bluuebunny/crossref_metadata_2025 huggingface dataset:
A Refractive-Index Interpolation Fit Criterion for Materials Used in Optical Design
Authors: Komiski Ronald J.
Published: February 2023

Optical designers need to know the index of refraction of optical materials in order to design and accurately predict the performance of an optical system. The indices must' be known at wavelengths that are pertinent to the system being designed not the ones in the vendor's brochure or the technical publication where the data was found. For optical glasses, the vendors have been aiding the designer since the late 1960s by providing an interpolation formula and coefficients. This allows the designer to accurately determine the index of the glass at any wavelength in the visible and very near infrared. Infrared or ultraviolet transmitting materials usually do not have vendor supplied coefficients, and the raw index data available is often of uncertain accuracy. What does a designer do when he needs the information after the glass has passed the inflection point in its dispersion curve or needs to use an optical material other than glass?
The Design of High Performance Aplanatic Achromats For The Blue and Near Ultra-Violet Waveband
Authors: Al-Baho T. I. J. , Learner R. C. M. , Maxwell J.
Published: February 2023

Medium aperture thin achromatic aplanatic doublets manufactured from
optical glass offer a cost effective solution for some high performance applications [1].
Easily Fabricated Wide Angle Telescope
Authors: Owen R. Calvin
Published: February 2023

This paper describes an easily fabricated telescope which forms a high quality image of an extremely wide angle object field on a flat image surface. The telescope uses only reflectors, and thus has no chromatic aberrations. An eccentric portion of the symmetrical field of the telescope is used, such that no part of the aperture is obscured. The mirrors are surfaces of revolution described exclusively as flats, spheres or conic sections, all of which are easily tested and verified in manufacture using well-known, conventional null tests. Each mirror shares a common axis, facilitating telescope alignment. One mirror is used twice, providing the function of a secondary and tertiary mirror, while eliminating the need to align a separate tertiary mirror.
A Theory of Color Correction by Use of Chromatic Magnification
Authors: Ames Alan J.
Published: February 2023

This paper considers a novel approach to color correction by a compound lens group with an adjacent single thin aplanat, which introduces chromatic magnification.
Prescribed Profile Gradient Index Glasses Of Macro Dimensions and Large ΔN
Authors: Blankenbecler Richard , Hagerty James J. , Rindone Guy E.
Published: February 2023

New gradient index glasses of macro dimensions, large Δn's, in controlllable index profiles have been developed. This new lens material will enable a realization of new optical design possibilities.
Dynamics of ablation of tissue with 193-nm pulses
Authors: Srinivasan R.
Published: February 2023

The mechanism by which UV laser pulses bring about the etching of tissue surfaces with a minimum of thermal damage to the substrate has been a matter of controversy. There are two aspects to this problem which are: (i) the reaction path in which the chemical bonds are actually broken, and (ii) a quantitative model of etch behavior as a function of pulse width, wavelength, and fluence. The second aspect is addressed here. A model is proposed1 which relates the time-dependent passage of the laser pulse to experimental parameters which control the etch behavior. A photochemical mechanism is assumed and the rate of decomposition of the polymer in its excited state is viewed as a process which competes with alternative processes which do not lead to decomposition. The width of the laser pulse is a critical factor because it is only the flux of absorbed photons above a threshold value that will be available for bond-breaking. The predictions made from this model regarding the relationship between the pulse width and fluence thresholds are being tested and have yielded encouraging results.
In praise of tomography
Authors: Goulard Robert
Published: February 2023

The images of semitransparent objects, if taken from many angles or at many frequencies, can be reconstructed into an accurate description of such objects. These methods can be used with radiation or acoustic beams, in emission or absorption, on intensities or phase velocities, or in any hybrid combination of the above. In this paper, the back filtering methods are compared with the iterative superposition methods. The problems arising from the desirability of both wide angular coverage and high speed measurement rates are considered in the context of various fluid dynamics cases.
Multibeam laser vibrometry for materials and structure evaluations
Authors: Fitzpatrick G. L. , Skaugset R. L.
Published: February 2023

At tripod-mounted system for making multibeam laser Doppler measurements has been constructed and is currently undergoing further development and testing. Such a system holds great promise in applications ranging from the evaluation of rock structures (a purpose for which it was originally intended) to the inspection of modern aerospace composite materials. The system has a number of unique features. It employs separate send and receive telescopes (Maksutov Cassegrain design) and an optical fiber grating (25 μm or larger optical fibers arranged in a grating or crossed gratings) located in the send scope for producing the sampling laser beams on a distant target (5–30 m or greater). The associated electronics currently processes four channels corresponding to four laser spots on the surface of interest. Measurements of the relative arrival times of an elastic wave disturbance, the peak particle velocity, and the average frequency of motion of the surface are displayed in numerical format. Experimental results on a range of targets are presented. Plans for an eight-beam, tripodmounted system, and systems with square arrays, are also described.
Studies of adiabatic dissociation in angular velocity and internal-state distributions of atomic fragments
Authors: Gerber Gustav
Published: February 2023

We discuss the nature of nonadiabatic coupling in state-to-state dissociation dynamics. Illustrative examples will be drawn from our experiments on alkali and alkaline earth dimers.
New application of a traditional Chinese medicinal sclerosing agent in combination with a YAG laser for the treatment of cavernous hemangioma of the eyelids and conjunctivae
Authors: Zhou Yo-Cheng
Published: February 2023

The treatment of cavernous hemangioma of eyelids and conjunctivae in the maxillo-facial region is a difficult problem. Radiotherapy, surgical excision, and cryotherapy are harmful to the eyeball and its surrounding tissue. Also, a laser beam is hard to handle when applied to the conjunctivae. A new technique of ablating these lesions using a traditional Chinese medicinal sclerosing agent, 10% liquid alumen, with a YAG laser was used to treat cavernous hemangioma of the eyelids and conjunctivae satisfactorily. Advantages of this combined therapy include: (1) superb hemostasis; (2) simplicity, safety, and effectiveness; (3) no damage to eyeball and its surrounding tissue; (4) avoidance of reconstructive procedures; and (5) minimal or no postoperative pain or other side effects.
Doppler-free two-photon-excited fluorescence spectroscopy of OH in flames
Authors: Goldsmith John E. M. , Rahn Larry A.
Published: February 2023

We have used Doppler-free two-photon-excited fluorescence spectroscopy to fully resolve the pressure-broadened line shape of OH A2Σ+ ← X2Π transitions in low-pressure flames. This method uses two counterpropagating laser beams to excite the transition. Since the Doppler shifts for the two beams exactly cancel, the resulting signal consists of a sharp Doppler-free peak centered on a Doppler-broadened and much weaker background. Because measurements were made in the postflame gases of low-pressure stoichiometric hydrogen–oxygen flames, water was the dominant collision partner. A narrowband pulse-amplified cw ring dye laser system with a FWHM bandwidth of 45 MHz at 620 nm made it possible to fully resolve the OH linewidth at pressures down to 20 Torr. All the observed transitions consisted of doublets due to hyperfine splitting of the OH A2Σ+ state. Values of the broadening and shift of OH transition line shapes due to collisions with water measured using this technique are reported.
Laser-induced etching
Authors: Ashby Carol I. H.
Published: February 2023

There are three categories of laser-assisted chemical reactions which have been employed to etch metals, semiconductors, and other inorganic materials. Lasers can be used to locally heat a solid to accelerate the rate of a thermally activated process. This is the most universally applicable method of laser-induced etching. Alternatively, the laser can be used to generate reactive gas-phase or liquid-phase species by photolytic decomposition of precursor molecules. Appropriate reactants have been identified for a wide variety of materials. Finally, the laser can be used to create photo-generated electrons and holes in semiconductors; these carriers then participate directly in the etching process. Highly selective etching can be achieved by capitalizing on the surface electronic properties which influence carrier generation or subsequent behavior. These three types of laser-induced reaction are reviewed.
Laser-induced vapor deposition of gold
Authors: Baum T. H.
Published: February 2023

Dimethylgold (III) acetylacetonate and its fluorinated derivatives are ideal precursors for the deposition of gold. Thermal decomposition from the vapor phase allows high quality metal to be produced. A comparison of the gold complex utilized and the overall rates of deposition are highlighted; the presence of fluorine substituents in the complex causes an increase in the complex vapor pressure and in the observed rates of gold deposition.
Laser excitation spectroscopy: a probe of metal ion binding in polymers
Authors: Wong Eric K. L. , Richmond Geraldine L.
Published: February 2023

The structure and the function of many macromolecules and organic polymers are dependent on the specific sites bound to metal ions. Metal binding in some ionic polymers is in the form of ionic clusters. The objective of our laser-induced fluorescence studies is to gain a better understanding of the structure and binding properties of these clusters by using europium ions as probes. Eu(III) has many unique spectral properties which make it a good luminescent probe of the metal binding in polymers. The energy, fluorescence quantum yield, and lifetime of the excited state of the 7F0 → 5D0 transition near 580 nm are very sensitive to the environment of the ions. By studying this transition in detail, it is possible to obtain unique optical information about the metal–molecule interaction. Metal binding in the perfluorosulfonate membrane, Nation (DuPont), has been studied here as function of such parameters as metal ion concentration and pH. The resulting excitation spectra show multiple peaks corresponding to different ionic environments. The results of these experiments are discussed in terms of the known macroscopic binding properties of this film.
Short pulse laser-produced plasma x-ray sources
Authors: Campbell E. M. , Landen N. , Perry M. , Kruer W. L.
Published: February 2023

The interaction of intense laser radiation (l > 1013 W/cm2) with plasmas has been extensively studied for the past decade. Since the primary motivations for these studies has been laser-driven inertial confinement fusion and XUV laser research, pulse lengths have ranged from 20 ps to > 1 ns with the majority of experiments being conducted with pulses longer than 100 ps. The physics characterizing the laser-plasma coupling in such experiments is qualitatively well known with the intense laser pulse interacting by a variety of processes with a low density (ne ≲ n
c
≃ 1021 λ−2 μm, λ is the laser wavelength) rapidly expanding (v > 107 cm/s) plasma that forms early in the pulse. The interaction of intense ultrashort pulses (τ ≲ 1 ps) with plasmas, however, has not been extensively studied. The physics are of fundamental interest in the study of the early formation of laser plasmas, energy transport, and of the generation of ultrashort x-ray bursts. Such x-ray flashes, if sufficiently short, would be useful as a probe for exciting and studying relaxation processes in solids, in high resolution x-ray imaging, and in characterizing the impulse response of a wide number of x-ray detectors. In this presentation, we describe the results of a series of experiments characterizing the x-ray emission of a high density plasma irradiated with a 1-ps, 1–2-mJ dye laser focused to peak intensities of 1013 to 2 × 1014W/cm2. Measurements of the total yield of XUV and x-ray energy (50 eV to 3 keV) spectra, and spatial and temporal characteristics of the emission are reported.
Time-resolved x-ray diffraction and spectroscopy using synchrotron radiation
Authors: Mills Dennis M.
Published: February 2023

Although the pulsed nature of the radiation emitted from storage rings has for some time been exploited for studies in the visible vacuum ultraviolet region of the spectrum, only recently have synchrotron radiation users begun experiments that emphasize time resolution. Time-resolved x-ray experiments performed at synchrotron radiation sources fall naturally into two categories, those which do not depend on the actual time structure of the emitted radiation but rather rely on the high flux, and those which take explicit advantage of the modulated or pulsed nature of the x-ray beam. Although not always the case, experiments of the latter group generally have a finer time resolution and it is with these experiments that this presentation is concerned. Pulse durations of 100-1000 ps are most typical for synchrotron radiation sources with repetition rates from 0.5 to 50 MHz. These characteristics combined with the continuous spectral distribution make synchrotron radiation a highly attractive source when compared with other sources of pulsed x rays. In fact synchrotron radiation has been used both as a pump and a probe beam for the study of transient phenomena. Shorter pulses and high flux per pulse may soon be a reality with construction of advanced photon sources planned for the near future.
Silver clusters as the active sites for surface-enhanced Raman scattering
Authors: Furtak Thomas E. , Roy D.
Published: February 2023

We have identified the long debated origin of the short-range component of surface-enhanced Raman scattering (SERS) as

Ag

4
+

clusters which are stabilized by co-adsorbed molecules or by low substrate temperature on rough Ag surfaces. The assignment has been supported by vibrational mode calculations which include the effects of adsorption of the cluster, image interaction with the metal, and co-adsorbed anions in the electrochemical environment. The observed modes at 73, 110, and 161 cm−1 correspond to those calculated at 75, 100 and 118, and 170 cm−1. The adsorbed clusters act as Lewis acid sites onto which other molecules such as pyridine are bonded thus leading to SERS beyond the usual electromagnetic factor which is due to macroscopic roughness. The mechanism of the added enhancement is through charge transfer excitation between the adsorbed molecules and the clusters and through HOMO—LUMO transitions within the cluster.
Optical properties of fractal clusters
Authors: Sheng Ping , Chen Z. , Lindsay H. M. , Weitz D. A. , Meakin P.
Published: February 2023

Optical scattering and absorption characteristics of fractal clusters are calculated with a self-consistent scheme in which the multiple scattering and local field effects are treated exactly in the dipole approximation. Our results indicate that for optical scattering the gold colloidal aggregates with fractal dimension D = 1.75 behave essentially as low dimensional objects and therefore can be accurately described by the (single-scattering) Born approximation. However, the absorption spectrum of the clusters is shown to be significantly affected by the proximity of the gold particles to their nearest neighbors in the aggregate structure. Comparison with experimental data is shown.
Multilaser threshold photoionization spectroscopy of jet-cooled moles and Van der Waals clusters
Authors: Wallace Stephen C.
Published: February 2023

The dynamic properties of the excited states of polyatomic molecules show a considerable sensitivity to intermolecular interactions, both in terms of lifetimes and photoionization thresholds. Using multilaser, threshold photoionization spectroscopy in conjunction with picosecond time-resolved fluorescence emission studies, it has been possible to characterize the fundamental photophysical properties of a range of model biological molecules in a supersonic beam. A number of novel features, such as conformational effects on photoionization thresholds, solvent-induced interstate decoupling, femtosecond radiationless transition rates, and cluster ion stabilization energetics are presented.
Photodissociation dynamics of small cluster ions
Authors: Bowers Michael T. , Kim Hyun-Sook , Kuo Chau-Hong
Published: February 2023

In the last several years we have developed methods for studying the photodissociation dynamics of small cluster ions.1 The method consists of crossing a fast (8-keV) mass-selected cluster ion beam with a polarized laser beam and performing mass and energy analysis on the products. Changing the laser polarization also allows product angular distributions to be obtained (asymmetry parameter analysis). The method allows determination of photodissociation cross sections, branching ratios, product kinetic energy distribution, internal energy distributions (in favorable cases), symmetry of the photoabsorption transition, nature of the excited state photoaccessed (bound or repulsive), and information on the dissociation mechanism. Approximately twenty systems have been studied so far. We concentrate on (SO2)2. Results have been obtained between 600 and 350 nm (2.07 and 3.54 eV). Over most of this range photodissociation dominates over photodetachment. Details of the photodissociation mechanism and observations about the excited states accessed are given.
Photodissociation dynamics of cluster anions
Authors: Castleman A. Welford , Albertoni C. R. , Marti K. , Hunton D. E. , Keesee R. G.
Published: February 2023

Studies of the dissociation dynamics of cluster ions provide insight into the process of energy disposal for mass-selected species. Detailed investigations of the photodissociation of the cluster anions

(

SO

2

)

2
−

and

CO

3
−

(

H
2

O

)

n

(
0
≤
n
≤
3
)

have been accomplished for mass-selected ion species using an intracavity dye laser pumped with an argon-ion laser. in the case of

CO

3
−

, the unhydrated parent ion is observed to have a bound electronic excited state through which absorption of a second photon proceeds to a repulsive state leading to the ejection of O-. There are two possible mechanisms for

CO

3
-

hydrate dissociation: one is a repulsive and the second a predissociative mechanism. In both, cluster dissociation is initiated by the same

2

A
1

←
2

B
1

transition from the ground to a weakly bound excited state of the core ion and leads to the loss of all water molecules within the time of observation. In the photodissociation of

CO

3
-

,

CO

3
-

(

H
2

O

)

1
,
2
,
3

, and

(

SO

2

)

2
-

considerable excess energy is partitioned into relative translation of the photoproducts. Through studies of energy release in

(

SO

2

)

2
-

with photons of parallel and perpendicular polarization, evidence has been obtained that the lifetime of the complex preceding photodissociation is less than a rotational period. The implications of the findings are discussed in terms of phase space theory.
Quantum mechanics of classically chaotic systems
Authors: Heller Eric J.
Published: February 2023

We begin by discussing the properties expected of eigenfunctions of a classically chaotic Hamiltonian system using simple Correspondence Principle arguments. The properties involve nodal surfaces, coordinate and momentum space amplitude distribution, and phase space distribution. The eigenfunctions of the stadium billiard are examined, and it is found that the periodic orbits of shortest periods and smallest stability parameter profoundly affect the eigenfunctions: scars of higher wavefunction density surround the special periodic orbits. Finally a theory is presented for the scars, showing that they must exist, and relating them directly to the special periodic orbits. These same periodic orbits cause level density fluctuations.
Pulse propagation in molecules
Authors: Ackerhalt Jay R. , Milonni Peter W.
Published: February 2023

The propagation of infrared laser pulses through a molecular medium is studied theoretically. It was shown previously that the classical time dynamics of single molecule MPE is chaotic leading to a fluence-dependent excitation.1 Therefore, it is important to study the effect of the chaotic molecular dynamics back on the laser pulse envelope and to compare the results with experiment. The primary emphasis of this work is to understand the spatiotemporal coherence of the laser pulse envelope.
Molecular spectra and dynamics using coherent optical methods
Authors: Hochstrasser Robin M.
Published: February 2023

Nonlinear spectroscopy has proved to be very useful in learning about dynamic processes in molecular systems. The multiple field configuration allows more information to be obtained than is available from linear spectroscopic or time domain measurements. Results on coherent Raman effects, high field Raman effects, transient three- and four-wave interactions and highly resonant responses of molecules in liquids and solids are presented. Some four-wave effects such as DICE are extremely useful in discerning excited state dynamics. The effects of inhomogeneous line broadening in determining the nonlinear response are also discussed along with some new examples of line narrowing in anticorrelated distributions.
Femtosecond time-resolved impulse-stimulated Raman scattering: recent experiments and theory
Authors: Nelson Keith
Published: February 2023

Coherent terahertz-frequency optic phonon oscillations and decay are observed directly by femtosecond time-resolved impulsive stimulated Raman scattering. This time resolution permits study of vibrational dephasing and relaxation in organic molecular crystals at high temperatures (> 300 K)as well as low temperatures. The results can be used to deduce the microscopic mechanisms through which vibrational equilibrium is reached in these crystals. Current experiments aimed at direct measurement of homogeneous and inhomogeneous vibrational dephasing times as well as vibrational population lifetimes are discussed. Finally, preliminary results of similar experiments on low-frequency vibrations of molecules in solution are presented and discussed. The possibilities for measurement of electronic excited state-phonon interactions and observation of large-amplitude vibrational motion are suggested.
Ultrasensitive coherent Raman technique with picosecond lasers
Authors: Schauer Mark , Pellin M. J. , Biwer B. M. , Gruen D. M.
Published: February 2023

The sensitivity of the Raman-induced Kerr effect is greatly enhanced through the use of picosecond lasers. Experiments in dilute solutions of benzene indicate that sensitivity at the monolayer level is achievable. Applications to transparent media, to fluorescing samples, and to in situ measurements of electrode surfaces are discussed. Comparisons are made to surface-enhanced Raman spectroscopy and to coherent anti-Stokes Raman spectroscopy.
Coherent pump dynamics, depletion, and transverse effects on the superfluorescence/Stokes/probe (SF, St, Prb) beam buildup and its asymptotic evolution of a stabilized on-axis swept-gain Raman forward amplifiers/spectroscopy studies
Authors: Mattar F. P. , Berman P. R.
Published: February 2023

A computer movie illustrating a rigorous multimode calculation of SF, St, Prb buildup in Raman studies is presented. This coherent copropagational study based on Maxwell-Bloch formalism1 includes phase and transverse variations, nonlinear asymmetric dispersion, pump spatial depletion, and time-dependent variations in population inversion density. Theλ scheme is selected so that the active transitions are optically thick for both the pump (α
p
l > 5) and the SF (α
sf
l > 35) pulses. This choice of Beer lengths, i.e., of oscillator strengths, insures that the two pulses never cease to overlap and optimizes the SF initially small signal growth. The pump interacts like a self-induced transparency while the SF, St, Prb evolves as a small-area in a two-level emitter which can be described as a nonlinear pendulum in the pane wave. For a given ratio of Beer lengths, distinct Fresnel numbers, atomic density numbers, small signal SF, St, Prb time-integrated energy stabilization or self-focusing may arise, as observed experimentally. For a sufficiently larger propagation distance, an asymptotic evolution of a quasisolitary nonhyperbolic-secant pulse of constant area is reported.
Optical ray tracing for crossed beam photothermal deflection spectroscopy
Authors: Sell Jeffrey A.
Published: February 2023

A geometrical algorithm for optical ray tracing is used to trace the trajectories of probe laser beam rays in photothermal deflection spectroscopy (PDS) of a static gas. Rays are traced as a function of various parameters such as time, pump beam energy, radius, pulse duration, and absorber gas concentration. The exit angle is also computed and compared with the deflection angle calculated analytically, with very good agreement for a pump pulse duration shorter than the thermal diffusion time. For a long pump pulse duration, the analytical expression is inaccurate due to the neglect of thermal diffusion during the pump pulse. Probe beam ray crossing is examined and found to be unimportant for most common PDS situations. The saturation of the PD signal is found for high absorber concentration or pump pulse energy; this is due to excessive heating of the absorber. Finally, the maximum probe beam deflection occurs when the deflection is measured at a time corresponding to the end of the pump pulse.
Spectroscopy of new chromium/neodymium-doped oxide laser materials: garnets and aluminates
Authors: Boulon G. , Garapon C. , Monteil A.
Published: February 2023

Applications to laser materials processing requires a novel solid state laser characterized by higher efficiency and larger output energy than the standard commercial materials. There is a revival of interest in the laser-type materials doped either by rare-earth ions (Nd3+, Er3+, Ho3+) or by metal-transition ions (Ni2+, Co2+, V2+, Cr3+, Ti3+). The spectral range of the emission is located in the near infrared and we have the possibility to obtain both a single-frequency laser with rare-earth centers and a tunable-frequency laser with metal-transition centers. In this paper we deal with: Nd3+-doped GGG-type garnets and Nd3+-doped lanthanum magnesium aluminate; Cr3+-doped GGG-type garnets and Cr3+-doped lanthanum magnesium aluminate; Cr3+/Nd3+-codoped GGG-type garnets.
Full aperture triple-pass Nd:YAG laser amplifier
Authors: Krasinski J. , Aschoff H. , Pete J. , Heller D. F.
Published: February 2023

Single- and double-pass amplifier configurations that can efficiently extract stored energy over the entire aperture of the gain medium are commonplace; so too are multipass configurations where each pass through the medium extracts energy over aslightly different spatial path. Usually these latter require critical alignment and are limited to an effective extracting aperture that is less than that of the gain medium.
Mode control of high efficiency diode pumped Nd:YAG laser
Authors: Kortz H. P. , Adlas
Published: February 2023

For optical pumping of Nd:YAG lasers with diode lasers the collinear end pump geometry has become the scheme of choice. Conditions for overlap and its influence on the control of transverse modes are the subject of this paper. In addition to the requirement of matching the size of the pump beam to the diameter of the lasing mode (usually the TEM00 mode) one must also try to achieve a small mode diameter to obtain high enough intensities and thus reach lasing threshold. While this is fairly straightforward for single stripe diode lasers, the task becomes quite different for multiple stripe diode laser arrays which have a higher total power but no higher brightness. Focusing to a tight spot size will also result in a very short focal range and a highly divergent pump beam, which will become larger than the TEM00 mode size before it can be fully absorbed.
Laser trapping of Rayleigh particles by a single-beam gradient force optical trap
Authors: Ashkin A.
Published: February 2023

The principles of the single-beam gradient force optical trap are considered. Laser trapping and manipulation of individual sub-micron colloids, viruses, and bacteria have been observed for the first time. Light scattering measurements were made from single particles and fixed arrays of particles. Methods of measuring particle size and orientation are discussed. Optical separation of individual particles is possible. The single-beam gradient trap operates over a range of 105 in particle size. Its use opens much of the submicron Rayleigh size range to optical trapping manipulation.
Studies of enzymes by resonance Raman spectroscopy
Authors: Carey P. C.
Published: February 2023

By creating a resonance Raman probe in the active site of an enzyme, it is possible to obtain the vibrational spectrum associated with those bonds undergoing catalytic transformation. The approach involves reacting thionoesters RC(= S)OCH3 with a class of enzymes known as cysteine proteases which have an essential SH group in their active sights HS-enzyme. The reaction produces an intermediate RC(= S) S-enzyme which is a dithioester with a λmax near 315 nm. The 324-nm excited RR spectra of the dithioester provide a wealth of detail on the substrate during catalysis; the confirmation of the substrate in the active sight can be monitored and characterized, structure rate constant relationships developed, reaction pathways mapped, and evidence sought for geometric distortion. The novel findings stemming from the RR data are difficult to reconcile with the conventional view of enzyme mechanism.
Resonance Raman spectra and solvation dynamics of transient dihalide radical ions in aqueous solution
Authors: Tripathi G. N. R.
Published: February 2023

The upper electronic states in the near-ultraviolet transition (2Σ
g
←2Σ
u

+
) of dihalide radical ions

(

Cl

2

⋅
¯

,

Br

2

⋅
¯

,

I
2

⋅
¯

)

are known to be dissociative. We have observed the resonance Raman spectra of these highly reactive species (and also

Cl
 

Br

⋅
¯

) prepared by pulse radiolysis methods in aqueous solution. The resonance Raman observations combined with low photodissociation yields (10-24%) indicate that the excited state lifetimes are of the order of vibrational period of the radical molecules. From the extrapolated convergence of the vibrational progressions in the Raman spectra, the bond dissociation energies are evaluated as 1.6, 1.3, and 0.9 eV for

Cl

2

⋅
¯

,

Br

2

⋅
¯

,
 
and
 

I
2

⋅
¯

, respectively. Overtone linewidths in the resonance Raman spectra are observed to increase linearly with the vibrational quantum number, and loss of discreteness is evident at much lower energies than the dissociation limits. The dissociation energies calculated on the basis of solvation energies of the product ions are considerably lower than the spectroscopic values and compare well with the energies corresponding to the loss of discrete vibrational structure. The above observations can be reconciled on the basis of the solvation dynamics of the dissociative Σg+ state of the radical ions at ~10-12-s time scale.
Laser Raman phonon spectroscopy of solid-state photoreactions: photodimerization of O-methoxy trans cinnamic acid
Authors: Ghosh Urmi , Misra T. N.
Published: February 2023

Solid-state photodimerization reaction of O-methoxy trans cinnamic acid has been studied by laser Raman phonon spectroscopy. The progress of reaction has been estimated by monitoring the monomer 315-nm electronic absorption band which decreases in intensity with reaction progress and disappears in the dimer spectrum. The disappearance of the aliphatic C = C stretching monomer mode 1622 cm−1 in the infrared spectrum of the dimer suggests cyclobutane ring formation. Other infrared features also suggest four center type dimerization. In the monomer crystal, Raman phonon bands are observed at 32.5,57.5,65,89,95.5, and 160 cm−1. With reaction progress the sharp 32.5-cm−1 phonon shifts to lower frequency and finally disappears. This suggests softening of this mode with reaction progress and that the reaction is mediated by this phonon. This is the first example of phonon mode softening in solid state photoreaction. In the partially dimerized crystal, the monomer phonon bands lose their intensity and new phonon bands appear. When the reaction is almost complete, a new phonon spectrum is observed. The appearance of the segregated phonon spectra in the partially dimerized crystal suggests that the reaction is heterogeneous and the reactant and the product form separate lattices.
Droplet whispering gallery mode laser
Authors: Campillo A. J. , Lin H.-B. , Eversole J. D.
Published: February 2023

We report lasing characteristics of 40-60-µm diam rhodamine 590:water solution droplets pumped by 532-nm Q-switched pulses. Water was employed to avoid competition from whispering mode stimulated Raman scattering normally encountered in the alcohols when using nanosecond or shorter pulse excitation. We have been able to establish the threshold and find that the low level for lasing (104 W/cm2 for 10−4-M solution) is consistent with cavity Q approaching 104. We have also obtained stable high quality lasing spectra and have identified many of the mode features. At 30-Hz excitation rate the spectral emission from a stream of droplets is stable in real time. Consequently, the rhodamine/water solution droplets reported here provide a useful model system for theory/experiment comparison. Our data appear consistent with a physical model of the droplet blanketed by many narrow ribbonlike regions, each lying on a great circle of the sphere and each possessing a distinct orientation. Oscillation is primarily of TM mode character although along some ribbon orientations TE modes lase as well. Mode features are easily tuned in frequency by varying particle size. In the far field, the lasing particle approximates a coherent point source emitting uniformly in all directions.
Optical bistability of a single aerosol particle
Authors: Arnold Stephen
Published: February 2023

The optical bistability of a single micron-sized aqueous aerosol particle is reported for the first time. The particle, which is an (NH4)2SO4 solution drop containing a small trace of organic dye, is levitated in an electrodynamic chamber and stabilized by background water vapor. The mechanism for the effect is associated with the photothermal evaporation which accompanies the visible excitation of a structure resonance. A theoretical model suggests that a solid particle should also exhibit a similar effect due to the photothermal modulation of its refractive index.
Laser Doppler velocimetry for submicrometer particle size determination
Authors: Dovichi Norman J. , Zarrin Fahimeh
Published: February 2023

In laser Doppler velocimetry, two laser beams are crossed within a sample. Interference between the two beams generates a set of light and dark fringes within the intersection region of the beams. A particle passing through the fringe region will generate a modulated light scatter signal. Conventionally, the modulation frequency of the light scatter signal is used to estimate the velocity of the particles. However, the modulated light scatter signal generated by laser Doppler velocimetry also provides excellent noise immunity for particle size determination. To utilize the light scatter signal for precise particle size determination, it is necessary to align particles to pass through the center of the fringe region. We utilize the sheath flow cuvette to produce a thin stream of particulate suspension at the center of the interference fringe region. For polystyrene particles in water, the relative standard deviation of the light scatter distributions typically falls in the 1-2% range and is dominated by the intrinsic size distribution of the particle standards. Particles as small as 40-nm radius may be studied using a low-power He-Cd laser.
Contribution of rotational diffusion to quasielastic light scattering from fractal clusters
Authors: Lindsay H. M. , Lin M. Y. , Weitz D. A. , Klein R. , Meakin P.
Published: February 2023

In quasielastic light scattering the decay of the autocorrelation function of the scattered light is due to both translational and rotational diffusion. The clusters formed by the kinetic aggregation of colloids have a random structure, which is scale invariant or fractal. This results in a large contribution from rotational diffusion when the size of the cluster becomes comparable to or greater than 1/q, where q is the scattering vector. We measure the scattering from gold colloid clusters, which are aggregated in two different ways, producing clusters with fractal dimensions of 1.8 and 2.1. Both aggregation mechanisms can be simulated by computer, generating the coordinates of the individual particles comprising the clusters. We use these to calculate the total decay of the autocorrelation function, and explicitly include the contributions of rotational diffusion in terms of the moments of the angular anisotropy to the scattering. We find that, when the cluster size becomes larger than 1/q, the higher-order moments contribute significantly to the total scattering. We discuss the effects of this on the autocorrelation function, as both the cluster size and scattering vectors are varied, the shape of the predicted values of the autocorrelation function is compared with experimental results.
Diffusive and convective evaporation of irradiated droplets
Authors: Armstrong Robert L. , Zardecki A.
Published: February 2023

The evaporation of a spherically symmetric liquid droplet subject to a high-irradiance laser flux is investigated on the basis of a hydrodynamic description of the system composed of the ejected vapor and ambient gas. For low irradiance beams, diffusive mass transport and conductive energy transport are the dominant interactions between the droplet and its environment.1 In this isobaric case, changes in the state of the ambient medium are small. For higher-flux beams, convective mass transport becomes significant, and droplet vaporization is accompanied by the production of strong shock waves in the surrounding gas. Following Knight,2jump conditions at the droplet boundary aid us in solving the hydrodynamic boundary value problem. An extension of Knight’s analysis to include both diffusive and convective mass flux allows the transition regime between the low-flux isobaric case and the high-flux shock-wave dominated case to be investigated. Numerical solutions illustrating droplet vaporization and ambient-medium hydrodynamic effects are presented for selected droplet-beam configurations.
Stable 1.25-W cw far-infrared laser radiation at the 119-μm methanol line
Authors: Farhoomand Jam , Pickett Herbert M.
Published: February 2023

Far-infrared (FIR) cw laser radiation of 1.25 W has been obtained at the 119-μm (2522.8-GHz) methanol line with a CO2 input pump power of 115 W. This is the highest power and conversion efficiency reported to this date on this transition. The frequency drift of the free-running laser is less than ±200 kHz ph. The improved performance of the FIR laser was achieved by (1) using reflecting optics wherever possible to minimize CO2 mode degradation caused by damaged antireflection coating of transmitting optics; (2) enclosing the input and output assemblies within the lasing medium to minimize the external effects on the cavity length as well as eliminating the mechanical instabilities associated with the use of bellows; (3) cooling the resonator wall to 0 °C and adding He as the buffer gas. The combined pressure of CH3OH and He was 500 mm Hg. We believe that the major source of the laser frequency drift is thermal in nature and an active thermal stabilization scheme should further improve the frequency stability of the laser. This laser, which has also been tested at other frequencies ranging from 600 GHz to over 3000 GHz with improved results, will prove to be essential in generating tunable laser sidebands for spectroscopic measurements or other experiments which require a frequency stable FIR source.
Micrometer-size droplets as optical cavities: lasing and other nonlinear effects
Authors: Chang Richard k. , U. Yale
Published: February 2023

Just within the liquid-air interface of micrometer-size droplets, the internal field at the incident wavelength is enhanced and efficient optical feedback is provided for the internally generated inelastic radiation. At specific discrete wavelengths corresponding to morphology-dependent resonances of a droplet (e.g., a sphere or spheroid), the droplet can be envisioned as a spherical Fabry-Perot for two internally generated waves counterpropagating around the circumference and experiencing gain when these waves pass through the localized regions of the incident pump wave. Examples are presented of laser emission from dye-containing ethanol and ethylene glycol droplets and of stimulated Raman emission from CCl4 and water droplets (with or without anions such as

NO

3
−

; and

SO

4

2
−

). Examples of asymmetrically broadened spectra of the stimulated emission caused by intensity-dependent index of refraction modulation are given. At higher pumping levels, laser-induced plume ejection and avalanche breakdown giving rise to continuum and discrete atomic emission have been observed. Photographs of individual droplets which have achieved lasing, stimulated Raman oscillation, and avalanche breakdown thresh-olds are shown.
Thermooptical modeling of flashlamp-pumped zigzag slabs
Authors: Gelinas Robert J. , Doss Said K. , Murty Susarla S.
Published: February 2023

One objective in high average power laser research is to attain high beam quality in zigzag slab systems. The physical effects that must be controlled in these flashlamp-pumped convectively cooled slabs are thermal gradients, thermoelastic stresses, and material deformations; these effects govern wavefront phase distortions and beam depolarization in the absence of any significant mechanically induced stresses. This presentation describes the thermooptical mechanics of wavefront phase distortions in zigzag slabs. We identify, from both computations and laboratory measurements, the causes of beam phase distortions that are frequently observed in output beams from zigzag slabs. The thermal stress codes TECATE, TOPAZ, and NIKE and the ray tracing code BREW are used to compute isocontours of optical path differences (OPDs). Material deformations are found to dominate phase distortions in the neodymium-doped glass zigzag slabs considered here; alternative strategies and design criteria that can minimize OPDs in these slab systems are discussed. (Poster paper)
Study of triplet states by equal-frequency two-photon transitions in Na2
Authors: Xia Hui-Rong , Xu Jian-Wen , Pan Zuo-Di , Cai Ji-Guang , Ma Long-Shen , Cheng L-Shen
Published: February 2023

The experiments were arranged with a pulsed dye laser and a cross oven. A double-pen chart recorder simultaneously traced the two-photon excitation spectra monitored by two photomultipliers with interference filters centered at 3600 and 4300 Å, respectively. The observed two-photon transitions with a linewidth of ~0.2 Å were distributed discretely and nonuniformly and were close to the calculated values for searching the intermediate singlet-triplet mixing levels in Na2. This means that the observed signals were individually enhanced by a near-resonant mixing level. While most of the corresponding recorded lines in the two traces had coincident wavelength locations and comparable intensities, a part of the lines at the longer wavelength sides of the traces with moderate or weaker intensities appeared alternately. The upper states for the lines which only appeared in the 4300 Å trace or in both of the traces were assumed to be (2)3Π
g
and a higher (n)3Λ
g
state, respectively. Temperature and total pressure was varied. Finally, the laser beam was split into two with combined polarization situations. These aided the identification of the two- photon transitions.
Comparison in efficiency between energy pooling and two-photon excitation processes
Authors: Xia Hui-Rong , Xu Jian-Wen , Cai Ji-Guang , Cheng L-Shen
Published: February 2023

The results were compared of experiments with a pulsed dye laser scanned between 5820 and 5920 Å or 6200 and 6700 Å for Na2in a cross oven monitored by a PMT (with a UV filter) and a 0.5-m grating monochromator. The energy pooling process was observed around each of the D lines of Na with an excitation linewidth of ~1 Å (5 times wider than the others). The fluorescence energy was distributed mostly in the D lines, a few percent in the red band, more than 1 order of magnitude weaker in the 4300 Å diffuse band and very weak signals in the green region. This means that the process starting from the atomic first resonant transition could not efficiently populate high-lying states in Na2. In contrast, many molecular two-photon excitations between 6200 and 6700 Å with a linewidth of 0.2 Å contributed as much as 50% of the fluorescence energy out of the A-X red band. While one part of these excitations distributed their fluorescence over three or four electronic spectral bands centered at 3200, 3600, 4350, and 5200 Å with bandwidths of a few angstroms, other excitations were found to concentrate 30% of their fluorescence energy in the 4300-Å diffuse band.
Studies of the diffuse bands of K2, Rb2, and Cs2
Authors: Luh W.T. , Bahns J.T. , Lyyra A. M. , Sando K. M. , Kleiber P. D. , Stwalley W. C.
Published: February 2023

Direct dye laser excitation of the K2 yellow (566-580-nm), Rb2 orange (590-610-nm) and Cs2 near-infrared (702-722-nm) diffuse bands has been investigated. Experimental results are consistent with

2
3

Π
g

(bound)
←

1
3

Σ
u
+

(free)

excitation followed by bound → free fluorescence. For Rb2 and Cs2, spin-orbit interactions become so significant that the 23Π
g
state is strongly split into three independent component states and this is observed in the spectra. We have investigated the free-bound-free fluorescence of the K2 yellow diffuse band in particular detail. Theoretical treatment and quantum-mechanical simulation of free-bound-free resonance fluorescence are described for comparison with our single longitudinal mode dye laser direct excitation experiments and measurements of the weak absorption in the same spectral region.