bluuebunny/crossref_metadata_2025 huggingface dataset:
Absorption spectrum of (ArKr)* in the ultraviolet
Authors: Kane D. , Eden J. G.
Published: February 2023

Recent experiments reported by Pratt, Dehmer, and Dehmer have examined the electronic structure of NeXe, ArXe, and KrXe in the vicinity of the separated atom limits by resonantly enhanced multi photon ionization. However, little is known of the rare gas hetero-nuclear molecules near the potential minima of the Rydberg states. This paper describes experiments in which the absorption spectrum of the lowest electronic excited state of ArKr has been studied by inter-Rydberg laser spectroscopy. Specifically, excited Kr atoms are first produced by two-photon excitation of the Kr 6p[3/2]2 state at 103,363.4cm-1 in a mixture of 1040-TorrAr and 40-TorrKr(300 K pressures). Following the rapid relaxation of the 6p atoms into the 5s states, ArKr excited molecules are formed by three-body molecule collisions of Kr(5s) with two ground state Ar atoms. An adjustable time after the arrival of the first laser pulse (typically 700 ns), a dye laser beam excites the ArKr species to a higher-lying Rydberg state. Dissociation of the highly excited molecule is detectable by observing Kr atomic emission at 820 nm. A highly-structured band that is attributed to ArKr has been observed near 372 nm. Temporally resolved and pressure-dependent studies of this band show clearly that it is associated with neither Kr2 nor Ar2. The identification of this band as well as the remainder of the molecule’s UV absorption spectrum is discussed.
Experimental study of laser accelerated thin foils
Authors: Serov R. V. , Aleksandrov V. V. , Goncharov S. F. , Pashinin P. P. , Perov V. Y. , Yanovsky V. P.
Published: February 2023

Ablative acceleration of thin foils heated by laser irradiation is of great interest in connection with laser fusion as well as with generation of strong shocks. Taking into consideration these applications of the accelerated foil, the most important parameters are final velocity, mass, and density, the last being decreased as the foil thermally expands. Optical diagnostic methods are convenient to use and provide good spatial and temporal resolution; however, in their application to dense plasmas from accelerated foils an obstacle arises in that light does not penetrate into plasma with a density ⪞1022 cm-3. Nevertheless, combining several optical methods and diagnosing different foil regions at the front and rear sides of the foil makes this problem soluble. Actually, three methods have been used:(1) the space-time diagram of the critical density surface movement at the front (irradiated) side of the foil was traced by integrating the velocity time dependence obtained from the time-resolved second harmonic spectrum; (2) the movement of the plasma density surface corresponding to an optical shadow (~1020 cm-3) at the rear side of the foil was monitored by optical probing using multiframe shadowgraphy and interferometry; (3) the foil’s center of mass velocity was measured with a hollow ballistic pendulum allowing considerable improvement in accuracy. Experiments were performed with two channels of the UMI-35 laser facility with an intensity of 5 × 10,2W/cm2 and a pulse duration of 6-8ns. Thin Mylar foils with thicknesses ranging from 6 to 25μm have been accelerated to velocities of the order of 100 km/s. The dependence of accelerated foil velocity and thermal expansion on foil thickness is discussed.
Kinetic spectroscopy using a color center laser
Authors: Stephens J. W. , Hall J. L. , Lander D. R. , Curl R. F. , Kasper J. V. V. , Tittel Frank K.
Published: February 2023

Infrared kinetic spectroscopy is being developed using a pulsed excimer laser for ultraviolet photolysis and a color center laser spectrometer as an infrared probe in the 2.3–3.0-μm region. Sub­microsecond time resolution is possible with the 14-ns excimer laser pulses and the InSb detectors currently employed. Previous work on the Br, OH, and NH2 radicals has led to the development of three monitoring schemes based on the use of either balanced detectors, magnetic rotation, or short-time monitoring. Kinetic studies of the NH2 + NO reaction have measured the branching ratio of the two primary product channels by monitoring a number of precursors and products. Current work on the C2H radical produced by photolysis of acetylene has indicated an ~ 1-μs lifetime for this radical, demonstrating the ability to detect short-lived species. Other work includes the production of highly reactive O(1D) atoms by the photolysis of O3, providing a method for generating free radicals from stable molecules by hydrogen atom abstraction. Additional studies on the spectroscopy and kinetics of other free radicals are discussed.
Infrared laser absorption eddy correlation measurement devices for trace atmospheric gases
Authors: Zahniser M. S. , Kebabian P. L. , Anderson S. , Freedman A. , Kolb C. E.
Published: February 2023

We discuss the development of two open path IR absorption instruments for eddy correlation measurements of fluxes of atmospheric trace gases which impact greenhouse and acidic dry deposition problems. One instrument, designed for CH4 measurements, uses a tunable IR He-Ne laser operating at 3.39/µm. The second, based on a tunable diode laser system, will be used to detect a variety of molecules including N2O, O3, and HNO3. Since these measurements are made in the free atmosphere, the instrument must discriminate against spectral features of the atmospheric background, especially water vapor. The chosen approaches to this problem are described, including the use of a frequency-modulated source and detection at both the first and second harmonic of the modulation frequency. The multipass cell must exhibit minimal sensitivity to the expected vibration of its supporting structure; methodsof achieving this are described.
Propellant combustion study by coherent anti-Stokes Raman scattering
Authors: Vu Thieu H. , Cheung Wan Yee , Field Richard
Published: February 2023

We have used the method of coherent anti-Stokes Raman scattering (CARS) in our study of double base propellants containing varying ratios of nitrocellulose and nitroglycerine. We have chosen N2 and H2, among other major combustion products, to measure the temperatures of the propellant flames in air and in inert atmospheric conditions.
Injection controlled operation of broadband excimer lasers
Authors: Zhu Y. , Sauerbrey R. , K.Tittel Frank , Wilson W. L.
Published: February 2023

Highly efficient and extremely narrow spectral output has been demonstrated for an injection controlled electrically excited XeF (C → A) and Xe2Ci laser media. Amplification of an injected tunable dye laser pulse was achieved throughout the entire blue-green spectral region. Experiments were performed by exciting optimized gas mixtures with an intense electron beam. Several different confocal unstable resonator geometries were investigated. In the case of the XeF (C → A) excimer transition, a maximum output of ~ 150 mJ was measured at 482.5 nm for a cavity with magnification M = 1.08, which corresponds to an energy density and intrinsic efficiency of ~8J/liter and ~ 6%, respectively. The tuning range was from 435 to 535 nm.1 An analytical model of the injection process was developed. A set of nonlinear coupled rate equations described the laser process. This model was used to describe the injection controlled excimer laser performance as a function of delay time between the dye laser injection and e-beam pumping pulse, as well as to assist the optimization of the confocal unstable resonator design.
Laser Raman and fluorescence microprobing techniques: some applications
Authors: Wallart Francis , Dhamelincourt Paul
Published: February 2023

The analytical potential of these techniques is Illustrated by examples of analysis performed in various domains.
Theory, operation, and applications of the NRL CARS microscope
Authors: Duncan M. D.
Published: February 2023

We describe a technique that permits molecular specificity in microscopy while retaining good spatial resolution. Specificity is achieved by using Raman scattering from characteristic molecular vibrations, and high resolution is obtained by imaging the distribution of visible anti-Stokes radiation. Images have been obtained from a variety of pure organic liquids, from deuterated water in onionskin cells, deuterated liposomes, and other samples. Thermal and dielectric breakdown damage to even fragile biological materials is made negligible by choice of duty cycle and average power. Sample fluorescence is avoided by choice of anti-Stokes imaging. Imaging through (usually astigmatic) spectrometers is not needed. Deuterium substitution can be used as a general purpose and artifact-free stain. The combination of high spatial resolution, excellent molecular discrimination, and digital image processing (background subtraction, etc.) provice the CARS microscope with capabilities not found in any other current microscopic imaging technique.
Use of incoherent light to generate coherent excitation
Authors: Hartman S. R.
Published: February 2023

Time-delayed four-wave mixing signals in Na vapor using intense 7-ns pulses of 12-Å wide incoherent light centered at the Na D doublet display a 1.9-ps beat corresponding to the 6-Å splitting of the Na D lines. Collisional relaxation from an argon buffer gas is observed for relaxation times as short as the inverse bandwidth of the excitation noise. The effect of noise field induced relaxation is also examined.
Theory for coherent multicolor laser excitation of localized states
Authors: Hutchinson John S.
Published: February 2023

By studying the dynamics of the laser excitation process in a dressed states picture, we have recently shown that, in many cases of photochemical interest, the time scale for molecular excitation is many orders of magnitude slower than the time scale for in tramolecular relaxation. As a result, single laser radiation offers little if any control over the form of the initial excitation in these cases. However, if one tunes two (or n) different lasers to two (or n) different molecular eigenstates, then a superimposition of the eigenstates will be prepared coherently. Furthermore, that coherent superimposition will continue to be the molecular state as long as the lasers are on. This coherent multicolor (CMC) excitation can be used to destructively interfere with the relaxed portions of the excited eigenstates. The result is excitation of a nonstationary molecular state which does not evolve in the presence of the laser field. The localization is locked in by the coherence of the multicolor excitation. We apply the CMC proposal to preparation of localized vibrational overtones of molecular local modes and to the separation and selective control of excitations of singlet and triplet vibronic states. Control of unimolecular reaction rates and branching ratios is proposed and illustrated.
Selective IR laser photoisomerizations in solids
Authors: Shirk James S. , Marquardt C. L.
Published: February 2023

IR excitation of selected vibrational modes of a variety of molecules trapped in solid rare gases causes a photoisomerization. The reactions are generally single photon processes which involve a rotation about a single bond. The quantum yields for photoisomerization have now been measured in both the forward and re verse directions for several molecules. The range of excitation includes both the fundamental and first overtone vibrations. These quantum yields vary from 0 to 1. The vibrational photochemistry is not consistent with a statistical redistribution of energy in the guest molecule before reaction. The guest molecules are not isolated in a gas phase sense; vibrational energy flow to the lattice competes with reaction and intramolecular (guest) energy redistribution. It is likely that relaxation of the guests can occur via specific pathways. Evidence is presented to show that the products and the quantum yields for their formation depend on the relaxation rates and pathways. It is thus possible to create product distributions by even broadband (nonlaser) IR irradiation that are impossible thermally.
Superradiance: a review of concepts
Authors: Eberly J. H.
Published: February 2023

An overview is presented of the current state of theoretical understanding and experimental observation of superradiance and superfluorescence.
Progress in the gamma-ray laser program at Texas. 2: coherent techniques for pumping a gamma-ray laser
Authors: Wagal S. S. , Reittinger P. , Juengerman E. , Eberhard C. D. , Collins C. B.
Published: February 2023

As its name implies, coherent upconversion would allow nuclear materials to be pumped with an intense but conventional coherent source such as a laser. Threshold powers would be much lower than usually projected for a gamma-ray laser and the pump sources could be drawn from a more mature technology. This scheme for pumping a gamma-ray laser depends on the development of states of nuclear excitation dressed by the photons of the pump field. Of particular importance is that the metastability of adressed isomeric state would be released, and with it the stored energy. Recently we published a Letter showing a rather close agreement between our first experimental measurements and a dressed state theory. As described in this paper, additional spectroscopic detail has been measured which now shows strong quantum structure that resulted from the formation of a resonance arising from certain dressed states of Fe-57 driven by intense rf fields. Moreover, these dressed states of nuclear excitation were found to have just the properties expected. Critical significance accrues from this result because the dressed states were created in iron nuclei diluted in nonmagnetic stainless steel by the transfer of a driving B-field that had been greatly enhanced by the ferromagnetism of an adjacent layer. In this way the dependence of dressed nuclear states on the ferromagnetism of their diluent was eliminated.
Classical and semiclassical calculation of nuclear-electron coupling
Authors: Noid D. W. , Hartmann F. X. , Koszykowski M. L.
Published: February 2023

One aspect of making a gamma-ray laser concerns the rapid re lease of energy stored in a long-lived nuclear isomer. A proposed method for the release of this energy is to pump the isomerto a nearby, shorter-lived nuclear excited state. This excited state subsequently decays to a lasing transition. In this paper, we consider the dynamical coupling of the nucleon and electron motion using classical dynamics and calculate the perturbation on the spectra. In our model,1 a valence excited proton is bound as an independent particle to the nuclear core using a Woods-Saxon potential. The electron is bound to a core of protons and the valence proton by a Coulomb potential. Initial conditions for the classical trajectories were chosen to be semiclassical states of the separable Hamiltonian. A method2 to extract spectral information from classical trajectories is then used to calculate both transition intensities and frequencies. For some isomers, very strong coupling and chaotic motion were observed.
Nuclear transitions induced by atomic excitations
Authors: Bounds J. A. , Dyer P. , Haight R. C. , Wender S. A.
Published: February 2023

In the two-step pumping scheme for a gamma-ray laser, the most uncertain step is that of exciting the nucleus from a long-lived storage isomer to a nearby short-lived state that then decays to the upper lasing level. For a crystalline structure host, the radiation inducing this interlevel transfer step must be used efficiently so as not to destroy the crystal. High-intensity sources of photons are available only for relatively low quantum energy, but it is difficult to couple a long-wavelength photon directly to the very small nucleus. We propose experiments to induce this transfer by first exciting the atomic electrons. We expect nuclear excitation to take place through exchange of a virtual photon in the near field of the electrons. As a test case, the 75-eV123mU isomer might be excited by electronic motions induced by a bright source UV laser. We propose to detect conversion electrons from the decay of this isomer, measuring the 26-min decay curve.
Ultraviolet resonance Raman studies of monocyclic and polycyclic aromatic hydrocarbons
Authors: Asher Sanford A.
Published: February 2023

UV resonance Raman studies of benzene have demonstrated that the Raman intensities are dominated by vacuum UV transitions. Because of the weak oscillator strengths and the significant homogeneous linewidths in the condensed phase, little Raman enhancement iscontributed by the ~240-260-nm B2
u
transition. In the gas phase, however, the smaller homogeneous linewidth results in resonance enhancement. We show experimentally the distinction between resonance Raman scattering and single vibrational level fluorescence. Raman studies of substituted benzene derivatives illustrate that the resonance enhanced vibrational modes are those which distort the nuclear framework and electron density and the bond lengths in a fashion characteristic of the transition moment to the resonant excited state. Raman excitation profile studies of polycyclic aromatic hydrocarbons such as pyrene clearly show the underlying Franck Condon substructure of the diffuse absorption bands. The strong resonance enhancements permit studies of polycyclic aromatic hydro-carbons at ppb concentrations. The analytical utility of UV Raman spectroscopy is illustrated by studies of polycyclic aromatic hydrocarbons in coal liquid samples and in biological matrices.
Optical bistability switching with external noise
Authors: Arimondo E. , Dangoisse D. , Fronzoni L. , Incani O. , Rahman N.
Published: February 2023

In an optically bistable system the switching time, i.e., the time required to switch the system between the off and on states, is a sensitive measure of noise and fluctuations. For a control parameter close to the threshold of the bistable operation, the critical slowing down takes place and large fluctuations in the switching times are originated.
Bichromatic emission in a homogeneously broadened ring dye laser: evidence of a new mode structure hierarchy
Authors: Lawandy N. M.
Published: February 2023

We present experimental measurements on a high-Q rhodamine 6G ring dye laser which was found to exhibit bichromatic emission with splittings of the order of 15–80 Å while operating in the range of 2–6 times above threshold in the bidirectional mode. Experiments were performed with the insertion of a low loss Faraday isolator (loss < 1%) in order to examine the effects of saturation gratings on the bichromatic emission. The results showed that even though the intracavity power went up, owing to the elimination of spatial hole burning, the bichromatic emission was completely eliminated in the operating range between 1 and 10 times above threshold. In addition the sidelight fluorescence of the jet was spectrally examined in order to search for sideband splittings similar to those found in Na atoms in a strong resonant field. No evidence of splittings or fluorescence shape change was found when the laser was 1–10 times above threshold. When a weak reflection from an intracavity element was allowed to make a single pass through the active part of the jet in a direction opposite to that allowed by the Faraday rotator, bichromatic emission was recovered at high pump powers (2–5 W). This is believed to be a consequence of a Bragg grating which appears when the weak beam is sent through the active medium. We describe the experiments and the results which we obtained, as well as offer a theory which consistently explains our observations and perhaps those of others.
Advances in chemical lasers
Authors: Miller Joseph
Published: February 2023

High power chemical lasers present a fascinating array of special environments and associated technology development subjects. Included are: processes to produce the source reactants; supersonic mixing and reacting flow fields; the production and dissipation of multiple vibrational–rotational molecular states; optical gain extraction in complex geometries; media inhomogeneity effects, and waste energy and reaction products removal. Some configurations desire wavelength selectivity, special optical components, and coherent cavity or beam combining. Progress has been made in these areas in recent years in behalf of cw and repetitively pulsed hydrogen fluoride and deuterium fluoride lasers, subsonic and supersonic oxygen-iodine lasers, and potential shorter wavelength chemical lasers based on chemically excited higher electronic states. This paper presents a brief review of the technical approach in some of the technology areas and the status in achieving practical, integrated high power chemical lasers.
High energy free-electron lasers
Authors: Shoffstall Donald R.
Published: February 2023

Several free-electron laser experiments have been designed to address wavelength scaling, energy scaling, and operational efficiency. Two modes of FEL operation are being examined: amplifier and oscillator. Major program participants include Lawrence Livermore National Laboratory, Los Alamos National Laboratory, and an industrial team led by the Boeing Aerospace Company.
Ultrahigh speed Schottky barrier and PIN photodiodes
Authors: Wang S. Y. , Carey K. W. , Kolner B. H. , Collins D. M.
Published: February 2023

With the advent of using light as the carrier frequency the trend is toward high speed transmitters and receivers to capitalize on the high bandwidth afforded. We have been concentrating on the receiver end and particularly the photodiode. GaAs Schottky photodiodes fabricated on molecular beam epitaxy have demonstrated-3-dB bandwidths in excess of 100 GHz at a wavelength of 600 nm. For longer wavelengths, 1.06 and 1.30 μm, we have developed a front side illuminated double heterostructure InP/GalnAs/lnP PIN photodiode with the -3-dB bandwidth in excess of 18 GHz. This device bandwidth is insensitive to wavelength in the 1.06–1.6-μm range. In addition, the dark current is < 100 pA at the operating voltage of −4 V for a 50-μm diam device with a 25-μm diam bondpad. High speed characterization techniques using electrooptic sampling, a microwave spectrum analyzer, and standard sampling are discussed. Growth techniques of the PIN photodiode using atmospheric organometallic vapor phase epitaxy are also discussed.
High gain-bandwidth-product avalanche photodiodes for multigigabit data rate
Authors: Campbell Joseph C.
Published: February 2023

For long-wavelength (1.3- and 1.5-μm) high-bit-rate (>400-Mbit/s) lightwave systems the highest receiver sensitivities have been achieved with III–V compound avalanche photodiodes with separate absorption and multiplication regions (SAM-APDs). Initial APDs of this type exhibited poor frequency response owing to charge accumulation at the heterojunction interfaces. A significant improvement in the bandwidth was achieved by introducing a transition region between the multiplication and absorption layers (SAGM-APD). Early SAGM-APDs exhibited bandwidths in the 1–3-GHz range and gain-bandwidth products as high as 18 GHz. Recently, the progression of new lightwave systems to higher and higher bit rates has stimulated efforts to further increase the bandwidth of these SAGM-APDs.
Near-threshold ion photofragment spectroscopy
Authors: Sarre P. J. , Walmsley J. M. , Whitham C. J.
Published: February 2023

We have recorded high-resolution laser photofragment spectra of the astrophysically important ions CH+ and SiH+. The experiments are designed to give information on the region of internuclear distance between the atomic and molecular limits for systems where dissociation occurs into atoms possessing electronic angular momentum, in this case C+(2P) or Si+(2P). A-keV beam of Ch+ (SiH+) is irradiated coaxially with cw single-mode tunable laser radiation which induces transitions from the X1∑+ ground state to predissociated levels of the A1∏ state and other electronic states which correlate with the C+(2P) + H(2S) or Si+(2S) limit. An electrostatic analyzer provides mass and energy selection of the photofragment C+ or Si+ ions which are detected with an electron multiplier. Information is obtained from transition frequencies, hyperfine splittings, predissociation linewidths, and also from the photofragment kinetic energies and angular distributions. Over thirty transitions to 1∏ levels have been detected in CH+ (Ref. 1); in SiH+ we have observed transitions to levels which almost certainly lie between the Si+(2P1/2,2P3/2) + H(2S) fine structure limits. We have also recorded numerous resonances in both ions which arise from transitions to triplet states which correlate to the same dissociation limit and are observable because of strong nonadiabatic couplings.
Vibrational relaxation of adsorbed molecules
Authors: Cavanagh R. R. , Casassa M. P. , Heilweil E. J. , Stephenson J. C.
Published: February 2023

Time-resolved measurements of vibrational relaxation rates have determined the population decay of vibrationally excited OH groups: adsorbed on high surface area SiO2; in model silanols, and as defect sites in quartz.1 Depopulation of the vibrationally excited OH oscillator was found to occur on a time scale of 80–300 ps. The temperature dependence of the vibrational relaxation rates in quartz (OH) and on SiO2 (OH and OD) were all found to follow a simple multiphonon relaxation model.2 However, the relative rates for the two isotopes (rateOD/rateOH = 1.6) on SiO2 didnotscale as predicted by the theoretical models (rateOD/rateOH = 13). Recent measurements of isotopically substituted silanols (R3SiOH and R3SiOD dilute in CCl4) also find OD decay times comparable with those of OH. The observed decay rates appear to be dominated by processes which proceed through a SiOH bending mode. Prospects for extending these methods to longer wavelengths with improved temporal resolution are discussed.
Interfacial studies of silver-aqueous electrolytes by optical second harmonic and differential capacitance
Authors: Rojhantalab Hossein M. , Richmond Geraldine L.
Published: February 2023

Optical studies of the electrostatic and surface structure of the metal-liquid junction require probes which are insensitive to bulk phase properties yet sensitive to an atomic level to interfacial interactions. Second harmonic generation is the unique probe for such measurements. In addition to the second-order effect intrinsically present at the symmetry breaking interface, an additional condition from the application of the dc electric field has also been recently demonstrated. Due to the high field strength present in the electrochemically double layer (107V/cm), this third-order effect appears to dominate in the SH production here. To understand the relative contributions to SHG at the electrode surface, we have examined the effects of the excess surface charge, Xm, as imposed by the dc field on the SH production. The experiments involved simultaneous measurement and comparison of the concentration of the specifically adsorbed ions by differential capacitance, and the SH signal on the same electrode surface. Various binary mixtures of electrolytes at constant ionic strength were used. The potential dependence of SH signals was monitored by applying linear potential sweep voltammetry within the ideally polarizable region on smooth and electrochemically roughened metal surfaces.
Molecular and topographic imaging of surfaces by surface laser spectroscopy
Authors: Van Duyne Richard P.
Published: February 2023

No summary was available at press time.
Imaging of surface atoms and their wave functions with a scanning tunneling microscope
Authors: Demuth J. E. , Hamers R. J. , Tromp R. M.
Published: February 2023

The scanning tunneling microscope (STM) provides a direct method to image atomic scale features on surfaces.1 We describe a new methodology for performing STM which allows us to delineate electronic and geometric contributions to STM images so as to produce spatially- and energy-resolved images of surface state wave functions.2 This new approach allows both topographic and spectroscopic data to be obtained simultaneously and is applied to study the Si(100) 2 × 1 and Si(111)7 × 7surfaces. We present images of the occupied and unoccupied surface state orbitals of these surfaces and directly relate them to the underlying surface atomic positions. These energy resolved states are not only shown to correspond directly to those obtained in normal and inverse photoemission studies, but to be localized to specific atomic sites in these unit cells. The applicability of this approach to study isolated or extended surface defects and/or adsorbed molecules will also be discussed.
Observation of quantum jumps in a single atom
Authors: Bergquist J. C. , Hulet R. G. , Itano Wayne M. , Wine-Land D. J.
Published: February 2023

One of the experiments made possible by the trapping and cooling of a single atom is to observe the quantum jumps to a metastable state in the atom by monitoring the resonance fluorescence of a strong transition in which at least one of the states is coupled to the metastable state. When the atomic electron moves to the metastable state, the fluorescence from the strongly driven transition disappears. When the electron drops back into the strongly driven transition, the fluorescence abruptly returns. Statistical analysis of these random interruptions to the fluorescence signal implies photon antibunching in the emission of the weak photon.
Laser control of atomic motion
Authors: Balykin Victor I. , Letokhov V. S. , Minogin V. G. , Sidorov A. I.
Published: February 2023

This paper presents the results of experimental and theoretical investigations on the control of atomic beam motion by light pressure of laser radiation. Collimation, focusing, and compression of an atomic beam are considered. Collimation of an atomic beam was achieved under the interaction of laser radiation with atoms when the light pressure force depended only on the atoms’ velocity. A similar regime of atomic beam interaction with radiation was performed under transversal irradiation of a beam by the axisymmetric field. The latter was formed by laser radiation reflected from the conical mirror surface of a reflecting axicon. The axis of an atomic beam coincided with that of the axicon. The collimation regime was reached under negative detuning of the laser radiation frequency from that of the atomic transition one by a value equal to a few homogeneous widths. Under positive detuning by the same value beam decollimation was observed.
Measurement of axial velocity distribution of a laser-cooled atomic beam
Authors: Hall J. L. , Zhu M. , Salomon C.
Published: February 2023

We measured the axial velocity distribution produced by frequency-chirp-cooling a sodium atomic beam, including heating effects produced by an optional frequency-fixed postcooling interaction. Frequency sweeps were produced via a voltage-tuned oscillator feeding a broadband, efficient electrooptic modulator to produce a frequency-agile sideband on the output of a dual-frequency dye laser(Δv = 1.712GHz). After the chirp-cooling, the frequency was held stationary for an adjustable time T before the intensity was reduced 30-fold and the frequency jumped to provide a single readout point on the number of atoms vs frequency curve. All frequency sweeps were derived with rf techniques from a single laser so the velocity scale is absolute and uncontaminated by drifts. The + 880-MHz sweep in 1.6 ms gave an effective absorption rate of 10.7 photons/μs (saturation = 1 gives 31 photons/μs, 1 photon gives 3 cm/s). The swept sideband power was 10 mW in Wo ~ 4 mm, decreasing to ~ 350μW for readout. The measured velocity-offset and –drift rate were 24 MHz and 8 photons/μs at T = 15μs, with the velocity offset increasing to 40 MHz and the rate decreasing to 4 photons/μs at T = 100 μs. Over the same time interval, the velocity width monotonically increased from 12.1 to 17 MHz. The presence of heating—rather than cooling—infixed frequency conditions implies the existence of an optimum chirp rate and is not anticipated by some theories of the laser atom cooling dynamics.
Experimental study of light forces on atoms: diffraction and diffusion
Authors: Gould P. L. , Ruff G. A. , Martin P. J. , Picque J. L. , Stoner R. E. , Pritchard D. E.
Published: February 2023

We have observed both diffractive and diffusive regimes in the transfer of momentum to an atomic beam by a standing-wave radiation field. The momentum transfer was measured by passing a well-collimated beam of sodium atoms through a focused standing-wave laser waist. A narrow velocity distribution beam was obtained by utilizing a supersonic expansion and a two-state system was realized by optically pumping the beam prior to the interaction. The transverse momentum transferred to the atomic beam by the radiation field was measured by scanning a detector downstream from the interaction. The overall momentum resolution of the apparatus is less than the momentum of a single photon. The transition from diffractive to diffusive behavior is associated with an increase in the average number of spontaneous decays occurring during the interaction. In the diffractive regime, spontaneous decay is insignificant and momentum transfer proceeds by pairs of absorption/stimulated emission processes. This produces momentum exchange quantized in even multiples of photon momentum, the so-called Kapitza-Dirac effect; the deflection patterns show oscillatory structure. In the diffusive regime, spontaneous decay is important and causes fluctuations in the radiative forces. In addition, the recoil distribution associated with spontaneous decay results in a washing out of the diffraction peaks associated with stimulated processes, resulting in a smooth deflection pattern.
Parametric processes and gain saturation in resonantly enhanced optical phase conjugation in Na vapor near a two-photon resonance
Authors: Wunderlich Rainer K. , Garrett W. R. , Payne M. G.
Published: February 2023

Experimental studies have been made of conjugate wave generation in a Na metal vapor heat pipe. Detailed measurements of gain profiles, pump beam absorption, and parametric wave generation at infrared frequencies for phase conjugation near the two-photon resonance with the Na 4d2D5/2 state, yield details of the effects of parasitic processes on degenerate four-wave mixing. Studies are conducted with an excimer-pumped dye laser system with ~4 ns pulses of < 10mJ/pulse, traversing Na vapor heat pipe. Included in the measurements are pump beam depletion, probe and conjugate beam intensities, and infrared light which is generated by the strong pump beams through stimulated Raman (SR) and amplified spontaneous emission processes. The role of ac Stark shifting in degenerate four-wave mixing near the 4d level is studied. We find a new effect involving a large contribution to the ac Stark effect from the internally generated SR photons. We observe a rapid onset with pressure of stimulated Raman emission accompanied by a dramatic increase in the ac Stark profile of the 4d level, and the sharp onset of gain saturation for the phase conjugate signal, due to the competition of these two processes. This effect results in an ac Stark coefficient which can be very nonlinear in laser power and Na pressure.
Multiwave mixing and multiphoton ionization in strontium vapor
Authors: Bohmer K. , Reif J. , Matthias E.
Published: February 2023

Atomic strontium vapor in a thermionic diode is irradiated by the light from a tunable dye laser at two-photon resonance on the 5s5d1D2 state. At a laser intensity of ~ 108 W/cm2 and a vapor pressure of several torrs, not only three-photon ionization occurs but also the generation of new frequencies due to a nonlinear polarization is observed. Simultaneously, strong and strictly directed beams are generated which are resonantly enhanced by the 5s5p1P1 and 5s6p1P1 states, respectively. Close to the first resonance, four-wave mixing causes braodband two-photon emission, the bandwidth of which is determined by the region of negative dispersion due to phase matching. On the other hand the process via the 6p state is exactly resonant as can be shown by comparison in every case with the respective fluorescence light. At higher pressures (~ 10Torr), however, a second line appears, which is also shifted to the side of negative dispersion.
Efficient stimulated rotational Raman conversion in deuterium
Authors: Burnham Ralph , Hirsch Jeffrey
Published: February 2023

Stimulated rotational Raman scattering in hydrogen has been shown to be an extremely efficient mechanism for frequency con version and optical beam combining.1 In this work we have investigated deuterium as a rotational Raman medium. A frequency-doubled Q-switched Nd:YAG laser was used to pump a single pass 0.5-m Raman cell containing deuterium gas at densities between 1 and 10 amagats. Conversion into rotational and vibrational Stokes and anti-Stokes orders was measured as a function of deuterium pressure, laser power, and focusing geometry. By using circularly polarized pump light, it was possible to suppress all Raman orders except first rotational Stokes and to obtain an overall energy conversion efficiency of 72% into first Stokes at pressures between 4 and 6 amagats. Time-resolved oscillograms of the pump and Raman laser outputs show that during the first 2 ns of the 8-ns FWHM pump pulse Raman conversion is suppressed, while during the remainder of the pulse conversion to the first rotational Stokes proceeds with near unit quantum efficiency. The initial delay in onset of the Raman process is thought to arise from the transient buildup time associated with the relaxation time of the Raman medium.
Theory of atomic motion in laser light
Authors: Cohen-Tannoudji C.
Published: February 2023

Simple physical pictures using the dressed atom approach are introduced for understanding atomic motion in laser beams.1 New cooling schemes are suggested.
Photofragment spectroscopy with VUV lasers: product correlations and alignment
Authors: Hepburn J.W.
Published: February 2023

The experimental technique that provides the most detail about photofragmentation dynamics is pump-and-probe photofragment spectroscopy, in which laser spectroscopy is used to detect the products of laser photolysis. One of the major limitations of this technique is the development of state-sensitive laser detection for the atomic and diatomic products of small molecule photolysis. By using tunable vacuum ultraviolet generated by frequency mixing, the number of photofragment products that can be detected by laser spectroscopy is greatly expanded.
High resolution spectroscopy and soft x-ray lithography using high-repetition-rate laser-produced plasma light sources
Authors: Ginter Marshall L. , McIlrath Thomas J.
Published: February 2023

Laser-produced plasmas are convenient laboratory light sources for many experiments in the ~1-200-nm region. We describe the properties of such a source when driven by either of two high repetition rate laser systems: a Nd:YAG laser (1064 nm) with ~600 mJ, 25-ns pulses, and a 10-Hz repetition rate and a krypton fluoride laser (249 nm) with ~300 mJ, 20-ns pulses, and a 150-Hz repetition rate. Power densities in the incident pulses at the focal spot on the plasma source targets generally were around 1011 W cm-2. The source’s cyclindrical metal targets can be rotated to provide fresh material for every shot1 and the plasma is viewed at right angles to the incident laser beam with the normal to the surface at the focal spot being ~45° to both the laser beam and the viewing direction. The source provides a simple, inexpensive laboratory competitor to synchrotron radiation for both spectroscopy and lithography, as demonstrated by the examples presented.
Bound—free absorption (photoassociation) in KrF
Authors: Schloss J. H. , Geohegan D. B. , Eden J. G.
Published: February 2023

Bound — free absorption of ultraviolet radiation by colliding pairs of rare gas-halogen atoms represents a potentially serious loss mechanism in the excimer lasers. This paper reports an investigation of the photoassociative production of KrF[Kr + F + ℏω)(248nm) → KrF(B)] in various Kr/F2 mixtures in order to obtain an absolute cross section forthe process. The studies involved the use of two KrF lasers. The first laser (I1 < 500 MW cm-2) was used to dissociate F2 and was fired ~1 μs prior to the firing of the second (l2 < 100 MWcm-2). The latter served to photoassociate the Kr-F collision pairs. Because of the efficient conversion of KrF(B) to Kr2F(42Γ), spontaneous emission from the Kr2F(42Γ) state was monitored to measure the photoassociation absorption strength. The intensity dependence of the photoassociation process was measured as a function of the intensity of each laser and the partial pressures of the reactants. The effective cross section obtained for the absorption is 3.2 × 10-18 cm2, a factor of 2 larger than the Kr2F absorption cross section at 248 nm. Also investigated were the effect of the time delay between the two KrF lasers, rates for quenching of Kr2F(42Γ) by both Kr and F2, and the wavelength dependence of the photodissociation effect. The impact of this process on KrF lasers is discussed.
Spectral narrowing of a storage ring free-electron laser using a birefringent plate
Authors: Elleaume Pascal
Published: February 2023

It has been proposed to reduce the spectral width of a free-electron laser using a birefringent plate at the Brewster angle. The linewidth can be controlled by rotating the plate. This would be particularly useful for a storage ring FEL where a linewidth of 10-5–10-6 should be achievable without significant reduction of gain. Sapphire looks like a good candidate in the 0.15-1.0μm wavelength range.
Nonlinear intracavity optical devices for free-electron lasers
Authors: Cutolo Antonello , Schultz John
Published: February 2023

Several kinds of nonlinear optical devices have been proposed to exploit and extend the tunability and pulse structure of free-electron lasers, for example, the acoustooptic output coupler designed for the MK III infrared FEL at Stanford University [Appl. Opt. 23,2935 (1984)].
3-D simulation of the self-focusing phenomenon in FELs using a novel method
Authors: Tang C.-M. , Sprangle P. , Ting A.
Published: February 2023

In a high gain FEL, the radius of the radiation field can remain approximately constant over many Rayleigh lengths due to the self-focusing phenomenon. Fully 3-D simulations of the FEL in this operating regime, including energy spread and finite emittance, can be costly. In this paper we present a technique that could reduce the computational requirements for a strongly self-focused FEL. The radiation field is expanded in a set of Hermite polynomials in which the arguments and coefficients are determined by the particular source term in the wave equation somewhat like a WKB expansion. In this novel formalism, the lowest-order terms are a good approximation to the exact solution. We present 3-D numerical results with this technique and compare them with the analytical results.
CO2 laser front end for the Paladin FEL
Authors: Lowenthal D. D. , Barrett D. A. , Demboski J. S.
Published: February 2023

This paper describes the design, fabrication, and testing of a turnkey CO2 laser system constructed by Spectra Technology, Inc. for the LLNL Paladin FEL. The laser forms the front end driver for the FEL experiment and must deliver > 250 mJ in 50 ns at a rep rate of up to 1 Hz. In addition, the laser must operate in a single longitudinal mode and have a transverse TEM00 beam profile. The pulse-to-pulse energy must be consistent over 1-h run times and the intensity, within the 50-ns pulse, must be flat to ≲ 20%. The delivered laser system employs three atmospheric UV preionized discharge lasers, and a low pressure cw laser that provides the single longitudinal line lock capability, as well as an alignment tracer beam. Fifty-nanosecond pulses are sliced from the oscillator output with a CdTe switch and Brewster stack polarizers. Technical features of the laser are described which are required to meet the laser system specifications. Performance data for the completed laser are presented.
M2 Parameter of Multimode Laser Diode Beam Transformation in Real Asymmetric Optical Systems
Authors: Jabczynski Jan
Published: February 2023

Generalization of M2 parameter on the case of asymmetric, multimode laser beam and array of laser beams is proposed. The geometrical method of propagation of beams of this type in real asymmetric optical systems, not restricted to paraxial approximation, is presented. The quality of lens design destined to transform of this type beam is discussed and the appropriate criterion based on transformation of M2 parameter is proposed. The examples of application of this method to the problem of diode laser beam formation are presented and discussed.
Cemented Aplanatic Doublet Corrected for Secondary Spectrum
Authors: Ditteon Richard , Guan Feng
Published: February 2023

The typical cemented achromatic doublet has one free degree of freedom which may be used to correct spherical aberration. In addition, it is possible to choose the glasses of the doublet so that either coma or secondary spectrum may be corrected. We have developed both a numerical and an analytical method for searching for pairs of glasses. With these methods, we were able to conduct an extensive search and to find a glass pair capable of correcting both coma and secondary spectrum at the same time.
New Direct Derivation of Monochromatic Off-Axis Aberration Coefficients
Authors: Malacara Daniel , Malacara Zacarías
Published: February 2023

A new direct and simpler manner to find the monochromatic off-axis primary aberration coefficients is presented. The advantage of this derivation is that a good geometrical insight of the definition and meaning of these aberrations is obtained. Several interesting characteristics of these aberrations are easily visualized with this method.
Aberration Calculation Methods and Aberration Correction Strategies for the Design of Apochromatic Optical Systems
Authors: Maxwell Jonathan
Published: February 2023

The correction of higher order chromatic aberrations in high performance wide spectral band optical systems is the main barrier to achieving improved performance. These higher order chromatic aberrations appear in the form of longitudinal secondary spectrum, transverse secondary spectrum and chromatic variations of the monochromatic aberrations. The origins of some of the chromatic variation aberrations are discussed and some analysis methods for these aberrations are reviewed, with some suggestions for simple extensions to the methods that can be used for their calculation.
Modelling of, and Design for, Thermal Radial Gradients in Lenses for Use with High Power Laser Radiation
Authors: Beckmann Leo H. J. F.
Published: February 2023

The residual absorption of materials for use in handling of carbon dioxide laser radiation causes radial thermal gradients in rim cooled lenses. A model is presented, which considers the effects of thermal expansion, the varying refractive index over the ray height, and ray bending due to the radial index gradient. The last effect is predominant in most practical lenses. The model has been verified experimentally using lenses with 1% to 2% absorption, and agreement between measured and calculated focal shift within 10 percent has been reached.

The effect has practical consequences for the design of high performance lens systems, because the thermal gradient also affects the spherical aberration. As one may expect, that lens absorption gradually increases over the lifetime, a design should be optimized for a somewhat higher temperature gradient than would be found in new lens elements. A design example is discussed.
Development of a Software for Optical Design
Authors: An Liansheng , Li Lin
Published: February 2023

A personal computer aided software for optical design: SOD88, which is the most prevalent software in optical design of China, is described in the paper. The main functions, mathematical models and distinguishing features of most programs in the software are also introduced. Many precision optical instruments, such as satellite cameras, planetarium systems, metallography mioroscopes, etc. have been designed with the help of SOD88. And now SOD88 is playing more and more important rules in today’s modernization of China.