bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient operation of an array pumped Er3+-doped silica fiber laser
Authors: Wyatt R. , Armitage J. R. , Ainslie B. J. , Craig S. P.
Published: February 2023

Recently, diode laser-pumped operation of the 1.5-µm
transition in Er3+-doped silica fibers has been
reported.1,2 The limited pump power available from the
single stripe sources used in those experiments restricted the maximum
output powers to below 200 µW and slope efficiencies
to a few percent. Using a diode array pump source, we achieved output
powers in excess of 5 mW at 15 % slope efficiency. A Spectra Diode
Laboratories SDL 2432 ten-element diode array was placed in an
external cavity to improve spatial coherence of the array output and
allow efficient coupling into the fibers used here. Typical launched
powers were 50-70 mW at 806 nm for an array drive current of 500 mA.
At these pump levels, a small-signal absorption of ~15 dB at the pump
wavelength, and ~50% output coupling, is found experimentally to yield
maximum efficiencies at a lasing wavelength near 1.56
μm. This is consistent with a numerical model of a
longitudinally pumped three-level laser, which includes excited state
absorption.
Measurement of solar magnetic fields
Authors: Hagyard M. J.
Published: February 2023

We review the use of polarimetric techniques in measurements of the magnetic field in the sun’s atmosphere. The basic principles of the inverse Zeeman effect and the radiative transfer of polarized light are presented to demonstrate how the vector magnetic field on the sun can be determined in magnitude and direction from measurements of the Stokes parameters describing the state of the emergent polarized light. A brief overview is given on the different instrumental techniques used to measure this polarized light, and a comprehensive description is given of the Marshall Space Flight Center’s vector magnetograph. The major problems associated with the polarimetric technique used in this instrument are described; these include instrumental polarization, the higher sensitivity to circular polarization (which is intrinsic to the inverse Zeeman effect), crosstalk of the circular polarization into the linear component, and Faraday rotation.
Object support reconstruction and phase retrieval
Authors: Fienup J. R. , Thelen B. J. , Crimmins T. R.
Published: February 2023

The reconstruction of an object from the modulus of its Fourier transform—the phase retrieval problem—occurs in several important uses such as astronomy and wavefront sensing. Reconstruction is possible only if sufficiently powerful object-domain constraints are available. Non-negativity and support constraints (knowledge that the object is zero outside some region of support) are the two most commonly encountered constraints. We have devised new methods for determining object support constraints from the support of the autocorrelation (which can be computed from the Fourier modulus).
Recognition of 3-D objects from multiple views
Authors: Wu Ron , Stark Henry
Published: February 2023

In earlier work1,2 we enabled rotation and scaleinvariant pattern recognition of images by using circular harmonic functions for rotation-invariance and Mellin transforms for scale invariance. More recently,3 we applied these results to the recognition of 3-D objects from a series of 2-D images. We review this method.
Parametric transformation
Authors: Ritcey James A. , Atlas L. E. , Marks R. J. , Park D. C. , Oh S.
Published: February 2023

The parametric transformation is investigated to achieve invariance in optical pattern recognition. Two or more appropriately chosen feature vectors are parametrically combined to form a training vector. If chosen correctly, the training vector can be invariant under operations such as shift, scale, and transposition. As a simple and pedagogical shift-invariant example, consider a signal X(t) and its low- and high-pass-filtered versions, XLP(t) and xHP(t). Visualize a template formed by a parametric plot of these two functions on the (XLP, xhp) plane. Consider a shifted signal,

X
^

(
t
)

=
X

(

t
−

t
0

)

. We analogously form

X
^

LP

(
t
)

and

X
^

HP

(
t
)

on the (xLP, xHP) plane resulting in the same trajectory as that of the template. This concept can be extended to two dimensions to achieve rotation, shift, and scale invariance. To reduce the occurrence of false classification, the dimension of the parametric transformation can be increased. Indeed, for many cases of Importance, the parametric transformation becomes invertible to a member of the categorization class in the limit as the number of dimensions grows. When invertible, there are no false alarms due to the algorithm structure.
Fundamental characterization of phase conjugation by stimulated Brillouin scattering
Authors: LeFebvre Michael J. , Pfeifer Shirley J. , Johnson Roosevelt , Dickinson Paul H.
Published: February 2023

In an effort to generate a flat phase front from the output of a laser system, great interest in the uses of phase conjugation has arisen. A simple technique of implementing phase conjugation is through use of a stimulated Brillouin scattering cell filled with either a liquid or a gas. Here we cover fundamental characterization of phase conjugation by stimulated Brillouin scattering. The experimental objectives are to characterize the launched and SBS return diagnostics to quantify the physics of the SBS process. A spatially filtered Nd:YAG laser was used so that accurate low-energy UV experiments which address key phase conjugation issues could be performed. The laser parameters which were varied include the bandwidth and energy. The system parameters which were varied include f/No., aberration strength, and spatial frequency.
Conical emissions and phase conjugation in atomic sodium
Authors: Pender John , Hesselink Lambertus
Published: February 2023

Conical emissions in atomic sodium in which the cone wavelength is the same as the pump wavelength have been reported. These emissions appear about a single pump when the laser is tuned to the blue side of the D2 line but do not appear for red detunings. If two counterpropagating pumps are used, conical emissions appear for both blue and red detunings.
Double phase conjugation in strontium barium niobate
Authors: Salamo G. J. , Miller M. J. , Clark W. W. , Wood G. L. , Sharp E. J. , Neurgaonkar R. R.
Published: February 2023

Recently, three new double phase-conjugate mirrors1 using barium titanate have been reported. These mirrors involve two mutually incoherent laser beams which are independently directed into a passive photorefractive crystal. There they interact and cause the phase conjugate of each beam to form. We report on another configuration which is particularly suited for strontium barium niobate. This new configuration utilizes two extraordinary polarized laser beams entering the crystal from opposing faces along a common plane of incidence containing the c axis. The two opposing faces are parallel to the c axis. For certain incident angles, the laser beams which cross in the crystal bridge together forming a single beam which runs nearly perpendicular to the c axis. Shortly afterward, the phase-conjugate beams appear. This effect occurs for incident beam angles of +10 to +65° (where a beam at +90° points in the positive c-axis direction).
Four-wave mixing measurements in cerium-doped SBN:60
Authors: Lawson Chris M.
Published: February 2023

There has recently been interest in the use of SBN crystals for a variety of optical computing applications which utilize phase-conjugate signals arising from four-wave mixing (FWM). The large photorefractive effect exhibited by these crystals allows them to be used for nonlinear optical processing and volume holography with readily accessible optical powers. To assist In development of SBN-based commercial and military devices for these optical processing uses, we mapped out a number of the characteristics of phase-conjugation processes in cerium-doped SBN:60.
Lightweight silicon carbide optical components
Authors: Arnold Joe F.
Published: February 2023

The requirements for extremely lightweight low- distortion/high-stiffness optical components continue to grow across a wide spectrum of use from very small scanner mirrors to very large space- based telescope mirrors. The traditional materials for these applications, low-expansion glasses and beryllium, have limitations in both properties and fabricability, and both are very expensive and time-consuming to fabricate into lightweight configurations. Silicon carbide has a modulus equal to or greater than beryllium, a density equivalent to aluminum, a low coefficient of thermal expansion, and a high thermal conductivity, making it an excellent material, propertywise, for many uses. It is also relatively inexpensive, abundant, and nontoxic. Until recently silicon carbide was limited in application to the desired devices by its extremely difficult fabricability. It simply could not be formed into lightweight structures. A new process developed by United Technologies Optical Systems (UTOS) now not only allows the fabrication of lightweight structures but also allows them to be structurally highly efficient. Using their precision forming process, UTOS can now fabricate honeycomb sandwich structures that are both lighter and stiffer than even beryllium structures due to limitations in achievable configurations of the beryllium fabrication processes. Many low- weight high-performance applications may benefit from this technology.
Learning image structure from centroid scale-space maps
Authors: Freeman Mark O. , Saleh Bahaa E.A.
Published: February 2023

Every object has a unique centroid. However, a given entity might be considered an object by itself or part of a larger object depending entirely on the scale at which it is viewed. We demonstrate that by tracking centroids of an image through a complete range of scales, a representation results that reveals some of the underlying structure of the image. We call this representation a centroid scale-space map. We show that this has a particularly simple form compared with other scale-space representations. The centroid scale-space map is formed by cross-correlating an input image f(x, y) with the windowed centroid kernel

(
x
+
i
y
)
⋅
circ

(

x
2

+

y
2

/
r

)

. The zero-crossings of the cross-correlation outputs correspond to centroid locations. These zero-crossings are mapped against both the scale coordinate rand the space coordinates (x, y) to form a centroid scale-space map. A real-time optical correlator based on degenerate-four-wave mixing is suggested to perform the correlations.
Computer generated scenes and simulated Imaging
Authors: Reichenbach Stephen E. , Park Stephen K.
Published: February 2023

Image processing and computer vision research is frequently difficult to evaluate because it is based on an experimental approach that is inadequately defined or insufficiently detailed. This paper suggests a model-based research paradigm for digital image processing and computer vision. Specifically, we present techniques for generating artificial scenes and simulating imaging systems that form a versatile and precise research test-bed. This approach is flexible, allowing for a variety of scenes and systems; accurate, providing exact control over all variables; and portable, facilitating replication on various computer systems. Two types of computer generated scenes accurately model the important characteristics of real scenes. Fourier scenes are 2-D Fourier series. Techniques for generating ensembles of Fourier scenes allow precise control over important statistical characteristics. Digital scenes are digital images with superresolution—high resolution relative to the sampling rate. Techniques for generating digital scenes provide precise control over spatial structure. The imaging-system simulation software provides a flexible end-to-end imaging environment that can be varied and controlled much more easily than physical systems. The software simulates the important components of the imaging process from the device point spread function, sampling, and noise in image formation to the image reconstruction of the display device.
Noise tolerance of power cepstra and phase correlation In Image registration
Authors: Lee Dah Jye , Mitra Sunanda , Krile Thomas F.
Published: February 2023

Precise registration and subsequent matching of sequential images is a difficult task in many applications. Power cepstra of feature-based segmented images can be used for correcting the translational shift. The phase information in phase correlation technique is critical to the computation of the peak and is easily affected by the added noise. Since only the magnitude is involved in the computation of power cepstrum, the constraints that arise from the limitation of the phase components are absent in power cepstrum technique. The effects of the illumination change and the added noise are less than that on the phase correlation. Hence the power cepstrum registration method can have higher tolerance to noise. For typical feature-based images, the power cepstrum technique can detect and correct a spectral shift even when the SNR is as low as 0.17. The phase correlation technique for registration cannot be expected to have such high noise tolerance.
Space-domain inversion of the finite-length line spread function
Authors: Hansen Eric W. , Dallas William J. , Barrett Harrison H.
Published: February 2023

One practical method for obtaining the point spread function (PSF) of an imaging system is to measure the response of the system to a line source of illumination extending across the entire image field. If the system is rotationally symmetric, the well-known Abel inversion then enables the computation of the PSF from the line spread function. Some systems, notable x-ray image intensifiers, are space-variant, and the line source must be restricted to an isoplanatic patch. Correspondingly, the formula for computing the PSF from this finite-length line spread function (FLSF) is different from the Abel inversion. Such a formula has previously been derived by transform methods. A simple space-domain approach yields an inverse FLSF transform kernel in the form of a finite series of corrections to the Abel inversion. For a sufficiently long line source, the kernel reduces to just the Abel inversion, and as the source becomes vanishingly small (so that the FLSF is identical to the PSF), the kernel approaches an identity operation, as expected.
Parallel processor for optimization and estimation problems: algorithms
Authors: Seacat R. H. , Barrett Harrison H. , Shoemaker R. L. , Roney T. J. , Smith W. J.
Published: February 2023

The simulated annealing algorithm is a generalized optimization algorithm suitable for the reconstruction of images from data obtained through coded aperture projections. The best estimate of an unknown object is the estimate that minimizes an energy function derived from the known and inferred properties of the original object and the process.
Mechanisms and dispersion of crystalline optical activity
Authors: Nelson Donald F.
Published: February 2023

A long-wavelength lattice dynamic calculation applicable to crystals of any structural complexity and of any symmetry (that allows optical activity) reveals three mechanisms causing optical activity in crystals: first-order wave vector dispersion of the bonding forces; electric dipole-magnetic dipole interference; and electric dipole-electric quadrupole interference. Only the first mechanism has been found from lattice dynamics theories previously, while quantum mechanical derivations have produced only the second two. The first mechanism gives terms in the rotatory power proportional to

ω
2

/

(

ω
i
2

−

ω
2

)

(

ω
j
2

−

ω
2

)

, while the latter two give terms proportional to

ω
2

/

(

ω
i
2

−

ω
2

)

. Both types have been proved necessary to fit the frequency dispersion in particular crystals. Thus the present theory produces all the known mechanisms and needed dispersion from a single unified approach.
Polarization effects on Brillouin gain in single-mode fibers
Authors: Horiguchi Tsuneo , Tateda Mitsuhiro , Shibata Nori , Azuma Yuji
Published: February 2023

Stimulated Brillouin scattering is one of the most important nonlinear effects in single-mode fibers. Brillouin gain depends on the polarization states of pump and Stokes fields. Stolen1 has demonstrated that the Brillouin threshold optical power in fibers is higher by a factor of 2 with scrambled polarization states than with maintained linear polarization states. However, little attention has been paid to the Brillouin gain in single-mode fibers where the polarization state is not maintained and not completely scrambled. We investigated the polarization dependence of the Brillouin gain in an ordinary single-mode fiber. The Brillouin gain measured for a 5-km single-mode fiber showed a G [1 + Kcos(2θ + ϕ)] dependence, where G is the Brillouin gain with scrambled polarization states, θ is the incident polarization direction angle of the pump or Stokes (probe) fields relative to an arbitrarily fixed azimuth in the fiber cross section, and K and ϕ are constants. The value of K reached as high as 0.31. The Brillouin gain distribution along the single-mode fiber is also presented.
Two-channel polarization modulation ellipsometer
Authors: Jellison Gerald E.
Published: February 2023

A new polarization modulation ellipsometer has been designed and constructed where both polarizations of the exit beam are detected and analyzed. Light from a monochromator passes through a polarizer and photoelastic modulator (driven ~50 kHz), reflects off the sample, and then passes through a Wollaston prism, which acts as the analyzer. Both exit beams are individually detected with either photodiodes or phototubes and analyzed using digital voltmeters to determine the de component and two lock-in amplifiers to determine the fundamental and first harmonic. By setting the (polarizer-modulator) angle to ±45° and modulator and analyzer angles to ±22.5 or ±67.5°, all the associated ellipsometric parameters (N= cos2ψ; S = sin2 ψ sinΔ) can be measured allowing for determination of the ellipsometric angles ψ and Δ as well as β = N2 + S2 + C2, which is a measure of the surface depolarization.
Effect of varying the input polarization on an external cavity controlled ensemble of five diode lasers
Authors: Pang L. , Corcoran C. , Rediker R. H.
Published: February 2023

Results are presented for an external-cavity laser with five gain-elements controlled to operate as a coherent ensemble by a spatial filter. Experiments show that the laser operates either in a symmetric or antisymmetric mode. The effect of varying a single element’s polarization on the ensemble’s output polarization has been investigated and is explained.
Index-guided lateral modes observed from gain-guided twin-stripe laser diode arrays
Authors: Heflinger Donald G. , Chang Michael B. , Fenner Wayne R.
Published: February 2023

Gain-guided twin-stripe lasers have been observed to lase in index-guided modes. This index-guide is created by a dip in the carrier concentration between the stripes. The first lasing mode of a twin-stripe array, having 4-μm wide stripes with a 8-μm center-to-center spacing, is the zeroth-order index-guided mode. This mode has been identified by a single-lobed far field and a near-field profile tightly confined between the stripes. At higher currents, a double-lobed near-field intensity profile is observed to lase simultaneously at a 10-20-Å wavelength shorter than the wavelength of the fundamental. Although the far field is double-lobed, suggestive of an out-of-phase gain-guided array mode, careful measurements of the near field indicate that this double-lobed mode is the first-order index-guided lateral mode. The small lateral extent beyond the stripes in the near field and the lack of interference fringes between the stripes is inconsistent with a gain-guided super-mode.
High-power mode-locked Nd:fiber laser pumped by an Injection-locked diode array
Authors: Duling I. N. , Goldberg Lew , Weller Joseph F.
Published: February 2023

The need for sources compatible with today’s fiber-optic communication systems has led to the investigation of rare earth-doped monomode fibers as an active medium. Neodymium-doped silica fibers are readily pumped by common laser diodes, but with the limited power available in single-stripe devices, the power from the fiber laser has been limited to a few milliwatts. By using an injection-locked diode array it is possible to get a diffraction-limited high-power beam to use as a pump source for the fiber laser. Fiber laser output powers of up to 15-mW cw have been obtained using this method. If an acoustooptic modulator is inserted in the cavity, pulses as short as 120 ps are produced. It is expected that if an all-fiber modulator is used, the cavity losses will be reduced along with the pulse width. The laser can also be operated in a Q-switched mode by inserting an acoustooptic deflector into the cavity as well. The laser was allowed to prelase prior to Q-switching which maintained the pulse width, and the peak power in the output train was increased to 1 kW. This power should be sufficient to produce nonlinear effects in the fiber.
Raman solitons and self-phase modulation
Authors: Wolfson R. , Druhl K. J.
Published: February 2023

Homogeneous broadening leads to the decay of Raman solitons,1,2 if pump and Stokes are not exactly on Raman resonance. This is due to a dispersive frequency shift at the soliton center. Media with strong self-phase modulation (SPM) can balance this dispersive effect and even show an amplification of peak pump intensity. In this case, the net decrease in pump power is compensated by narrowing from SPM. We present analytical and numerical results, which demonstrate this effect for media with strong Stark shift.
Transient solitons in stimulated Raman scattering
Authors: Menyuk Curtis R.
Published: February 2023

The normalized equations describing transient stimulated Raman scattering are1,2where A1and A2represent the pump and Stokes waves, Xis the material excitation, ϵis its damping rate, and χ and τare normalized distance and time. One readily finds that K(τ)=|A1(χ, τ)|2+ |A2(χ, τ)|2is constant for all χ. If, in addition,

I
∞

=

∫

−
∞

∞

K

(
τ
)
d
τ

is finite, implying that K(τ) → 0 as |τ|→∞, it can be shown that X(χ, τ) →0 everywhere in τas χ → ∞. Solitonlike structures which move in τwith respect to the pulse cannot persist. Ultimately, the structure must reach the back or forward end of the pulse and disappear. Structures which are stationary with respect to the pulse cannot persist either since X→ 0. Hence solitonlike and breatherlike structures cannot persist at all.
Do laser beams really go straight?
Authors: Levenson M. D. , Richardson W. H.
Published: February 2023

Spontaneous emission into the oscillating mode of a laser is responsible for the well-known phase diffusion and Schawlow-Townes linewidth limit. Similar emission into higher-order transverse modes of a laser oscillating in a TEM00 mode causes jitter in the beam axis. This jitter causes spatial noise that can be easily detected. The positional accuracy of the center of a laser beam is limited by the presence if vacuum fluctuations in the TEM01 mode, even in the absence of fluorescence, leading to a fundamental limit on the pointing accuracy of a laser. When fluorescence is present, the spatial noise appears at beat frequencies between the fundamental and higher-order modes.
Efficient passive holographic optical interconnects using resonated holograms
Authors: Griffith Paul C. , Collins Stuart A.
Published: February 2023

Holograms show promise as optical interconnects both for electronic intra and interchip applications and for numerical optical computing. We are concerned with applications where it is desirable to store many interconnects in the same hologram while maintaining good diffraction efficiency. To deal with the problem of low-diffraction efficiencies present in holographic materials with many superimposed exposures, resonant mirrors are added to reflect the light back and forth through the hologram, thus increasing reconstruction efficiency. Up to 100% efficiency is possible in lossless multiexposure holograms.
Two- and four-wave mixing in a photoconductor thermoplastic device
Authors: Peri David
Published: February 2023

The photoconductor thermoplastic (PC-TP) device is a real-time erasable holographic storage device characterized by relatively high light sensitivity and in situ recording, development, and readout. We report on the use of the PC-TP device in an optical beam amplification via two- and four-wave mixing. The relative phase shift between the intensity interference pattern and the recorded grating is an important factor for efficient power transfer. It is controlled by proper choice of angles of incidence for the beams. Amplification by a factor of 5 has been achieved in a single pass through the device. The analysis of two-wave mixing in the PC-TP device, including the gain dependence on the phase shift, the beam ratio, and device efficiency, is presented. Four-wave mixing has also been analyzed, and preliminary experimental results are presented.
Microscope using optical phase conjugation
Authors: Brody Philip S. , Garvin Charles
Published: February 2023

Phase contrast imaging by the backward passage of a phase-conjugate beam through a phase plate that was used to produce the original phase distorted beam depends on the phase conjugate of the original field passing back through the specimen after the specimen has been shifted. We demonstrated this previously using self-pumping in barium titanate to produce the phase-conjugate field and a mechanical means to shift the plate. The intensity images show the gradients of plate optical thickness with respect to the shift direction of the specimen’s optical thickness.1 We note that an image should also result if the slide remains stationary but component elements of the specimen move. Taking advantage of this last we have developed a microscope which shows dynamic processes within biological phase objects. The stationary elements on the slide do not show up; the image shows only those elements that move. The device includes a stage of digital processing which removes coherent artifacts and also adds gradients in intensity of moving elements in the bright field intensity image.
Photon statistics of superimposed nonclassical fields
Authors: Teich Malvin C. , Saleh Bahaa E. A.
Published: February 2023

Antibunching, photon-number squeezing, and quadrature squeezing represent characteristics of nonclassical electromagnetic fields that have been observed in the laboratory. Experiments involving nonclassical light often make use of beam splitters to superimpose light beams. We discuss the photon statistics that arise from the superimposition of two arbitrary (not necessarily independent) quantum fields at a device such as a beam splitter. The photomixing density operator of the superimposition field is presented, and the behavior of the balanced mixer is examined in the general case.1 The failure of classical probability theory as a descriptor of the relationship between the photon statistics at the output and at the input of the beam splitter is elucidated.
Optical matrix manipulation techniques for search problems
Authors: Haney M. W. , Athale R. A.
Published: February 2023

Tree search and graph matching problems are ubiquitous in artificial intelligence. Applications areas include scheduling, theorem proving, and scene labeling/interpretation for computer vision. In general these problems have exponential time complexity and become intractable rapidly as the number of variables grow.
Design of a J-K flip-flop using polarization-encoded optical shadow-casting
Authors: Awwal A. A. S. , Karim M. A.
Published: February 2023

The lensless optical shadow-casting scheme1 has been shown to perform combinatorial logic operations. To make a more powerful system, the realization of sequential logic operations is necessary. With a powerful design algorithm,2 we have demonstrated the design of various combinational logic units like that of a full adder/subtracter, multiplication units, trinary adders, and programmable logic arrays using a polarization-encoded optical shadow-casting system. We present the design of a basic memory unit, a J-K flip-flop, as an example; we believe this is the first of its kind reported in the literature. Three approaches have been considered in designing the J-K flip-flop that result in three different system configurations. The performance of these modules is compared in terms of size of the input pixels and architectural constraints.
Optical liquid crystal TV and hologram-based position-coded multiple-valued logic and arithmetic operations
Authors: Kostrzewski Andrew , Li Yao , Ha Berlin , Kim Dai Hyun , Eichmann George
Published: February 2023

Truth-table look-up processing methods have been effectively used in the implementation of parallel optical digital computation. A new optical implementation of multiple-valued logic operations that employs an optical holographic look-up table addressed by a pair of position-coded liquid crystal TVs is proposed. Realizations of optical modified signed digit post as well as residue logic and arithmetic processing elements are presented. Experimental results are included.
Symbolic substitution-based flagged arithmetic unit design using polarization-encoded optical shadow-casting
Authors: Cherri A. K. , Karim M. A.
Published: February 2023

Carry-free arithmetic operations using modified signed-digit (MSD) number representation are performed. The MSD arithmetic-based flagged symbolic substitution,1 where an additional bit is used along with each pair of the input bits to characterize the next less significant pair of bits, is implemented using the polarization-encoded optical shadow-casting system (POSC).2 Two different designs using the POSC scheme are proposed for implementing the MSD addition and subtraction. The input codes and source patterns for the POSC system are determined for both an MSD adder and MSD subtracter. The design process consists of grouping the rows of the MSD adder/subtracter truth table in terms of an overlap operation2 so that the solution of the corresponding overlap equation yields the input pixel encoding of the POSC system for a particular output mask and a fixed source pattern for achieving the desired arithmetic output.
Performance of virtual amplitude biphase-only correlation filters with input scene clutter
Authors: Dymek Michael S. , Sun Tsi-Shung
Published: February 2023

Correlation filter functions implemented with biphase-only modulators represent the state of the art in real-time programmable optical correlators for target recognition. High optical throughput, however, results at the expense of distortion-invariant performance. We present results of computer simulations and experiments using biphase-only modulation for the filter functions, which are designed to approximate the performance of correlation filters having both biphase and biamplitude modulation. Specifically, we investigated the effect of clutter in the input scene on correlation performance using these virtual amplitude filters and compared them with those for classical method filters and previous biphase-only filter designs.
Raman response function of silica-core fibers
Authors: Stolen Roger H. , Gordon J. P. , Tomlinson W. J.
Published: February 2023

Nonlinear propagation of short high-intensity optical pulses in single-mode optical fibers is best treated in the time domain using the nonlinear Schrodinger equation. Here we show how Raman gain is included in such a time domain analysis as a response function. The essential feature of the approach is the recognition that all the nonlinear index is not instantaneous. Introducing such a noninstantaneous component of the nonlinear index produces in the frequency domain real and imaginary parts of the third-order susceptibility, which can be identified with a Raman contribution. The noninstantaneous component of the nonlinear index is the response function. We develop the response function for silica-core fibers from measurements of the Raman spectrum. The response function has a strong peak at 40 fs corresponding to the 430-cm−1 maximum in the gain spectrum.
Schawlow-Townes linewidth for coupled lasers
Authors: Falvey Suzzanne E. , Chow Weng W.
Published: February 2023

Coupling two or more optical resonators can lead to desirable properties such as selective mode suppression, enhancement of intracavity laser power, frequency stabilization against cavity-length fluctuations, and phased laser arrays. For these applications it may be desirable to know the fundamental limit to the coherence of coupled lasers.
Extraction efficiency in Q-switched Nd3+lasers
Authors: Fan T. Y.
Published: February 2023

Analyses of Q-switched Nd3+ lasers on the 1.06-µm 4F3/2—4/11/2 transition often assume the 4/11/2 lifetime is zero, but this a poor assumption because even the lowest estimate for this lifetime1 of 10 ns in Nd:YAG Is of the same timescale as typical Q-switched pulses. In models which have included finite lower laser level relaxation time, Boltzmann occupation factors of the upper and lower laser levels relative to their total manifold populations have not been taken into consideration.2 A model has been developed for homogeneously broadened Q-switched Nd3+ lasers, which includes finite lower laser level relaxation time and Boltzmann occupation factors. The model Indicates that extraction efficiency, which is the fraction of the upper manifold population that becomes stimulated photons, depends on the number of times above threshold, the ratio of the lower laser level to cavity lifetime, and the Boltzmann occupation factors of the lower and upper laser levels. Using the model for the 1.064-μm Nd:YAG transition, a maximum reduction of 32% In extraction efficiency, relative to the case of a lower level lifetime of zero, is predicted.
Time evolution of hot spots in end-pumped solid-state laser rods
Authors: Farrukh U. O. , Buoncristiani A. M. , Byvik C. E.
Published: February 2023

An analytical study of temperature distribution in actively cooled rods is applied to end-pumped solid-state lasers. The pump is assumed to be a single pulse of a highly focused Gaussian beam whose waist lies close to one end of the rod. High intensity spots cause thermal gradients leading to optical path distortions and stress-induced damage. A hot spot is formed at the position of the pump waist. The hot spot weakens and moves as a result of the active cooling of the rod. Data on the evolution of hot spots in Nd:YAG and Ti:A1203 laser rods are provided.
Changes in time scale and sensitivity of responses of human cone pathways
Authors: Hamer Russell D. , Tyler Christopher W.
Published: February 2023

The critical duration t
c
is the maximum stimulus duration which the visual system can linearly integrate. In the classic literature on temporal integration in the visual system, t
c
varies at most by a factor of 3 between dark-adapted and fully light-adapted conditions. Little attention has been given to pure cone-mediated temporal summation or to the role of probability summation in the variation of t
c
with luminance.
Path integrals and propagators in guided-wave optics
Authors: Hawkins Raymond J.
Published: February 2023

Path integration has proved quite useful in the treatment of propagation problems in a variety of fields and in quantum mechanics in particular. It is, therefore, natural that the formal similiarity between the Schrodinger wave equation and the paraxial optical wave equation should inspire the use of path integration in optics. Path integrals have been used in optics for over a decade, and their use in optics is increasing. Although path integration is often used to study optics problems in an analytic manner, this formalism is increasingly found to provide the basis of efficient computational techniques. I discuss recent applications of path-integral-based analytic and computational approaches to problems ranging from computer-aided device design in integrated optics to development of a path integral expression for the time-evolution operator associated with Maxwell’s equations.
Generalized coupled-mode formulations for two curved weakly guiding single-mode fibers
Authors: Cheng Yuehua , Lin Weigan
Published: February 2023

A generalized coupled-mode theory1 is developed to study the coupling system of two curved weakly guiding single-mode fibers. Our theory takes into account the local fields, nonorthogonality, and phase interference between guide modes in the curved optical waveguides. In similar special cases, the coupling mode formulations and coupling coefficients1 agree with those obtained from the Hardy-Streifer coupled-mode theory.2
Nitrous oxide as a dynamic tracer in the 1987 airborne Antarctic ozone experiment
Authors: Loewenstein M.
Published: February 2023

In situ, N2O measurements were made using a laser absorption spectrometer, ATLAS, on twelve flights into the Antarctic vortex as well as on five transit flights outside the vortex region in Aug. and Sept. 1987 as part of the airborne Antarctic ozone experiment. Vertical profiles of N2O were obtained within the vortex on most of these flights and outside the vortex on several occasions. Flights into the vortex region show N2O decreasing southward between 53°S and 72°S latitude on constant potential temperature surfaces in the lower stratosphere. The data lead to two important conclusions about the vortex region: (1) The lower stratosphere in Aug./Sept. 1987 was occupied by old air, which had subsided several kilometers during the polar winter; (2) the N2O profile in the vortex was approximately in a steady state in Aug./Sept. 1987, which indicates that the spring upwelling, suggested by several theories, did not occur.
High density femtosecond virtual excitations In dc-blased quantum well structures
Authors: Knox Wayne H. , Chemla Daniel S. , Miller D. A. B. , Stark J. B.
Published: February 2023

Virtual excitation of semiconductors has been demonstrated to yield ultrafast optical nonlinearities.1 We report studies of the effects of virtual excitations in a quantum well structure biased by a dc field perpendicular to the layers. In such a sample, electrons and holes exhibit a quantum-confined Stark effect creating a real transition dipole. The interaction of an intense femtosecond light pulse which is below the energy threshold for real optical transitions with this system is the object of the present study.
100-fs time-resolved dynamics of infrared excitonic nonlinearities in InGaAs quantum wells
Authors: Bar-Joseph Israel , Sucha G. , Wegener M. , Islam M. N. , Chemla D. S.
Published: February 2023

Femtosecond time-resolved spectroscopy in the visible and near IR has recently been extensively used to investigate GaAs-based semiconductors. So far it has not been possible to extend this technique to IR materials. Investigations on this time scale of the InGaAs-based heterostructures are very important both for applications in lightwave communication systems and fundamental semiconductor physics.
Ultrafast modulations in time-delayed four-wave mixing experiments
Authors: DeBeer D. , Usadi E. , Hartmann S. R.
Published: February 2023

Two transient time-delayed four-wave mixing experiments have been performed on the Na D doublet and modulations of 1.9 ps and 980 as have been observed. These periods correspond to the difference and sum frequencies of the two Na D lines. Both experiments were performed using 7-ns pulses of light with frequency components at each of the D-line transitions. The effects of superimposition-state modulations are observed in the integrated TDFWM signal as a function of the time delay. As the time delay is varied, the lowest diffraction order mixing signal is modulated. Higher diffraction order mixing signals contain modulation components at integral multiples of the beat frequency.
Gain curve manipulation: a new approach to generate broadband pulses
Authors: Choa F. S. , Burr G. W. , Liu P. L.
Published: February 2023

Ultrafast optical pulses with a broad spectrum are very useful in studying materials. The usual way to generate white-light pulses is done by highly nonlinear processes. The generated white light is noisy, not well collimated, and not uniform across the beam. We report the use of synchronously pumped dye lasers to generate stable well-collimated broadband pulses with durations in the pico­second to femtosecond range. The broadband comes from two effects: the fast gain modulation and the gain peak suppression. The fast gain modulation transfers power from high gain modes to low gain modes and makes them oscillate. A transmission valley is then introduced into the cavity and makes the gain minus loss curve flat. The number of oscillation modes can thus be further increased.
Streak camera studies of line-narrowed dye lasers
Authors: Rankin M. B. , Davis J. P. , Giranda C. , Squicciarini M. F. , Bobb L. C.
Published: February 2023

This paper describes temporal characteristics of light pulses from a commercial Nd:YAG-pumped dye laser (Quanta-Ray DCR-2A/PDL-2). The dye laser is of Hansch design with a ×100 beam expander and an intracavity etalon and uses coumarin 500 (C500) or DCM as the active medium. A Hamamatsu C2830 streak camera with 40-ps resolution produces time records of the 355-nm pump light, the 500-nm dye laser output, and its 250-nm second harmonic. These records show complex temporal structure undetectable with an ITT F4000 biplanar photodiode and Tektronix 7104 oscilloscope.
Femtosecond Ti:Al2O3 injection seeded laser
Authors: Schulz P. A. , Lagasse M. J. , Schoenlein R. W. , Fujimoto J. G.
Published: February 2023

A Ti:Al2O3 amplifier has a very wide (200-nm) gain bandwidth and thus excellent potential for amplifying and tuning of femtosecond laser pulses. We have used a Ti:Al2O3 injection seeded laser pumped by a 2-mJ copper vapor laser to amplify the output of a synchronously pumped dye laser. To pump the dye laser a mode-locked Nd:YAG laser is pulse compressed to 5 ps using a fiber and grating pair and frequency doubled. A single pulse from the 82-MHz 400-fs pulse train of the dye laser is selected using an acoustooptic modulator. This pulse is mode matched and coupled with a beam splitter into the Ti: Al2O3 laser. A wavelength-independent Faraday isolator is placed in the beam path to protect the acoustooptic modulator from the high-power Ti: Al2O3 laser output. The injection seeded laser1 employs an 8% output coupler. With only 0.1 pJ of incident seed energy at 790 nm, the Ti: Al2O3 laser is mode-locked. The output is a 100-ns pulse train with pulses spaced by 2.1 ns, which is determined by the Ti: Al2O3 cavity length. A single pulse contains 1 µJ and has a pulse width of 1.5 ps. These pulses have been recompressed with a grating pair to 300-fs pulse widths.
Pulse statistics of synchronously pumped mode-locked lasers
Authors: Vermuri G. , Roy Rajarshi
Published: February 2023

We present quantitative estimates of the peak pulse height fluctuation in a model of synchronously pumped mode-locked dye laser operation. The effect of the mismatch between pump and dye laser cavity round-trip times, the strength of the pumping pulse, the level of spontaneous emission, and the cavity loss per transit on the mode-locked dye laser pulses are studied by computer simulations of a model introduced by G.H.C. New and his co-workers. It is shown that a decrease in the level of spontaneous emission leads to a decrease in the normalized variance of the peak pulse height, while the pump pulse strength has little influence on the normalized variance. The role of the cavity loss per transit, pump pulse strength, and spontaneous emission on the correlation time of the peak pulse heights is clearly displayed. The role of the cavity loss per transit on the formation or suppression of satellite pulses is investigated. A model for mode locking by synchronous pumping of a titanium-doped sapphire laser with a relaxation time much longer than the cavity round-trip time is also presented. The model explicitly accounts for the long relaxation time of the active medium as well as the length of the cavity. The effect of the mismatch time between pump and solid-state laser cavity on the mode-locked pulses is shown.
Applied research of an acoustic speckle pattern
Authors: He Duo-Min , He Ming-Shia
Published: February 2023

Speckle is a lively and rapidly evolving field not only for the study of speckle phenomena but also for practical application. In optics, speckle metrology has now matured to the point where a whole monograph1 is available, and commercial equipment is being specially built for particular applications. But in acoustics, speckle is more commonly considered so bothersome that it is eliminated, e.g., the noise in acoustic imaging.
Holographic interferometry using optical crystals
Authors: Hafiz A. , Magnusson R. , Wilson D. R. , Black T. D.
Published: February 2023

Holographic interferometry is an important diagnostic technique with a large number of practical applications. Global visualization of spatial refractive-index distributions may be obtained using this technique. Holographic interferometry allows the resultant refractive-index distributions to be quantitatively evaluated without disturbing the phenomena under study. To date, holographic film has been used as the recording medium in most of the holographic-interferometry experiments reported in the literature. The use of film is basically undesirable due to the tedium involved in developing the exposed film and the necessity of a darkened work area. Self-developing, or photorefractive, optical crystals offer an alternative to the use of film in holographic interferometry.
Precision of surface figure measurements of large deformable mirrors using grazing incidence interferometry
Authors: Ritter Michael W. , Duncan A. L. , Malin M. , Metheney W. W.
Published: February 2023

A grazing incidence interferometer (Gil) using sinusoidal phase modulation was developed at LMSC to sample the surface figure of large deformable mirrors along narrow swaths utilizing small optical components mounted along the periphery of the mirror to control the shape of the mirror. The instrument is described, and results of tests used to calibrate it are discussed. The statistical limitation to the resolution of the figure sensing due to electronic noise and vibration of the optical components was measured to be <10−4 waves. The actual total resolution was measured by comparing the Gil to a polarization interferometer (PI) in a Ritchey-Common test-bed. The standard deviation of the measured Gil resolution is between 3.9 × 10−4 and 2.4 × 10−4 waves. The larger limit of this resolution measurement is set by errors in the PI calibration. The smaller limit is set by examining the error distribution in the best fit between the two instruments and extracting those errors due to the PI.
Feedback stabilized phase measuring holographic interferometry
Authors: Crawforth L. , Munce A. C.
Published: February 2023

Phase measuring holographic interferometry is a powerful technique for quantitatively determining surface deformations. The phase measuring method requires that the average optical phase between the interfering object and reference waves be shifted with a high degree of accuracy. Improved accuracy in deformation measurements has been obtained by directly measuring the average phase between the two beams and then employing that information in a real-time feedback loop to control the motion of a piezoelectric translator, which serves as the phase stepping device. The average phase is determined by dithering the piezoelectric translator and measuring a portion of the resultant interference distribution with a photodiode. The signal from the photodiode is demodulated with a lock-in amplifier and used as an error signal for a digital controller to obtain phase steps of exactly 90°. The digital controller can also be useful in compensating for low-frequency phase fluctuations in the optical system caused by vibrations. The end result is that the need for PZT calibration is eliminated, the phase steps are of higher accuracy, and errors in the deformation calculation due to vibration-induced phase fluctuations are reduced.