bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Design with Wood Lenses
Authors: Caldwell J. Brian
Published: February 2023

Flat-surfaced radial gradient index lenses, also called Wood lenses [1] or rod lenses have found widespread use as elements in imaging arrays for photocopiers and fax machines.[2] However, there exist very few designs for more complex multi­element lenses which utilize Wood lenses.
Ellipsoidal Mirrors as Modular Elements in the Design of Off-Axis Optical Systems
Authors: Stavroudis Orestes N.
Published: February 2023

The idea of using confocal ellipsoids in the design of off axis systems arose in considering a complicated attachment for a space borne telescope. The best approach to the problem was to arrange in tandem pairs of ellipsoids which shared a focus. The work led to this study of the properties of these pairs and to criteria for the establishment of a pseudo axis, and symmetry with respect to this axis for field errors and image errors.
Zoom Lenses with a Single Moving Element
Authors: Johnson R. Barry , Feng Chen
Published: February 2023

A method to identify potential solutions of imaging problems incorporating zoom lenses having two generic moving elements and a spatially-fixed image surface was presented in a companion paper entitled “Insight into First-Order Zoom Lens Design.” While studying this method, it was observed that for certain optical configurations one of the moving elements was required to move only slightly over the entire zoom range. As a consequence, we investigated the possibility of having one of the moving elements remain essentially stationary over a least some reasonable zoom range.
An ultra high performance zoom lens for the visible waveband
Authors: Neil Iain A.
Published: February 2023

The paper commences with a review of zoom lens developments from the 1950's to the present day. Improvements in optics, mechanics, and electronics are discussed and, together with cost versus performance factors, used to explain an increasing trend towards adopting zoom systems for more applications. To illustrate the level of performance already attained, an ultra high performance zoom lens is described in detail with comparisons drawn from equivalent fixed focal length lenses. Finally, future trends and new applications, such as HDTV, are considered in terms of zoom lenses.
Practical Use of Generalized Simulated Annealing Optimization on Microcomputers
Authors: Hearn Gregory K.
Published: February 2023

The use of Generalized Simulated Annealing algorithms has been studied by several authors for its potential value to overcome the traditional shortcomings of damped least squares optimization. Damped least squares is likely to converge to local minima and once found the method cannot escape this condition by itself. As a result the effectiveness of this type of optimization is strongly linked to the qualities of the starting point, the merit function definition, and the selection of variables.
Ray-Tracing Through Progressive Ophthalmic Lenses
Authors: Bourdoncle B. , Chauveau J.P. , Mercier J.L.
Published: February 2023

Automatic ray-tracing through an ophthalmic Progressive Addition Lens (PAL) has been realised.
Corrections of Aberrations Using HOE's in UV and Visible Imaging Systems
Authors: Yang Zishao , Rosenbruch K.J.
Published: February 2023

An approach was developed to correct the chromatic aberrations of a holographic optical element (HOE). The effective use of different diffraction orders of two properly constructed HOE's makes it possible to obtain dispersion-free imaging for at least two arbitrary wavelengths. This kind of doublets behave the same as one HOE at each design wavelength. For example, one point can be imaged perfectly into its conjugate without the limitation of virtual imaging known in the past for achromatic doublets. Experimental results are presented.
X-Ray Lens Design
Authors: Thomas N. L. , Bionta R. N. , Skulina K. , Makowiecki D. M.
Published: February 2023

Fresnel zone plates and phase plates were developed for use with copper K-alpha X-rays (8 Kev λ = 1.54 Å). Alternating layers of transparent and opaque materials are sputtered onto a substrate, sliced perpendicular to the coating, thinned to a desired thickness and polished. Phase plates are made with a phase shifting layer in place of the opaque layers. Each material combination has a characteristic phase length, or thickness necessary to cause a relative phase shift of π between X-rays passing through the two materials. When phase plates are sliced to a thickness of integral multiple phase lengths, constructive interference occurs in the focal plane, with up to a four-fold increase in intensity compared to a zone plate. The design considerations and comparisons with experiment will be presented.
Optical Design of High Aperture Aspherical Projection Lens
Authors: Osawa Atsuo , Fukuda Kyohei , Hirata Kouji
Published: February 2023

According to the recent innovation in plastic molding technology for aspherical lenses, an unique lens system, mostly constructed by aspherical lenses has been appearing. A typical and successful example of such lens system is the projection lens for a large screen television, which is expected to become the main stream for the coming HDTV era in the near future, because of its compactness, light weight, and proper luminance level. We have been trying to find an explicit way in the aspherical optical design for this projection lens.
Interactions of excimer lasers with polymers
Authors: Liu Y. S. , Cole H. S. , Philipp H. R.
Published: February 2023

Interaction of high photon energy (> 5-eV) radiation from excimer lasers with polymeric materials has drawn much interest because of its potential importance in material processing such as etching and patterning which have found use over a number of diversified fields such as medicine, polymer science, and microelectronics. The laser etching process is noncontact, maskless, selective, and offers a high spatial resolution. Although the topic has been the subject of numerous recent studies, basic parameters for understanding interactions between polymers and high energy photons are not well understood. In this paper we present the results of a recent study on VUV optical properties of several polymeric materials including polymethyl methacrylate (PMMA), polystyrene (PS), polyvinylacetate (PVA), polyimide (PI), and polycarbonate (PC) and review parameters that are critical for understanding the interaction of polymers with excimer laser radiation. Results of a study of the surface compostions using small area x-ray photoelectron spectroscopy of two kinds of polymer, PMMA and PS, irradiated with an ArF laser at a photon energy of 6.4 eV are discussed. A simple model is then presented to show how various parameters including optical constants, photon energy, laser fluence, and polymer structures affect characteristics of photon etching observed in these polymers.
Internal biological tissue temperature measurements using zirconium fluoride IR fibers
Authors: Sinofsky Edward
Published: February 2023

The availability of zirconium fluoride fibers with improved midinfrared transmission has extended the range of remote thermography. One application is measurement of the internal temperature of biological tissue during and after exposure to laser energy. Such measurements are important for verification and calibration of predictive thermal models allowing rational selection of such parameters as power, wavelength, pulse duration, and total fluence. This technique may also help to determine when vaporization will occur with a minimum zone of thermal injury. The infrared signal can be sensed by circuitry to terminate the exposure automatically when the selected tissue temperature is reached. This scheme should be more accurate than visual interpretation of the degree of blanching. We report predictions of the signal level as a function of tissue temperature for detection through the fiber by a thermoelectrically cooled lead selenide photodetector. We also explore the resolution limits in space, time, and temperature, and compare our measured values with results of modeling calculations performed at USCI.
Optical and thermal aspects of laser tissue interaction
Authors: Welch Ashley
Published: February 2023

The portion of a laser beam that penetrates tissue is absorbed and scattered. The distribution of light intensity in the tissue is of prime importance with regard to photochemical reactions and the rate of heat generation. Determination of the distribution of laser light in tissue requires (1) measurement of the optical properties of the media of interest and (2) a theory or model for computing the light distribution. Unfortunately these are not independent steps.
Laser diagnostics beyond two dimensions
Authors: Long Marshall B. , Yip Brandon
Published: February 2023

Laser-diagnostic imaging techniques have become a useful tool for measurement of quantities such as species concentration and temperature in reacting and nonreacting turbulent flows. These techniques are valuable for determining the spatial character of large-scale structures in these flows because of their capability for simultaneous measurement at a large number of points in a plane intersecting the flow. A basic characteristic of turbulence, however, is its 3-D nature and thus fully 3-D data would be desirable. A new experimental technique has been developed which can produce an instantaneous 3-D mapping of the gas concentration in an aerosol-seeded flow. Three-dimensional measurements are obtained by measuring the 2-D gas concentration distribution in many closely spaced parallel sheets. These measurements must all be completed in a short time to effectively freeze the flow. This is accomplished by sweeping a thin sheet of rapidly pulsed laser illumination (30-kHz pulses from a cavity-dumped argon-ion laser) through the flow and recording the scattered light intensity from different laser pulses on different regions of a computer-controlled detector. The resulting volume measurements can be visualized using computer graphics to display surfaces of constant material properties.
Laser probing of alignment effects in collisional energy transfer: the anisotropy of the interaction potential
Authors: Meyer H. , Dressler R. A. , Bussert W. , Neuschafer D. , Leone S. R.
Published: February 2023

Recently there has been considerable experimental and theoretical interest in the study of orientation and alignment effects as a probe of geometry-dependent aspects of potential energy surfaces. In this contribution we report experiments in which the collisional alignment of the electronic orbital angular momentum of excited Ca atoms and of the rotational angular momentum of

N
2
+

ions are investigated. The effect of orbital alignment on the slightly exothermic energy transfer process from

Ca

(

4
s
5

p
1

P
1

)

to

Ca

(

4
s
5

p
3

P
J

)

in collisions with different rare gas atoms is studied in a crossed beam experiment. Initial orbital alignment is introduced by exciting Ca with a linearly polarized, pulsed ultraviolet laser. The relative inelastic cross section as a function of the initial alignment is measured by time-gated total fluorescence detection. The transition probability depends on the configuration of approach: for He and Ne enhancement is observed for the perpendicular vs the parallel approach while Xe leads to an opposite effect. In a flowing afterglow experiment the rotational alignment of

N
2
+

ions drifted in He buffer gas is studied. The extent of alignment is determined as a function of field strength and total angular momentum by measuring the degree of polarization of laser-induced fluorescence vs the angle of polarization of the exciting laser. Since the probed (J, M
J
) distribution is the result of many collisions, the alignment can be related to the rate coefficients for specific (ΔJ, ΔM
J
) transitions and therefore reveals information on the anisotropy of the

N
2
+

buffer gas interaction.
Inelastic collisions in laser excited alkali atoms
Authors: Allegrini M. , Gozzini S. , Moi L.
Published: February 2023

We review recent progress in inelastic collisions between two laser-excited alkali atoms, with special emphasis on heteronuclear systems.
Mechanistic and diagnostic aspects of photodynamic enhancement and stone fragmentation
Authors: Boni Arthur A. , Davis Steven J. , Rosen David I.
Published: February 2023

Metastable oxygen molecules in the singlet delta state, O2(1Δ), are believed to be the active species that are produced during laser irradiation of hematoporphyrin derivative (HPD), attached to tumors, and are responsible for cancer cell destruction. Although the presence of O2(1Δ) has been inferred by indirect chemical measurements, it has not been detected in real time. In this work, we review the optical characteristics of O2(1Δ) and describe an optical diagnostic procedure for its real-time detection during laser irradiation. In vitro experiments using both pulsed and cw dye lasers are described. Additionally, recent work has been presented whereby repetitively pulsed dye laser radiation can be delivered through a fiber-optic probe to induce fragmentation of kidney stones and gallstones.
Arterial aneurysm model using laser energy
Authors: LoCicero Joseph , Hartz Renees. , McCarthy Walter J. , Shih Shou-Ren
Published: February 2023

A consistent occurrence in laser-assisted vascular anastomosis appears to be the formation of aneurysms. This study was undertaken to determine the effects of a precisely quantitated amount of laser energy on the arterial wall. Femoral and carotid arteries of ten New Zealand rabbits were exposed and measured. Through a 6-mm anterior longitudinal incision, low power CO2 laser energy (power density 270 W/cm2) was delivered in 0.5-s pulses to a 0.9-mm2 area (four rows of ten spots). The arteriotomies were closed with sutures. The contralateral vessels served as sham controls and were opened and stretched in a similar manner to the method used for laser injury. At 12 weeks, the vessels were re-measured and the incidence of fusiform aneurysm formation (>1.5 times original diameter at re-operation) was 20% for carotid arteries and 80% for femoral vessels. There was also a 10% aneurysm rate in the sham operated femoral arteries. All aneurysms remained patent and microscopic study revealed extensive medial necrosis in each aneurysm.
Trace contaminants in laser gases
Authors: Weiss M. J.
Published: February 2023

The question of contamination in laser gas mixtures is important, particularly when laser output power is severely limited. In these cases, it is useful to know how the level of contamination is related to degradation of laser performance. When the laser body is sealed, analysis via an intrusive technique obviously cannot be done without drastically altering the environmental conditions in which the laser is operating. In this study, impurity levels of contaminants are quantitatively evaluated while maintaining the operating conditions of the laser discharge. This evaluation uses the technique of optical emission spectroscopy to monitor emission in sealed helium-neon laser systems. The effect of impurities such as N2, O2, CO, and hydrocarbons on optical emission is discussed. The emission spectra for these species depend largely on their concentrations. This technique starts with mixtures containing known concentrations of contaminants prepared in very clean conditions. The sample is then discharged under the same pressure and discharge current at which the laser is normally run. The optical spectrum is taken over the desired wavelength region and analyzed with a high resolution (3/4 m) monochromator.
Visible and ultraviolet absorption spectrum of Kr2F(42Γ)
Authors: Geohegan D. B. , Eden J. G.
Published: February 2023

This paper presents the first measurements of the absolute photoabsorption spectrum of Kr2F(42Γ) from 248 to 600 nm. Absolute cross sections were measured at thirty-seven wavelengths using a fluorescence suppression technique. An extension of this approach was developed to measure relative absorption cross sections over a given spectral range as a dye laser was continuously scanned. Absorption scans were made for 337 ≤ λ ≤ 600 nm and were scaled to the absolute cross sections within each spectral region. The excited Kr2F molecules were formed by laser irradiation of Kr/F2 mixtures (typically 1000-Torr Kr:1-Torr F2) at 193 or 248 nm. In each case, photoabsorptive losses induced by a delayed probe beam resulted in an obvious suppression of the Kr2F(42Γ) spontaneous emission. The resulting absorption spectrum displays a distinct absorption maximum (σ = 1.0 × 10−17 cm2)at ~337 nm. The red wing of the absorption profile displays several reproducible secondary maxima (at 397, 426, and 471 nm) as the cross section falls to < 5 × 10−19cm2 at 600nm. Two of the three undulations have not been predicted theoretically. On the blueside of the peak, the cross section drops to ~1.5 × 10−18 cm2 at 248 nm. Although the peak absorption is located near the predicted wavelength, the 42Γ → 92Γ absorption cross section is weaker than the associated

Kr

2
+

1

(

1
/
2

)

u

→
2

(

1
/
2

)

g

transition by a factor of ~3. Preliminary measurements of the

Kr

2
+

absorption cross section and the implications of these results for the Kr2F laser are also discussed.
Reduction of 1 + 1 REMPI spectra to population distributions: saturation and intermediate state alignment effects
Authors: Jacobs D. C. , Madix R. J. , Zare R. N.
Published: February 2023

A two-step methodology is presented for extracting ground state population distributions and alignment factors from 1 + 1 resonance-enhanced multiphoton ionization (REMPI) spectra. In the first step the ion signal is corrected for variation with laser intensity on a shot-to-shot basis, generating an isopower spectrum. In the second step populations and alignments are derived from the isopower spectrum by correcting for the interdependent effects of saturation and intermediate state alignment. Both classical and quantum-mechanical models are presented and their attributes are noted. This analysis procedure is applied to a room temperature thermal distribution of nitric oxide using the 1 + 1 REMPI process in which lines of the NO A2Σ+—X2Π (0,0) band constitute the resonant transition. The present treatment is able to recover the known rovibrational population distribution, independent of branch choice, over a wide range of practical operating conditions.
Transient excited singlet state absorption in the laser dye α-NPO
Authors: Venkateswarlu Putcha , George M. C. , Rao Yerneni V. , Jagannath H. , Chakrapani G.
Published: February 2023

Transient excited singlet state absorption spectrum of the laser dye, α-NPO (8 × 10-5 M/liter in toluene) was recorded in the 4500-6200 Å region with an optical delay of ~ 3 ns between the pump and the probe beams. Nine maxima and three shoulders are observed for the first time in the spectrum. A shoulder at 21090 cm-1 and three maxima at 20,530, 18,685, and 17,980 cm-1 are tentatively attributed to transitions from the vibrational levels at 26,740, 27,350, 29,170, and 29,885 cm-1 belonging to the first excited singlet electronic state S1, respectively, to a common upper level at 47,855 ± 25 cm-1 while three other maxima at 20,035, 19,525, and 17,570 cm-1 and another shoulder at 16,945 cm-1 are attributed, respectively, to transitions from the same four vibrational levels of S1 to another common upper level at 46,805 ± 70 cm-1. Transitions from the different vibrational levels of S1 to three different upper vibrational levels at 47,645 ± 30, 43,130, and 48,760 cm-1 could similarly be assigned to the remaining three maxima at 20,320, 18,445, and 16,390 cm-1 and the shoulder at 22,020 cm-1. Absorption from the higher vibrational levels of the excited state S1 may be understood on the basis of the fact that the pump and probe beams, each of ~ 8-ns pulse width, interact simultaneously with the molecules for ~ 5 ns.
Spatial and temporal characteristics of the XeCl laser discharge
Authors: Vill A. , Babichenko S. , Poryvikina L.
Published: February 2023

The structure and dynamics of the discharge as well as the kinetics of a XeCl laser were studied spectroscopically with spatial and temporal resolution. The discharge and the XeCl density distribution have a clear structure that is usually averaged by round-trip gain. The density distribution of the excited particles is not uniform, not only across the axis of the electric field but also along the field (where it has a layerlike character). Most clearly evident is the layer near the cathode in which electron energy is high and mainly He is excited. The other part of the discharge is also divided into layers, perhaps due to a strong nonlinearity such as dissociative electron attachment to HCI.
Optical diagnosis and growth kinetics of direct-laser written microstructures
Authors: Herman Irving P. , Magnotta Frank , Kotecki David E.
Published: February 2023

Monitoring the growth kinetics and properties of micron-dimension structures prepared by direct-laser writing is of interest because of the similarities and differences vis-a-vis large-area thin-film growth and because of the potential application of localized laser techniques to microelectronics fabrication. This paper presents some of the recent progress in these areas. Specific topics to be discussed are the characterization by in situ optical probing of laser-written microstructures and the anlysis of the initial phases of growth in direct-laser writing.
Ultraviolet laser-assisted thin-film deposition
Authors: Solanki R.
Published: February 2023

Photodeposition involves use of UV, visible, or IR radiation to assist or enhance a chemical reaction that results in the formation of a thin film on a given substrate. This presentation covers various aspects of UV laser-assisted deposition. Properties of some of the photodeposited films, which include conducting, insulating, and semiconductor films, are presented and their properties compared with those obtained via conventional means. Finally, the advantages and limitations of this deposition technique are discussed.
Infrared photodissociation spectroscopy of unsupported metal clusters and metal cluster complexes
Authors: Cox D. M. , Zakin M. R. , Brickman R. O. , Trevor D. J. , Reichmann K. C. , Kaldor A.
Published: February 2023

The recent development of a general source to produce gas phase metal clusters using laser vaporization combined with mass selective detection techniques has enabled new studies of the fundamental chemical and physical properties of clusters as a function of their size. In our laboratory we have developed and applied a variety of experimental techniques to measure ionization thresholds, magnetic moments, and gas phase reactivities of metal clusters. We now report the first observation of infrared laser-induced dissociation (IR-LID) of metal cluster–adsorbate complexes in a molecular beam. Specifically, using a high-power pulsed CO2 laser as the infrared source, we have measured the IR-LID spectrum for the iron clusters containing chemisorbed methanol as a function of the number of iron atoms for a known number of chemisorbed molecules. For clusters which have chemisorbed only one methanol, strong IR adsorption is observed near 985 and 1075cm−1, adsorptions presently assigned to the C–O stretch of chemisorbed methoxy radical and bridging hydrogen, respectively, i.e., the methanol is dissociatively chemisorbed. Both the feasibility and potential utility of IR-LID for characterizing metal cluster–adsorbate interactions have been demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only on the availability of appropriate high-power IR laser sources.
Chemistry of size-selected silicon clusters as studied by Fourier transform mass spectrometry
Authors: Reents W. D. , Mandich M. L. , Bondybey Vladimir E.
Published: February 2023

Direct laser vaporization of materials provides a simple method to form small ionic silicon clusters. These clusters may be kept in the ion trap of a Fourier transform mass spectrometer (FTMS) for up to several seconds. The capabilities of the FTMS are then used to determine bimolecular rate constants, identify reaction products, and evaluate product distributions of the ionic silicon clusters.
Overview of above threshold ionization: there is only one physics
Authors: Freeman R. R.
Published: February 2023

The phenomenon of above threshold ionization (ATI) has been under intense investigation for nearly 10 years now. During this time not only have many diverse experimental and theoretical investigations been reported, but several major conferences have been held as well with the professed goal of achieving some consensus in the interpretation of the basic phenomena. Still, the ATI research community remains largely fragmented and confused about the basic physics and is in danger of dividing into separate camps. In this paper I argue that the fundamental ideas necessary to understand the experimental results in ATI have already been put forward by many authors, often in other fields. For example, theorists interested in nonlinear Compton scattering worked out the form of the interaction of high intensity light with electrons, and plasma physicists wrote down the consequences of this interaction for real-life measurements of kinetic energies of electrons produced in focused, high-intensity beams. Many investigators concerned with the nonlinear interaction of high-intensity light on bound electron systems had to understand the concept of optical field ionization and have subsequently applied this knowledge to the measurement of spectra obtained in multiphon ionization of molecules with IR light. I will show that if the relevant conclusions of these and other works are combined with the body of experimental and theoretical work from the ATI community, a rather simple and appealing description of ATI emerges, one which emphasizes the universality of its nature.
Folk wisdom in optical design
Authors: Smart Anthony E.
Published: February 2023

Successfully implementing a complex or sophisticated optical system usually requires more than a knowledge of optical design and ability to use contemporary software codes. To create excellent systems also requires experience above and beyond what may be learned from textbooks. It is these hard-won lessons that may be described by the colloquialism folk wisdom. It can be valuable to be aware of the warnings embedded in apparent partiality or opinions offered without apparent justification. Many times a warning may be disregarded without apparent consequences: on other occasions raising a question initiates further study and can prevent serious problems. In this paper is outlined a number of such areas. Merely bearing them in mind during the system conceptualization and design phases can improve efficiency, effectiveness, and ultimate success. Some factors considered are costs, mechanical constraints, parts choice, specification and procurement, available adjustments, initial alignment, retention of alignment, deterioration of performance with aging, and others.
Chromium-sensitized rare-earth garnet lasers
Authors: Huber G. , Duczynski E. W. , Mitzscherlich P.
Published: February 2023

Cr-doped garnets such as YSAG and YSGG emit broadband Cr fluorescence in the near-infrared spectral region. Due to a resonant dipole-dipole interaction between Cr3+ and rare earth ions like Nd3+, Tm3+, and Ho3+, efficient nonradiative transfer can be achieved in such Cr-sensitized systems. Even Cr3+ in YAG with a rather narrowband emission at a strong crystal field site can be used to sensitize especially Tm3+ because of the overlap between the Cr emission and Tm absorption in YAG.
Raman-Mie scattering from optically levitated single particles
Authors: Kiefer W.
Published: February 2023

We report on a Raman microprobe technique where micron-sized solid particles or liquid droplets are trapped in stable optical potential wells using only the force of radiation pressure from a continuous gas laser. We demonstrate this technique with Raman spectra from spherical as well as nonspherical single particles of sizes ranging between ~5 and 40μm. The particles are stably supported by a vertically directed focused TEM00-modecwargon-ion laser of ~500 mW. From the optically levitated single microparticles we took the light-scattering spectra, which, in the case of spherical particles, show pronounced structural resonances. The observed resonances could be assigned by using the well-known Lorenz-Mie formalism, and a good correlation is found between experimental and theoretically predicted spectra. It was further found that, for particular liquid droplets, quite high-order numbers of the natural modes of oscillation of a sphere play a dominant role. We describe the intensities of the resonances in the Raman-Mie spectra particularly through the volume averaged internal field intensity. We also show that the internal angle-averaged electric field intensity is localized near, but not confined to, the sphere surface.
Time-resolved Raman spectroscopy of picosecond conformational intermediates in the bacteriorhodopsin photocycle
Authors: Atkinson G. H. , Brack T. L. , Blanchard D. , Siemankowski L.
Published: February 2023

The biochemical activity of the bacterium halobacterium halobrium is initiated through light-driven chemical changes occurring in its purple membrane. The purple membrane is comprised of the protein bacteriorhodopsin (BR) which contains a single retinal chromophore. The structural and conformational changes in this protein-bound retina caused by light abosrption are thought to initiate the proton and ion transport across the membrane that is essential for biochemical activity. The value of BR as a model for the molecular dynamics associated with the retinal chromophore in visual pigments and for proton and ion transport across membranes is well established. Picosecond time-resolved resonance Raman (PTR3) spectroscopy has been used to record the vibrational spectra of conformational intermediates in BR formed within a few picoseconds of optical excitation. A two-laser pump-probe configuration using an actively mode-locked cw Nd:YAG laser to synchronously pump two cavity dumped dye lasers is used to obtain PTR3 spectra. Several molecular motions within the retinal chromophore, formulated in terms of a normal coordinate approximation, have been monitored by PTR3 spectroscopy over the initial 40-ps interval. These molecular motions characterize the overall conformational and structural changes in retinal chromophore occurring on the picosecond time scale.
Interferences in the Raman excitation profile for the intensity of normal modes of aggregated chlorophyll a
Authors: Haley L. V. , Collier T. L. , Mattioli T. A. , Thibodeau D. L. , Koningstein J. A.
Published: February 2023

If dry chlorophyll a is dissolved in dry nonpolar solvents, aggregation takes place and the degree of aggregation depends on the con centration of this large molecule. The pulsed laser-induced Raman spectrum of such solutions contains contributions from many species, including scattering from excited states in case the laser wavelength is in resonance with the Soret band. At resonance, the Raman intensities experience changes but the presence of close-lying short-lived excited states causes sharp interferences. They occur over a range of 50 cm-1 in the Soret band having a width of ~500 cm-1. Such patterns are fingerprints for such complicated molecules. Temporal aspects due to excited state Raman scattering also influence these profiles. Besides results on chlorophyll a in solution, we also show such interferences for electronic Raman scattering and discuss differences between the electronic and vibrational scattering processes.
Highly efficient emerald laser
Authors: Lai Shin T.
Published: February 2023

We report highly efficient quasi-cw laser operation in emerald. A crystal of 3 mm in length was pumped longitudinally by a krypton laser at 647.1 nm in a nearly concentric cavity. A64% output slope efficiency was measured with an output coupler of 1.16% transmission at 768 nm. The maximum output power reached 1.65 W with 3.63 W of pump power and was pump power limited. These results are among the highest in efficiency reported in laser-pumped Cr lasers operating in a quasi-cw mode. The calculated round trip laser loss was 0.11% in our sample, corresponding to 0.36%/cm. The laser quantum yield was 76%. A tuning range of 720-842 nm was achieved with a single element birefringent filter. Excitation spectra indicated that the relative fluorescence quantum yield was close to unity in the visible region of the emerald absorption bands. The calculated emission cross section was 3.3 × 10−20cm2 at 750 nm for the c-axis polarization. The excited state absorption was estimated from the laser results to be 20% of the stimulated emission cross section at 768 nm. The pump power threshold of the present laser was at 230 mW with a 60-µm pump beam radius. A scheme for the miniaturization of a tunable emerald laser to accept diode pumping is also discussed.
Thermal lensing characterizations of a- and c-axes alexandrite laser rods
Authors: Leslie K. , Yeh J. J. , Whelen C.
Published: February 2023

We have measured the thermal lensing characteristics of a- and c-axes alexandrite laser rods using a diode laser operating at 790 nm as a probe and polarization parallel and perpendicular to the b-axis. In the case of c-axis rods, significant differences between the two polarization directions were found. While the average thermal lensing rates are comparable, the thermally induced lensing is much less astigmatic for beams polarized parallel to the b-axis than for those along the a-axis. For a-axis rods, the average lensing rate is 28% less than those of the c-axis but it is more astigmatic when the probe beam is polarized along the b-axis. The thermally induced nonspherical aberrations were also measured by passing probe beams at different radial locations. Similar to the average lensing rate, the a-axis rod was found to have much fewer nonspherical aberrations than the c-axis. The results provide explanations to the resonator stability conditions of the LANL 100-W laser. The results also provide guidelines to the proper choice of alexandrite laser rods for different performance requirements. A theoretical explanation of the observations based on crystal symmetry is discussed. The experimental techniques employed are presented.
High-efficiency distributed-feedback lasers optimally designed for stable single-mode operation
Authors: Ishikawa H. , Soda H. , Kotaki Y. , Kihara K. , Imai H.
Published: February 2023

A distributed-feedback (DFB) laser emitting at 1.3-μm wavelength has been optimally designed to achieve stable single-mode operation well above threshold current. We fabricated DFB lasers with first-order corrugation in a newly developed buried heterostructure. One end of the laser cavity is as cleaved and the other end is low reflectivity coated. Optimum designing has been done on the structure taking account of phases of corrugation at facets and also the effect of spatial hole burning in the longitudinal direction caused by the nonuniform field distribution. The important result is that the spatial hole burning in the longitudinal direction drastically deteriorates the stable single-mode operation at the high optical output power level when the product of the coupling coefficient and the laser length is large. The configuration has been designed to minimize the nonuniformity of the optical field in the longitudinal direction. The optimally designed lasers exhibited a very low threshold 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.
Ultrashort pulse chirp parameter determination by interferometric methods
Authors: Fischer R. , Rempel C. , Gauger J. , Tilgner J.
Published: February 2023

For pulses shorter than 1 ps, only indirect methods can be used. Besides conventional second-order autocorrelations and the detection of the pulse-bandwidth product, two interferometric techniques have been proposed: fringe resolved second-order autocorrelation (FRACF) and linear autocorrelation (LA), i.e., the Fourier spectrum of the pulse. Especially interesting is the measurement of the phase dependence on the length of the pulse duration, the so-called chirp. We have performed calculations of the FRACF and the LA with a fast Fourier transform algorithm for different pulse shapes and chirp functions. The results show for both the FRACF and the LA the typical narrowing of the main peak when the chirp increases. It was already known that FRACF shows side maxima in the presence of chirp, but we have shown that such side maxima also occur in the case of LA if the chirp is nonlinear. Because of the simpler mathematical expression, the LA is easier to interpret. We compare the results of both methods for two different pulses: a hyperbolic secant pulse with a chirp function which is typical of colliding pulse-mode locking of dye lasers and a Gaussian pulse shape where the time dependence of the phase is caused by self-phase modulation.
New generation of high power laser systems based on multiple-pass amplifiers
Authors: Jackel Steven , Lalluz R. , Yarkoni E. , Givon M. , Arad B. , Eliezer S. , Zigler A.
Published: February 2023

Small, medium, and large solid-state rod amplifiers have typical diameters d and gains g of: l,d = 0.5-3cm, g = 15-50; II, d = 3-7cm, g = 5-15; lll, d = 7-12 cm, g = 2-5. Many applications require overall rod system gains of g = 103-106, terminating in class II or III sized beams. Conventional laser systems achieve this required gain using chains of increasingly larger amplifiers. A new generation laser would use only one or two multiple-pass amplifiers. We have successfully built multiple-pass (and multiple-beam) amplifiers with large fill factors, high coupling efficiency, nonresonant geometry, and using passive optics for polarization and angularly controlled beam steering. Gains of > 103 with output intensities in the saturated region were routinely achieved with triple-pass units. Diffraction-limited 100-GW, 1-4-ns temporally shaped laser pulses in one or two beams were obtained with only two multiple-pass amplifiers at half the cost of a conventional laser. Frequency conversion was successfully accomplished. Phase conjugation (Brillouin in organic liquid) and polarization compensation are being incorporated into an ultrahigh performance unit with good preliminary results. Ring laser configurations are being adapted to substantially improve intra amplifier and inter amplifier isolation. These additional improvements will yield multipass systems at a quarter of the cost of conventional lasers. (Poster paper)
Frequency shift of stimulated Raman scattering in H2 + CH4 mixture
Authors: Zhao Zhensheng , Pan Zhonghan , Shen Deli , Cui Yiben , Hu Xuejin , Liu Songhao
Published: February 2023

Stimulated Raman scattering of H2 + CH4 mixture was investigated using frequency doubling of Nd3+:YAG lasers (532 nm) as a pumping source. A Raman cell, 1000 mm long, 15-mm diameter, was first filled with 10-atm H2 then CH4 was gradually pressed into the cell. As the CH4 increased, it was observed that the intensity of the first-order Stokes line of H2 became weaker and that of the first-order anti-Stokes line became stronger. Then, as the intensity of both S1 and AS1 weakened and the profiles of the lines broadened, suppression and coupling between H2 and CH4 appeared. The frequencies of S1 and AS1 [obtained by an optical spectrum analyzer (OSA) WP-4] shifted with changing CH4 pressure. A preliminary explanation of the mechanism of the frequency shift is given.
Third harmonic generation with high efficiency
Authors: Fischer R.
Published: February 2023

For third harmonic generation in cubic-nonlinear media, the influence of intensity-dependent parts of the refractive index must be taken into account because the corresponding susceptibilities for the parametric process and the process of self-action are of the same order. The intensity dependence of the index of refraction may destroy the phase matching and therefore lower the efficiency. It is well known that at low efficiencies (in the parametric approximation) it is easy to compensate the nonlinear mismatch by a proper linear one. The problem is more complicated beyond the parametric approximation. We present numerical results concerning this question. The maximum efficiency and the dependence of the harmonic on the (normalized) length of the nonlinear medium were calculated for different cases. Neglecting the dispersion of the third-order nonlinear susceptibility, the efficiency is determined only by one parameter Δk ·
l
nl
/2, where Δk is the usual linear mismatch Δk = K3 − 3k1, and
l
nl
is the nonlinear interaction length (which is inversely proportional to the input intensity of the fundamental wave and the effective third-order nonlinearity). Whereas for Δk = 0 the maximum efficiency (defined here as ratio of the amplitudes) is 0.55, one gets for an optimum mismatch of (Δk)opt = −0.27 (2/lnl) a maximum attainable efficiency of 0.92; i.e., also in the case including pump depletion it is possible nearly to compensate the nonlinear mismatch. However, as we also show, the dispersion of the nonlinear susceptibility can lower the maximum possible efficiency.
Laser absorption and fluorescence studies of the lithium 2S—3D transition
Authors: Tisone G. C. , Hargis P. J.
Published: February 2023

Laser absorption and fluorescence spectroscopy were used to study the dipole-forbidden 2s2S to 3d2 D transition in lithium at 319.6 nm and the two-photon allowed transition between the same two levels at a wavelength of 639.2 nm. Transmission of the incident pump laser radiation and the intensity of the single-photon fluorescence signal from the 3d2 D to 2p
2
P transition at 610.4 nm were measured as a function of lithium vapor density (1013−1016 cm−3) and incident laser intensity (104−108W/cm2). Absorption line shapes and fluorescence lifetimes were also measured. The single-photon absorption cross section calculated from our 319.6-nm absorption data agrees to within a factor of 2 with theoretical calculations. Estimates of the two-photon absorption cross section are complicated by an anomalous increase in the610.4-nm fluorescence intensity when the 639.2-nm pump wavelength is shifted ~0.035 nm to the red and by saturation effects. The general dependence of the fluorescence intensity on lithium vapor density and pump laser intensity is explained by saturation of the incident pump laser radiation. The results of this work were used to establish single-photon and two-photon laser diagnostic measurements of absolute lithium vapor number densities for ion-diode experiments.
Tunable UV coherent radiation and infrared stimulated radiation generated by hybrid pumping in the Na2-Na system
Authors: Wang Zu-Geng , Tang Xiao-Ling , Zhang Kai-Chang , Qin Lijuang , Cheng L-Shen
Published: February 2023

For the first time by means of two-photon hybrid excitation in the Na2-Na system, which is distinguished from the usual two-photon excitation in atomic vapor, tunable UV coherent radiation (between 337.6 and 339.1 nm and between 358.0 and 359.6 nm) and tunable infrared stimulated radiation (3.38-3.46 µm) were generated. By optically pumping with a pulsed dye laser scanning from 614.5 to 617.4 nm for sodium vapor in a heat-pipe oven, Na2 was excited by the first photon absorption from the

X
′

Σ
g
+

to the

A
′

Σ
u
+

state. The energy was transferred to Na by Na2*-Na collision to populate the levels 3p1/2,3/2 in Na, which was followed by another photon excitation from the same beam up to near the 5S level, resulting in SERS (3P1/2-4P and 3P3/2-4P) and OPSE(5S → 4P and 4P → 4S) radiation. Assuming the detunings of pumping frequency ω1, from ω(5S,3P3/2) and ω(5s,3p1/2) to be Δ1 and Δ2, respectively, the three UV coherent radiation components were supposed to be generated by the following mixing processes: ωUV = 2ω1 − ω(5S − 4P);

ω

U
V

′

=
2

ω
1

−

[

ω
(
5
S
→
4
P
)
+

Δ
1

]

;

ω

U
V

′
′

=
2

ω
1

−

[

ω
(
5
S
→
4
P
)
+

Δ
2

]

, and also

ω

U
V

′
′
′

=
2

ω
1

−
ω
(
4
P
→
4
S
)

. The SERS and the UV signals were tuned as the pumping wavelength was tuned. The measured wavelengths agreed well with the calculated values.
UV and violet stimulated diffuse band radiation by two-photon pumping in Na2
Authors: Wang Zu-Geng , Zhang Kai-Chang , Tang Xiao-Ling , Cheng I-Shen
Published: February 2023

This paper reports the UV and violet diffuse band radiation generated by two-photon pumping in Na2 by focusing the pumping beam (~ 10 mJ) from a pulsed dye laser into a heat-pipe oven containing sodium. Measurable forward stimulated diffuse band radiation existed at 350.0-385.0 nm and 405.0-460.0 nm over the whole pumping region from 620.0 to 670.0 nm. The radiation corresponded to transitions from different high-lying triplet g states to the lowest triplet state. The signal intensity related to the pumping wavelength. The stronger signals were there where two-photon pumping was enhanced by singlet-triplet mixing levels. The weaker signals were assumed to relate to the collisions either transferring energy from the

A
′

Σ
u
+

to the b3Π
g
state after the first photon excitation and then pumped by the second photon excitation from the b3Π
g
state to a high-lying state, or were due to collisional transfer from a high-lying singlet to a nearby triplet state.
Li 2 3 E u + − 3 E g + transition and UV absorption band
Authors: Jin Feng , Zhang Chune , Ma Zuguang
Published: February 2023

We present the first observation of triplet infrared absorption over a 1.13-1.17-μm range to the

Li

2

3

E
u
+

−
3

E
g
+

transition, an estimation of the absorption coefficient, which is ~1.5 m-1 in view of the vapor column length of 0.6 m at 1080°C, an investigation into the possibility of achieving triplet laser oscillation. The triplet absorption spectrum of lithium dimer peaks near 1.154μm with a bandwidth of ~ 500 Å, but intense absorption on the shorter wavelength side to the peak is also obvious. According to Konowalow’s calculations for the electronic transition dipole moment functions, there should be a maximum dipole moment for the

3

Σ
g
+

→
3

Σ
u
+

transition at the Li internuclear separation of 6.5 a.u., which corresponds to the vibrational level v' = 2 of triplet state

3

Σ
g
+

. Our results are in excellent agreement with Konowalow’s prediction. The Li lower energy level belongs to a repulsive electronic state

(

X
3

Σ
u
+

)

. The absorption transition that occurred might be from somewhere near the turning point of this repulsive curve. To observe an efficient triplet absorption, as described above, higher buffer gas pressure (200 Torr) and higher heat-pipe oven temperature (1100°C) are important. In the same experiment we have identified a new UV absorption band centered at 3900 Å.
Laser-induced fluorescence spectroscopy of Hg2 excimers
Authors: Niefer R. J. , Supronowicz J. , Atkinson J. B. , Krause L.
Published: February 2023

Pump-and-probe methods were used to excite high-lying

I

(

O
u
+

)

and J(1
u
) states of Hg2, whose transitions to various lower states cause emission of fluorescence bands centered at 420 nm

(

J

1
u

→

AO

g
±

)

, 513 nm (J1
u
→ E2
g
), 632.6 nm (J1
u
→ F1
g
), 451.4 nm

(

I

O
u
+

→
B

1
g

)

, and 422.6 nm

(

I

O
u
+

→
A

O
g
+

)

. The transitions from

I

O
u
+

and J(1
u
) to the repulsive

X

O
g
+

ground state give rise to Condon internal diffraction patterns. A comprehensive investigation of the fluorescence bands and of the corresponding excitation spectra, some of which overlap, permitted unambiguous assignment of the bands to transitions between particular electronic states whose positions were located on the potential energy diagram. The experiment yielded vibrational constants for the molecular states as well as qualitative information about the relative internuclear separations for the various states.