mode and multimode est fibers.
194 citations
PARC1
TL;DR: Silicon nitride (Si(3)N(4) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE( 0) mode at lambda(0) = 6328 A have been successfully grown by low-pressure chemical vapor deposition.
Abstract: Silicon nitride (Si(3)N(4)) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE(0) mode at lambda(0) = 6328 A have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si(3)N(4) was separated from the substrate by a steamoxide SiO(2) buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.
190 citations
TL;DR: This paper considers various multiplex system designs that might be used with multimode fiber transmission systems, and the required multiplexer size and material properties are calculated as functions of the basic parameters of the fiber system.
Abstract: The capacity of optical fiber transmission systems could be increased by multiplexing several signals at different wavelengths on each fiber. This paper considers various multiplex system designs that might be used with multimode fiber transmission systems. In each case, the required multiplexer size and material properties are calculated as functions of the basic parameters of the fiber system. For fiber systems of the type currently being tested, a compact (~2 mm in diameter × 1 cm long), rugged, three-channel multiplexer could be constructed using a blazed plane reflection grating and graded-refractive-index (GRIN) optics; and it appears that such devices could be produced using available materials and technology. Multiplexers using thick gratings or multilayer dielectric filters are larger, more complicated, and require materials at the very edge of available technology. Multiplexers using a multiple thick grating or hologram could be even smaller than the blazed-grating devices, but materials having the required characteristics have not been demonstrated.
TL;DR: The possibility of making multilayer reflecting coatings by using materials whose dielectric susceptibility is very near to unity at the frequency under consideration is discussed and explicit expressions are obtained for the value of reflection coefficient and the optimum thickness of layers.
Abstract: The possibility of making multilayer reflecting coatings by using materials whose
dielectric susceptibility ∊ is very near to unity at
the frequency under consideration is discussed. For the pair of substances with
a given Re∊ and Im∊ the
explicit expressions are obtained for the value of reflection coefficient and
for the optimum thickness of layers. The published data on
Re∊ and Im∊ allowed us to
choose the pairs of substances for which one may hope to create (in principle)
the mirrors for normal incidence with R ~ 50% at
λ ≳ 30 A.
TL;DR: This note describes a convenient working technique for measuring the minimum size focused spot formed by a lens system that is routinely capable of measurement precision of better than ?
Abstract: This note describes a convenient working technique for measuring the minimum size focused spot formed by a lens system. The technique is routinely capable of measurement precision of better than ?lambda. The theory of knife-edge scanning is presented, and the relationship of the measured spot profile to the actual spot profile is shown to be relatively insensitive to the acceptance solid angle of the photodetector. Finally, some typical results of high resolution microscope objectives are presented.
TL;DR: Experimental data is presented on intensity modulation effects detected in several different multimode step index fibers found in long length, low-loss optical fiber coils as direct acoustic sensors.
Abstract: A new class of hydrophones is currently being developed, which utilize optical beams and interface directly to fiber optic transmission and processing links. Some of these sensors employ an optical fiber itself as the transduction element and possess significant advantages and versatility. The details of these fiber sensors and their advantages are discussed.
TL;DR: Determination of an unknown length from the measured fractional fringes is aided by the development of analytical equations for the length and its uncertainty, and criteria are given for selecting the wavelengths.
Abstract: The development of stabilized multifrequency lasers makes fractional fringes an increasingly attractive technique for length measurement. Determination of an unknown length from the measured fractional fringes is aided by the development of analytical equations for the length and its uncertainty, and criteria are given for selecting the wavelengths.
TL;DR: A stochastic leaf radiation model based upon physical and physiological properties of dicot leaves has been developed and results indicate that this approach gives accurate estimations of actual measured values fordicot leaf absorption, reflection, and transmission as a function of wavelength.
Abstract: A stochastic leaf radiation model based upon physical and physiological properties of dicot leaves has been developed. The model accurately predicts the absorbed, reflected, and transmitted radiation of normal incidence as a function of wavelength resulting from the leaf-irradiance interaction over the spectral interval of 0.40-2.50 microm. The leaf optical system has been represented as Markov process with a unique transition matrix at each 0.01-microm increment between 0.40 microm and 2.50 microm. Probabilities are calculated at every wavelength interval from leaf thickness, structure, pigment composition, and water content. Simulation results indicate that this approach gives accurate estimations of actual measured values for dicot leaf absorption, reflection, and transmission as a function of wavelength.
TL;DR: To overcome difficulty operating in the saturation mode, for suitable systems the fluorescence signal is then no longer a function of quenching rates or laser power and very low detectability limits appear possible.
Abstract: Laser based spectroscopic diagnostic tools offer the possibility of spatially and temporally resolved measurements of species concentrations in complex reacting gas flows of engineering interest. The major problem associated with such measurements is the effect of quenching reactions on the fluorescence signal. To overcome this difficulty operating in the saturation mode is proposed. For suitable systems the fluorescence signal is then no longer a function of quenching rates or laser power. Very low detectability limits appear possible.
TL;DR: The solar absorptance of a single ideal film on an idealized metallic substrate has been calculated as a function of its optical constants to determine the optimum parameters for selective absorber applications.
Abstract: The solar absorptance of a single ideal film on an idealized metallic substrate has been calculated as a function of its optical constants to determine the optimum parameters for selective absorber applications. High normal solar absorptances (>0.9) are possible for single uniform interference films if n < 1.5 and 0.2 < k < 0.8, values that are achievable using cermet materials. Grading the refractive index of single interference films improves the absorptance, with optimum results given by a uniformly increasing dielectric constant through the layer. With such a linear grading to air, normal solar absorptances of greater than 0.9 can be achieved for n < 1.5 and 0.1 < k < 5. Grading an absorbing material with a dielectric also improves the performance of the absorbing material. For bulk films, the optimum profile with minimum material is one where the dielectric constant increases slowly at the surface of the film.
TL;DR: The XUV spectroheliograph, Apollo Telescope Mount experiment S082A, is described, a slitless Wadsworth grating spectrograph that employed photographic recording that had aberrations and the provisions necessary to maintain optimum imagery and reliability in a space environment are discussed.
Abstract: The XUV spectroheliograph, Apollo Telescope Mount experiment S082A, is described. The instrument was a slitless Wadsworth grating spectrograph that employed photographic recording. The grating was of 4-m radius, ruled with 3600 grooves/mm. By rotating the grating to positions where the normal was at 255 A or 400 A, the spectral ranges 175-335 A and 320-480 A, respectively, were covered with 2-sec of arc spatial resolution. Close to the normal the resolution reached 2 sec of arc, but at the extreme limit, 630 A, it was 10 sec of arc or worse. The aberrations of the instrument are discussed in detail as are the provisions necessary to maintain optimum imagery and reliability in a space environment. During the mission about 1020 exposures were made covering 171-335 A or 320-630 A.
TL;DR: The sensitivity of the photoacoustic technique was found to be limited to about 1 x 10(-5) cm(-1) in the authors' samples due to radiation scattered onto the transducer, but the technique is capable of measuring absorption coefficients in the 10(-6)-cm (-1) range using laser powers of about 1 W.
Abstract: An investigation was made of a photoacoustic technique for determining the optical absorption coefficient in solids. A train of laser pulses was passed through the solid, and a piezoelectric transducer attached directly to the sample measured the amplitude of the elastic wave generated by the absorbed radiation. Calibration was performed at a wavelength of known absorption. The sensitivity of the technique was found to be limited to about 1 × 10−5 cm−1 in our samples due to radiation scattered onto the transducer, but the technique is capable of measuring absorption coefficients in the 10−6 cm−1 range using laser powers of about 1 W.
TL;DR: These measurements have been based on measurements of the absolute reflectance for the particular barium sulfate samples whose scattering and absorption coefficients were measured, and this method gives results that are different from earlier measurements; the differences are significant for measurement of the optical properties of atmospheric aerosols.
Abstract: We have measured the Kubelka-Munk scattering and absorption coefficients for a barium sulfate white reflectance standard. These measurements have been based on measurements of the absolute reflectance for the particular barium sulfate samples whose scattering and absorption coefficients were measured. This method gives results that are different from earlier measurements; the differences are significant for measurements of the optical properties of atmospheric aerosols.
TL;DR: In this article, a three-mirror telescope with a geometric spot size of less than 0.1 sec of arc in an easily accessible flat field of 1.5° and excellent stray light suppression is introduced.
Abstract: A new configuration of a three-mirror telescope is introduced that combines high performance with practicality. A geometric spot size of less than 0.1 sec of arc in an easily accessible flat field of 1.5° and excellent stray light suppression are the outstanding features.
TL;DR: A miniature argon arc has been designed and tested as a new transfer standard of spectral radiance for the wavelength range from 114 nm to 330 nm, and provides an intense, stable, and reproducible uv continuum with dc power requirements of less than 1.5 kW.
Abstract: A miniature argon arc has been designed and tested as a new transfer standard of spectral radiance for the wavelength range from 114 nm to 330 nm. Calibration has been performed using two primary standard sources: the hydrogen arc from 130 nm to 330 nm and the blackbody line radiator from 114 nm to 130 nm. The mini-arc provides an intense, stable, and reproducible uv continuum with dc power requirements of less than 1.5 kW. The arc characteristics have been investigated, and the sensitivity of the radiant power output to various operating parameters has been measured. The rms uncertainty in the spectral radiance is estimated to be 5.3% above 140 nm and 10.1% between 114 nm and 140 nm, due primarily to uncertainties in the primary standard sources.
TL;DR: Equations and tables are provided for designing high reflectors with reduced peak electric field intensity that should enhance the laser damage threshold for reflectors in which the damage is correlated with peakElectric field intensity in one of the two coating materials.
Abstract: Equations and tables are provided for designing high reflectors with reduced peak electric field intensity. This approach should enhance the laser damage threshold for reflectors in which the damage is correlated with peak electric field intensity in one of the two coating materials.
TL;DR: A review is given of several newly developed methods for measuring low absorption losses in optical rnaterials with special emphasis on how thermocouple and photoacoustic calorimetry can be used to determine both bulk and surface absorption simultaneously.
Abstract: A review is given of several newly developed methods for measuring low absorption losses in optical rnaterials. Transmission, emittance, and calorimetric techniques are described with special emphasis on how thermocouple and photoacoustic calorimetry can be used to determine both bulk and surface absorption simultaneously. The advantages and disadvantages of the various approaches are discussed, and estimates are given of the sensitivities that can be achieved with the different techniques. Finally, a new ac interferometric calorimetric method for measuring low bulk losses is proposed.
TL;DR: The measurements with monochromatic illumination agree with the predictions of a mathematical model developed to take account of reemission following the absorption of luminescence, but there is a need for further spectral sensitization and for reduced matrix loss coefficient.
Abstract: Luminescent greenhouse solar collectors are potentially useful for concentrating sunlight onto photovoltaic power cells. Measurements of the performance of small-scale collectors made of two commercially available materials (Owens-Illinois ED2 neodymium-doped laser glass and rhodamine 6G-doped plastic) are presented. The results are encouraging, but they indicate a need for further spectral sensitization and for reduced matrix loss coefficient. The measurements with monochromatic illumination agree with the predictions of a mathematical model developed to take account of reemission following the absorption of luminescence. Under solar illumination, the model predicts photon flux concentrations of about 15 for optimized full-scale collectors made of the materials studied and concentrations of 110 for reasonably improved glass.
TL;DR: The two level model is further developed and extended for use in intensity regions slightly lower than that required to saturate the resonances completely, and it has proved feasible to measure both the C(2) number density in the (3)II(u) state and an excited electronic state lifetime of ~10(-12) sec.
Abstract: The technique of saturation spectroscopy is applied to measure the concentration of C2 in the 3Πu state in oxyacetylene flames. The two level model is further developed and extended for use in intensity regions slightly lower than that required to saturate the resonances completely. As a result, it has proved feasible to measure both the C2 number density in the 3Πu state of ~1016/cm3 and an excited electronic state lifetime of ~10−12 sec, both of which depend only on the Einstein A coefficient. The experimental setup is described in detail, and possible extensions of the technique to other atomic and molecular systems are discussed.