bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency modulation spectroscopy with tunable diode lasers
Authors: Cooper David E.
Published: February 2023

Frequency modulation spectroscopy with injection modulated lead-salt diode lasers offers the prospect of quantum-noise-limited detection of numerous atmospheric trace gas species. This sensitivity limit would allow detection of absorptions <10−7 in the mid-IR region and consequently detection of numerous atmospheric trace gases at the ppt level. The technique uses sample absorption to convert some of the laser frequency modulation (FM) into amplitude modulation (AM). The laser injection modulation and subsequent AM detection are usually accomplished in the radio frequency (rf) region where the diode laser excess noise is low. Unfortunately, a number of technical problems arise when the technique is used in the laboratory. These include incidental amplitude modulation of the diode laser and FM to AM conversion by external etalons, both of which shift some of the low-frequency laser noise into the rf region. We review several approaches to FM spectroscopy with diode lasers, discuss some of the experimental difficulties in implementing the technique and methods of overcoming the sensitivity limitations imposed by residual amplitude modulation. Finally, we discuss our most recent laboratory results and the prospects for sensitive monitoring instruments using FM spectroscopy.
Measuring the refractive index of infrared material with an improved method
Authors: Chang Ming-Wen , Hsu Tzu-Min , Chen Jehng-Huei , Yang Sheng-Jenn , Chen Kuo-Chew
Published: February 2023

Minimum deviation of the prism and autocollimation technique was used to measure the refractive index of IR material. Improvements to the measuring method were made by using (1) monochromatic light such as a laser to measure the apex angle and (2) surface coating on one side of a prism instead of a prism mounting to a mirror. These improvements increase the accuracy of the measurement to four significant figures. If the slit is narrowed, better accuracy, i.e., to five significant figures, can be achieved.
Refractive-index model and stress in Ag-doped glasses
Authors: Houde-Walter Susan N.
Published: February 2023

Empirically based models are currently in use for predicting the refractive-index distribution from dopant concentrations in ion exchanged glass for waveguide and gradient-index applications.1-3 Two of these models predict, either explicitly3 or when applied with the appropriate parameters,1 a linear variation of refractive index with silver dopant concentration. Five silver-doped aluminosilicate glass samples were fabricated by ion exchange to test the models. A wide range of dopant distributions was made with local compositions up to 14-mole % silver and exchange depths up to 3.3 mm. Concentration distributions were measured by energy dispersive spectroscopy.4 Refractive-index distributions were measured by ac interferometry.5 The measured refractive index (0.6471 μm) is linear with concentration for small (<1.0-mole % silver) dopant levels but otherwise departs significantly from the model. The index model should be improved by the inclusion of compressive stress due to the unequal radii of the exchange ions.
Ultrashort all-optical switching in glass dual-core fiber nonlinear couplers
Authors: Friberg S. R. , Oliver M. K. , Smith P. W.
Published: February 2023

Ultrafast all-optical switching devices are attracting considerable interest as switching elements for future high-bit-rate switching systems. The glass nonlinear coupler is a promising candidate for a practical ultrafast all-optical switch: it offers subpicosecond response times without thermal effects and can operate at rates far higher than those possible with electronic devices. We report experimental studies of switching characteristics of glass dual-core fiber nonlinear couplers with lengths ranging from 5 to 200 cm. These results encompass a range of coupling lengths varying from one to many (where the coupling length is the low-power transfer distance for light to couple from one waveguide of the coupler to the other), whereas our previously reported measurements were for a multiple coupling-length device only. A nonlinear coupler gives particularly useful switching characteristics when it is a single coupling length. Our data include both quasi-cw results using 200-ns Q-switched pulses from a 1.06-μm Nd:YAG laser and the response of slow detectors to 80-ps pulses in a mode-locked Q-switched pulse train from the same laser.
Effects of finite spectral width on nonlinear wave propagation in single-mode optical fibers
Authors: Wang Likarn , Yang C. C.
Published: February 2023

In designing high-bit-rate fiber communication systems, the transmission of solitons has been suggested after the possibility of the cancellation between dispersion and nonlinear effects was realized. Many publications on the propagation of a modulated sinusoidal wave in a single-mode fiber can be found in the literature. However, the out puts from most kinds of laser, especially from a semiconductor laser, bear finite spectral widths. The components of such a spectral distribution are usually supposed to be mutually independent and hence incoherent because of their random phases. Therefore, a pulse modulation of such a cw laser output produces a collection of many pulses with different central wavelengths corresponding to the aforementioned incoherent spectrum. In this research, we investigate the effects of this finite spectral width on nonlinear propagation in a single-mode optical fiber. To this end, the split-step technique is used to solve the wave equation governing pulse propagation. This numerical technique is iterated in those pulses with different central frequencies. Mutual interactions among those pulses can be clearly seen.
Fine tracking error and Its effect on the performance of unguided optical communication systems
Authors: Miller Ted L.
Published: February 2023

The performance of an unguided, or free space, optical communication system depends in a complex way on many system and environmental parameters. Because of the angular compactness of the antenna pattern that can be achieved at optical frequencies, fixed angular pointing offset and stochastic pointing fluctuations can be significant factors in determining overall system performance. Angular offset and pointing fluctuations give rise to both reduction in and fluctuation of received optical power or energy per bit. This increases bit error probability.
Theoretical computational method for finding the wave aberration of an eye from the retinoscopic reflex
Authors: Houck C. , Mistry M. , Howland Howard C.
Published: February 2023

We have shown previously1 that, given the wave aberration of the eye, one may compute the retinoscopic reflex for known degrees of defocus of the eye and eccentricity of the light source relative to the retinoscopic aperture. We now describe a theoretical computational method by which the coefficients of a wave aberration polynomial may be recovered from the distribution of light at the subject’s pupil in retinoscopic illumination. Practical applications of this method for finding the wave aberration of the eye using photoretinoscopy are discussed.
New approach to apochromatic color correction
Authors: Sigler Robert D.
Published: February 2023

Refractive optical systems using lenses of common low-cost optical glasses and selected optical liquid can attain a level of color correction previously possible only with expensive and difficult to work abnormal dispersion glasses or crystals. In addition to providing dramatic color correction these liquids have good availability, reduced material cost, and low-light scatter. The material selection, design, athermalization, and mechanical aspects for glass-liquid lens objectives are developed.
Design of a multiwavelength ultraviolet microobjective
Authors: Westcott Mark R.
Published: February 2023

Recent developments in microlithographic lenses have taken advantage of higher resolution and improved depth of focus associated with reduced wavelength. As wavelengths have dropped below 400 nm, commercially available microscope objectives have become inadequate focusing components in several testing setups used to qualify today’s sophisticated reduction lenses. These testing applications require formation of a diffraction-limited aerial spot at numerical apertures up to 0.5. In addition, this performance must be achieved at several narrowband UV wavelengths. Fortunately, the microobjective must operate only over a single spectral line for a given application. This suggests that spherochromatic correction is required but not parfocality. Also, only minimal field coverage is necessary to align the microobjective for single-point aerial image formation.
The unusual world of unstable resonators
Authors: Siegman Anthony E.
Published: February 2023

The transverse eigenmodes of unstable optical resonators have since their first discovery displayed unusual, even bizarre, eigenvalue and eigenmode properties, into which we are gaining new insights even today, two decades later. Many of these properties arise because the unstable resonator eigenmodes are highly nonpower orthogonal or biorthogonal. As one consequence it becomes possible to inject more energy into an unstable resonator mode that one has in the injecting signal. Unstable resonator modes also experience an excess spontaneous emission or quantum noise at a rate significantly greater than one noise photon per mode. A virtual-source analysis, based on adding up all the edge waves generated inside an unstable system, can help in calculating and understanding the complex mode properties of the unstable resonator.
Photoreceptor sampling and aliasing in the human retina
Authors: Williams David R.
Published: February 2023

No summary of this tutorial or biographical information was available at press time.
Neural magnifications and visual performance
Authors: Schein Stanley J.
Published: February 2023

Limits on visual performance may be established at different neural stages, from photoreceptors (Williams) through ganglion cells (Rodieck) to visual cortex. To help identify the limiting types of neuron, one may compare changes with the eccentricity of their spatial density and receptive-field dimensions with change in performance. Cones form a monolayer, thus measurement of their spatial density should be straightforward. The measurement of ganglion cell spatial density in cells/deg2 is more difficult, since central ganglion cells are displaced laterally from their cone inputs.
Absorption and scattering by heterogeneous particles
Authors: Kerker Milton , Bhandari Ramesh
Published: February 2023

Many particles of great interest contain particulate inclusions, which leads to the question of how to estimate the absorption and scattering by such complex bodies. We are developing a new model which utilizes a Monte Carlo algorithm for calculating the absorption and scattering of electromagnetic radiation by a particle containing inclusions which in turn absorb and scatter light.
Two-photon spectroscopy of Rb Rydberg states
Authors: Ito Nobuhiko
Published: February 2023

Doppler-free two-photon transitions to Rydberg states in alkali metals have been recommended as a potential source of reference lines or secondary standards for wavelength calibration, because they cover a wide range of the visible spectrum.1 Observation of spectral lines for the two-photon transitions was made possible by use of a thermionic diode detector cell similar to that originally designed by Harvey.2 The Pyrex cell enclosing the diode detector and containing natural Rb was placed in a two-chamber oven so that the temperature of the cell body and that of the sidearm Rb supply could be controlled independently.
Electric quadrupole admixture in mixed forbidden lines of Sb I
Authors: Hults Malcolm , Czerwinska J. , Heldt J.
Published: February 2023

There are two forbidden spectral lines of neutral antimony (Sb I) in the visible range which are mixtures of magnetic dipole (MD) and electric quadrupole (EQ) radiation. Their Zeeman effect was studied previously to determine the relative intensities of these two types of radiation by using separated isotopes (121 and 123) and observing in both parallel and perpendicular directions to the magnetic field.1 Observation of interference between MD and EQ allows the determination of relative percentages of the two types of radiation in the line. A new computer simulation technique, recently developed and proved very useful in similar studies on Bi I and Bi II,2 was applied to a comparison of the old microphotometer traces for Sb I with the new predicted patterns. Much more reliable results are now obtained which do not differ much from the previously reported data.
Radiative and nonradiative transition of Pr3+ and Eu3+ in LaP5O14, LiNbO3, and SBN
Authors: Chen Ting , Chang Gui-Lan , Yao Lie-Ming , Chen Wen-Ju
Published: February 2023

The absorption and fluorescence spectra as well as lifetimes of Pr3+ and Eu3+ in LaP5O14, LiNbO3, and SBN(Sr0.61Ba0.39Nb2O6) for the transitions between the 4f
n
states are presented. Comparisons of the calculated lifetimes based on Judd-Ofelt theory and absorption data with the experimental results have been made. For Eu3+, there is good agreement between the theoretical and experimental values. The spectral linewidths of Eu3+ in SBN are much broader than those in EuP5O14. For the 5D0—7F2 transition, the strong dependence of the fluorescence peak frequency on the excited wavelength and the strong dependence of the fluorescence intensity on temperature reflect the partly disordered nature of the structure of SBN. For Pr3+ in PrP5O14, the discrepancy between the theoretical and experimental results arises from the strong cross-relaxation among the Pr3+ ions. In low-doping LiNbO3 and SBN the fluorescence spectral linewidths and intensities of Pr3+ are much larger than those in PrP5O14, and the lifetimes of Pr3+ in the former hosts are at least 3 orders of magnitude longer than those in the latter host.
Cross sections and line shapes for transitions to autoionizing levels of atomic oxygen accessed from the 3P(3PJ) two-photon excited state
Authors: Buck Jesse D. , Bischel William K.
Published: February 2023

We are engaged in experiments to probe highly excited autoionizing levels of atomic oxygen using a double-resonance laser ionization scheme. Oxygen atoms are prepared by subjecting O2 to a microwave discharge at a pressure of ~0.2 Torr. A pump laser provides 225.7-nm photons to populate the 3p levels by two-photon absorption, also ionizing a small fraction of the excited atoms by absorption of a third photon. A second probe laser delayed by ~10 ns is scanned over energies of interest, and the ion current enhancement is recorded. We have observed ion signals from the 3d′(3S°, 3P°, 3D°) autoionizing states at ~124,000 cm−1. Absolute ionization cross sections are obtained by reference to the known value of 5.3 × 10−19 cm2 for 225.7-nm photons. A variety of autoionizing line shapes are observed, and further work is in progress to identify the nature of this behavior. We are also measuring cross sections for nonresonant ionization as the probe laser is tuned through the ionization continuum. The continuum data are useful for guiding the development of accurate theoretical descriptions of the final state in the ionization process.
Subharmonic instabilities in resonant interactions with bichromatic fields
Authors: Koch Karl , Oliver Brian J. , Stroud C. R. , Hillman Lloyd W.
Published: February 2023

The response of a two-level atom interacting with a 100% amplitude modulated field is known.1 In this work we investigate the stability of this stationary state solution to the growth of probe fields. Specifically we consider the gain of a 100% AM probe field, both in phase and in quadrature to the strong field, at the one-third subharmonic of the strong AM field. This case is of particular interest because the beat frequencies generated by all the field components with the nearest other field component are degenerate. We use Floquet's theorem in solving for the stationary-state response of the atoms. The solution is obtained using matrix-continued fractions. The effects of strong AM field intensity and of relative damping times on the gain and dispersion of the probe fields are presented.
Resonance fluorescence with modulated excitation
Authors: Chakmakjian Stephen H. , Koch Karl , Stroud C. R. , Hillman Lloyd W.
Published: February 2023

We report our results on measurement of the total fluorescent power radiated by two-level atoms excited by a 100% amplitude modulated or bichromatic laser field. For the case of single-frequency excitation, it is well known that the total fluorescent power monotonically saturates as the intensity of the field is increased. This occurs because the inversion of the atoms approaches zero at high field strengths. In contrast, when the field is bichromatic the total fluorescent power displays resonant peaks as the strength of the driving field is increased. This occurs because there is enhanced absorption when the modulation frequency coincides with the Rabi freqeuncy or one of its subharmonics.
Four-detector photopolarimeter: general analysis and optimization
Authors: Azzam R. M. A. , Elminyawi I. M. , Elsaba A. M.
Published: February 2023

This polarization sensor1 is analyzed for a general arrangement of four detectors with an arbitrary spatial configuration and any reflection characteristics (r
i
, ψ
i
, Δ
i
) of the individual detector surfaces. The instrument matrix A, which relates the output signal vector I to the input Stokes vector S by I = A • S, and its determinant are derived explicitly. The essential condition that A be nonsingular (det A ≠ 0) is satisfied in general with uncoated planar absorbing detector surfaces assuming that the plane of incidence (POI) is rotated between the first and second and second and third reflections. Consequently, no single-layer or multilayer coatings are required, especially when the extinction coefficient of the detector material is ≫0. Interestingly, the differential reflection phase shift Δ is unrestricted for the first and third detectors and has an optimum value of 90° for the second. The optimum rotation angles of the POI are 45° (or 135°). The optimum values of the surface parameter ψ are 27.37°, 22.5° (or 67.5°), and 0 (or 90°) for the first, second, and third reflections, respectively. (The last value indicates that the third detector may act as a linear polarizer.) The following are also considered: (1) partition of energy among detectors; (2) specific light-beam paths; (3) efficient calibration schemes; (4) effect of tilting the last detector; and (5) fundamental differences between this and other polarimeters.
Four-detector photopolarimeter: first experimental results
Authors: Azzam R. M. A. , Grosz F. B. , Elminyawi I. M. , Masetti E.
Published: February 2023

A polarization-state detector (PSD) is constructed of four windowless Si photodetectors that are arranged so that the incident beam is relayed from one detector to the next by three specular reflections at oblique incidence (>50°) and forms a nonplanar path with adequate rotations (~60°) of the plane of incidence between successive reflections. The attenuated beam of a small circularly polarized He-Ne laser is passed through a rotatable polarizer and quarterwave retarder to produce every possible state of total polarization needed for calibration and testing.
Pressure sensor using optical fibers
Authors: Iwamoto Katsuharu , Kamata Isao , Kawakami Osamu , Miyagawa Hideo
Published: February 2023

Strain gauge pressure transducers have been widely used for measuring pressure. Electrical cables are subject to the influences of electromagnetic induction that accompany large currents and high voltages associated with power apparatus and power machines within a plant. Accordingly, the output from the pressure transducer is subject to errors.
Improvement of a noninvasive optical probe
Authors: Xu Zhizhi
Published: February 2023

In recent years, a noninvasive optical probe was developed for some integrated circuits.1,2 it has been improved by using a multilongitudinal-mode 1,3-μm laser diode and a Wollaston prism for probing a Si integrated circuit.3
Methods of optical spectral analysis
Authors: Guarino Lori A.
Published: February 2023

Optical spectrum analyzers are convenient instruments for testing parameters such as the emission spectrum of laser diodes or light emitting diodes, the deterioration of the laser diode spectral width due to phenomena such as chirping, and the presence of side modes when measuring single-longitudinal- mode laser diodes. A comparison of optical spectral analysis methods including interference spectrophotometric methods and dispersion spectrophotometric methods is given. Emphasis is placed on diffraction grating and Fabry-Perot inteferometer techniques. The importance of parameters such as dynamic range, resolution, and elimination of effects of polarization is discussed. Examples are given of the use of spectrum analyzers to measure the effects of changes in temperature and current as well as the effects of phenomena such as mode hopping and chirping.
Nonuniform Bragg holograms with complex refractive index
Authors: Jannson Tomasz , Jannson Joanna
Published: February 2023

It has been known for years that the bandwidth of typical Bragg-Lippmann holograms, based on dichromated gelatin (DCG) and PVA-based polymers, is much broader1 than could be expected based on the fully uniform Kogelnik theory. Indeed the typical holographic processing is highly nonuniform, particularly in the z direction; thus both fundamental parameters of Kogelnik’s theory; the coupling constant and off-Bragg parameter, become functions of the z coordinate.1 This fact constitutes the basis for the more general theory based on the well-known (from quantum mechanics) WKB approximation.1 On the other hand, it became evident that the analysis of UV and XUV holograms2 requires the introduction of both a complex bias refractive-index and refractive-index modulation. Unfortunately, the elegant analytic model based on the WKB method does not hold for highly nonuniform Kogelnik parameters. Such a situation, however, is quite typical in DCG holography where an experimental hologram bandwidth can easily exceed 100 nm, while the theoretical bandwidth, based on Kogelnik’s theory, can still be below 20 nm. Therefore, the generalization in both directions, high-grating constant vertical nonuniformity and complex refractive index, is necessary.
Low-noise intereference gratings
Authors: Chen H. , Hershey R. , Leith Emmett N.
Published: February 2023

Experiments are described for producing low-noise diffraction gratings by the interference of multiple light beams from an extended source. Noise levels of the interfering beams are measured in varying conditions of coherence and compared with the noise levels of coherent beams. We note that, although for any given beam-generating system, incoherent light produces lower spatial noise than does coherent light, it is also true that a system for producing incoherent illumination fringes necessarily has more elements than does a system for producing fringes with coherent illumination and thus has more noise generating sources. The incoherent light system must thus overcome the handicap of being the inherently noisier system. A certain level of incoherence is thus needed simply to bring the incoherent system noise down to the level of the simpler coherent system. An additional degree of incoherence tilts the balance in favor of the incoherent system.
Temperature-dependent photorefractive two-beam coupling in GaAs
Authors: Chiou Arthur E. , Chang Tallis Y.
Published: February 2023

Photorefractive two-beam coupling in semi-insulating GaAs (nominally undoped) is investigated as a function of temperature ranging from 77 to ~330 K. The experiment consists of two beams (pump and probe) from a cw Nd:YAG laser at 1.06 μm intersecting in a GaAs crystal and monitoring gain in the probe and loss in the pump. The intensity of each beam was ~1 W/cm2. Our results show that the coupling efficiency increases with increase in temperature and decreases with decrease in temperature. In fact, near liquid nitrogen temperature, the direction of energy coupling switches; to our knowledge, this phenomenon has not been experimentally observed. This implies that there is electron–hole competition1 in our sample. At ~330 K, the coupling efficiency increases to about twice the room-temperature efficiency; the magnitude of the change cannot be explained adequately with a single-level model. Our results extend the recent report2 where dark conduction plays a major role in a single-level single-carrier model. We also study the temperature effects on optical absorption, dark conductivity, and grating formation and erasure times. Optical absorption decreases at both lower and higher temperatures.
Quasispace invariance for coherent imaging of diffuse objects
Authors: Hereford James M. , Rhodes William T.
Published: February 2023

Vignetting by lens apertures can cause imaging systems that are space-invariant for incoherent imaging to be strongly space-variant for coherent imaging. We show that systems of this type exhibit a form of shift-invariance for coherent objects that are diffuse. The shift-invariance applies specifically to the expected value of the optical intensity of the image distribution. Conditions for shift-invariance are briefly reviewed, the quasispace-invariance principle is explained, and experimental results are presented.
High focal dark field for phase imagery
Authors: Ojeda-Castaneda J. , Mosso A.
Published: February 2023

In phase imagery it is convenient to block out the uniform background in which a phase structure is immersed. This technique is called dark ground imagery, and it is usually implemented in an approximate fashion by placing in the exit pupil plane either a central obscuration or a phase disk with delay of 180°.
Sampling by the human retina predicts grating resolution within 2.0°
Authors: Hirsch Joy , Curcio Christine A.
Published: February 2023

Cone center-to-center spacings were determined on a strip of human retina extending from the foveal center along the temporal horizontal meridian to ~2.0° of retinal eccentricity. The retina was obtained from a 35-year-old male (H4 of Curcio et al,1) and has a cone density close to the average reported for young adults.1 A retinal whole mount2 was viewed with Normarski differential interference microscopy at a level just vitreal to the ellipsoid-myoid junction. Positions of the cone centers were digitized from photomicrographs, and the distributions of nearest-neighbor distances3,4 were obtained for adjacent 0.165°2 windows. We find an increase in receptor spacing over this 2.0° region that is similar to that previously reported for monkey3 and human.5
Infrared frequency standards and their measurement
Authors: Clairon A.
Published: February 2023

Many laboratories have developed IR frequency measurement techniques, particularly for the determination of the 88-THz He–Ne/CH4 laser frequency. Disagreements of the order of 10−10 remain between various values, which can be explained by the gas laser effect, the residual Doppler effect, and the hyperfine structure of the F2(2) methane line. Other laboratories, particularly in the U.S.S.R., have developed better lasers allowing the resolution of the F2(2) line or operation with the E line of methane. At the LPTF we have developed stabilized CO2 lasers by saturated absorption with OsO4 in an external Fabry-Perot cavity; they have a reproducibility of 2–3 × 10−13 and an accuracy of 2 × 10−12; furthermore, they can be measured with an uncertainty limited by their accuracy. These CO2/OsO4 frequency standards are particularly useful for near-IR and visible frequency measurements.
Precision interferometry with stabilized lasers
Authors: Devoe R. G. , Fabre C. , Jungmann K. , Hoffnagle J. , Brewer R. G.
Published: February 2023

Interferometers are essential tools for measuring optical wavelengths and frequencies. We demonstrate a new form of interferometry that is both simpler and more precise than conventional methods. Stable laser and electrooptic FM sideband techniques make a direct electronic measurement of the mode spacing of an ultrahigh finesse cavity with subhertz precision (0.4-Hz rms) over a 50-THz region. A new interferometer equation is derived in which all variables can be measured directly in situ. Experiments indicate errors below 10−10 over a 50-THz bandwidth and that the technique can be improved to the 10−12 level or beyond. No drift due to mirror aging has been observed over 420 days for a rate of <2 × 10−12/day. Our results indicate that low-loss multilayer dielectric mirrors are far more suitable for precision interferometry than previously thought, and we show how wavelength comparisons for 10−9 accuracy can be made with simple and inexpensive apparatus.
High-resolution optical multiplex spectroscopy
Authors: Winters M. P. , Hall John L. , Dinse K. P.
Published: February 2023

We have developed a frequency-multiplex laser spectrometer using the concept of stochastic excitation to provide an effective optical excitation bandwidth of >200 MHz and an inherent spectral resolution of a few kilohertz. A frequency-stabilized Ar+ laser is phase-modulated by a pseudorandom binary sequence (PRBS) running at a clock frequency of 200 MHz. The detected system response to the stochastic optical field is cross-correlated with an identical time-delayed PRBS to give the equivalent of a free induction decay signal. A time-to-frequency transformation then gives the transfer function of the optically absorbing/dispersing system. The calibration and linearity of the frequency axis are dependent only on the oscillator used to clock the PRBS generators, thus avoiding the problems of drift and nonlinearities in ordinary sequential-scan spectroscopy. The multiplexing scheme allows a spectrum to be obtained in much less time than sequential scanning or, equivalently, gives a higher SNR for the same amount of data taking time. We have demonstrated the spectrometer by observing Doppler-free transitions in molecular iodine. We also describe the use of digitally filtered binary sequences and active control of residual amplitude modulation to improve the SNR of the spectrometer and possibilities for increasing the excitation bandwidth of the system.
Derivation of an augmented Blrge-Mecke rule for molecular constants
Authors: Nicholls R. W.
Published: February 2023

An augmented version of the empirical Birge-Mecke rule

ω
e

/

B
e

∼

ω
e

r
e
2

=
const

, relating rotational and vibrational frequencies of molecular electronic states, derived by a semiclassical analysis of the motion of a Morse oscillator in the v = 0 level, is

μ
A

ω
θ

x
θ

r
e
2

=

h
/
2

π
2

c

E

rot

/

E

vib

2

∼
135

. Erot is the rotational energy excited by the time-averaged anharmonic oscillation, and Evib is the zero-point energy ω
e
/2. Comparison with the molecular data for 184 Morselike electronic states in Huber and Herzberg’s compilation1 shows that the above equation holds well and that Erot/Evib = 1.141475 ± 0.030898. (12 min)
Optimum end reflectivity in external semiconductor lasers
Authors: Wu Qun , Zhang Hanyi , Wang Jianglin , Zhou Bingkun
Published: February 2023

The external cavity semiconductor laser is one of the suitable sources for coherent optical communication systems. Coldren and Koch1 have given design relationships for the external cavity semiconductor laser whose facet is uncoated. However, the performance of external cavity semiconductor lasers is influenced by the reflectivity of the laser facet. The threshold and side-mode suppression ratios are calculated and represented as 3-D figures vs end reflectivities (including laser facet and external cavity mirror). The calculated optimum ranges of end reflectivities were found to agree with the experiments.
Long-term stability of a portable integrated 1.3-µm external-cavity semiconductor laser with a narrow linewidth
Authors: Huo Yujing , Xu Zhizgi , Zhou Bingkun
Published: February 2023

Using a glue technique, we have developed a portable integrated external-cavity single-mode semiconductor laser with a narrow linewidth.1 One significant advantage is that a single longitudinal mode of the laser can be obtained without mechanical adjustment.
Semiconductor-diode array pumped solid-state laser systems: a prospectus
Authors: Krupke William F.
Published: February 2023

We review immediate and projected uses of solid-state lasers made possible by efficient and powerful semiconductor-laser-diode arrays as pump sources.
Near-field distribution and output wavelength tuning of a coherent array of discrete diode lasers
Authors: Rediker R. H. , Liew S. K. , Corcoran C.
Published: February 2023

High-spectral-purity pulse and cw coherent output have been obtained from a linear array of five discrete external-cavity diode lasers by placing in the cavity a spatial filter at the Fourier plane of the lens system between the AR-coated diodes and the feedback mirror.1,2 Results are reported on the intensity and phase distribution of the near field of the ensemble. Two modes of operation are shown to exist: in one, the outputs from adjacent diodes are in phase; in the other they are 180° out of phase. These modes of operation are switched by moving the filter laterally by half of the spacing between the centers of its slits. Limited tuning of the output wavelength has been accomplished by tilting the filter and thereby, in effect, varying this center-to-center spacing. The experimental results are compared with those predicted by theory and clearly validate the model of ensemble operation used to explain previous results.
X-ray optics at the Marshall Space Flight Center
Authors: Wyman Charles L.
Published: February 2023

MSFC has been involved with solar and stellar x-ray programs from the earliest days of the space program. In fact, its predecessor organization, the Army Ballistic Missile Agency (ABMA), flew the first orbital x-ray detector on Explorer VII. Over the years MSFC has been involved in numerous payloads for measuring solar and stellar x rays, including two solar x-ray telescopes on the Apollo Telescope Mount, the HEAO-2 (Einstein) Observatory, Spacelab payloads, a variety of sounding rockets, and now the Advanced X-Ray Astrophysics Facility (AXAF) program. The history of involvement with x-ray astronomy payloads at the MSFC is outlined dating back to the work at ABMA on Explorer VII. Technological advances achieved over the years are discussed. The AXAF program is briefly described.
Significance and analysis of x-ray pupil diffraction
Authors: Glenn Paul
Published: February 2023

Pupil diffraction usually defines the achievable resolution in conventional optical systems. However, since diffraction-limited resolution is proportional to radiation wavelength (for a given aperture size), diffraction is usually ignored for x-ray systems with wavelengths in the angstrom regime. Nonetheless, high-resolution x-ray systems are arising which use very narrow annular apertures, relatively long x-ray wavelengths, or both. In a surprising number of these systems, pupil diffraction can have a non-negligible effect on resolution. There is excellent work in the literature describing the diffraction pattern from such apertures in terms of Airy rings and ring groups. It can be shown that this approach is equivalent in a wide range of conditions to considering an infinite 1-D slit with a width equal to the actual annular width. It can be shown that the energy enclosed in the focal plane dimension transverse to the slit is very close to the energy encircled in the true annular system focal plane. In short, the system designer can make an excellent first approximation of pupil diffraction effects in an x-ray system by applying standard single-slit diffraction formulas to the annular aperture width and x-ray wavelength.
Hybrid singlet arbitrarily dispersive element
Authors: Stone Thomas , George Nicholas
Published: February 2023

Hybrid elements containing optical power with both diffractive (holographic) and refractive components are shown to be useful for obtaining arbitrary, or in a special case, achromatic, dispersive characteristics. In one configuration a volume holographic element is coated on the surface of a crown glass lens, and by varying the power distributions among the refractive and holographic components while maintaining constant overall optical power the effective Abbe V numbers of the resultant hybrid element are shown to span all real numbers except a narrow interval around zero.
Optical coupling techniques to match laser sources to nonlinear crystals
Authors: Lin J. T. , McKinney R. E. , Savrda S. L. , Montgomery J.
Published: February 2023

New crystals of KTP and beta-barium-borate (BBO) have been recently identified as highly efficient crystals with nonlinear coefficients of 15 and 4.6 times the KDP, respectively. The BBO crystal has the advantages of very wide temperature acceptance width and high damage threshold.1 However, due to the rather large walk-off angle (~50 mrad) of this crystal, a good quality pump is usually required for high conversion efficiency. We present the first direct comparison of the SHG efficiency of a YAG laser (1064 nm) by using KTP, BBO, and CD* A with crystal lengths of 3, 7, and 25 mm, respectively. The phenomena occurring in loci of nonlinear phase-matching directions for these three crystals were observed and compared. We found that, particularly for BBO crystal, the SHG efficiency is a strongly decreasing function of the divergence of the pump field. Data have been collected for cases employing conventional spherical imaging and also asymmetric imaging using both cylinder lenses and anamorphic prisms. Improved efficiency was obtained by asymmetric focusing. Data were compared with a computer model.
Anomaly in electron shadow scattering off atoms
Authors: Sambasivan R.
Published: February 2023

Hans Bethe in 1966 theoretically predicted the shadowlike diffraction effects in the forward (θ ≈ D – 1°) elastic scattering cross sections of low-energy electrons off atoms such as He, Ne, and Ar and explained them as being due to the coupling of inelastic scattering channels. By scattering 10-25-eV electrons off Ne in the forward direction (θ up to 20 mrad), Geiger and Moran1 found the diffraction effects (superimposed on the Born approximation). This shadow diffraction occurs not at the atom edge (radius γ0) but at the sheath surrounding (radius R) the atom due to agglomeration of the inelastic scattered electrons.
Color center formation by two-photon absorption at 532 nm in cubic zirconia
Authors: Mansour Nastaran , Mansour Kamjou , Soileau M. J. , Van Stryland E. W.
Published: February 2023

We report the generation of color centers in yttria (Y2O3) stabilized cubic zirconia (ZrO2) by 532-nm radiation. Oxygen ion vacancies exist in yttria stabilized cubic zirconia1 and can trap electrons forming F
+
centers. We observed permanent changes in transmission after irradiating the sample at high irradiance with 532-nm pulses of 40-ps to 20-ns (FWHM) duration. In this case valence band electrons are generated by two-photon absorption and are trapped by the oxygen ion vacancies. The induced color centers are long-lived with a measured lifetime of ~2 h at room temperature. These defects and thus the absorption can be bleached by repetitively irradiating at low irradiance at the same wavelength.
1.06-μm nanosecond laser amplifications via degenerate multiwave mixing in Si
Authors: Khoo I. C. , Normandin R. , Michael R. R. , Liu T. H. , Finn G. M.
Published: February 2023

The process of degenerate four-wave and multiwave mixing in a nonlinear medium (with an intensity-dependent refractive index) is reexamined in the context of probe beam amplification and related phase conjugation. In general, such multiwave mixing processes (involving pump, probe, and various diffracted beams) require a self-consistent solution of several coupled Maxwell wave equations to explain and quantitatively fit the experimental observations with the theory.
Applications of liquid crystal TVs to monochromatic and polychromatic adaptive real-time pattern recognition
Authors: Yu Francis T. S. , Jutamulia S. , Lin T. W. , Yelamarty R. , Gregory Don A.
Published: February 2023

Recently, many uses of liquid crystal television (LCTV) in real-time signal processing have been reported. The joint transform architecture is an alternative approach to optical pattern recognition. The joint transform method has proved suitable for adaptive programmable correlation because no matched spatial filter is required. The reference pattern may simply be generated by a computer and input to a low space-bandwidth product, electronically addressed spatial light modulator. Conversely, it is very difficult to generate a dynamic Fourier plane VanderLugt-type complex-matched spatial filter. A new implementation of the real-time joint transform correlator architecture using inexpensive LCTVs is discussed. A color LCTV consisting of three primary color pixels is also investigated to perform real-time color pattern recognition based on joint transform architecture.
Detection of peripheral aliasing for gratings seen in the Newtonian view
Authors: Still D. L. , Thibos Larry N.
Published: February 2023

Previous experiments have shown that aliasing in peripheral vision can occur for gratings far beyond the classical resolution limit.1 That result was obtained by forming high-contrast gratings directly on the retina as interference fringes, thus providing an estimate of the upper limit to the aliasing spectrum of spatial frequencies. We now report a similar estimate for Newtonian view, that is, when the object is seen through the natural pupil and optical system of the eye. The visual stimulus was a circular (2.3° diameter) patch of horizontal sinusoidal grating surrounded by a uniform field of the same mean luminance (125 cd/m2) and placed 20° into the horizontal nasal field of the observer.
Motion reversal in peripheral retina
Authors: Coletta Nancy J. , Williams David R.
Published: February 2023

At high spatial frequencies, drifting interference fringes viewed in the fovea and parafovea can appear to move opposite to their true direction. We have previously shown that aliasing by the cone mosaic is responsible for this motion reversal. We measured forced-choice psychometric functions for direction discrimination as a function of the spatial frequency of drifting vertical interference fringes. For a regular sampling lattice, the perceived direction of motion should reverse at integer multiples of the lattice Nyquist frequency. Despite disorder in the cone mosaic, the data in the fovea and parafovea agree with this prediction. At each retinal location tested, motion reversals occur at two spatial frequencies which correspond to one and two times the cone Nyquist frequency. However, in the periphery, from 10 to 25° eccentricity, the first motion reversal occurs at a lower frequency than would be predicted from cone sampling. The reason for this discrepancy is unclear, but it probably involves postreceptoral mechanisms. Nonetheless, the Nyquist frequency obtained at the second motion reversal agrees with peripheral anatomical cone spacing data.
Perceived motion reversal in parafoveal aliasing
Authors: Smith Robert A. , Cass Peter F.
Published: February 2023

At last year’s meeting, we reported a dissociation between detection and orientation discrimination for gratings viewed eccentrically. Specifically, at 7° in the superior visual field, orientation discrimination is limited to ~8 cycles/deg, while simple detection persists to about twice that frequency. We proposed that the discrimination limit represents degradation of the image by aliasing. Coletta and Williams1 have described a distinctive property of visual aliasing: moving images whose spatial frequency is above the Nyquist limit produce an alias which appears to move in the opposite direction. We asked subjects to discriminate the direction of motion of gratings at frequencies near the discrimination limit. It is very difficult to see motion in these stimuli, but for a small range of frequencies around the discrimination limit there is a clear statistical tendency to perceive motion in the reversed direction. In the absence of any obvious alternative, we regard this as strongly supporting the hypothesis that aliasing occurs in normal parafoveal vision.
Modeling shifts in perceived spatial frequency between the fovea and periphery
Authors: Davis Elizabeth Thorpe
Published: February 2023

Reported frequency shifts between the fovea and periphery1 are quantitatively modeled here using data for spatially localized stimuli; test stimuli were presented in either the superior or inferior visual fields. The model assumes a set of frequency channels in which a nonlinear contrast transfer function (CTF) follows the output of each channel and the labeled channel outputs are combined in a weighted average. Frequency tuning, overall sensitivity, and nonlinearity of CTFs for a set of channels are assumed to change as a function of visual field eccentricity. Parameter values for these factors were based on published reports2 or on measurements obtained for observers tested previously in the frequency shift paradigm. Theoretical predictions using the latter parameter estimates produce closer fits to the data. Furthermore, although frequency shifts were slightly larger for test stimuli presented in the superior than inferior visual field, these differences are not significant. Parameter estimates for superior vs inferior visual fields of these observers also do not differ significantly. However, an important question remains: Why don’t observers perform like ideal observers and perhaps alter the perceptual frequency labels of peripheral mechanisms to eliminate frequency shifts between fovea and periphery?
Pattern adaptation in detection and discrimination
Authors: Burbeck Christina A.
Published: February 2023

Previous findings indicate that detection and discrimination of sine wave gratings do not occur at a common site. The effects of pattern adaptation are fundamentally different for detection and discrimination,1 and frequency discrimination is based on the object spatial frequencies, whereas contrast detection thresholds are based on the retinal spatial frequencies.2 These findings raise the question: are the effects of pattern adaptation on frequency discrimination3 tied to the object spatial frequencies or to the retinal spatial frequencies? We were unable to replicate Regan and Beverley's results. However, we were able to replicate the well-known perceived spatial frequency shift, which also entails spatial frequency comparisons, and found that it depends on the retinal (not object) spatial frequencies of the test and adapt gratings. Finally, we show that the perceived spatial frequency shift predicts that frequency discrimination thresholds should be altered by pattern adaptation but that the primary predicted effect should be enhancement of frequency discrimination sensitivity at the adapting frequency and not dimunition of frequency discrimination sensitivity away from the adapting frequency as Regan and Beverley reported.