bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization Dependence of the Ionization of Helium and Neon by 120 Femtosecond Pulses at 614 nm
Authors: Fittinghoff D. N. , Bolton P. R.
Published: February 2023

A strong polarization dependence is observed for the helium and neon ion yields for the higher charge states produced by 120-fs pulses of 614-nm light.
Does the Pondermotive Force Prevent Atomic Stabilization?
Authors: Katsouleas T. , Mori W. B.
Published: February 2023

The drift of an atomic electron in the pondermotive (v x B) force of a laser can take the electron away from the atom and prevent stabilization.
Stability Analysis of Relativistic and Charge-Displacement Self-Channeling of Intense Laser Pulses
Authors: Borisov A. B. , Shiryaev O. B. , McPherson A. , Boyer K. , Rhodes C. K. , Solem J. C.
Published: February 2023

Theoretical modeling of the stability of relativistic and charge displacement self-channeling of high power laser pulses in plasmas leads to the establishment of stability maps for self-channeling propagation of laser pulses. The problem of stability of relativistic and charge displacement self-channeling of intense ultrashort laser pulses in cold undercritical plasmas against small azimuthal perturbations is analyzed. The problem is studied for both an initially uniform plasma and for a preformed plasma column. In the plane of dimensionless parameters ρo = roωp,o/c and η = Po/Pcr, which depends on the initial values of the focal spot radius, power of the laser beam and the unperturbed density of the plasma, the boundary separating the regimeis of the stable self-channeling and of the strong filamentation is defined. It is found that for ρ
o
≈ ρeig,o (ρeig,o being the dimensionless radius of the zeroth eigenmode of the studied problem) the relativistic and charge-displacement self-channeling is stable for any value of initial power Po > Pcr. It is also shown that in the case where η ≈ 10, the relativistic and charge-displacement self-channeling is stable for practically any value of ρo. It is found that the location of the boundary separating the two regimes of propagation is essentially independent of the initial curvature of the phase front of the beam. The dependence of the location of the stable region on the parameters governing the amplitude of the azimuthal perturbation is also weak. The results emphasize the extreme importance of the stabilizing role of charge-displacement in these plasma interactions. A procedure for optimization of laser beam and plasma parameters for experimental realization of the relativistic and charge-displacement self-channeling is developed. The proposed method of investigation of the stability and the optimization of the self-channeling of laser pulses can be applied generally to various cases involving nondissapative media with saturating nonlinearities.
Electron Energy Distributions in Plasmas Produced by Intense Short-Pulse Lasers
Authors: Glover T. E. , Falcone R. W. , Crane J. K. , Perry M. D.
Published: February 2023

We report the first measurements of time-resolved electron energy distributions in plasmas of interest to recently proposed x-ray laser schemes.
Short-Pulse X-Rays from Porous Targets
Authors: Gordon S. P. , Donnelly T. , Hamster H. , Sullivan A. , Falcone R. W. , Sheppard R. , Price D. , White B. , Osterheld A.
Published: February 2023

We have exploited the enhanced absorption of laser energy by structured targets to develop efficient short- pulse x-ray sources. We measured enhancement of x-ray emission from grating targets and 1 mJ of x-ray emission above a kilovolt from porous gold targets. We also studied broadband emission and K-shell spectra from porous aluminum targets.
Generation of Ultrabright Beams in High Energy NdrGlass and KrF Laser Systems
Authors: Key M. H. , Barr J. R. M. , Barzanti L. , Chang Z. , Damerell A. R. , Danson C. N. , Edwards C. B. , Evans J. M. , Hancock S. , Hanna D. C. , Hooker C. J. , Houliston J. R. , Hutchinson M. H. R. , Kidd A. K. , Luan S. , Mercer I. P. , New G. H. C. , Norreys P. A. , Osvay K. , Pepler D. A. , Rodkiss D. A. , Ross I. N. , Schäfer F. P. , Shaw M. J. , Sibbett W. , Smith R. A. , Szatmari S. , Taday P. , Toner W. T. , Winstone T. , Wyatt R. W. , Zhou F.
Published: February 2023

The development of ultrabright lasers is progressing rapidly particularly in the direction of table-top-terawatt systems operating at high pulse repetition rate with relatively low pulse energy. The highest pulse energies and highest absolute powers are being generated by the adaptation of larger-scale high energy laser systems operating in single pulse mode. The maximum focused intensity from either type of laser is determined by the beam brightness B which can be expressed in units of Watts cm-2 sterad-1. The focused intensity is then approximately B/f2 where f is the focal length to diameter ratio of the focusing optic. Brightness can be expressed as B = PS/λ2 where P is the power, λ the wavelength and S the Strehl ratio, quantifying the ratio of brightness in a beam with less than diffraction limited quality to that in a diffraction limited beam.
Recent Progress of Terawatt Excimer Laser Sources
Authors: Tittel F. K. , Mossavi K. , Szabó G.
Published: February 2023

Subpicosecond pulses first in the visible and more recently at 193 nm have been amplified in an electron- beam excited XeF(C→A) and ArF(B→X) excimer laser amplifier to pulse energies in the hundred millijoule range. Details of the current experimental program and future prospects will be described.
Angstrom-level noncontact profiling of mirrors for soft x-ray lithography
Authors: Glenn Paul
Published: February 2023

We have previously described a new noncontacting profilometer with Angstrom-level precision and accuracy1,2,3. We have used this instrument to measure a variety of profiles, from diametral scans of steep aspheres to axial and circumferential scans of cylindrical elements. Here we review the theory of operation, show some relevant measurement results, and discuss the upgrades underway that will make the instrument particularly well suited to the exotic mirrors needed for soft X-ray lithography.
Design and Analysis of Multi-Mirror Soft X-Ray Projection Lithography Systems
Authors: Shealy David L. , Wang Cheng , Viswanathan V. K.
Published: February 2023

Recently, there have been a number of reports where two-mirror inverted Schwarzschild microscopes, which were coated with appropriate multilayers, have been used in soft x-ray projection lithography experiments and have obtained resolutions as small as 50 nm [1-3]. A projection optics design survey [4] reported that the Schwarzschild type optics will have a field of view less than 1 mm with a resolution of 0.1 microns. However, it has been demonstrated [4,5] that four-mirror projection systems can be designed by conventional techniques to have a resolution less than 0.1 micron over a 20 mm field of view with distortion limiting system performance. Canon has disclosed [6] a number of three- and four-mirror projection lithography systems which are reported to yield 0.25 micron resolution over large fields of view.
Soft x-ray spectra from laser plasma effectively heated by a pulse train laser
Authors: Hirose Hideo , Hara Tamio , Ando Kozo , Negishi Fumiko , Yashiro Hidehiko , Aoyagi Yoshinobu
Published: February 2023

Considerable progress has been made in the development of soft x-ray laser since 19851-2). Until now a powerful laser of single or double pulses has often been used to produce high density plasma. Recently we observed ASE (amplified spontaneous emission) in some lines of A1 X and A1 XI in a recombining plasma produced by a very low power laser of only 2 J which was composed of a train of many low power pulses separated by about 350 picosecond3). To understand more clearly the effect of multipulse irradiation on the production of laser plasma and x-ray emissions including ASE, in this paper we constructed a pulse train forming system and investigated the emitted soft x-ray spectra for various pulse trains. Our final goal is to develop a table top x-ray laser in the water window wavelength.
Longitudinal pumping by an ellipsoidal reflector for short-wavelength lasers
Authors: Midorikawa Katsumi , Tashiro Hideo , Watabe Toshihisa , Obara Minoru
Published: February 2023

We have designed and tested an ellipsoidal reflector to pump short-wavelength lasers by soft x-ray radiation from laser produced plasma. A gaseous medium supplied by a slit nozzle was pumped longitudinally along the optical axis in the region of the second focus. Soft x-ray absorption and VUV emission of gaseous medium have been investigated.
A Search for Gain on 2p-2s Transitions in a Collisionally Excited Ge Plasma
Authors: Enright G.D. , Baldis H.A. , Dunn J. , La Fontaine B. , Villeneuve D.M. , Kieffer J.C. , Pépin H. , Chaker M.
Published: February 2023

Soft x-ray amplification in collisionally excited Ne-like Ge plasmas has been extensively studied. Gains in excess of 4 cm–1 have been reported for the 3p-3s transitions. Significant gains have been observed over a wide range of irradiance conditions. The present experiments make use of a novel focusing arrangement[1] that employs a segmented wedge array (SWA) to overlap several line foci to produce a highly uniform linear plasma. The reproducibility of the XUV spectra was improved allowing gain to be inferred on a core-excited 2s2p63d-2s2p63p J=2-1 transition[2]. The 3d-2s quadrupole (E2) emission from the upper state of this transition was also identified in the L-shell emission spectrum. These measurements have now been extended into the 60-80 Å region where gain on 2s2p63s-2s2p53s and 2s2p63d-2s22p63d transitions is expected. Observation of gain on these Ne-like transitions would be significant as it would allow Ne-like lasers to scale to shorter wavelengths, into the "water window".
Tolerances of a Reflective Imaging System
Authors: Itou Masaaki , Terasawa Tsuneo
Published: February 2023

A number of reflective imaging systems have been designed for use in soft X-ray projection lithography.1,2 Optical surface figure errors in these imaging systems, however, degrade resolution as well as cause changes in image positions, which in turn degrade overlay accuracy. We therefore evaluate the figure tolerances of a four-mirror imaging system by ray-tracing calculations.
Constraints on Pulse Power and Duration for Soft X-ray Lithography Systems
Authors: Liddle J. A.
Published: February 2023

In any of the high-throughput lithography systems designed to operate at 0.25μm design rules and below, SXPL, X-ray 1:1, projection ion-beam or projection e-beam, there will be a significant amount of power flowing through the system. The effect of thermal loading must be included in the system design, for example, in the provision of heat sinks or the use of certain materials to reduce the effects of thermal expansion. In most cases distortions due to steady state heating can be compensated for or reduced to an acceptable level. However, in the case of a pulsed source, there are fundamental limits to the possible range of pulse power and duration that can be employed.
Cryogenic targets for Laser Plasma X-Ray Lithography Sources
Authors: Richardson Martin , Gabel Kai , Jin Feng , Silfvast William T.
Published: February 2023

It is now generally recognized that the source of preference for soft x-ray projection lithography is a high repetition-rate (1200 Hz) laser plasma source1. The design of this source is usually envisaged as comprising a compact high repetition-rate laser, preferably a solid-state laser, diode-pumped, and a renewable target system capable of operating for prolonged periods of time. For a production-line facility, this would imply uninterrupted shot cycles of > 3 x 106 shots. In addition, current cost scenarios of the complete irradiation system suggest that the unit shot cost must be in the vicinity of $ 10-6 per shot2. These stringent requirements press the boundaries of current technologies. Moreover, recent studies of the particulate matter ablated from solid and tape targets under laser irradiation conditions similar to those deemed optimum for 13 nm soft x-ray generation, suggest that these types of targets will be unsuitable3. The levels of neutral clusters of particulate matter and of high velocity ions are many orders of magnitude above those that can be tolerated in an environment requiring the long-term preservation of expensive, high-reflecting multilayer collecting optics. It is thus our viewpoint that considerable progress must be made in the design of efficient soft x-ray-emitting laser plasmas for them to satisfy the needs of projection lithography.
Enhanced performance of KrF laser-induced x-ray sources and multilayer mirrors for soft x-ray projection lithography
Authors: Bijkerk F. , Louis E. , Shmaenok L. , Voorma H.-J. , van der Wiel M.J. , Schlatmann R. , Verhoeven J. , van der Drift E.W.J.M. , Romijn J. , Rousseeuw B.A.C. , Vob F. , Désor R. , Nikolaus B.
Published: February 2023

The rapid development of high average power excimer lasers pushes the potential of a laser plasma x-ray source for SXPL. Now that the problem of debris production is solved at least at the prototype level [1] the source might be a candidate for operation in an industrial environment. The development of high reflectivity multilayer coatings for soft x-rays at normal incidence makes it possible to produce a demagnifying x-ray optical system. Together with an x-ray reflection mask all ingredients to develop a SXPL system are present. A cooperation of research institutes, semiconductor industry, resist and laser manufacturers has been set up to develop the process technology required.
High Average Power Mode-Locked Co:MgF2 Laser*
Authors: Johnson B. C. , Rosenbluh M. , Moulton P. F. , Mooradian A.
Published: February 2023

The use of Co:MgF2 as a laser material was first demonstrated in the early years of laser development [1]. More recently, vibronic lasers such as Co:MgF2 have proven to be versatile, broadly tunable, cw and pulsed sources of infrared radiation [2,3]. We report here the first tunable, cw mode-locked operation of this laser.
Generation of 90 fs Pulses with a CPM Laser Pumped by a Frequency-Doubled CW Mode-Locked Nd:YAG
Authors: Norris T. , Sizer T. , Mourou G.
Published: February 2023

The chief advantage of the synchronously-pumped dye laser with a frequency-doubled cw mode-locked Nd:YAG is that it allows for synchronous amplification using pump pulses shorter than 100 ps.1-2 The colliding pulse mode-locked dye laser, on the other hand, has the advantage of producing stable ultrashort pulses. We have developed a dye laser which is both synchronously pumped and colliding pulse mode-locked, yielding 90 fs pulses synchronized to an RF source with a jitter less than 20 ps.
Photoinduced Electron Transfer in Polymethylene Linked Donor Acceptor Compounds: A-(CH2)n-D
Authors: Staerk H. , Kühnle W. , Mitzkus R. , Treichel R. , Weller A.
Published: February 2023

In recent years much valuable information on the dynamical behaviour of dissolved flexible molecules has been obtained from measurements of picosecond and nanosecond fluorescence and absorption kinetics [1 - 3]. Our attention in this field has been concentrated on the question of conformational requirements for fluorescence quenching, leading to exciplexes or radical pairs, and on the mechanisms of electron back transfer.
Picosecond Transient Absorption Spectra of Metalloporphyrins: Zinctetraphenylporphyrin
Authors: Doust Tom , Giorgi Linda , Gore Bryson , Porter George
Published: February 2023

Metalloporphyrins and related compounds have been widely used as sensitisers in the photolysis of water for solar energy storage. In particular, zinc porphyrins have been used with considerable success in this laboratory in hydrogen generating systems (1). Whilst this photochemistry originates from relatively long lived triplet states, a knowledge of the primary photophysics is clearly important. Furthermore, in heterogeneous photochemical systems, reaction often occurs from excited singlet states, as it does in photosynthesis. We present here excited state absorption spectra of zinctetraphenyl porphyrin.
Picosecond Spectroscopy on the Primary Process in the Photoconversion of Protochlorophyllide to Chlorophyllide a
Authors: Kobayashi Takayoshi , Iwai Jun-ichi , Ikeuchi Masahiko , Inoue Yorinao
Published: February 2023

A key step in the development of chloroplasts in higher plants is the reduction of the precursor protochlorophyllide (PChlide) into chlorophyllide (Chlide), which is then esterified by phytol. The reduction process is activated by light and it involves the attachment of two hydrogen atoms. Spectroscopic studies of etiolated leaves or isolated etioplasts at low temperatures have been extensively performed for the investigations on the primary states of the chlorophyllide formation. However little is established about the detailed mechanism of this process at the present stage of research.
Soliton Shaping Mechanisms in Passively Mode-Locked Lasers and Negative Group Velocity Dispersion Using Refraction
Authors: Martinez O. E. , Gordon J. P. , Fork R. L.
Published: February 2023

We have developed analyses of soliton shaping mechanisms in a colliding pulse passively mode-locked laser and of the adjustable group velocity dispersion obtainable from pairs of prisms2,3,4. We find that the soliton mechanisms aid in generating pulses which are shorter by the order of a factor of two than otherwise obtainable and also provide improved stability of the laser against changes in the net gain. The negative group velocity dispersion, which we show necessarily accompanies any angular dispersion, is of interest in that it provides an experimental means of introducing adjustable low loss group velocity dispersion in the laser resonators. This should be useful in examining these soliton shaping mechanisms.
The Soliton Laser
Authors: Mollenauer L. F. , Stolen R. H.
Published: February 2023

The soliton laser1 is a novel mode-locked device employing a length of single mode fiber in its feedback loop. Its pulse width can be made to have any desired value, down to a small fraction of a picosecond, through choice of the fiber’s length. Operation is based on the ability of single mode fibers, in the region (λ> 1.3 µm) of negative group velocity dispersion, to support periodic soliton pulses, as well as to narrow broader pulses of the same energy.2,3 As the fiber is the all-important control element, pulse shape and width are largely independent of factors, such as details of gain dynamics, pump pulse width, etc., that are normally of prime importance in mode-locked lasers.
Picosecond Transient Raman Spectroscopy: The Excited State Structure of Diphenylpolyenes
Authors: Gustafson T.L. , Chernoff D.A. , Palmer J.F. , Roberts D.M.
Published: February 2023

The spectroscopy of diphenylpolyenes, particularly the ordering and structure of the electronic excited states, is of interest because of the role that polyenes have in various photochemical and biological processes. These molecules have been studied vigorously for many years, both by steady-state measurements (1) and, more recently, by direct observation of the dynamics with high time resolution (2).
Third Oder Nonlinear Susceptibilities of Dye Solutions Determined By Non-Phasematched Third Harmonic Generation
Authors: Penzkofer A. , Leupacher W.
Published: February 2023

The third order nonlinear susceptibilities
χxxxx(3)(−ω3;ω1,ω1,ω1) of the dyes rhodamine 6G, fuchsin and methylene blue in methanol are determined versus concentration by non-phasematched third harmonic generation with picosecond light pulses from a mode-locked Nd-glass laser. For quantitative measurements a special experimental arrangement is used that avoids disturbing light production by surrounding media. The contributions from air are suppressed by slightly focusing the light beam to a sample cell in a vacuum chamber. The cell windows are adjusted to an even integer of the coherence length ℓcoh=π/Δk (Δk=k3-3k1=3ω1 (n3-n1)/c is the wave vector mismatch) so that the third harmonic signal at the exit surface is equal to the third harmonic signal at the entrance surface. The output third harmonic signal originates only from the sample under investigation. By laterally displacing the slightly wedged cell the Maker fringe pattern of light generation is detected for transparent media.
Subpicosecond Electro-Optic Sampling Using Coplanar Strip Transmission Lines
Authors: Meyer K.E. , Mourou G.A.
Published: February 2023

A sampling technique using the electro-optic effect capable of characterizing subpicosecond electrical signals has recently been demonstrated. In this system 100 fs pulses from a colliding pulse mode-locked laser were used to generate the electrical test signal via a Cr:GaAs photoconductive switch. A second beam of pulses was used to probe the birefringence induced by the electrical pulses as they propagate down a balanced stripline fabricated on LiTaO3. Signal averaging allowed submilli­volt signals to be recovered. The best temporal response of the system was achieved with the velocity matched geometry, which was obtained for a particular angle of incidence of the probe beam on the electro-optic crystal In this configuration a risetime of 500 fs was obtained. During this work it was observed that strong dispersion effects were taking place when the wavelength of the electromagnetic signal approached the cross-sectional dimensions of the transmission line. Temporal resolution is improved and dispersion effects are reduced as the dimensions of the stripline are reduced. In order to further improve the temporal response of the sampler in this configuration, the thickness would have to be reduced to the order of 10 μm, which presents severe fabrication difficulties.
Femtosecond Laser Interaction with Metallic Tungsten and Nonequilibrium Electron and Lattice Temperatures
Authors: Fujimoto J.G. , Liu J.M. , Ippen E.P. , Bloembergen N.
Published: February 2023

Multiphoton photoelectron emission from metals has been the subject of experimental and theoretical investigation for several years [1]. The development of high intensity ultrashort pulse laser sources has made possible the extension of these studies into the picosecond time regime [2,3]. For intense pulses of short enough duration, it has been postulated that a transient nonequilibrium between the electrons and phonons may be generated [4]. This phenomenon has been termed anomalous heating and is predicted when the laser pulse durations are comparable to or shorter than the electron-phonon energy relaxation time. Because of the smaller heat capacity of the electron gas, heating of the electrons to temperatures in excess of the lattice melting temperature would then be possible. Previous experimental investigations of photoelectron emission have been performed with picosecond pulses in attempts to observe anomalous heating [2,3]. To date, none have achieved the temporal resolution necessary for such an observation. However, very recently, indirect eveidence of transient heating has been reported using picosecond reflectivity measurements in copper [5].
Picosecond Dynamics of Polaritons in Anthracene - a Spectrochronographic Study
Authors: Aaviksoo J. , Freiberg A. , Lippmaa J. , Reinot T. , Saari P. , Savikhin S.
Published: February 2023

One of the most promising fields for picosecond spectroscopy is resonant secondary emission, as by making use of this optical response there is no need to apply strong excitation or additional probing on the sample, which may disturb the processes under study. The introduction of a sensitive spectrochronography method [1] has made the temporal resolution of hot luminescence spectrum possible [2], providing thus a direct measure of the vibrational relaxation processes in the excited electronic state of an impurity centre. The physical situation is more intriguing when light-matter interaction cannot be considered in the perturbation approach and one has to use polaritons to describe the properties of the secondary spectrum [3]. Some special features in the temporal behaviour of the polariton luminescence spectrum of anthracene were revealed already in a nanosecond study [4]. Since the first report on picosecond luminescence kinetics [5] we have carried out a systematic study of polariton dynamics in anthracene crystals at low temperatures in order to distinct between the scattering/luminescence processes and to elucidate the effective decay channels of the primary excitations.
CW Modelocked Nd: Phosphate Glass Laser
Authors: Strobel Scott , Lee Chi H. , Burdge Geoffrey L.
Published: February 2023

A stable CW modelocked Neodymium glass laser operating at 1.053 µm has many applications; for example laser fusion and ranging. So far, CW modelocking in this wavelength region has been achieved with a Nd:YAG crystal, yielding 100 picosecond pulses. We have obtained 33 picosecond pulses from a Neodymium phosphate glass laser. Shorter pulses (even subpicosecond) are expected because of the larger spectral bandwidth of the phosphate glass.
Stable Active-Passive Mode Locking of a Nd: Glass Laser Using #5 Saturable Dye
Authors: Goldberg Lawrence S. , Schoen Paul E.
Published: February 2023

While the stability of passively mode locked Nd:YAG lasers has been greatly improved through use of intracavity acoustooptic loss modulators, relatively little attention has been given to the Nd:glass laser, especially in the very short pulse regime [1-6]. In this hybrid approach, the active loss modulation reduces the inherent statistical nature of the early stage pulse build up, while retaining the effect of the saturable absorber as nonlinear loss element and Q switch for final stage pulse shortening. In this paper, we report on active—passive mode locking of a Nd:phosphate glass laser through use of the new #5 saturable absorbing dye, which has enabled generation of ~6 ps duration transform-limited pulses largely free of occurrences of satellite pulse structure.
Novel Method of Waveform Evaluation of Ultrashort Optical Pulses
Authors: Guo Feng-Chen , Kobayashi Tetsuro , Morimoto Akihiro , Sueta Tadasi , Cho Yoshio
Published: February 2023

For the measurement of ultrashort optical pulses SHG auto-correlation method has been most popularly used1,2. For this case, an adequate pulse shape such as sech2, Gauss, etc., is presumed and then the correlation-width is converted into the pulsewidth. Since one SHG correlation curve dose not correspond identically to one pulse waveform, this method includes inevitable ambiguity and is, particularly, not applicable to the pulse with unfamiliar or unpresumable waveform.
Rapid Quenching of the Excited State of F-Centers by −OH Defects in KCl
Authors: Jang Du-Jeon , Corcoran Timothy C. , El-Sayed M. A. , Gomes Laercio , Luty Fritz
Published: February 2023

It was shown1 that the electronic luminescence and photoionization of the excited F (F ) centers in KCl reduces drastically with increasing amounts of −OH molecular defects, suggesting a strong coupling between F* centers and −OH defects. Previously, the rate of the fluorescence quenching due to the coupling could not be determined due to the instrumental resolution. The main purpose of this work is to measure the rate of the quenching using picosecond techniques to determine the type of the electronic coupling (i.e., mutipolar vs electron exchange) as well as the phonon assistance in the process. Our results are obtained from the ground state bleach recovery kinetic studies of the F-centers as a function of −OH concentration and temperature using a picosecond streak camera absorption spectrometer.2
Photoemissive Sampling of Picosecond Electrical Waveforms
Authors: Weiner A. M. , Marcus R. B. , Lin P. S. D. , Abeles J. H.
Published: February 2023

The development of high-speed electrical devices and circuits which operate in the picosecond range has stimulated a need for measurement techniques with correspondingly high temporal resolution. Optoelectronic sampling methods, in which psec on fsec laser pulses are used to interrogate the waveform on the test sample, have been developed for this purpose [1–3]. In this talk we describe a new approach in which sampling of electrical waveforms is achieved by spectral analysis of photoelectrons generated by ultrashort light pulses. Our technique is applicable to silicon based devices as well as to devices based on compound semiconductors.
High Speed Circuit Measurements Using Photoemission Sampling
Authors: Bokor J. , Johnson A. M. , Storz R. H. , Simpson W.
Published: February 2023

We report the development of a new technique for measurement of high speed signals in electronic devices. The method is based on the energy analysis of electrons emitted from the surface of a metallization line on the device by multiphoton photoelectric effect in vacuum using a low powered, cw mode-locked laser source. Changes in the potential of the surface give rise to shifts in the photoemitted electron energies, which can be measured using a simple, retarding field electron energy analyzer. Since the method involves the direct measurement of voltage on a metal line, it can be used on any type of electronic device, regardless of the electronic material being used to fabricate the device. Furthermore, the opacity of the metal eliminates the possibility of perturbation of device performance by absorption of the laser radiation in the semiconductor.
Picosecond Laser Study of the Collisionless UV Photodissociation of Energetic Materials
Authors: Mialocq Jean-Claude , Stephenson John C.
Published: February 2023

It is of interest to establish the pathways and mechanisms for the UV photodecomposition of nitrocompounds in order to cast new light on the physical and chemical processes occurring in the thermal decomposition of energetic materials. We report a picosecond pump-probe study of the collision-free dissociation of gaseous energetic materials after photoexcitation by picosecond laser pulses at 266 nm. Model compounds under study are nitroalkanes (RNO2) and dimethylnitramine (DMNA) in the gaseous phase.
Nonlinear Responses of Picosecond Photodetectors to Photogenerated Carriers
Authors: Carruthers T. F. , Weller J. F.
Published: February 2023

We report a simple means of measuring device response times which is similar to cross-correlation techniques on linked pairs of photodetectors but which avoids the bandwidth limitations imposed by interconnecting transmission lines and largely eliminates the need for elaborate device mounting procedures [1,2]. Measurements are therefore possible on devices, such as those which must be mounted singly or those which are embedded in an integrated circuit without direct electrical access, whose intrinsic response speeds were previously not observable.
Femtosecond Pulse Generation From Passively Mode-Locked Continuous Wave Dye Lasers 550 Nm - 700 Nm
Authors: French P M W , Taylor J R
Published: February 2023

The passively mode-locked continuous-wave dye laser has provided the source of the temporally shortest pulses since its inception in 1972(1). However, over the past fourteen years only a single combination of active/passive dye has been used, namely that of Rhodamine 6G and DODCI, consequently limiting the spectral extent of the system to ~ 610 - 640 nm. With optimised and dispersion compensated cavities being capable of producing pulses as short as 27fs(2), additional passively mode-locked cw dye lasers present an attractive and simple alternative to conţinuum generation (3) or external pulse compression of synchronously pumped dye lasers (4) as the source of frequency tunable femtosecond pulses.
Solvation Dynamics in Polar Liquids: Experiment and Simulation
Authors: Maroncelli M. , Castner E.W. , Webb S.P. , Fleming G.R.
Published: February 2023

Current theoretical studies by a number of workers have focussed attention on the importance of solvation dynamics in determining the rates of reactions in solution1. This is especially true of reactions involving substantial charge redistribution in the reaction coordinate in polar solvents, where solvation energies may be quite large. The first step in testing these ideas is to obtain direct, microscopic measures of the kinetics of dipolar solvation. Experimentally, such information is available by monitoring the temporal evolution of the electronic spectrum of a probe solute after instantaneously changing its charge or dipole moment. Spectral shifts as a function of time directly monitor the course of solvation as the system reequilibrates to the new solute charge distribution.
Fractal Behaviors in Two-Dimensional Excitation Energy Transfer on Vesicle Surface
Authors: Tamai Naoto , Yamazaki Tomoko , Yamazaki Iwao , Mataga Noboru
Published: February 2023

Excitation energy transport and trapping in molecular assemblies have been the subject in recent theoretical and experimental photophysics. Very little is known about the dynamical characteristics of dipole-dipole energy transfer in restricted geometries of one- and two-dimensional molecular arrangements. The present paper reports on the two-dimensional excitation energy transfer between dye molecules adsorbed on vesicle surface by using a picosecond time-correlated, single-photon counting apparatus [1]. The fluorescence decay curves of the donor are analyzed on the basis of a theoretical framework of "fractal" [2], following a manner of Klafter and Blumen [3]. The fractal denotes a self-similar structure with dilatational symmetry which will have great potential to describe a multitude of irregular structures [2].
Ultracoherent Transient Spectroscopy
Authors: Warren Warren S.
Published: February 2023

A major and ongoing focus of our research effort has been the development of laser pulse sequences analogous to those used in nuclear magnetic resonance, to study relaxation phenomena in condensed phases. Sequences of multiple rectangular 90° and 180° pulses with various phases have been used extensively in high resolution and solid state NMR for nearly three decades, and have been shown to enhance forbidden transitions, selectively refocus some intermolecular interactions, or even increase physiological image contrast for tumor identification. By contrast, the conventional approach to optical coherent transient spectroscopy (splitting a single high power pulse into several parts) generates pulse sequences with well defined delays, but generally totally unknown phases; in addition, the pulse shape is not easily controlled. This approach has proven extremely useful in the past, particularly if noncollinear pulses are used to exploit propagation effects, but growing recognition of the fundamental complexity of condensed phase relaxation processes (and the defects of a two-level approximation) reveals a fundamental need for a more powerful approach.
Experimental Observation of High Order Solitons in a Colliding Pulses Mode Locked Laser
Authors: Salin F. , Grangier P. , Roger G. , Brun A.
Published: February 2023

In recent years, generation of femtosecond light pulse from colliding pulses mode-locked (CPM) ring dye laser (1) has led to pulses shorter than 0.1 ps. To explain the formation of these pulses, recent theories (2) introduce both self phase modulation (SPM) and group velocity dispersion (GVD) in the equations describing the pulse evolution during a single cavity round trip. The mathematical form of these equations has led to consider "soliton-type shaping mechanism "but to our knowledge no experimental proof of the soliton character of the pulse has been found.
Picosecond Relaxation of Nonthermal Wannier Excitons in GaAs
Authors: Schultheis L. , Kuhl J. , Honold A. , Tu C.W.
Published: February 2023

The energy and momentum relaxation of optically excited free electron-hole pairs occurs via carrier-carrier scattering within a few hundred femtoseconds /1/. In contrast, little is known about the fast (momentum) relaxation processes of the excitonic groundstate. This lack of knowledge is partly due to the polariton character of excitons in a bulk semiconductor which impedes optical dephasing experiments in the time as well as in the frequency domain. A further problem especially for nonlinear experiments is the high absorption coefficient (105 cm−1) at the excitonic resonance leading to reabsorption of the nonlinear signal and necessitating a high excitation level, at which exciton-exciton interaction renders the interpretation of the experimental data /2/.
Anomalous Pulse Duration Dependence of the Quasicontinuum Absorption Spectrum
Authors: Mukherjee P. , Kwok H.S.
Published: February 2023

The study of the infrared absorption spectrum of large polyatomic molecules can potentially yield insight into the nature of interaction between the large number of vibrational states in the molecule. We report here a study of the effect of pulse durations on such spectra. Various polyatomic molecules were studied.
Picosecond Dephasing Time Measurement by CSRS Using Temporally Incoherent Nanosecond Laser with Short Correlation Time
Authors: Kobayashi Takayoshi , Hattori Toshiaki , Terasaki Akira
Published: February 2023

Until now all reported studies of transient spectroscopy with incoherent light, including photon echo and pump-probe spectroscopy, were concerned with two-level systems where quasi-monochromatic light of only one frequency couples the two levels.[1-4] However, there exist various coherent transient phenomena where light of two or more frequencies are concerned, and time resolution of the transient spectroscopies using these phenomena are also expected to be limited not by the duration of used light pulses but by the correlation time of the radiation fields.[5]
Electron Transfer in Homologous Azurins
Authors: Petrich J.W. , Longworth J.W. , Fleming G.R.
Published: February 2023

Using time correlated single photon counting, we have studied electron transfer rates, kET in the homologous blue-copper proteins, azurins, obtained from Pseudomonas aeruginosa (Pae) and Alcaligenes faecalis (Afe). The salient difference between these proteins lies in the position of their single tryptophan residues. The tryptophan in azurin Pae, W48, is buried in the hydrophobic core of the protein while the tryptophan in azurin Afe, W118, lies on the protein surface, exposed to the solvent [1]. kET for the reaction W* + Az-Cu (II)→W*+·+Az-Cu(I) was determined to be 1 × 1010 s−1 and 0.5 × 1010s−1 for Pae and Afe, respectively ; i.e. kET(W48)/kET(W118) = 2.
Protein Dynamics and Hemoglobin Reactivity in the Femtosecond and Picosecond Domain
Authors: Houde D. , Petrich J. , Rojas O.L. , Poyart C. , Antonetti A. , Martin J.L.
Published: February 2023

The knowledge of the mechanism and the time scale, by which a structural change in one of the region of a protein is transmitted to other regions is essential for an understanding of the function of many biomolecules.
Transient Vibrational Heating of Molecules after Internal Conversion
Authors: Seilmeier A. , Kaiser W.
Published: February 2023

After electronic excitation most organic molecules return to the electronic ground state via radiationless processes. Internal conversion is one of the most important relaxation mechanisms. There exists a great number of data on internal conversion rates which give only information on the time required by an ensemble of molecules to return from the first excited electronic state to the ground state So. After internal conversion the energy still resides in the individual molecule.
New Continuum Sources for Subpicosecond Absorption Spectroscopy
Authors: Glownia J. H. , Misewich J. , Sorokin P. P.
Published: February 2023

The production of energetic (1.5-10 mJ), ~350 fsec, ~308 nm pulses was recently shown to be obtainable through amplification in XeCl gain modules.1 With the use of these pulses, we have now generated energetic subpicosecond broadband continua in two distinct spectral regions: ~296-360 nm in the UV and ~2.2-2.7 µm in the IR. We have also recently upcon-verted the IR continuum into the visible by four wave mixing in Rb vapor.2 These experiments are briefly outlined below.
Induced Spectral Broadening of a Weak 530nm Picosecond Pulse by an Intense 1060nm Picosecond Pulse in Glass
Authors: Alfano R.R. , Li Q.X. , Jimbo T. , Ho P.P. , Manassah J.T.
Published: February 2023

We report the first observation of an induced ultrafast supercontinuum pulse (IUSP) generation due to the presence of another intense pulse in a BK-7 glass. The enhancement of the spectral bandwidth of the weak pulse at λ1 by propagating an intense laser pulse at λ2 in condensed media is attributed to induced phase modulation1. This new effect has technological importance in communications and signal processing.
Picosecond Optical Pulse Generation using Electro-Optic Modulation Method
Authors: Kobayashi Tetsuro , Amano Kazuhiko , Fujita Tomihiro , Uemura Takuji , Morimoto Akihiro , Sueta Tadasi
Published: February 2023

A pulse compression method utilizing electrooptic phase modulation1,2 can be applied not only to forced modelocked lasers but also to cw lasers3. With this method, the temporal pulse position is electrically controllable and the pulsewidth does not depend on laser power and linewidth. It is superior to the ordinary pulse compression method using self-phase modulation of an optical fiber4 in stability and controllability. In picosecond or shorter range, however, any successful results have not been reported. In this paper, we report the first successful experimental result of pulse compression in picosecond range with this method as well as the result of theoretical analyses.
The Elimination of The Dynamic plash in A picosecond streak image Tube
Authors: Huanwen Zhang
Published: February 2023

The cause of producing dynamic flash in a picosecond streak image tube has been analyzed, it has been convinced that the flash is produced by the discharge between the deflector and the anode cone hole in the tube. The material with small reflective coefficient has been chosen as deflectors. The measure has been taken to screen reflected photoelectrons and other stray electrons. The dynamic flash in the tube has been effectively eliminated.
Optical Pump-Probe Spectroscopy of Dyes on Surfaces: Ground-State Recovery of Rhodamine 640 on ZnO and Fused Quartz
Authors: Anfinrud P. A. , Causgrove T. P. , Struve W. S.
Published: February 2023

In recent years, time-resolved fluorescence spectroscopy has been investigated for dyes adsorbed onto fused quartz [1] and semiconductors [2,3]. On quartz, the monomer fluorescence dynamics are nonexponential and tend to dominated by excitation trapping by dye aggregates; the phenomenological lifetime measured in the limit of low coverage is often comparable to the fluorescence lifetime observed in solution [1]. On ultraviolet-bandgap semiconductors like TiO2, much more rapid fluorescence decay is typically found [2,3], even at low coverage. The channel responsible for this accelerated decay on semiconductors is widely believed to be electron injection into the semiconductor space-charge region. However, the photocurrent efficiencies of liquid-junction solar cells with dye-coated single-crystal semiconductor photoelectrodes are generally small, and the possibility exists that dye electronic excitation may instead decay rapidly and nonradiatively into semiconductor modes [3]. To differentiate between these decay mechanisms, we have done optical pump-probe measurements of ground-state recovery dynamics of rhodamine 640 adsorbed on fused quartz and on ZnO at submonolayer coverages.
Femtosecond Optical Studies on Primary Excitations in Polydiacetylene Single Crystals
Authors: Greene B. I. , Orenstein J. , Millard R. R.
Published: February 2023

Considerable interest has been directed toward an understanding of the optical and electrical properties of polyconjugated molecular solids. Numerous experimental and theoretical studies have attempted to define the relevant energy levels of these systems. Dynamics associated with the relaxation of primary excitations have been of key interest. In this paper we report new spectroscopic data that we feel has potential significance to several ongoing research efforts in this area.
Generation of Ultrashort Nd:YLF Pulses by cw Passive Mode Locking with a Nonlinear External Cavity
Authors: Chee J.K. , Cheung E.C. , Kong M.N. , Liu J.M.
Published: February 2023

Recently, it has been demonstrated in a Ti:Al2O3 [1] that the nonlinear external coupled-cavity acted as a passive mode-locker to generate a stable train of pulses without synchronous pumping or active mode-locking. To date, all the demonstrations of coupled-cavity mode-locking using a nonlinear external cavity are in lasers with gain media which have extremely broad bandwidths, such as color center crystals [2] or Ti:Al2O3 [1]. To our knowledge, cw passive mode locking in a narrow-bandwidth neodymium laser, such as Nd:YAG or Nd:YLF, has never been demonstrated. In this paper, we report cw passive mode locking operation of the Nd:YLF laser with a nonlinear external coupled-cavity using an optical fiber as the nonlinear medium. We have obtained nearly transform-limited pulses as short, as 3.67 ps at usable average output power up to 7 W.
Additive Pulse Modelocking in Ti:Al2O3 Diode Pumped Nd:YAG, and Nd:YLF
Authors: Goodberlet J. , Jacobson J. , Wang J. , Schulz P.A. , Fan T.Y. , Fujimoto J.G.
Published: February 2023

The development of ultrashort pulse solid state lasers is important for a wide range of ultrafast studies. The Ti:Al2O3 laser has an extremely broad tuning range from 670 nm to greater than 1000 nm and thus is a natural choice for femtosecond generation and spectroscopy. The diode pumped Nd:YAG and Nd:YLF have the potential for developing an compact ultrashort pulse source suitable for applications in electro-optic sampling and high speed signal processing.
Femtosecond color center lasers near 2.8 μm with HgCdTe multiple quantum well saturable absorber
Authors: Cesar C.L. , Islam M.N. , Soccolich C.E. , Feldman R.D. , Austin R.F. , German K.R.
Published: February 2023

We have used HgCdTe multiple quantum well (MQW) saturable absorbers to passively modelock two color center lasers ( CCL ) near 2.8 μm. The KCl:Li CCL generates pulses as short as 120 fs and the RbCl:Li CCL generates pulses as short as 190 fs, which are the shortest pulses in the mid-infrared wavelength range. These CCL are the only direct laser source of sub-picosecond pulses in this wavelength range. Our results extend the semiconductor passive modelocking technique previously applied to the NaCl CCL system (1) to different wavelength range, saturable absorber material and laser systems. Both pulse durations are close to the 150 fs estimated LO phonon collision thermalization time for HgCdTe MQW (2) and are shorter than the 275 fs pulses obtained with the NaCl CCL (1). The NaCl CCL used an InGaAs/InAlAs MQW saturable absorber that has a thermalization time of 200 fs. These results are consistent with the proposal that the pulses are generated by the fast saturable absorption due to the thermalization, through LO phonon collision, of a cold carrier distribution (1).
New Aspects of the Primary Charge Separation in the Photosynthesis of Bacterial Reaction Centers
Authors: Zinth W. , Holzapfel W. , Finkele U. , Lauterwasser C. , Dressier K. , Hamm P. , Kaiser W.
Published: February 2023

During the primary electron transfer in the reaction center (RC) of photosynthetic bacteria the special pair, the neighboring bacteriochlorophyll and the subsequent bacteriopheophytin molecules are of major importance. It is accepted that a pair of bacteriochlorophyll molecules provides the primary electron, which is transferred to a bacteriopheophytin H within several picoseconds. The details of this primary electron transfer, especially the role of the accessory bacteriochlorophyll B located between P and H, however, are still in a state of debate /1-3/.