bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Voltage, Polarization-Independent Optical Switch in Ti-Indiffused Lithium Niobate
Authors: Nightingale J. L. , Vrhel J. S. , Salac T. E.
Published: February 2023

Polarization-independent optical switches are attractive in fiber optic instrumentation and telecommunication systems because of their compatibility with conventional optical fiber. Several different types of polarization-independent switches have been proposed and demonstrated [1-3]. In general, these switches have had high switching voltages, complex electrode structures, or demanding fabrication tolerances. We report on a new type of polarization-independent switch, using the balanced-bridge switch concept. This switch employs a simple electrode structure, has a low switching voltage, and is inherently polarization insensitive. Using this concept, we have demonstrated polarization-independent switching at optical wavelengths of 830 and 1150 nm.
Application of Integrated Optics to High Speed Instrumentation
Authors: Dolfi David W.
Published: February 2023

Applications of integrated optic components have primarily been focused toward telecommunications and sensors. A third, growing area, and the subject of this talk, is their use in instrumentation for performing measurements on high speed optical systems and components. In the frequency domain, this would include bandwidths in the tens of Gigahertz, while in the time domain, it covers pulse widths of picoseconds and tens of picoseconds.
Short Pulse Generation and microwave/millimeter wave Narrowband Modulation in Semiconductor Lasers
Authors: Lau K.Y.
Published: February 2023

The field of high speed semiconductor lasers has undergone substantial advances since the first demonstration of a laser with modulation bandwidth beyond 10GHz[1]. Much of the present understanding on the high speed modulation of semiconductor lasers comes from a small signal analysis of the laser rate equations. The present state of the art is exemplified by the demonstration of a 16GHz bandwidth (-3dB)[2] contricted mesa laser and a 22GHz bandwidth vapor phase regrown buried heterostructure laser[3], both at a wavelength of 1.3μm. On a parallel front, there has been substantial progress in using laser diodes for picosecond pulse and microwave/millimeter wave signal generation. Picosecond optical pulse sources are major tools for studying ultrafast physical and chemical phenomena. A compact and reliable semiconductor picosecond laser source is highly desirable, especially for instrumentation applications such as picosecond optical sampling for non-invasive characterization of high speed electronic curcuits. Demonstrated methods of picosecond pulse generation from a laser diode include mode-locking and gain/Q switching. Gain switching is a very simple technique of producing short pulses from a laser diode, although the pulse width seldom falls much below 20ps unless a saturable absorber is introduced into the cavity. Factors affecting gain-switched pulse width will be examined, along with Q-switching by means of an intracavity modulator. Presence of a saturable absorber in a laser diode can also cause repetitive Q-switching, or self-pulsation, whose frequency is tunable with injection current. Previous efforts on passive mode-locking has led to pulses of a few picosecond wide. Recent efforts concentrated on the use of high speed semiconductor lasers and to modulate/mode-lock the laser at frequencies above the relaxation oscillation frequency[4,5,6]. Such high frequency mode-locking technique was first demonstrated at 17GHz[4], in which 12ps pulse were generated, and recently similar configurations have succeeded in generating subpicosecond optical pulses[5] and at 40GHz[6]. The mode-coupling technique has been considered for narrow band modulation of the diode at millimeter wave frequencies. Recent studies[7] have shown that it is possible to mode lock semiconductor lasers at millimeter wave frequencies approaching and beyond 100GHz. The mode-locked output usually takes the form of sinusoidal modulation, and can be regarded for practical purposes as a highly efficient means of directly modulating an optical carrier in a narrow band at millimeter wave frequencies.
Repetition Rate Dependence of Gain Compression in InGaAsP Optical Amplifiers
Authors: Wiesenfeld J. M. , Eisenstein G. , Hansen P. B. , Tucker R. S. , Raybon G.
Published: February 2023

Semiconductor optical amplifiers will be important components for high-repetition rate optical systems, such as optical time division multiplexed systems [1]. Several groups have studied the properties of optical amplifiers when used with ultrashort input optical pulses [2-4]. If the input pulse is sufficiently energetic, it can compress (saturate) the gain of the amplifier by removal of a fraction of carriers from the active region by stimulated emission [2,4]. After passage of the input pulse, the amplifier gain will recover with a time constant, τ. When the separation between input pulses becomes comparable to or smaller than τ, the gain experienced by a particular pulse will depend on the previous pulse pattern incident on the amplifier, because the gain may not have time to recover to its original value between pulses. Thus, it is important to understand the effect of gain recovery on the gain experienced by a randomly modulated pulse stream, because the finite gain recovery time may lead to inter-symbol interference (ISI). To gain insight into this problem, we study gain compression of an InGaAsP optical amplifier when used with multi-gigahertz repetition rate pulse streams.
Laser Assisted Processing for Integrated Optics
Authors: Willner Alan E. , Podlesnik Dragan V.
Published: February 2023

A brief overview of the physics of laser-controlled etching will be given to facilitate understanding of realizable optical and electrooptical structures. A review of demonstrated devices will be presented. This will include high-resolution diffraction gratings, integral lenses and turning mirrors. The status of waveguides fabricated in GaAs/AlGaAs structures by direct laser writing will be included.
Laser-Assisted Selective Chemical Etching for Active Trimming of GaAs Waveguide Devices
Authors: Brown Robert T.
Published: February 2023

In the fabrication of III-V integrated optic and microelectronic devices, there is a need for improved etching processes. As reported previously [1], laser-assisted wet chemical etching techniques have been developed for alloy-selective patterning of GaAs/AlGaAs layered structures. Such techniques are potentially very important for the fabrication of a large variety of hetero-structure devices. These techniques have utilized a CW dye laser tuned to a wavelength above the band edge of GaAs, but below that of the AlGaAs layer (e.g., a wavelength of 0.85 μm) to etch GaAs. Using the laser spot to spatially define the etched area, selectivities in excess of 100 for GaAs over Al.40Ga.60As were achieved at etch rates in excess of 2 μm/min. Typical etch features are shown in Fig. 1. The feature on the left corresponded to an etch time of 15 sec, while the feature on the right, illustrating high selectivity at the AlGaAs interface, corresponded to an etch time of 45 sec. Recent studies, with an arrangement similar to that in Fig. 1, have shown that etch selectivity can be achieved based on differences in doping level and doping type as well as on differences in chemical composition.
Tunable Multiple-Quantum-Well Distributed-Bragg-Reflector Lasers as Tunable Narrow-Band Receivers
Authors: Koch T. L. , Choa F. S. , Heismann F. , Koren U.
Published: February 2023

There has been a growing interest in densely spaced incoherent wavelength-division-multiplexed (WDM) optical communications systems as an alternative to coherent (heterodyne) systems. Recent work has reported an MQW-DBR laser simultaneously functioning as a local oscillator and photodetector/mixer in a coherent (heterodyne) system[1]. In this work we demonstrate the potential of a broadly tunable multiple-quantum-well (MQW) DBR laser geometry to perform as a complete narrow-band tunable incoherent receiver. Biased just below threshold, the device simultaneously integrates the functions of a tunable filter, resonant optical amplifier, photodetector, and if desired, an FSK discriminator. Using identical devices for both an FSK transmitter and an FSK receiver, we demonstrate transmission at speeds up to 250 Mb/s with a preliminary sensitivities in the ~-30 dBm range for 10−9 BER. Speed is limited by the transmitter FM response, and independent speed measurements indicate a receiver bandwidth of at least 1.7 GHz.
Nonlinear and Electro-Optic Polymer Waveguide Devices
Authors: Lytel R. , Lipscomb G.F. , Stiller M. , Thackara J. , Ticknor A.
Published: February 2023

Nonlinear polymer materials have low dielectric constants, large electro-optic coefficients, and low optical loss. We review our fabrication methods for producing active channel waveguide devices, and describe several new active polymer waveguide devices.
Permanently-induced Linear Electro-Optic Effect in Silica Optical Fibres
Authors: Li Luksun , Payne David N.
Published: February 2023

Permanent electric-field-induced linear electro-optic effects have been observed in fused-silica optical fibres subjected to strong electric fields by means of internal electrodes. This electric-field-poling phenomenon can be used to construct a Pockels modulator and other electro-optic devices.
Integrated Optical Polarizers at 830 and 1300 nm
Authors: Leslie D. E. , Nightingale J. L. , Fejer M. M.
Published: February 2023

Integrated optical polarizers are important components in many fiber optic systems, particularly fiber optic gyroscopes. Designing polarizers with high polarization rejection and low excess loss, which can be easily and reliably fabricated is critical in these applications. Many techniques have been used to construct polarizers, the most promising being metal/dielectric overlays [1,2,3] and proton-exchanged waveguides [4].
Fundamentals of the Optical Tolerance Budget
Authors: Smith Warren J.
Published: February 2023

A tutorial introduction to the statistical philosophy of establishing a tolerance budget with a step by step description of the process for a sample case.
The Impact of International Optical Standards on Lens Design
Authors: Parks Robert E.
Published: February 2023

In 1979 the International Standards Organization formed a technical committee to work on standards for optics and optical instruments. An optical drawing standard developed as part of the committee’s work will be published in draft form shortly. This standard will be adopted quickly by the world’s largest users and manufacturers of optics. Concurrently, the US military has been mandated to adopt voluntary standards whenever they exist. This will speed the adoption of the ISO optical standards in the US. We will address some of the economic and practical implications of the development.
Design Challenges for the 1990's
Authors: Shafer David
Published: February 2023

The past decade has featured some dramatic advances in areas touching on lens design. These include new levels of ease and accuracy in aspheric fabrication, a better appreciation of cost/weight/package size/performance tradeoff issues, an amazing increase in computing speed, better cost, accesibility. user-friendliness, and nascient signs of computer intelligence. Impressive as these advances are. we are ultimately forced to realize that there is no replacement in the near term for good old human thinking.
Refractive Designs for Visible to Mid-Wave Infrared Wavelengths
Authors: Figoski John W. , Sepulveda Cesar A.
Published: February 2023

Remote sensing applications require monitoring ground reflectances through the visible and into the infrared spectrum. Many refractive designs exist for the visible (0.4μm to 0.7μm) as well as medium-wave infrared, MWIR, (3.0μm to 5.0μm) applications. However, design solutions that bridge the gap between these two spectral regions are not very common. Recent work at SBRC has uncovered several solutions with reduced secondary color in the 1.0μm to 3.0μm band and that even extend from 0.5μm to 5.0μm.
Rank Down Method for Automatic Lens Design
Authors: Ooki Hiroshi
Published: February 2023

Since 1950's, many mathematical methods have been proposed for automatic lens design. At present, 1990, some of them are still being used widely whereas some of them are forgotten.
A Simple Method for Finding the Valid Ray-Surface Intersection
Authors: Freeman David E L
Published: February 2023

In general, there are two or more mathematical solutions to the intersection of a ray with a surface. In fact, only one of these can represent the real physical situation, - the valid ray-surface intersection.
Lens with Maximum Power Occupying a Given Cylindrical Volume
Authors: Reardon Patrick J. , Chipman Russell A.
Published: February 2023

Using the concept of a limiting lens and the matrix method of paraxial optics, we determine the maximum optical power which can be achieved given a particular lens diameter, length, and two refractive indices. The geometry for this analysis is shown in Figure 1. A series of k identical symmetric positive lenslets of diameter D, with zero edge thickness and index of refraction n2 are positioned in succession with zero distance between adjacent lenslets. The center thickness of the positive lenslets is defined as t
α
= D/α where the thickness parameter α is a real number, α ≥ 1.0. The surrounding media fills the remaining volume with index n1 < n2. The total length from the first to the last vertex of the assembly is L. As the number of lenslets approaches infinity while keeping L constant, the lens will have the maximum power attainable for the given volume and refractive indices. This infinite series of infinitesimally thin identical symmetric positive lenslets is defined as the limiting lens. For the limiting lens, both α and k must approach infinity.
The Design of Double-Gauss Objective by Using Concentric Lenses
Authors: Juang Jeng-Dang , Chang Ming-Wen
Published: February 2023

This method developes a system which consists of a single positive component, followed by a negative meniscus that is concave to the rear, followed by another negative meniscus lens that is concave to the front, and a final positive single lens. The stop is at the middle. Assume the same refractive index for those four elements and the power of the 1st element equals to that of the 4th, the 2nd element equals to the 3rd.
Expert Systems in Lens Design
Authors: Dilworth Donald C.
Published: February 2023

The SYNOPSYS
TM
expert-systems program XSYS
TM
is a radical departure from traditional methods of lens design. Typical problems that were presented to XSYS
TM
, and show how the program can find useful, sometimes unexpected, starting points will be described.
A Multi-Aperture Spectrometer Design for the Atmospheric Infrared Sounder (AIRS)
Authors: Pagano Robert J. , Hatch Marcus R.
Published: February 2023

Accurate knowledge of the Earth's vertical atmospheric temperature structure is fundamental to numerical weather prediction. The National Weather Services (NWS) have stated an ultimate goal for temperature sounding of 1 degree accuracy and 1 km vertical resolution throughout the troposphere. To approach this goal next generation temperature sounders must have increased spectral coverage and increased spectral resolution. Extensive simulations indicate that a temperature sounder with spectral resolving power (λ/Δλ) of 1200 and wavelength coverage from 3.4 - 17 μm will significantly improve the rms temperature retrieval accuracy. The Atmospheric Infrared Sounder (AIRS) for the Earth Observing System (Eos) has been designed to meet these requirements.
A Simple Quadratic Extrapolation Method for the Correction of Specific Aberrations in Lens Systems
Authors: Maxwell J. , Hull C.C.
Published: February 2023

The need to achieve control of specific aberrations and to investigate the structural aberration properties of lens systems, has led to the development of an interactive design tool based on multi-dimensional quadratic extrapolation. A quadratic approximation to the non-linearly varying aberrations allows the step length of this differential correction technique to be extended and the underlying relationships between goups of constructional parameters and aberrations are revealed. Examples are given.
A Simple Quadratic Extrapolation Method for the Correction of Specific Aberrations in Lens Systems
Authors: Maxwell J. , Hull C.C.
Published: February 2023

A change in the vector of aberration coefficients, Δa, is given, to a first-order approximation, by equation (1). A is a square matrix of first-order partial differential coefficients with respect to the variable parameters for the current design and Δx is the vector of applied parameter changes.
Interactions of laser radiation with a biological cell
Authors: Qiao Gu
Published: February 2023

Using the Maxwell electromagnetic theory, eigenmodes in a biological cell such as a spherical optical cavity consisting of a spherical medium and its interface with surrounding medium are revealed, each of which can take the form of vector spherical harmonics. The expression for the light field within the biological cell exposed to laser radiation with a planar wavefront is ascertained when taking account of these eigenmodes. Furthermore, the internal medium with absorption loss may intensely affect the light field. Finally, some properties of coherent radiation within the cell are analyzed; essential conclusions are as follows: (1) There are good eigenmodes within the cell to use as a spherical cavity with high-Q value. (2) Within the cell small, spontaneous emissions, such as incoherent spontaneous emission, superradiance and spontaneous emission, superradiance and spontaneous Raman re-scattering may be amplified. (3) With a strong internal field, it is possible that some nonlinear optical effects are induced. (4) The above-mentioned coherent radiations within the cell may be utilized for communication within the biological system; they possibly transfer genetic information.
Diagnostics of large scale structures in flames using laser tomography
Authors: Semerjian Hratch G. , Ray Steven R.
Published: February 2023

Laser tomography is an optical diagnostic technique based on multiangular absorption spectroscopy. The technique allows the rapid measurement of both species concentration and temperature throughout a 2-D or 3-D nonuniform flow field. This is accomplished by measuring absorption along M equally spaced parallel beams and N equally spaced angles, forming an M × N data set from which the property field (temperature and/or concentration) is reconstructed. The reconstruction is achieved by using Fourier transform, convolution, or maximum entropy techniques. Measurements of OH radical concentration and translational temperature have been carried out in an axisymmetric premixed methane/air flame, using a single measurement angle. The technique has now been extended to a six-angle system, where simultaneous measurements can be made at all six angles at repetition rates up to 10 kHz. Data have been obtained on the dynamics and the 3-D structure of large eddies formed in an ethane/air turbulent diffusion flame. The frequency of eddy formation is controlled by introducing fluctuations into the fuel stream, using a loudspeaker. Formation, shedding, and breakup of eddies, marked by the soot particles formed in the flame, can be observed in detail using the laser tomography technique.
Radiative scattering close-coupled calculations for isotope dependence of fine-structure branching in 3He-Na and 4He-Na optical collisions
Authors: Vahala L. L. , Julienne Paul S.
Published: February 2023

Assume that collisional redistribution occurs in a collision of two atoms in scattering state i by absorption of a photon through an isolated molecular state a to an isolated molecular state b, followed by separation to excited product scattering state f. If the separation velocity of the two atoms is sufficiently large, the final state can be approximated by the same recoil limit which has been developed for photofragmentation.1 Our close coupling calculations on Na + He systems show how the recoil limit for fine-structure branching rations is approached for both red and blue detuning as product separation velocity increases. Comparisons are made between the lighter Na-He system at thermal energies and the heavier Na-He system.
Double resonance techniques for high resolution spectroscopy of unstable molecules
Authors: Ernst Wolfgang E.
Published: February 2023

Free radicals often exhibit complex optical spectra. Dopplerfree laser spectroscopy is the appropriate tool in many cases, but its limitations may be reached already when the fine and hyperfine structure of a heavy diatomic is to be analyzed. Double resonance techniques help to simplify dense spectra and to assign lines. If microwave radiation is used in addition to a single frequency laser, small energy splittings in individual electronic states can be investigated independently. The recently developed microwave optical polarization spectroscopy (MOPS)1 has proved to offer the necessary high resolution and the sensitivity needed to study chemically unstable species at low concentrations. If a beam of the species can be produced, ground state level splittings and shifts in external fields can be measured with 10-kHz accuracy by using the molecular beam laser-microwave double resonance technique.2 The power of these methods has been demonstrated in applications to alkaline earth monohalide radicals. Local perturbations in excited states were revealed and details of the electronic structure could be derived from hyperfine structure and Stark effect measurements.
Colliding pulse mode-locking light pulses influenced by passing through a LiF color center crystal
Authors: Lin Xing , Zhang Weng Zhen , Wu Feng Tie
Published: February 2023

In experiments with passing a colliding pulse mode-locking (CPM) light pulse through a nonlinear medium LiF color center crystal, we find that, for an ultrashort pulse (~10-ps duration, 1.06-μm wavelength), the durations become slightly shorter when it passes through a LiF color center crystal of 1- and 3-mm thickness. The duration increases when it passes 54.5 and 68 mm (increasing ~6-7 ps). We measured the other parameters of CPM pulses passing through a LiF crystal with the following results: The pulse number of the train, pulse energy, and the duration of the whole pulse train decrease with increasing LiF crystal length. The pulse interval becomes slightly shorter, but it is not relative to the crystal length. We believe that these phenomena can be explained by the saturable character and nonlinear refractive-index property of the light intensity passing through a nonlinear medium. Conversely, we demonstrate the existence of a nonlinear refractive-index property when the light intensity acts on the LiF color center crystal.
Study of stimulated emission from high-lying F ′ Σ g + — B ′ Π 4 and new cascade radiation in Na2
Authors: Wang Qi , Xing Da , Liu Wei , Cheng Yongkang , Ma Zuguang
Published: February 2023

The first observation is reported of a stimulated emission at 0.75–0.81 μm for the high-lying

F
′

Σ
g
+

—

B
′

Π
4

transition and a new cascade radiation at 1.14–1.18 μm for the

F
′

Σ
g
+

→

2
′

Σ
4
+

—

2
′

Σ
g
+

transition in sodium vapor, two-photon resonantly pumped by an excimer laser–dye laser (rhodamine 6G) tunable over a 570–615-nm range. The lasing at 0.75–0.81 μm is recorded in Na2 at 500 °C and buffer argon pressures of 0.5, 5, and 100 Torr, respectively. At higher pressures the operating temperature range at which laser action can occur is very limited. A comparison of the theoretically calculated datum-Derslands table, the Franck-Condon factors, and experimental results—two-pump photon energy and observed lasing wave-length—shows that a kinetic channel should be as follows: the sodium dimers at the ground state are pumped to the vibrational level v = 15 for the high-lying excited state

F
′

Σ
g
+

through the vibrational level v = 24 for the intermediate state

F
′

Σ
4
+

and then

F
′

Σ
g
+

→

B
′

Π
4

stimulated emission at 0.75–0.81 μm occurred. In the same two-photon pumping conditions for the

F
′

Σ
g
+

state the second emission band was observed at 1.14–1.18 μm, which is characterized by the vapor temperature condition, originating in our opinion, from the final process of the cascade transition

F
′

Σ
g
+

—

2
′

Σ
4
+

—

2
′

Σ
g
+

.
Four-atomic rare-gas halide exciplexes and their impact on high-power laser kinetics
Authors: Sauerbrey R. , Tittel Frank K. , Zhu Y. , Wilson W. L.
Published: February 2023

This talk presents spectroscopic evidence for the existence of the four-atomic rare gas halide exciplex Ar3F.1 It is identified through its broadband emission from electron beam excited high pressure Ar/F2 and Ar/NF3 mixtures at (435 ± 50) nm. The temporal behavior of the Ar3F emission as well as the Ar2F/Ar3F intensity ratio shows that the four-atomic species is produced by three-body collisions from Ar2F. However, it is easily destroyed by two-body collisions due to its small binding energy of < 0.2 eV, which can be inferred from the binding energy of

Ar

3
+

. The assignment of the blue emission continuum is further confirmed by the observation of a similar, previously unassigned emission from liquid Ar/F2 mixtures.2 Abnormalities in the Ar2F kinetics found in earlier investigations can now be partially explained by the formation of Ar3F, and partially by electron quenching of ArF and Ar2F. The existence of four-atomic rare gas halide exciplexes could impact on the absorption behavior of rare gas halide lasers. Recently, doubts have been raised as to whether the main absorber in the KrF lasers is, in fact, Kr2F, because the absorption cross section of this molecule appears to be too small. The possible formation of four-atomic exciplexes has to be taken into account for the determination of the absorption cross sections of trimers, as well as for the investigation of scalability of rare gas halide lasers.
High resolution spectrum of electron beam pumped nitrogen laser and effect of foreign gas
Authors: Venkateswarlu Putcha
Published: February 2023

The 0–0, 1–0, and 0–1 bands of N2 ( ~ 3 Torr) excited by a 3-ns pulse of a 400-keV electron beam from a Febetron 706 generator were recorded in the 17th and 18th orders of a 7.3-m vacuum Ebert grating spectrograph. As many as 159 lines have been found to lase in the 0–0 band, 9 lines in the 1–0 band, and 17 lines in the 0–1 band. In the present study a larger number of rotational lines have been observed in all three branches of the 0–0 band than were reported by earlier workers (~ 20-Torr N2). This is probably because collisional deexcitations from higher rotational levels at low pressures of 3 Torr are less than those at low higher pressures. The analysis and the results obtained are compared with those of the earlier workers.
Laser-induced desorption from the (111) surface of BaF2
Authors: Matthais E. , Nielsen H. B. , Reif J. , Fallgren H. , Rosen A. , Westin E.
Published: February 2023

To understand the onset of laser-induced damage on surfaces of transparent ionic materials, we have studied the effect of tunable laser light on cleaved BaF2 (111) surfaces in ultrahigh vacuum conditions, using intensities well below the macroscopic damage threshold. Between 415 and 435 nm strong emission bands were observed for the positive ions Ba+, Ba2+, (BaF)+, F+, and for neutral fluorine. For power densities smaller than 5 × 107W/cm2 the emission yield varies from site to site. All active spots bleach out after a few thousand laser shots. We also find evidence that the desorption yield is sensitive to individual layers. From measurements of the photoelectron yield for various wavelengths a two-photon process was identified, indicating the existence of an occupied surface state with binding energy of about −4.3eV. Cluster calculations support this observation and predict in addition several excitonic states in the upper half of the band gap. We suggest that the wavelength-dependent desorption is triggered by a resonantly enhanced two-photon ionization from this occupied surface state leading to a positive charge-up of the surface which, in turn, results in the emission of positive ions.
Preparation, characterization, and oxidation of small metal clusters
Authors: Gole James L.
Published: February 2023

Using primarily high flux oven-based metal source configurations small alkali (Li
x
, Na
x
, K
x
), coinage (Cu
x
,Ag
x
), and group IVA (Si
x
,Ge
x
) metal clusters are being generated in supersonic expansions and agglomerating flows. Both the clusters and their oxidation to form the metal cluster oxides, M
n
O(n > 2), are being characterized using a combination of single and multiphoton laser fluorescent techniques, chemiluminescence, and mass spectrometry. Photodissociation studies on sodium trimer using laser-induced one- and two-photon atom fluorescence spectroscopy are now being extended to lithium trimer generating a bound-free mirror image spectroscopy which strongly complements the information obtained from bound-bound two-photon spectroscopy. Recent results obtained with an intense copper trimer source demonstrate an ability to (1) study fluorescence from strongly dissociative levels and (2) observe substantial temperature-dependent dynamic changes in spectral features associated with the fluxional nature of copper trimer. Using agglomerated cluster flows and taking advantage of previous experience in the study of chemiluminescent processes across a wide pressure range, we are probing the chemiluminescent emission resulting from the oxidation of small copper (Cu
x
+ O3), silver (Ag
x
+ O3), silicon (Si
x
+ NO2, N2O,O3), and germanium (Ge
x
+ O3, N2O) clusters. From these studies we have obtained the first quantal information on the energy levels and optical signatures of several metal cluster oxides and observed the manifestation of a unique dynamics associated with metal cluster oxidation processes.
Dynamics of cluster dissociation
Authors: Castleman A. W. , Keesee R. G.
Published: February 2023

Studies of cluster ionization and dissociation are of wide-ranging interest as they contribute to a further understanding of inter-molecular energy flow and energy disposal following multiphoton ionization, as well as on the changing properties of matter undergoing transitions from the gas to condensed phase. A major advance in the study of unimolecular dissociation and the spectroscopy of clusters has become available through the use of multi-photon ionization methods coupled with time-of-flight reflectron techniques. Using single and two-color pulsed lasers, the excess energy introduced into a cluster can be controlled. The power of the method is demonstrated by results of recent investigations of cluster fragmentation following internal ion-molecule reactions in hydrogen bonded cluster systems. The role of dissociation and the influence of the thermochemical stability of cluster ions in affecting the appearance of magic numbers in certain cluster distributions is discussed. The application of this method in studying spectral shifts and determining ionization potentials of probe molecules following successive clustering with a solvent species is also presented.
Ionic clusters
Authors: Kennedy Richard , Kung Chung-Yi , Foster Stephen C. , Miller Terry A.
Published: February 2023

Details of recent experiments involving charged clusters are described. In one experiment these clusters are prepared in a supersonic expansion and their laser-induced fluorescence spectra recorded. The clusters consist of a charged chromophore and neutral species bound to it. Results obtained include spectral shifts, cluster vibrational progressions, and resulting potential surfaces.
Photodetachment and photodissociation studies of semiconductor cluster ions
Authors: Liu Y. , Zhang Q. , O’Brien S. C. , Heath J. R. , Curl R. F. , Tittel Frank K. , Smalley R. E.
Published: February 2023

We have recently developed an ion source which is capable of producing both positive and negative semiconductor cluster ions cooled by supersonic expansion. Ions of a particular mass are selected and studied by laser photodetachment and photodissociation followed by time-of-flight mass analysis. The electron affinities (EA) of several semiconductor clusters have been measured by photodetachment threshold measurements on their negative ions. For GaAs clusters, an even/odd size alternation in EA is observed as in the ionization potentials of the neutrals, supporting the suggestion that the neutral even clusters have fully paired singlet ground states with no dangling bonds.1,2 Photodissociation studies reveal that negative silicon and germanium cluster ions fragment predominantly into 6–11 atom size clusters with 6–10 being the favorite fragmentation daughters.
Multiphoton excitation and ionization of atoms
Authors: Jara H. , Johann U. , Luk T. S. , McIntyre I. A. , McPherson A. , Schwarzenbach A. P. , Boyer K. , Rhodes Charles K.
Published: February 2023

New physical phenomena are expected to occur1 with irradiation of atomic and molecular materials with subpicosecond ultraviolet radiation at intensities above ~1018 W/cm2. One such phenomenon is electron-positron pair production.
Multiple excitation and ionization of atoms by strong lasers: is there any new physics?
Authors: Lambropoulos P.
Published: February 2023

Although, in certain conditions, a transition probability per unit time averaged over the laser pulse may be useful in interpreting general features of experimental results, in general events during the evolution of the pulse must be followed in detail because total ionization of various ionic species is apt to occur.1 As a result, at different stages of the pulse, processes of different order may appear. The end result is ionization. But a number of other processes such as wave mixing and lasing can coexist or even compete with ionization in the appropriate conditions. Employing calculated generalized cross sections, sequential ionization is calculated and shown to be the dominant mechanism in the conditions of recent experiments.2,3 But even in sequential processes, multielectron excitations may play a role in determining the cross section and the state of the ion. Examples of calculations in multielectron atoms illustrate the role of more than one electron excitation. Doubly excited states, for example, can in principle be employed in a sequence of transitions leading to a high lying doubly excited state. The probability of such transitions is estimated and the importance of various competing processes leading to sequential electron ejection is also discussed. In all cases, the structure of a particular atom and the frequency of the laser are found to play an essential role in the details of the process. Specific results pertaining to He, C, Sr, and Xe are discussed as examples of the behavior of multielectron atoms in strong laser fields.
High-resolution laser spectroscopy of atomic hydrogen
Authors: Hänsch Theodor W.
Published: February 2023

Recent advances in high resolution laser spectroscopy of the simple hydrogen atom are reviewed. Dramatic further improvements in resolution can be expected, promising unprecedented opportunities for tests of fundamental physical laws and for precision measurement of the Rydberg constant, the proton/electron mass ratio, and the charge radii of the proton and the deuteron.
Planning and implementing a formal test program for spaceflight instruments
Authors: Mauldin Lemuel E.
Published: February 2023

Effective test management is essential in flight hardware development. The test engineer faces the challenging task of developing management tools uniquely suited to the organization and hardware to be tested. The halogen occultation experiment (HALOE) project at the NASA Langley Research Center set up and successfully implemented an innovative management system for testing the HALOE instrument, an electrooptic remote sensor for the Upper Atmospheric Research Satellite. This paper presents the basic elements of that system. Although the details given may not be specifically applicable, they will provide the test engineer with helpful, general guidelines.
Practical aspects of designing a multiangle reflectometer
Authors: Nelson W. Titus , Livingston Rodney S.
Published: February 2023

In the course of designing a multiangle reflectometer the authors pursued several techniques which failed or were otherwise ill-conceived. The problems of designing a complicated, multidiscipline instrument are not always covered in books and advice from even well-respected colleagues can be misleading. Some of the topics discussed are experiences with optical components, coatings, data acquisition, and laser noise. The advantages of mounted sheet polarizers over Glan-Thompson prisms is dealt with.
Extended Foerster-Dexter model for correlated donor-acceptor placement in solid-state materials
Authors: Hartmann Francis X. , Rotman Stanley R.
Published: February 2023

In models of nonradiative energy transfer applied to doped solid-state laser materials, the distance between excited donors and neighboring acceptors critically affects the calculated energy transfer rates. In the generally successful formulation of nonradiative transfer theory,1 the donors and acceptors are taken to be distributed evenly throughout the crystal and are independent (uncorrelated) in position. We derive a general expression to treat donor-acceptor transfer rates for locally correlated donor-acceptor placement. Several specific cases appropriate to actual laser materials are (1) an excluded volume around a donor diminished in acceptor concentration and (2) an enhanced volume around a donor in which acceptors preferentially locate. Physical effects which can lead to such microscopic distributions are discussed.
Moving slab Nd:glass laser: experimental results
Authors: Basu Santanu , Byer Robert L.
Published: February 2023

The average power output from a Nd:glass slab laser is limited by thermal stress fracture because of the low thermal conductivity of glass. The moving slab laser concept increases the average output power much beyond the limit of the static slab lasers. In the moving slab laser the average thermal power is dissipated over the area of the slab while the gain is concentrated in a small region. The result is a gain enhancement and average power scaling of the area of the slab. In our first design we used a Brewster angle cut, zigzag path rectilinear slab of LHG-5 glass, 16.7 × 15 × 0.44 cm, which moved back and forth between two 4-mm diam krypton lamps and metal cooling plates by means of a computer-controlled linear motor. Static helium gas was used to thermally couple the glass to the cooling plates. At the limit of our power supply we obtained 43.8 W of average laser at 276 J/pulse and at 10-Hz repetition rate. At 30-Hz repetition rate and at 32 J/pulse the laser output was 13.5 W. The moving slab Nd:glass laser is in the process of scaling up to 300-W and 1-kW average power levels in two states of development.
Large GSGG:Nd,Cr boule growth and quality
Authors: Stokowski S. , Shinn M.
Published: February 2023

Gadolinium scandium gallium garnet codoped with Nd and Or (GSGG:Nd,Cr) is the laser material with the highest measured efficiency. Thus it has great promise for use in laser systems where efficiency, power, and beam quality are desired. As part of a program on developing slab lasers with multikilowatt outputs, we are growing 5-in. diam GSGG:Nd,Cr boules, from which we will cut 10- × 20- × 1-cm3 slabs. Our efforts have focused on using the Czochralski growth technique, which has proved successful in growing commercially large GGG. We constructed a station that we modified to incorporate a 9-in. diam by 9-in. deep iridium crucible. The melt charge is 50 kg and we pull ~35-40% of the melt. In this system we have pulled 5-in. diam undoped GGG, undoped GSGG, and codoped GSGG. In the course of this effort we have solved a spiral growth morphological problem by using calcium additions to the melt. However, to prevent forming Cr4+, which is a 1-μm absorber, we are employing the Ce3+-Ce4+ couple to compensate for the Ca% We present data on boule quality: birefringence, wavefront distortion, and absorption losses
Neodymium glass waveguide lasers
Authors: Djibladze M. I.
Published: February 2023

Generation and amplification characteristics are presented for solid-state lasers with neodymium silicate glass waveguides (60μm and 1 mm in diameter clad with passive envelopes) as their active elements. Their characteristics have been studied, and the possibility of obtaining powerful stimulated radiation with a predetermined radiation field distribution in the near zone was demonstrated. The optical coupling of separate waveguide active elements, causing the synchronous generation of groups of active elements, was also investigated. The essential role played in generation and amplification by the short-lived color centers developing in silicate glasses exposed to the violet component of the pumping spectrum was demonstrated. These IR-absorbing centers give rise to Q-switching of the waveguide resonator, resulting in emission of periodic giant pulses. When these color centers were absent, a quasi-continuous generation mode with relaxation oscillations was realized. The short-lived color centers can be described as weakly coupled excitons with a potential well depth of ~0.1 eV. Interaction of the photons emitted by neodymium with such color centers leads to their induced decay, causing bleaching and Q-switching. The influence of the color centers on amplification in active waveguides appeared significant: along with the light pulse amplification an appreciable (more than twofold) shortening of the amplified pulses was observed. A study of the sequence of ultrashort pulses revealed that the main reason for pulse compression is the induced decay of the short-lived color centers after absorbing part of the amplified pulse leading edge. Part of the amplified pulse leading edge is used in annihilating short-lived color centers, while the remainder is amplified more effectively due to lower color center losses.
ScBO3:Cr—a new room temperature near-infrared tunable laser
Authors: Lai Shin T. , Chai B. H. T. , Long M.
Published: February 2023

We report the first Cr3+ laser in a borate host crystal. The free-running laser wavelength was 843 nm in a nearly concentric laser cavity pumped by a krypton-ion laser at 647.1 nm. With a single element birefringent filter, a tuning range of 787-892 nm was measured using the first optically clear crystal. The output power slope efficiency was 29% lasing at 848 nm with an output coupler of 1.78% transmission. The laser round trip loss, including a possible excited state absorption, was calculated to be 1.3% cm. Spectroscopic measurements indicated that the material was clear of absorption loss in the lasing spectral region, and the relative fluorescence efficiency for the entire Cr absorption band in the visible region was nearly unity. The fluorescence lifetime at room temperature was 115µS. A study of lifetimes vs temperatures showed that the multiphonon relaxation process had an onset temperature of ~ 340 K. The peak emission cross section was calculated to be 1.2 × 10−20 cm2 at 873 nm for the c-axis polarization.
Two-wave mixing in liquid suspensions of microparticles
Authors: McGraw R. , Rogovin D.
Published: February 2023

Liquid suspensions of microparticles are two-component media with novel electromagnetic properties. For these media, laser-generated electrostrictive forces and torques can modulate the microparticle density and orientation in such a way as to alter the dielectric constant of the composite. In turn, this change gives rise to the formation of microparticle gratings which can serve as a nonlinear medium. For example, suspensions have been utilized to generate phase conjugate radiation in the visible. In addition, self-focusing and optical bistability have also been demonstrated at visible wavelengths. Here we examine the possibility of another nonlinear process occurring in these media; namely, coherent beam combination. Specifically, we examine the nonlinear response of a liquid suspension of microspheres to two nearly degenerate laser beams. These two waves create a moving grating composed of microparticles vibrating at the difference frequency. In turn, this oscillating grating scatters radiation from the higher frequency wave into the lower frequency beam via a process similar to stimulated Raman scattering, with the grating assuming the role of the acoustic wave. For a suspension composed of 10−3 volume fraction of 0.34-µm latex spheres in water, the nonlinear coefficient ϰ = 2.91 cm−3,with/the laser intensity in kW/cm2 at DF wavelenghts.
Explosion of droplets
Authors: Chitanvis Shirish M.
Published: February 2023

We prove that Maxwell’s equations for a deformable medium and the hydrodynamic equations together admit a self-similar set of solutions, under the assumption of spherical symmetry. As an example, we use our self-similar equations to study the motion of vapor expelled by a water droplet which is being heated by a high energy laser beam.1 We predict a vapor blowoff at high laser energies that depend on the optical properties of the aerosol. We shall attempt a qualitative comparison with the experimental results2 of Chang’s group at Yale.
Effect of aerosol particles on laser-induced breakdown
Authors: Chylek Petr , Jarzembski M. , Pinnick R.
Published: February 2023

Radiation from a pulsed Nd:YAG laser (wavelength 0.532μm) was used to investigate the effect of size and refractive index of liquid spherical aerosols on the breakdown threshold. The threshold breakdown intensity decreases with increasing droplet size; in most cases, however, no simple general dependence on refractive index has been found. Thus, the size and the refractive index are not sufficient to determine the breakdown threshold and other physical and chemical properties of aerosols have to be considered.
Longitudinal mode width in excimer lasers
Authors: Lombardi Gabriel G. , Long William H.
Published: February 2023

The time-averaged width of individual longitudinal modes of a multimode XeCl discharge laser oscillator was measured using time-delayed interferometry, a technique related to Fourier-transform spectroscopy. The beam from the laser was divided by the beam splitter of a Michelson interferometer. The arms of the interferometer were adjusted so that their lengths differed by an integral multiple of the laser cavity length. Interferograms were recorded using a CID camera and a videocassette recorder. Measurements of the interference fringe visibility, made at path length differences of up to three times the cavity length, were used to calculate the width of the longitudinal modes, averaged over the laser pulse. The width inferred in this way exceeds the transform-limited width by a factor of 7. This discrepancy is attributed to the time-varying refractive index of the gain medium, which causes the resonant frequencies of the optical cavity to change during the laser pulse. This phenomenon limits the temporal coherence of such lasers, unless a compensating change is made in the cavity length. The time-dependent populations of the atomic and molecular levels predicted by a computer model of the discharge plasma were used to calculate the refractive index. The principal cause of the refractive- index change was found to be the dissociation of HCl. A simple model of the effect of the time-varying refractive index on the laser frequency predicts fringe visibilities in good agreement with measured values.
Saturation of CARS resonances using multimode lasers: calculation of saturation line shapes and intensities
Authors: Lucht Robert P. , Farrow Roger L.
Published: February 2023

Saturation of coherent anti-Stokes Raman scattering (CARS) line shapes via two-photon pumping has been observed for vibrational Q-branch transitions in gas phase nitrogen using a single-axial mode pump and Stokes lasers.1 Saturation and line shapes for the single-axial mode case were calculated by solving the time-dependent density matrix equations for the nonlinear Raman interaction. The results of the calculations showed excellent agreement with experiment.