bluuebunny/crossref_metadata_2025 huggingface dataset:
Electro-optic Effect and Propagation Loss in Polymer Films Containing Nano-sized Droplets of Liquid Crystal
Authors: Matsumoto Shiro , Sugiyama Yasuyuki , Sakata Seizou , Hayashi Takayoshi
Published: February 2023

Droplets of liquid crystal (LC) have been energetically investigated during the last ten years.(1) Most of the research has aimed at making use of scattering(2) and diffraction,(3) which occurs either at the surface of individual droplets or at the surface of a layer consisting of many droplets. The droplets were mostly micro-sized. Our aim, however, is to make use of nano-sized LC droplets for active optical devices such as optical switches or tunable filters. The surfaces of nano-sized LC droplets are too small to scatter light, so the total intensity of transmitted light is not changed, but the phase or polarization can be controlled by the birefringence generated by the response of nano-sized LC droplets to an electric field shown in Figure 1. There have been only a few works(4) including ours,5) which have similar aims. We have already reported the preparation of droplets about 50 nm in diameter and shown they respond to an electric field. In this work, we prepared the polymers containing nano-sized LC droplets by various conditions and measured their electro-optic effect, propagation loss, and response time.
Difference in relaxation time between coherent and incoherent second-harmonic generation
Authors: Clays Koen , Olbrechts Geert , Van Steenwinckel David , Persoons André
Published: February 2023

The experimental technique of generating incoherent second-harmonic, also known as hyper-Rayleigh scattering, has become widely appreciated for the determination of the first hyperpolarizability β of nonlinear optical chromophores in solution. This technique was first demonstrated with nanosecond pulses from Neodymium-YAG lasers,1 but has also been extended to femtosecond pulses from Titanium-sapphire lasers.2
Return Loss Measurements for the Determination of Critical Materials Parameters for Polymer Optical Waveguides
Authors: Norwood R. A.
Published: February 2023

There is a significant amount commercial and research activity currently centered around the deployment of various optical networks, including wavelength division multiplexing systems1 and passive optical networks. Recently, there has been increased effort devoted to investigating the use of polymers as the materials for passive components in these systems, such as wavelength division multiplexers2 and splitters. Low loss polymer single-mode waveguides have been demonstrated in a number of systems to this point3,4 and it is likely that components with sufficiently low insertion loss will be available in the near future.
Passive alignment of optic fiber array using silicon V-grooves monolithically integrated with polymer waveguide devices
Authors: Chen Antao , Ziari Mehrdad , Steier William H.
Published: February 2023

Packaging is the crucial link between a laboratory demonstrated device and a reliable component in a practical system. To achieve and maintain the sub-micron alignment tolerances between fiber and waveguide is the major factor that makes the packaging of photonic devices labor intensive, time consuming, and costly[1, 2]. Fiber arrays are important in WDM multiplexers and demultiplexers where multiple fiber attachment is essential. To avoid the complexity of the active alignment and attachment of individual fiber to each waveguide, we experimented with the passive alignment of fiber arrays with silicon V-grooves. The V-grooves are made on the same substrate that the polymer device is built on. The waveguide channels aligned to the center of the V-grooves are also processed together with the V-grooves using the same photolithography and etching technology. This technique is fundamentally different from the use of silicon V-grooves as fiber carrier for LiNbO3 and semiconductor devices, in which V-groove and devices are made on different substrate and bonded together later[3,4]. The width and the position of V-grooves can be fabricated in submicron precision with mature microelectronics technology. The fiber placed in the V-groove is entirely self-aligned in both vertical and lateral directions. The idea and some fabrication results of this approach have been presented earlier[5]. In this paper, our recent results of fiber coupling experiments are reported.
Characterization of electrooptic polymers with high µβ chromophores for photonic device applications
Authors: Chen Antao , Garner Sean , Yacoubian Araz , Steier William H. , Chen Jinghong , Harper Aaron , Zhu Jingsong , He Mingqian , Sun Shajing , Wang Fang , Ra Younsoo , Mao Shane S. H. , Zhang Cheng , Dalton Larry R. , Chen Datong , Fetterman Harold R.
Published: February 2023

For electrooptic (EO) polymer devices to be accepted in high speed fiber communication systems, the operation voltage of these devices must be reduced to a level compatible with the high speed electronics that drives the polymer devices. A low operation voltage, or Vπ in the case of modulators, requires EO polymers with high electrooptic coefficients. The electrooptic effect comes from the nonlinear chromophores in the polymer and the alignment of these chromophores by poling. High electrooptic coefficients calls for chromophores with large nonlinearity, i.e., high µβ. The synthesis and characterization of EO polymers with high µβ chromophores1 have been the focus of recent research in the field of nonlinear optic polymers.
Polarization-Insensitive Digital Optical Switch Using an Electro-Optic Polymer Rib Waveguide
Authors: Lee Sang-Shin , Shin Sang-Yung
Published: February 2023

The digital optical switch (DOS) based on lithium niobate, semiconductors, and thermooptic polymers [1,2] has attracted much attention as a promising guided-wave switching device. Its advantages include wavelength-insensitive operation and relaxed fabrication tolerance. The guided-wave device in electro-optic (EO) polymers [3] has a small velocity mismatch and a low dielectric constant that are favorable for high-speed operation and small coupling loss to the fiber. Recently, we fabricated an EO polymer DOS with photobleached waveguides [4]. Though the DOS operates independent of the wavelength, but it is not polarization independent since the waveguide fabricated by using photobleaching (PB) method can not support TE modes [3].
Linear Electro-Optic measurements of Dye-Doped Polymers
Authors: Ghebremichael F. , Knize R. J.
Published: February 2023

The basic Mach-Zehnder interferometer was modified for use in in-situ temperature dependent linear electro-optic (LEO) measurements of thin films of 4-dimethylamino-4'-nitrostilbene (DANS) doped into poly(methyl methacrylate) (PMMA). Optimum interferometer phase stability was possible because of an incorporated electronic feedback system. Film thickness variation was compensated for in order to obtain more accurate LEO coefficient measurements and thus the second order susceptibility. Moreover, both the α-relaxation associated with the glass transition, Tg, and β-relaxation associated with the secondary transition occurring below Tg of PMMA + 2%wt.DANS were obtained.
Single-Mode Optical Interconnects in Ultra-Low-Loss Environmentally-Stable Polymers
Authors: Eldada Louay , Shacklette Lawrence W. , Norwood Robert A. , Yardley James T.
Published: February 2023

SINGLE-MODE passive optical components need to be produced in high volume and at low cost in order to meet the ever-increasing demands of the telecom industry. Although glass optical fibers provide a very convenient means for carrying optical information over long distances, they are very inconvenient for complex high-density circuitry. Devices produced in glass fibers are difficult to fabricate — especially when they have a high port count — and as a result are quite expensive. Polymeric materials, on the other hand, offer the potential to create low-cost highly-complex optical interconnection circuitry on a planar substrate. In addition, they provide the possibility for a much higher degree of ruggedness and hermeticity. We have developed in detail one technology for single-mode polymeric optical interconnection which addresses the needs of the telecom industry. Our polymeric waveguiding structures are very low loss (0.06 dB/cm at 1550 nm), temperature resistant (they can endure more than 65 years at 100°C before a loss of 0.1 dB/cm is thermally induced), humidity resistant (no humidity effects were observed on a bare device after 600 hours at 85°C 85% RH), and exhibit low dispersion and low birefringence.
A stochastic model for chromophore disorientation in guest-host nonlinear optical polymer system
Authors: Lee S.-J. , Medvedev G.A. , Caruthers J.M. , Lackritz H.S.
Published: February 2023

The temporal and thermal stability of nonlinear optical (NLO) properties of polymers doped with optically active chromophores has been studied by many researchers [1] because of its importance to predict the long term performance of these systems for practical applications. Until recently most of these efforts were focused on attempting to fit experimental data to empirical functions, such as stretched exponential [2] or lognormal [3], with no direct mechanistic interpretation of the parameters. It has been established that the decay of the second harmonic generation (SHG) signal after poling is clearly nonexponential, and its characteristics depend, in a complex manner, on processing and thermal history. Whereas there is general agreement that the complex character of the decay in NLO properties is caused by the coupling of the chromophores disorientation to the structural relaxation of the polymer matrix, the mechanism of this coupling is poorly understood. This research involves the application of a stochastic model, recently developed by our group, for structural relaxation in glasses [4] in order to describe orientational relaxation of chromophore particles, which is responsible for SHG decay in chromophore doped polymer glasses.
Study of photoinduced orientation of azobenzene amorphous polymer by Visible, FTIR and Raman spectroscopy
Authors: Labarthet F. Lagugné , Buffeteau T. , Sourisseau C.
Published: February 2023

Azo-dye containing polymeric systems have been a subject of intensive research in the last few years in the areas of photofunctional applications such as photon mode optical memories, transducing optical information, photoswitching of electron conductivity. The main interest of such doped or functionalized systems is due to their dichroic and birefringent properties when they are illuminated by a polarized light. Such an effect is a consequence of the reversible “trans↔cis” photoisomerisation with respect to the N=N double bond which causes a redistribution in the orientation of photochromic entities. In this respect, Dumont et al.1 have already reported the basis of a simple three-level theoretical model in order to explain the reorientation mechanisms of the azo molecules within a photoisomerisation cycle. Hereafter we thus report the results of a dynamical study of the photoisomerisation-induced reorientation of DR1-azo-dye in a polymer matrix (PMMA) by in-situ time dependent Visible and polarisation modulation FTIR spectroscopy measurements. The last part concerns the generation of high-efficiency diffraction patterns obtained by holographic way.
Laser Emission from A Monolithic Organic Single Crystal
Authors: Fichou Denis , Delysse Stéphane , Nunzi Jean-Michel
Published: February 2023

Recently, the possibility to realize a polymer laser diode has been investigated and it has been shown that optically pumped conjugated polymers generate stimulated emission in solution [1,2] and thin films [3-5]. In the latter case, it is necessary to build a microcavity around the polymer film in order to induce lasing. We demonstrate here that ultra thin (a few microns) single crystals of octithiophene (8T) naturally behave as luminescent optical resonators and are adapted to produce optically driven laser emission.
Design Philosophy For Progressive Addition Lenses
Authors: Guilino Günther H.
Published: February 2023

Although the basic ideas for the realization of progressive addition lenses (PALs) go back a lot further, the first patents which contain the essential characteristics of those PALs which have been successful on the market date back to the years 1953 (FR 658760 by Maitenaz) and 1954 (US 287 8721 by Kanolt).
Physical Quality Assessment of Multifocal Contact Lenses to Correct Presbyopia
Authors: Baude D. , Obrecht G. , Chavel P. , Joyeux D. , Taboury J.
Published: February 2023

To correct presbyopia with contact lenses, three means exist for a long time: monovision, translating bifocals and simultaneous vision. The main feature of the last one is to produce on the retina, two or more images from a single object, each corresponding to a different optical power. However, only one of these images can be in-focus at one time. The out-of-focus images of an extended object produce a loss of contrast in the in-focus image, with respect to sharp images produced by a spherical lens. So it is necessary to devise specific tools to assess the physical quality of these multifocal contact lenses correcting presbyopia.
Correction of Presbyopia with a New Adjustable Spectacle Lens
Authors: Barnea Daniel I. , Peli Eli
Published: February 2023

In the quest for a solution to presbyopia and due to the inability to restore the eye's system itself, man in the last centuries resorted to a continuous evolution of increasingly sophisticated types of eyeglasses (Fowler and Patreas, 1991). What technology has had to offer so far, as practical products, were glasses that utilize rigid lenses. The most advanced solution on the market today is spectacles with progressive addition lenses (PAL) that provide a different, yet fixed power, in each direction of gaze. This is still a compromise with the real need of a dynamically varying power. While in some frequently occurring situations, such a grading approximates real needs, in many other situations the compromise forces uneasy head tilting and partially impaired vision.
Pupil Size and Visual Performance with Soft Bifocal Contact Lenses
Authors: Bullimore Mark A. , Jacobs Robert J.
Published: February 2023

There is a growing population of presbyopic contact lens wearers. Many of these individuals would like to retain the comfort, convenience and cosmesis of soft lenses and avoid the use of spectacle lenses to achieve adequate vision at distance and near. This demand has led to the development of a wide range of soft bifocal contact lens (SBCL) designs. The majority rely on "simultaneous- vision" where the in-focus image of the distant or near object formed by the appropriate portion of the lens is always accompanied by a superimposed out-of-focus image formed by the remainder of the lens. Simultaneous-vision may be achieved by various techniques. The traditional approach is the concentric design where a small (~2.5 mm) central near portion is surrounded by the distance portion (e.g. the Alges lens). Alternatively the distance portion may be placed at the lens center (e.g. the Bi-soft lens). A second approach is the aspheric design where a gradual transition in lens power between the distance and near portions is achieved by producing and back or front lens surface (e.g. the PA1 lens). Increases in asphericity will produce a more pronounced variation in surface power, thereby increasing the range of distances over which the lens is focussed but this will be at the expense of image quality (Charman and Walsh, 1988). A third approach is the diffractive design as employed in the Echelon lens (Klein and Ho, 1986). In this lens, images of distance objects are formed by refraction, while images of near objects are formed by diffraction. Diffraction is achieved by annular grooves on the back surface of the lens.
Plastic Photochromic Eyewear: A Revolution
Authors: Welch Cletus N. , Crano John C.
Published: February 2023

The discovery of a system based on silver halide crystallites suspended in an inorganic glass matrix resulted in the development of the first commercially acceptable photochromic lenses1,2. The convenience of having lenses that darken automatically upon exposure to sunlight has proven to be appealing to eyeglass wearers. An estimated 10 million pairs of silver-based photochromic prescription lenses were dispensed in the United States in 19893.
Optical and Clinical Issues in the Measurement of Corneal Topography
Authors: Applegate Raymond A.
Published: February 2023

It is a privilege to be invited to speak and provide this technical summary on optical and clinical issues in the measurement of corneal topography.
Optical Quality of the Human Eye Across the Visual Field
Authors: Navarro Rafael , Artal Pablo , Williams David R.
Published: February 2023

The optical quality of the eye has been the subject of many studies,
ranging from geometrical aberrations, to Line or Point Spread
Functions (LSF or PSF), or the Modulation Transfer Function (MTF).
While the great majority of these studies deal with foveal imaging,
little attention has been paid to the extrafoveal case, and as a
consequence, the off-axis image quality has been largely unknown. For
instance, there is only one published experimental LSF
result1, obtained with just one subject with a large pupil
(7.5 mm), which yielded poor optical quality even in the fovea.
Astigmatism: What's the Rule?
Authors: Zadnik Karla , Mutti Donald O. , Adams Anthony J.
Published: February 2023

Many studies suggest that a high proportion of infants have astigmatism >1.00D that virtually disappears by one year of age (Banks, 1980), but there is evidence that cycloplegic examination reduces this high prevalence significantly (Fulton et al., 1980; Dobson et al., 1984). Several investigations of infant astigmatism as summarized in Table 1.
Psychophysical Measurement of the Optical Quality of Varifocal Contact Lenses
Authors: Campbell Melanie C.W. , Charman W. Neil , Voisin Linda , Cui Chengwu
Published: February 2023

There are several designs of contact lenses currently available for the correction of presbyopia. No lens comes close to the ideal of providing a correction appropriate to the object of regard which covers the full entrance pupil of the eye1. Of interest are the compromises offered by specific designs and how well their on-eye performance compares with both their theoretical performance and in vitro measurements made on the lenses. One of the current classes of design consists of concentric simultaneous vision varifocal lenses. These lenses are usually limited to radial power profiles. The available range of corrective power under any particular set of lighting conditions is dependent on the pupil diameter of the individual wearer. The lens design usually cannot be modified to match the pupil diameter of the individual nor to increase the effective reading addition for the aging presbyope1. Their smooth variation in power is presumed to give reasonably good visual performance for a wide range of object distances. Moreover, unlike alternating designs, concentric varifocals give adequate near vision for all directions of gaze, and do not require decentration, which is difficult to achieve with soft lenses.
Visual acuity and Contrast Sensitivity after "Optical Implantation" of Multifocal Intraocular Lenses with a New Device
Authors: Eisenmann D. , Jacobi K.W.
Published: February 2023

Usually, the optical performance of intraocular lenses (IOLs) is investigated using in vitro measurements [1] or patients follow-up after IOL implantation [2]. In this study, we evaluated the optical performance of multifocal IOLs (MIOLs) by means of a new optical system: similar to an astronomical telescope, images produced by IOLs can be projected into the eye. This system gives a subjective impression of the actual visual perception through IOLs.
OPTICAL PERFORMANCE OF ASYMMETRICAL REFRACTIVE MULTIFOCAL IOLs
Authors: Eisenmann D. , Rückmann A. v. , Jacobi K. W.
Published: February 2023

In vitro measurements and clinical follow-up data of multifocal intraocular lenses (MIOLs) both agree, that an increase in depth of field is associated with a decrease in contrast of the retinal image [1,2].
Measurement of Toric Reference Surfaces with the Computed Anatomy Videokeratoscope (TMS-1)
Authors: Greivenkamp John E. , Mellinger Mark D. , Snyder Robert W. , Miller Joseph M. , Bechara Samir J. , Waring George O.
Published: February 2023

The accuracy of video keratoscopes on non-rotationally symmetric surfaces has not been established. In this work, we test the performance of one manufacturer's instrument (Computed Anatomy TMS-1, New York, NY) on a set of 5 precision toric reference surfaces. These surfaces have a base radius of curvature (ROC) of 7.80 mm, which corresponds to an equivalent comeal power of 43.25 D.
Improvements for Video-Keratography
Authors: Klein Stanley A.
Published: February 2023

Last year's meeting on Ophthalmic Optics featured two sessions on corneal topography with an excellent overview by Applegate (1992). This large interest in the field made me think that a technological breakthrough must recently have occurred in the algorithm for quantifying corneal curvature.
A COMPARISON OF THE ERRORS ARISING FROM THREE METHODS OF PHAKOMETRIC COMPUTATION
Authors: Dunne M. C. M. , Barnes D. A.
Published: February 2023

Phakometric determination of the crystalline lens surface powers traditionally requires measurement of Purkinje images I, III and IV which are formed by reflection at the anterior corneal surface, the anterior lens surface and the posterior lens surface, respectively1-3. In this case, any discrepancies between refractive error and lens power are taken up by a calculated axial length3. An alternative method has been described which uses only Purkinje images I and III4. Here, any discrepancies between refractive error and an ultrasonically determined axial length are taken up by the posterior lens power3. Both methods suffer from difficulties encountered measuring Purkinje image III due to its poor quality coupled with the fact that it is positioned in the vitreous chamber whereas the other images fall approximately in the iris plane5. A further technique has therefore been developed which uses only Purkinje images I and IV6. Now, any discrepancies between refractive error and an ultrasonically determined axial length are taken up by the anterior lens surface power. The present study aims to compare the errors arising from all three methods of phakometric computation.
Improved Ocular Telephoto System Using Diffractive Optics
Authors: Ting Albert C. , Chou Jim-Son
Published: February 2023

Patients with age-related macular degeneration have their life-styles dramatically altered due to the loss of central foveal vision.3,4 Various methods have been advanced to assist their vision, primarily through the use of magnification of the image on the retina. Some of these utilize the Galilean telescope principle1-5.
Optical Performance of Silicone Intraocular Lens
Authors: Sun Rong , Portney Valdmar
Published: February 2023

Measurement of optical quality of an intraocular lens (IOL) has been defined by ANSI standard Z80.7 in 1984.1 The minimum required resolving power of the IOL is 100 line-pairs per millimeter (lp/mm) in air using 3 mm aperture. For IOLs of typical powers, this resolution represents approximately 30% of the resolving power of a diffraction-limited lens. Previous studies demonstrated that most US. manufacturers provided high quality PMMA IOLs in terms of ANSI standards.2,3 In order to follow recent technology advances, a committee of manufacturers and ophthalmologists has been convened to revise the ANSI standards Z80.7 - 1984.
Comparison of Spheric, Low and High Asphericity Lenses for Hyperopia
Authors: Krefman Ronald A.
Published: February 2023

Aspheric lens design is recognized as the preferred method of reducing aberrations, minimizing magnification and ring scotoma, enhancing peripheral vision, and making high plus (over +10.00D) powered ophthalmic and aphakic lenses thinner and lighter weight. Aspheric lenses have progressively flatter curvature towards the lens periphery and can be categorized by the degree of asphericity or amount of "drop". Higher degrees of asphericity emphasize wider visual fields and minimizing the ring scotoma while lower asphericity lenses emphasize peripheral acuity and minimize distortion. In general, aspheric design improves the off axis performance of any high plus lens by reducing aberrations. The use of aspheric lenses also results in flatter, thinner and lighter weight lenses.
Measurements of the Stiles-Crawford Effect and of Increment Thresholds in Patients with Gyrate Atrophy of the Choroid and Retina
Authors: Caruso Rafael C. , Kaiser-Kupfer Muriel I. , Drews-Bankiewicz Malina A. , Valle David L.
Published: February 2023

As the Stiles-Crawford (S-C) effect of the first kind depends on the directional sensitivity of photoreceptors, it can be used in clinical research to identify and quantify photoreceptor involvement in retinal diseases. In this report, we describe abnormalities of foveal cone directional sensitivity and foveal cone thresholds in patients with gyrate atrophy of the choroid and retina (GA).
Confocal Microscopy of the Human In Vivo Cornea
Authors: Masters Barry R. , Thaer Andreas A.
Published: February 2023

The in-vivo observation of the living cornea by the technique of confocal microscopy provides en face images of high contrast and resolution1-4 . In contrast to Nipkow disk pinhole confocal microscopes,1-4 slit based confocal systems collect more light form the eye.5-6 The development of the wide-field specular microscope by Koester was limited by the low numerical aperture of the applanating cone objective7,8. Recent developments of a high numerical aperture for the wide-field specular microscope has resulted in a confocal microscope for the eye.9,10 We describe a new flying slit confocal microscope, illuminated with a halogen lamp, which has unique imaging characteristics for in vivo human confocal microscopy.
Psychophysical Application of a Parametric Model of the Ocular Modulation Transfer Function
Authors: Drasdo Neville , Thompson Caroline M
Published: February 2023

Contributions to the theory of image processing in the human visual system frequently attempt to relate psychophysical performance on a particular visual task to the supposed dimensions of receptive fields in specific groups of neurons. The existence of models of optical degradation for the human eye will enable such experiments to be conducted with an improved degree of precision. Although at present the most detailed information on the optical transfer function of the eye has been mainly limited to studies with monochromatic light (Artal,1989), the parametric model of Deeley, Drasdo and Charman (1989) provides a means of investigating contrasts with white light for central vision. According to this model the modulation transfer (MT) in the retinal image of a sinewave grating of spatial frequency (SF) formed by an eye of pupil size (P) in mm., is given by the following equation: This model must of course be applied with due caution because the inclusion of the effects of the phase transfer function become relevant with pupil sizes exceeding 4mm at large peripheral angles (Walsh and Charman, 1992). Nevertheless it is already possible to apply this model to psychophysical data obtained for example at the fovea and at 100 eccentricity in the temporal visual field. According to classical studies and schematic eyes the MTF would in fact be identical at these two points because they are symmetrical around the optic axis of the ocular components. In reality however this may not be quite correct and increased retinal scatter may occur, but the corresponding asymmetry is visible in most studies on the MTF in peripheral vision, and MT does not decline very signifiantly at this point.
Video Remote Keratometer for the Screening of Corneal Astigmatism
Authors: Miller Joseph M. , Mellinger Mark D. , Greivenkamp John E. , Palmer Millicent , Hunter David , Simons Kurt
Published: February 2023

The Video Remote Keratometer (VRK) is an ophthalmic instrument that permits the measurement of corneal topography from a sufficiently large distance that the subject is not threatened by its presence. Young children are frequently troubled by the presence of instrumentation held close to their faces and become uncooperative.
An Evaluation of the Optical Performance of the Eye
Authors: Liang Junzhong , Bille Josef
Published: February 2023

The optical performance can be evaluated by measuring the line-spread function[1,2], the point spread function[3], or the aberrations of the eye. The measurement of the wave aberrations of the eye has been attracting sustained interest over the last hundred years[4-7]. Recent demand for a fast and precise measurement of the aberrations of the eye in order to adaptively improve the performance of a Laser Tomographic Scanner[8] lead to the development of a new technique applying a Hartmann-Shack wavefront sensor[9,10]. This newly devoloped technique has the following advantages: (1) the test can be done in real-time and the measurement can be analysed automatically. (2) the repeatability and precision of the measurement can be very high. In this report, we will present an evaluation of the optical performance of the eye based on the precise measurements of the aberrations of the eye.
Reducing Aberration at the Fovea by Defocus
Authors: Cui Chengwu , Campbell Melanie C. W. , Voisin Linda , Charman W. Neil
Published: February 2023

Given a point object, the best image of an optical system is usually not the image at the paraxial image plane due to aberration(Welford,1986). It might be expected that the eye would alter its accommodative state to the best image plane instead of the paraxial image plane. Spherical aberration contributes to the well known change in refractive state in night myopia(Koomen, et al, 1956). It is also known that subjective best focus is spatial frequency dependent(Green et al, 1965; Charman et al, 1976). However, the possible link between defocus of the eye and aberration has not been investigated. In processing the data of retina blur from subjective measurement of ocular aberrations, little attention has been paid to the defocus term. The method of measuring aberration in semi-Maxwellian view(Campbell, et al, 1990) provides a possible way to measure the defocus term while the subject focuses on the same target that is used to analyze the aberration. In the following study, we have manipulated the amount of spherical aberration in the eye using varifocal contact lenses and studied the resulting defocus.
Collisional Relaxation Times for Nitric Acid Vapor
Authors: Farrow L. A. , Richton R. E.
Published: February 2023

It has been shown previously1 that it is possible to obtain information on gas phase collisional relaxation rates from the amplitude rather than the phase of the signal coming from the microphone of an optoacoustic cell. In that earlier work,1 we proposed a detailed theory, based on a numerical solution of the heat diffusion equation, to relate the microphone signal amplitude to collisional relaxation time. The theory was verified using mechanically chopped single frequency infrared laser radiation at moderate power levels and at suitable wavelengths for absorption by nitric oxide, a diatomic gas with known spectroscopic and thermochemical properties.1 In the present paper, we apply the theory to experiments on dry nitric acid vapor, a polyatomic gas with nine vibrational modes.2
Measurement of IR Multi Photon Absorption by Polyatomic Molecules Using the Photoacoustic Technique
Authors: Chin S.L. , Evans D.K. , McAlpine Robert D. , Selander W.N.
Published: February 2023

The single pulse photoacoustic technique for measuring infrared multiphoton absorption by polyatomic molecules is described in detail for the first time. The interaction volume of interest is the focal region (Fig. 1) in which the laser intensity can be very high to promote multiphoton processes. Compared to classical transmission technique with a parallel laser beam of very high intensity (practically very difficult), the present technique is simple but powerful. The microphone detects the energy released from the focal volume in front of it. As long as the microphone is closer to the focal volume than it is to the entrance and exit windows, the signal from the focal region will arrive at the microphone earlier than any other acoustic signal created in the cell. Fig. 2a shows two typical oscilloscope traces at two different time scales of the microphone signal by focusing a 10.6 µ TEA-CO2 laser pulse (~ 1 mJ/cm2) into 3 torr (1 torr = 0.133 kPa) SF6 through a 25.4 cm focal length lens. The focal region in front of the 1.27 cm diameter microphone can be approximated as a cylinder of uniform intensity and length ℓm because of the long focal length. The peak value of the first pulse is proportional to the energy absorbed by the molecules in the focal volume. Three questions are asked. (1) Why is the first peak proportional to the energy absorbed? (2) What are the other oscillations? (3) What is the pressure range for easy application of the technique? The answers are given below.
Laser Photoacoustic Spectroscopy of High Vibrational Overtones
Authors: Wong James S. , Moore C. Bradley
Published: February 2023

The nature of intramolecular energy transfer and mode coupling in highly vibrationally excited, polyatomic molecules can be studied by high overtone spectroscopy [1,2]. The details of the vibrational overtone spectrum corresponding to changes in vibrational quantum number of 5, 6, and 7 directly probe the vibrationally excited, final state. Since the absorption cross sections for these transitions are very small, typically less than one barn, photoacoustic spectroscopy can be used to detect these overtone absorptions.
Signal Enhancement in Photothermal Imaging Produced by Three Dimensional Heat Flow
Authors: Murphy J. C. , Aamodt L. C.
Published: February 2023

The development of photoacoustic microscopy (SPAM)(1,2) has provided a means of studying the surface and subsurface features of solids including subsurface voids or layer disbonding which modify the efficiency of thermal diffusion into the sample. We have recently introduced a new method of thermal imaging(2) which shares some of the features of SPAM but, rather than acoustic detection, uses the "mirage effect"(4) or deflection of an optical probe beam to determine the sample surface temperature distribution.(5) A theory of photothermal imaging has recently been developed for homogeneous samples(6) (i.e., samples containing no thermal diffusion boundaries important to the experiment). This development includes a full treatment of 3-dimensional diffusion in the sample and the gas. The theoretical results are in good agreement with those obtained experimentally.
Optoacoustic and Photothermal Material Inspection Techniques
Authors: Busse G. , Physik ZWE
Published: February 2023

Within three years local optoacoustic signal representation techniques used first for crack detection /1/ have become a convenient method for thermal structure imaging even on a microscopic scale /2,3/. It has been found that the phase angle is the quantity of more interest for imaging because the depth range is larger /4/ and the influence of optical surface absorption can be eliminated /3/. However, a disadvantage of the well established techniques based on gas microphone or piezoelectric detection is the need of physical contact with the sample.
Electron-Acoustic Microscopy: Questions and Prospects
Authors: Cargill G. S.
Published: February 2023

The first electron-acoustic micrographs were published less than a year ago.1,2 This paper points out several important technical questions about this new technique and discusses a few of its possible applications.
Photo Displacement Imaging
Authors: Ameri S. , Ash E.A. , Neuman V. , Petts C.R.
Published: February 2023

The renaissance of photo-acoustic spectroscopy {1} has recently led to several novel forms of imaging. Common to all of these is the use of a modulated laser (or electron) beam which is partially absorbed by the object to be imaged. The energy from the incident beam is transformed, with varying degrees of efficiency, into thermal energy giving rise to stress waves within the object, producing pressure changes in the adjacent air, and I.R. radiation from the object. All of these effects have been successfully used as the basis of imaging systems, {2, 3, 4}.
Photoacoustics in Photosynthesis
Authors: Malkin S. , Bults G. , Horwitz B. A. , Lasser-Ross N. , Cahen D.
Published: February 2023

Photosynthesis is a complex process in which light is utilized to split water and reduce carbon dioxide, incorporating inorganic carbon into organic matter. The reaction steps can be divided roughly into two classes, loosely called "light" and "dark" reactions. The first are involved in oxygen evolution from water and formation of highly reduced (NADPH) and high energy (ATP) intermediates. These serve as the raw materials for the following CO2 reduction and fixation ("dark" reactions), contributing reducing equivalents and energy.
Photoacoustic Studies of the Photocycles of Bacteriorhodopsin at Low Temperatures
Authors: Bechthold P.S. , Kohl K.-D. , Sperling W.
Published: February 2023

Halobacterium halobium is extremely halophilic and requires a high concentration of NaCl (CNaCl > 2M) for growth and maintenance of structure. It occurs in salt lakes (e.g. Dead Sea, salt ponds) and survives even in crystalline salt. Under conditions of limited oxygen supply, 1ight-energy-converting membrane patches, the so-called purple membranes, are synthesized within the outer membrane of the bacteria. The purple membrane contains practically only one protein, called bacteriorhodopsin (BR) (1), which is arranged in a two-dimensional lattice, whose structure is known within a resolution of 7Å (2). BR is a chromoprotein and the pigment of the purple membrane. The purple membrane can be isolated by lysis of the cells and following purification by different centrifugation steps. The chromophoric group of BR is retinal, alternatively either in the all-trans or 13-cis configuration (3). Other retinal isomers were not found in vivo. BR which contains all-trans retinal is called trans BR
BRtrans568, BR which contains 13-cis retinal is called 13-cis BR
BR13-cis548. The two BR isomers are interconvertible by means of several pathways (Fig. 1) (4). One pathway does not require light (‘dark adaptation’); the others are initiated by light. Each isomer forms its distinct primary photoproduct. In the case of trans BR, the photoproduct returns via dark reactions through a series of transients to its initial isomer, trans BR (trans BR cycle). The light-energy-converting process, i.e. the active transport of protons from one side of the purple membrane to the other, can be correlated to the trans BR cycle. The function of the 13-cis BR cycle is not yet known. In the case of 13-cis BR, the dark pathway is split: most of the molecules return to their initial isomer, 13-cis BR (13-cis BR cycle), but some, on an alter native path, go to trans BR. Both pathways are connected by light reaction pathways, which are occupied by photo-excitation of transients. The environmental light conditions determine the isomeric composition of BR. In the dark-adapted state, BR contains a mixture of 13-cis BR and trans BR in a ratio of 1:1. On illumination of a dark-adapted sample with moderate light (e.g. 1mW/cm2), nearly all BR molecules are found in the trans BR state within a few seconds. The photoproducts of each BR isomer can be identified by means of low temperature absorption spectroscopy. To overcome light scattering due to cracks forming in aqueous suspensions at low temperatures, the BR samples have to be suspended in a glycerol/water mixture (w:w = 2:1) for optical absorption measurements. Only photoacoustic spectroscopy enables us to examine the photoproducts and intermediates of the two BR photocycles in buffered aqueous suspensions at low temperatures. We thus obtained photoacoustic spectra of nearly the same quality as optical absorption spectra.
Photoisomerisation of DODCI Studied by Photoacoustic Spectroscopy
Authors: Schneider S. , Möller U. , Coufal H.
Published: February 2023

DODCI (3,3′-diethyldicarbocyanine iodide), a widely used mode­locking dye, was taken as an example to study the influence of concentration, modulationfrequency and light intensity onto the PA-spectrum of this compound. As has been shown by flashphotolysis DODCI isomerizes upon excitation to the first excited singulet state from the alltrans configuration to an isomere whose longwavelength absorption band is shifted bathocromic by about 45 nm /1/ (fig. 1).
Design, Properties and Applications of Helmholtz Resonant Photoacoustic Cells for Measurements at Variable Temperatures
Authors: Bechthold P.S. , Campagna M. , Chatzipetros J.
Published: February 2023

Helmholtz resonant cells offer advantages for variable temperature photoacoustic measurements, because they allow to keep the inner volume of the cells small and at the same time to separate the cooled or heated sample from the microphone and preamplifier which can be kept at room temperature(1-3). Since microphones and preamplifiers must not be heated, Helmholtz resonant cells are, in fact, the only appropriate design for high temperature experiments (3,4), while at cryogenic temperatures nonresonant cells may also be used(5). We constructed two resonant cells (2,3) which together are apt to cover the temperature range between 90 K and 1050 K. Both cells are supplied with two small valves used for gas exchange and pressure equilibration. Each cell is equipped with two heating filaments which allow the temperature of the sample to be stabilized with an accuracy better than 0.03 K. Temperatures are measured by Ni-Cr-Ni thermocouples or a platinum resistor.
Quantitative Fourier Transform Infrared Photoacoustic Spectroscopy of Condensed Phases
Authors: Teng Y. C. , Royce B. S. H.
Published: February 2023

The application of Fourier transform techniques to photoacoustic spectroscopy has enabled this method to be extended into the important infrared spectral region between 4000 and 400 cm−1 [1-6]. In making experimental measurements the photoacoustic cell contains the material to be studied and replaces the instrument’s detector. After suitable filtration to remove signal frequencies outside those inherent to the spectral range being studied, the cell output is processed by the standard electronics of the FTIR spectrometer. Because of the selective absorption of the sample in the photoacoustic cell the interferogram has an appearance normally associated with an emission spectrum. The spectral information is therefore distributed over a wide range of path length differences in the interferometer rather than being largely in the "central burst" feature of the interferogram. The selective absorption also means that not all the energy incident on the sample is absorbed and so the central burst is smaller in amplitude than the corresponding feature for a black body absorber. When the data contained in the interferogram is transformed to obtain an absorption spectrum the resulting peak heights are not in the ratios expected due to a number of artifacts introduced by the technique. This paper is concerned with a discussion of these artifacts and procedures that may be employed to remove them so as to obtain a quantitatively correct sample spectrum. Experimental results are presented on some polymeric systems.
Some Observations on Signal Production in Photoacoustic Fourier Transform Infrared Spectroscopy
Authors: Kirkbright G.F. , Spillane D.E.M.
Published: February 2023

Recent investigations (1,2,3) have shown that the spectral range of Photoacoustic Spectroscopy (P.A.S.) can be extended to include the Mid Infrared (2.5-25 μm) by utilising Interferometry and Fourier Transform techniques to improve signal recovery. These techniques have compensated for the low intensity level of sources in this region which has made conventional, dispersive P.A.S. difficult to perform.
Photoacoustic Determination of Absorption Coefficients for Airborne Particulates Collected on Teflon Filters
Authors: Palmer R. A. , Röhl R.
Published: February 2023

In transmission spectroscopy, the absorptivity (or absorption coefficient) of a substance is defined as a = A/bc, where A is the absorbance, b the path-length of light through a sample, and c the concentration of absorbing material in the sample cell. The absorbance is defined by A = log Io/(Io-Ia) with Io representing the intensity of the unattenuated light beam and Ia the intensity of the absorbed light. In photoacoustic spectroscopy (PAS), Ia corresponds to the signal from a given sample, S, and Io to the signal from a black body reference with identical thermal properties, R. The PAS analog to absorbance, Apas, can therefore be written as in equation 1.
Determination of Ammonium in Airborne Particulates Collected on Filter Membranes by Near Infrared Photoacoustic Spectroscopy
Authors: Röhl R. , Palmer R. A.
Published: February 2023

Part of our research is aimed at exploring the potential usefulness of photoacoustic spectroscopy (PAS) for the nondestructive quantitative analysis of airborne particulates deposited on filter membranes. To date, most of this work has been concerned with the determination of the molecular species H2O and NH4+ in the fine fraction of aerosols collected by dichotomous virtual impactor samplers on Teflon filters.
Photoacoustic Spectroscopy of Active Immobilized Chloroplast Membranes
Authors: Thomasset Brigitte , Thomasset Thierry , Barbotin Jean-Noël , Véjux Alain
Published: February 2023

Recently many enzymes, microbial whole cells and organelles, immobilized by various methods, were applied in many fields (1). The important problem of biological energy conversion has emphasized the use of immobilized photosynthetic systems such as chloroplast membranes (thylakoids) to produce hydrogen and ATP regeneration (2-4). After immobilization by various methods (4) large variations in the functional stability were observed in the activity yield of lettuce thylakoids. Since immobilized thylakoids in different environments (albumin, carrageenan, alginate, polyurethan) appear as solid and amorphous particles, photoacoustic spectroscopy (PAS) (already performed by one of us (5) on immobilized hemoglobin particles) is expected to provide a valuable method to characterize the processes of energy conversion. Furthermore, Cahen and coworkers (6-8) have extensively applied PAS to fundamental photosynthesis studies.
Absorption of Light by Pigments in Lichens Studied by Photoacoustic Spectroscopy
Authors: O'Hara Ellen P. , Tom Roderick , Moore Thomas A.
Published: February 2023

Spectroscopic studies of the absorption of light by pigments in lichen in situ have been hindered by the optical properties of the samples. Characteristic of many biological samples, the crustose lichen Acarospora schleicheri have a low reflectivity and high optical density. These properties make conventional transmittance spectroscopy and diffuse reflectance measurements difficult. Photoacoustic spectroscopy (PAS), however, is ideally suited for measuring the spectral characteristics of opaque and/or low reflecting samples.