bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the validity, relevance and feasibility of the continuum of care framework for maternal health in South Africa: a thematic analysis of experts’ perspectives
Authors: Mothupi Mamothena Carol , Knight Lucia , Tabana Hanani
Published: February 2020

Background

The continuum of care is a key strategy for ensuring comprehensive service delivery for maternal health, while acknowledging the role of the social determinants of health. However, there is little research on the operationalisation of the framework by decision-makers and implementers to address maternal health challenges. The framework should be measurable and feasible for implementation in low- and middle-income country contexts. In this study, we explore experts’ perspective on monitoring indicators for continuum of care and key issues related to their use in the South African context.

Methods

We conducted key informant interviews with a range of experts in decision-making and programme implementation roles in the health system and relevant sectors. Key informants provided their perspectives on systematically selected, nationally representative monitoring indicators in terms of validity, relevance and feasibility. We interviewed 13 key informants and conducted a thematic analysis of their responses using multi-stage coding techniques in Atlas.ti 8.4.

Results

Experts believed that the continuum of care framework and monitoring indicators offer a multisectoral perspective for maternal health intervention missing in current programmes. To improve validity of monitoring indicators, experts suggested reflection on the use of proxy indicators and improvement of data to allow for equity analysis. In terms of relevance and feasibility, experts believe there was potential to foster co-accountability using continuum of care indicators. However, as experts stated, new indicators should be integrated that directly measure intersectoral collaboration for maternal health. In addition, experts recommended that the framework and indicators should evolve over time to reflect evolving policy priorities and public health challenges.

Conclusion

Experts, as decision-makers and implementers, helped identify key issues in the application of the continuum of care framework and its indicators. The use of local indicators can bring the continuum of care framework from an under-utilised strategy to a useful tool for action and decision-making in maternal health. Our findings point to measurement issues and systematic changes needed to improve comprehensive monitoring of maternal health interventions in South Africa. Our methods can be applied to other low- and middle-income countries using the continuum of care framework and locally available indicators.
Cardiorespiratory fitness and accelerometer-determined physical activity following one year of free-living high-intensity interval training and moderate-intensity continuous training: a randomized trial
Authors: Jung M. E. , Locke S. R. , Bourne J. E. , Beauchamp M. R. , Lee T. , Singer J. , MacPherson M. , Barry J. , Jones C. , Little J. P.
Published: February 2020

Background

Free-living adherence to high-intensity interval training (HIIT) has not been adequately tested. This randomized trial examined changes in cardiorespiratory fitness (CRF) and accelerometer-measured purposeful physical activity over 12 months of free-living HIIT versus moderate-intensity continuous training (MICT).

Methods

Ninety-nine previously low-active participants with overweight/obesity were randomly assigned to HIIT (n = 47) or MICT (n = 52). Both interventions were combined with evidence-based behaviour change counselling consisting of 7 sessions over 2 weeks. Individuals in HIIT were prescribed 10 X 1-min interval-based exercise 3 times per week (totalling 75 min) whereas individuals in MICT were prescribed 150 min of steady-state exercise per week (50 mins 3 times per week). Using a maximal cycling test to exhaustion with expired gas analyses, CRF was assessed at baseline and after 6 and 12 months of free-living exercise. Moderate-to-vigorous physical activity of 10+ minutes (MVPA10+) was assessed by 7-day accelerometry at baseline, 3, 6, 9, and 12 months. Intention to treat analyses were conducted using linear mixed models.

Results

CRF was improved over the 12 months relative to baseline in both HIIT (+ 0.15 l/min, 95% CI 0.08 to 0.23) and MICT (+ 0.11 l/min, 95% CI 0.05 to 0.18). Both groups improved 12-month MVPA10+ above baseline (HIIT: + 36 min/week, 95% CI 17 to 54; MICT: + 69 min/week, 95% CI 49 to 89) with the increase being greater (by 33 min, 95% CI 6 to 60) in MICT (between group difference, P = 0.018).

Conclusion

Despite being prescribed twice as many minutes of exercise and accumulating significantly more purposeful exercise, CRF improvements were similar across 12 months of free-living HIIT and MICT in previously low-active individuals with overweight/obesity.
Is Supraclavicular Block as Good as Interscalene Block for Acute Pain Control Following Shoulder Surgery? A Systematic Review and Meta-analysis
Authors: Hussain Nasir , Costache Ioana , Kumar Nicolas , Essandoh Michael , Weaver Tristan , Wong Patrick , Tierney Sarah , Rose Peter , McCartney Colin J. L. , Abdallah Faraj W.
Published: February 2020

BACKGROUND:

Interscalene block (ISB) is the acute pain management technique of choice for shoulder surgery, but its undesirable respiratory side effects have prompted seeking alternatives. Supraclavicular block (SCB) is proposed as an ISB alternative, but evidence of comparative analgesic and respiratory-sparing effects is inconsistent. We compared the analgesic and respiratory effects of SCB and ISB for shoulder surgery.

METHODS:

Trials comparing ISB to SCB for shoulder surgery were sought. We decided a priori that SCB would be an acceptable alternative if it were noninferior for (1) postoperative 24-hour cumulative oral morphine equivalent consumption (primary outcome, noninferiority margin Δ = −25 mg) and (2) postoperative pain (secondary outcome, noninferiority margin Δ = 4.0 cm·hour–1); and superior for (3) postblock respiratory dysfunction (primary outcome). Opioid-related side effects and block-related complications were also evaluated.

RESULTS:

Fifteen studies (1065 patients) were analyzed. In single-injection blocks, SCB was noninferior to ISB for 24-hour morphine consumption (mean difference for SCB-ISB, MD [95% confidence interval {CI}] = −3.11 mg [−9.42 to 3.19], Δ = −25 mg); it was also noninferior for 24-hour pain scores (MD = 0.78 cm·hour–1 [0.07–1.49], Δ = 4.0 cm·hour–1); and decreased the odds of respiratory dysfunction (odds ratio [OR] [95% CI] = 0.08 [0.01–0.68]). Similarly, in continuous blocks, SCB was noninferior to ISB for 24-hour morphine consumption (MD = 0.46 mg [−6.08 to 5.15], Δ = −25 mg), and decreased the odds of respiratory dysfunction (OR = 0.22 [0.08–0.57]). SCB also decreased odds of minor block-related complications (OR = 0.36 [0.20–0.68] and OR = 0.25 [0.15–0.41] for single-injection and continuous blocks, respectively). Consequently, the null joint-hypothesis was rejected, and SCB can be considered an acceptable alternative to ISB.

CONCLUSIONS:

For acute pain control following shoulder surgery, high-quality evidence indicates that SCB can be used as an effective ISB alternative. SCB is noninferior for postoperative opioid consumption and acute pain, and it reduces the odds of postblock respiratory dysfunction.
Radiomics: from qualitative to quantitative imaging
Authors: Rogers William , Thulasi Seetha Sithin , Refaee Turkey A. G. , Lieverse Relinde I. Y. , Granzier Renée W. Y. , Ibrahim Abdalla , Keek Simon A. , Sanduleanu Sebastian , Primakov Sergey P. , Beuque Manon P. L. , Marcus Damiënne , van der Wiel Alexander M. A. , Zerka Fadila , Oberije Cary J. G. , van Timmeren Janita E , Woodruff Henry C. , Lambin Philippe
Published: February 2020

Historically, medical imaging has been a qualitative or semi-quantitative modality. It is difficult to quantify what can be seen in an image, and to turn it into valuable predictive outcomes. As a result of advances in both computational hardware and machine learning algorithms, computers are making great strides in obtaining quantitative information from imaging and correlating it with outcomes. Radiomics, in its two forms “handcrafted and deep,” is an emerging field that translates medical images into quantitative data to yield biological information and enable radiologic phenotypic profiling for diagnosis, theragnosis, decision support, and monitoring. Handcrafted radiomics is a multistage process in which features based on shape, pixel intensities, and texture are extracted from radiographs. Within this review, we describe the steps: starting with quantitative imaging data, how it can be extracted, how to correlate it with clinical and biological outcomes, resulting in models that can be used to make predictions, such as survival, or for detection and classification used in diagnostics. The application of deep learning, the second arm of radiomics, and its place in the radiomics workflow is discussed, along with its advantages and disadvantages. To better illustrate the technologies being used, we provide real-world clinical applications of radiomics in oncology, showcasing research on the applications of radiomics, as well as covering its limitations and its future direction.
Pure single-mode LiNdP4O12 solid-state-laser transmitter for 1.3-μm optical communication
Authors: KUBODERA KENICHI , NODA JUICHI , OTSUKA KENJU
Published: February 2020

Solid-state lasers have the following excellent properties for use as light sources in high-performance optical transmission systems: mode purity; wavelength stability; and narrow spectrum width. Recently we have fabricated GaAIAs-laser (LD)- pumped miniature solid-state lasers using Nd stoichiometric crystal LiNdP4O12 (LNP),1 These lasers exhibited stable pure single-mode operations, both longitudinally and transversely. This paper presents a high-bit-rate 1.3-μm transmitter module composed of an LNP laser oscillator, a YIG isolator, and a LiNbO3 directional coupler-type modulator.
Phase-compensated optical communication by four-wave mixing
Authors: Prisco John J.
Published: February 2020

A theoretical study was conducted concerning the performance of a degenerate four-wave mixer as an adaptive optical element1 in a line-of-sight optical communication system. Planar phase fronts propagating from a distant optical transceiver were corrupted by Kolmogorov atmospheric turbulence2,3 located between the mixer and the transceiver. The four-wave mixer accepted these perturbed phase fronts and reflected a phase-conjugated4 replica back through the same atmospheric turbulence.
High-speed performance of an IR light-pipe modulator
Authors: Leeb Walter R. , Bonek Ernst , Scholtz Arpad L.
Published: February 2020

We have built a high-speed electrooptic modulator for 10-μm wavelength from three cascaded CdTe crystals with dimensions of 0.8 × 0.8 × 35 mm3. 1Making up a total active length of 105 mm, they were embedded in a strip-line arrangement to form a traveling-wave modulator. Optically, the structure served as a light pipe.2 Velocity match between modulating rf and IR waves was achieved by careful selection of materials (BeO, Teflon) surrounding the GdTe crystals.
Hot electron generation and temperature measurements in CO2 laser plasma interactions
Authors: Schappert G. T.
Published: February 2020

CO2 laser matter interactions at intensities of 1012–1016 W/cm2 produce hot electrons through the resonance absorption mechanism. Simulations1 show that this source of hot electrons can be characterized by a Maxwellian energy distribution with a source temperature T
s
which scales with the laser intensity as I1/3. Other mechanisms, such as Raman or 2ω
p
instabilities, may also be involved in the hot electron generation.
Progress in frequency domain optical memories
Authors: Bjorklund Gary C. , Moerner W. E. , Schellenberg F. M.
Published: February 2020

For the last few years, there has been considerable research activity at the IBM San Jose Research Laboratory devoted to frequency domain optical memories based upon photochemical hole burning (PHB). The PHB phenomenon allows optical frequency to be utilized as an additional dimension for the organization of optical memories1 and offers the potential of achieving a 103 gain in achievable storage density over conventional optical memories and a factor of 3 × 104 gain over inductive magnetic recording.
Four-dimensional temporal-spatial holograms
Authors: Mossberg Thomas W.
Published: February 2020

In standard holographic applications, an object and a reference beam are simultaneously made incident on a recording material. Interference between these beams results in the storage of the spatial Fourier transform of the object pulse in the material. It is shown here that if the storage material is frequency selective (as in the case of inhomogeneously broadened absorbers), not only the spatial but also the temporal structure of the object pulse can be stored in and reconstructed from the material.
Optical bistability instabilities: regenerative pulsations, periodic oscillations, and optical chaos
Authors: Gibbs Hyatt M. , Derstine M. W. , Hopf F. A. , Kaplan D. L. , Rushford M. , Shoemaker R. L. , Weinberger D. A. , Wing W. H.
Published: February 2020

Bistability is associated with a theoretical S-shaped curve of output intensity vs input intensity. The negative-sloped regions of the curve are always stable. However, positive-sloped regions are not always stable as shown by McCall1 (regenerative pulsations), Bonifacio et al.2 (self-pulsing), and Ikeda3 (periodic oscillations and chaos).
Atom concentration measurement in a combustion-driven chemical laser medium
Authors: Gastaud M. , Voignier F. , Bousselet P.
Published: February 2020

The measurement of fluorine atom concentration is of great importance in understanding and predicting the performances of HF/DF chemical lasers. In situ measurements of F-atom concentration in the presence of F2 are required. Ganguli and Kaufman1 have suggested the reaction F + Cl2 → CIF + Cl, and more recently Ultee and Bonczyk2 have described a method based on the reaction F + HCI → HF + Cl to determine F-atom concentration. This work describes a method of quantitative measurement of fluorine atom concentration in an HF/DF combustion driven chemical laser medium.
Highly efficient performance of CO2 lasers by multipass amplification
Authors: Inoue M. , Fujita H. , Daido D. , Terai K. , Imamura K. , Matoba M. , Nakai S. , Yamanaka C.
Published: February 2020

In present CO2 laser systems for fusion research, single-pulse amplification systems are adopted, and the maximum efficiency of these systems is a few percent.1,2 Higher efficiencies ≳10 %, which are required for reactor drivers, could be achieved by adopting a system of multipass amplification in a single-gain media of large volume.
Nematic liquid crystal films as nonlinear optical imaging and switching media: theory and experiment
Authors: Khoo I. C. , Shepard S. , Nahar S. N. , Zhuang S. L.
Published: February 2020

Recent studies have shown that aligned nematic films will undergo reorientation by moderate intensity (a few W/cm2) optical fields or a combination of optical and de fields and will generate large nonlinear optical effects. This paper is addressed specifically to the quantitative aspects of the theory and experiments on all contributing factors (including the thermal indexing effect). It also considers the feasibility of applying these optical nonlinearities in real-time switching and imaging devices.
Optical harmonic radiation from an electron beam using the stimulated Cerenkov interaction
Authors: Wang D. Y. , Kimura W. D. , Piestrup M. A. , Fauchet A. M. , Edighoffer J. A. , Pantell R. H.
Published: February 2020

Recent experiments1,2 have demonstrated the stimulated Cerenkov interaction as a possible means to achieve bunching of a relativistic electron beam at optical wavelengths by using a laser beam to momentum modulate the electrons in a phase-matching medium such as a gas. The bunched electron beam then emits coherent Cerenkov radiation at the harmonics of the laser frequency.3
High-repetition rate 10-atm rf-excited CO2 waveguide laser
Authors: Løvold S. , Wang G.
Published: February 2020

Experimental results from an investigation of rf excitation of high-pressure CO2 waveguide lasers, performed to obtain continuous frequency tuning between line centers, are reported. Application of the rf technique has several potential advantages: stable output pulses; high-pulse repetition rate, good pulse-shape control by amplitude modulation of the rf excitation pulses; long sealed-off lifetime; and no requirement for preionization. We have recently obtained lasing at 10 atm,1 and this result opens the possibility of continuous tuning of rf CO2 lasers. For pulsed TE lasers the required gas pressure for continuous tuning is 2-5 atm2 for isotope mixtures and 8-12 atm3 for a single isotope. In this paper we report new results obtained with excitation power 4 times higher than in Ref. 1.
Cathode materials for sealed waveguide lasers
Authors: Smith A. L. S. , Shields H. , Webb A. E.
Published: February 2020

It is more difficult to make an effective long-life sealed-off CO2 waveguide laser (100-300 Torr) than a traditional low-pressure (10-30 Torr) dc-excited laser,1 because there are 1 or 2 orders of magnitude fewer particles in a typical waveguide device, and the times of diffusion are up to 1 order of magnitude shorter despite the higher pressure because of the much smaller distances involved. The effects of cathode material sputtering, gas cleanup at the electrodes, formation of gaseous complexes, and transport of cathode material into the waveguide bore and onto optical surfaces may all be expected to be accentuated. It has been claimed as a major advantage of rf rather than de excitation that it is not necessary to have electrodes in contact with the active gas constituents.
Experimental fabrication and evaluation of diffraction lenses in planar optical waveguides
Authors: Delavaux Jean-Marc , Forouhar Siamak , Chang William S. C. , Lu Ron Xin
Published: February 2020

For signal processing in planar waveguides, it is necessary to integrate, focus, collimate, image, or Fourier analyze guided-wave beams by efficient lenses that have both diffraction-limited performance and tow noise.
Ultrashort optical pulse generation with semiconductor diode lasers
Authors: Inaba Humio , Ito Hiromasa
Published: February 2020

There is great interest in ultrashort optical pulse generation using semiconductor diode lasers,1 since this may provide new capability not only for very high bit-rate optical communication and ultrafast data processing but also as practically useful sources for optical electronics with applications in a variety of fields such as physics, chemistry, life sciences, and engineering. The generation of short optical pulses from diode lasers, however, was studied by several workers more than a decade ago using homojunction GaAs lasers, mostly with double-section structures, operated at liquid nitrogen temperature.
Generation of subpicosecond pulses from passively mode-locked GaAs lasers containing saturable absorption
Authors: van der Ziel J. P.
Published: February 2020

Subpicosecond (0.65-psec) transform-limited pulses have been obtained using GaAs lasers passively mode locked in an external cavity.1 Still shorter pulses (0.56 psec) have been obtained using GaAs lasers in an actively mode-locked external ring cavity geometry.2 Of crucial importance to the attainment of these short pulses is the presence of a localized region of saturable absorption at the laser exit facet, which in our case was introduced in a controlled manner by proton bombardment.
New spatially resolved techniques for the detection of atoms and radicals in combustion environments
Authors: Goldsmith John E. M.
Published: February 2020

A clear need exists within the combustion research community for methods capable of making sensitive spatially resolved measurements of species concentrations. Several new crossed-laser-beam techniques for making such measurements are outlined here, including the first application of saturated absorption spectroscopy for making point absorption measurements and the first application of spatially resolved optical Stark modulation spectroscopy for monitoring electronic transitions in atoms.
Hew recombination lasers in a segmented plasma device employing foil electrodes
Authors: Macklin J. J. , Wood ii O. R. , Silfvast William T.
Published: February 2020

A technique using metal foil electrodes to produce segmented metal vapor plasmas in a recombination laser device has resulted in laser oscillation on 30 transitions in lithium, aluminum, calcium, and copper where the formation of segmented plasmas and subsequent production of laser action was not previously possible using bulk electrodes of these metals. Laser action was observed in the neutral and ion species, with emission wavelengths from 569.6 to 5460 nm as reported in Table I. Twenty- nine of these transitions have never previously been made to exhibit laser action by any excitation means. The use of foil electrodes should further extend the class of metal vapor recombination lasers when applied to additional metals.
4-bit 828-megasamples/sec guided-wave electrooptic analog-to-digital converter
Authors: Leonberger Fred J. , Woodward C. E. , Becker R. A.
Published: February 2020

We report the demonstration of an electrooptic analog-to-digital converter (ADC) operating at 828-megasamples (MS)/sec which has the potential for 4-bit resolution. This converter is the type originally proposed by Taylor1 and depends on a guided-wave interferometric modulator array to perform the conversion and on mode-locked laser pulses to perform the sampling. In recent years, two detailed design studies of this converter, a number of fundamental experiments, and several electrooptic converters2 have been reported. These latter devices operate below the demonstrated hybrid Si IC capability of 5 bits at 450 MS/ sec.3 The device reported here extends the sampling rate of electrooptic ADCs to the gigahertz range and is the largest bandwidth ADC demonstrated.
Amorphous silicon photovoltaic detector for guided-wave optics
Authors: Yumoto J. , Yajima H. , Seki Y. , Shimada J. , Nakajima M.
Published: February 2020

Photodetectors are required in most integrated optics applications, and the integration technology of photodetectors into the planar waveguide circuit is particularly important. Silicon is a promising substrate for integrated optics, because photodetectors are easily integrated into it.1,2 However, silicon is not piezoelectric. LiNbO3 is also a promising material for integrated optics because of its excellent performance in acoustooptic interactions and electrooptic effects. End-fire coupling of CCD arrays to the LiNbO3 waveguide has been reported.3
Compact high-speed coherent optical correlator using a laser diode
Authors: Kasahara K. , Ito S. , Nakaguchi T. , Takei T.
Published: February 2020

The coherent optical correlator (COC) is useful for target identification on a displayed image.1,2 The conventional COC uses a gas laser and an incoherent-to-coherent image converter (ITG).3 It has the following disadvantages:
Laser micromachining using liquid chemical etchants
Authors: Von Gutfeld Robert J. , Hodgson R. T.
Published: February 2020

We describe a new technique for rapid etching of ceramics, glasses, and single-crystal 〈111〉 silicon.1 in our experiments, a focused argon laser was directed horizontally onto a sample and submerged. vertically in a quartz cell containing a concentrated KOH solution. Etching occurs at the point of incidence of the laser on the sample accompanied by local boiling of the solution as well as local melting of the substrate. We have verified that rapid etching occurs only when melting occurs by measuring the volume removal rate as a function of laser power for a fixed laser pulse width when the sample was in KOH.
Apodization of large aperture Nova laser harmonic conversion crystal arrays
Authors: Linford G. J. , Haas R. A. , F  , Marchi T. , Peterson G. G. , Simmons W. W. , Summers M. A.
Published: February 2020

The new Nd:glass Nova and Novette laser systems at the Lawrence Livermore National Laboratory will require nonlinear KDP harmonic conversion crystal arrays to support inertial confinement target irradiation experiments at 526 and 351 nm. Since the 74-cm output aperture of the Nova/Novette laser systems is too large to permit the use of monolithic KDP harmonic conversion crystals, it was necessary for us to design and construct arrays consisting of from 9 to 25 square KDP crystal elements.
Improved passive mode-locking of a Nd:YAG laser using an antiresonant ring
Authors: Vanherzeele H. , Siegman A. E.
Published: February 2020

Recent work in other laboratories has demonstrated that improved passive mode-locking can be obtained in resonator configurations in which two mode-locked pulses coming from opposite directions collide in a thin saturable cell,1 The improvement is partly due to the fact that the pulse saturation effects are effectively doubled. Grating effects2 may also play a significant role in the pulse compression process.
Large aperture high-quality CO2 TEA lasers
Authors: Ernst G. J. , Boer A. G.
Published: February 2020

Compared with electron-beam excited CO2 lasers, discharge TEA lasers have the well-known advantages of simplicity, low cost, and high overall efficiency. However, the quality of a pulsed self-sustained laser system is mainly determined by the quality and reliability of the gas discharge, and unfortunately the stability and the homogeneity of the discharge become poor for large apertures. Another serious problem is that although calculations predict a laser efficiency of the order of 20%, this value never could be reached experimentally. This discrepancy is not due to lack of knowledge of the physical processes occurring in the laser medium but most likely to inhomogeneities in the gas discharge.
Long distance fault location system for single-mode and multimode fibers with a 1.3-µm YAG laser
Authors: Nakazawa Masataka , Tokuda Masamitsu , Uchida Naoya
Published: February 2020

Recently, it became possible to make high bit-rate long-length optical communication systems, using the OTDR technique.1 In general, the backscattered power level in a single-mode fiber is less than that in a multimode fiber by 10-15 dB for the same light-source power. From this point of view, a high-power optical source and efficient capturing technique for the backscattered signal are desirable to find imperfections in long-length single-mode fibers.2
Spatially resolved characterization of thin films
Authors: Abate Joseph A. , Jacobs Stephen D. , Piskorowski Walter S. , Pottenger Timothy P.
Published: February 2020

It has been stated1-2 that laser-induced damage to dielectric thin films is caused by the presence of defects of the order of 1 µm in dimension located in the thin film or at the film-substrate interface. Impurities are one type of defect, but another type might be the nonstoichiometric regions of the coating. In an attempt to establish further the existence of these defects and their relationship to laser-induced damage, we have adopted two optical characterization techniques capable of measuring optical absorption and stress-induced birefringence with high sensitivity and high spatial resolution. These techniques are the mirage effect3 and photoelastic modulation ellipsometry.4
Distinguishing the inverse spin Hall effect photocurrent of electrons and holes by comparing to the classical Hall effect
Authors: Zhang Yang , Liu Yu , Zeng Xiao lin , Wu Jing , Yu Jin ling , Chen Yong hai
Published: February 2020

The photo-excited electrons and holes move in the same direction in the diffusion and in the opposite direction in the drift under an electric field. Therefore, the contribution to the inverse spin Hall current of photo-excited electrons and holes in the diffusion regime is different to that in the drift regime under electric field. By comparing the classical Hall effect with the inverse spin Hall effect in both diffusion and drift regime, we develop an optical method to distinguish the contributions of electrons and holes in the inverse spin Hall effect. It is found that the contribution of the inverse spin Hall effect of electrons and holes in an InGaAs/AlGaAs un-doped multiple quantum well is approximately equal at room temperature.
Atomic clocks of the future: using the ultrafast and ultrastable
Authors: Hollberg Leo , Diddams Scott , Oates Chris , Curtis Anne , Bergquist Jim
Published: February 2020

The application of ultra-fast mode-locked lasers and nonlinear optics to optical frequency metrology is revolutionizing the field of atomic clocks. The basic concepts and applications will be reviewed using the latest results on optical atomic frequency standards.
Carrier-envelope offset dynamics and stabilization of femtosecond lasers
Authors: Helbing F. W. , Steinmeyer G. , Keller U.
Published: February 2020

We analyze physical effects governing the carrier-envelope offset (CEO) dynamics of femtosecond mode-locked lasers. The insight on the underlying mechanisms enabled us to phaselock the carrier-envelope offset (CEO) frequency of our laser to an RF reference oscillator with an unprecedented 20 mrad rms phase jitter (0.01 Hz - 10kHz bandwidth).
Femtosecond time-resolved X-ray diffraction study of ultrafast structural dynamics in laser-excited solids
Authors: Sokolowski-Tinten K. , Blome C. , Dietrich C. , Blums J. , Horn-von-Hoegen M. , von der Linde D. , Cavalleri A. , Squier J. , Kammler M.
Published: February 2020

Time-resolved x-ray diffraction with sub-300 fs, multi-keV x-ray pulses was used to study ultrafast lattice dynamics in laser-irradiated germanium and bismuth. In bismuth strong excitation of optical phonons is observed prior to disordering of the material.
A simple theory of the acousto-optic programmable dispersive filter used for femtosecond laser pulse shaping
Authors: Kaplan D. , Tournois P.
Published: February 2020

We discuss the operation of a newly introduced system for phase and amplitude programmation of ultrafast laser pulses operating from a few femtoseconds to a few picoseconds.The heart of the system is an acousto-optic birefringent device , the Acousto-Optic Programmable Dispersive Filter (AOPDF) which performs for low values of acoustic power density a convolution between the amplitude of an input optical signal and a signal S(t/α) where S(t) is the acoustic signal proportional to the electrical signal applied to the piezoelectric transducer of the device and α a scaling factor related to the ratio between the speed of sound and the speed of light in the material. The small value of α of the order of 10−7 enables the control of optical signals in the hundreds of Terahertz range with electrical signal within the tens of Megahertz range [1,2].
Methods for Complete Characterization of Single Attosecond Pulses
Authors: Quéré Fabien , Itatani J. , Yudin G.L. , Corkum P.B.
Published: February 2020

Determining the temporal profile of single attosecond X-ray pulses is a challenging experimental problem, mostly because the peak intensity of these pulses is not high enough to efficiently induce non-linear effects. This is also a major obstacle for pump-probe experiments with attosecond pulses.
Non-Equilibrium Charge Recombination Dynamics of Excited Donor-Acceptor Complexes
Authors: Nicolet Olivier , Vauthey Eric
Published: February 2020

Contrarily to the prediction of the semi-classical Marcus theory, the rate constant of charge recombination (CR) of excited donor-acceptor complexes (DACs) does not exhibit a bell-shaped free energy dependence, but rather shows a linear relationship when plotted in a logarithmic scale [1]. Moreover, this behavior continues down to very low driving forces, and the so-called normal region, i.e. the decrease of the rate constant with decreasing exergonicity, is not observed. There has been several hypothesis to account for this discrepancy, including variation of other parameters than free energy when going from one DAC to another and non-equilibrium dynamic effects [2], but there is still no conclusive explanation.
Real-time dynamics of a breather in trans-polyacetylene revealed by 4.7-fs visible pulses
Authors: Kobayashi T. , Adachi S. , Kobryanskii V. M.
Published: February 2020

The formation and the relaxation dynamics of a breather, a dynamic bound-state of a soliton pair, with a 44-fs period and a 50-fs decay-time in trans-polyacetylene was revealed by a time-frequency analysis of pump-probe signals.
Compact ultrashort hard-x-ray source driven by high-repetition rate femtosecond laser pulses
Authors: Egbert A. , Mader B. , Tkachenko B. , Fallnich C. , Chichkov B. N.
Published: February 2020

A compact, sub-10-picosecond, ultrashort hard-x-ray source based on the combination of a high-repetition rate femtosecond laser with a specially designed x-ray tube is demonstrated. A detailed analysis of spectral and temporal source characteristics is presented.
Correlated line broadening in three pulse multidimensional spectra of coupled vibrations
Authors: Venkatramani Ravindra , Mukamel Shaul
Published: February 2020

We present a theory for all three femtosecond, infrared four wave mixing techniques (−k1+k2+k3, k1−k2+k3, k1+k2−k3) in coupled, localized, vibrational systems which includes broadening effects with arbitrary time scales and degrees of correlation.
Molecular Mechanisms for Photodetachment in Water
Authors: Kloepfer J.A. , Vilchiz V.H. , Lenchenkov V.A. , Bradforth S.E.
Published: February 2020

Threshold electron ejection processes, such as photodetachment via optical charge-transfer-to-solvent (CTTS) excitation, provide very simple models for understanding solvent-controlled electron transfer (ET). In previous work, we have demonstrated that ejection from the prototypical CTTS system, the aqueous iodide anion, is to short range into a caged pair [1]. The electron subsequently either diffuses out of the cage, an activated process due to the attractive interaction between the nascent electron and the polarizable iodine neutral, or undergoes reverse electron transfer to reform I− [2]. In the current experiments, our goal was to gain additional insight into the molecular mechanism of ejection by exploring the effect of a large increase in the excitation energy and by isotopic substitution of the solvent. The results are rather unexpected and an ab initio characterization of the vertically prepared bulk CTTS wavefunction turns out to be particularly useful in rationalizing the dynamics of the electron.
Time-domain Differentiation of Terahertz Signals
Authors: Filin A. , Stowe M. , Kersting R.
Published: February 2020

We report on the transmission of terahertz signals through subwavelength grating structures. Time-resolved terahertz measurements show that the transmitted field is the first time-derivative of the incident signal.
Spectral amplitude and phase changes in diffraction of Terahertz pulses
Authors: Mitrofanov Oleg , Lee Mark , Pfeiffer L.N. , West K.W.
Published: February 2020

Diffraction of free-space traveling Terahertz pulses usually results in complex changes of the pulse waveform. In near-field microscopy a pulse passes through an aperture of subwavelength size, which in general distorts the pulse waveform depending on the aperture size, pulse bandwidth, frequency chirp, as well as distance to the sample [1,2,3]. The effects of the aperture are therefore essential in the data analysis. We experimentally demonstrate that pulse waveform deformation in diffraction on apertures can be reduced to simple spectral amplitude and phase changes if the aperture size is much smaller than the wavelength.
Evolution of pulse shapes during a conventional compressor scan in a chirped pulse amplification (CPA) system and its effect on electron acceleration in plasmas
Authors: Tóth Csaba , de Groot Joeri , van Tilborg Jeroen , Geddes Cameron G.R. , Faure Jerome , Catravas Palma , Schroeder Carl , Shadwick Brad A. , Esarey Eric , Leemans Wim
Published: February 2020

The skewness of the envelope function of 50–100 femtosecond Ti:sapphire laser pulses has been controlled by appropriate choice of the higher order spectral phase coefficients, and used for optimization of a plasma wake-field electron accelerator.
Reexamining CTTS dynamics of Na−(THF) - probing the excited state and electron using multipulse pump-probe
Authors: Sension Roseanne , Wang Zhaohui , Shoshana Ophir , Hou Bixue , Ruhman Sanford
Published: February 2020

Probing electrons ejected from photorexcited Na−(THF) with 30 fsec 2 and 3 pulse experiments suggests that the CTTS excited state decays in less than 200 fsec. An intermediate earlier assigned as Na−* is reassigned to a “dry” Na0.
Ultrafast site-specific mid-infrared spectroscopy of excited-state intramolecular proton transfer
Authors: Rini M. , Kummrow A. , Dreyer J. , Nibbering E. T. J. , Elsaesser T.
Published: February 2020

We present an ultrafast mid-infrared study of excited-state intramolecular proton transfer in 2-(2'-hydroxyphenyl)benzothiazole. Monitoring the C=O stretching mode of the product state reveals the reaction time, anharmonic coupling features and vibrational relaxation time scales.
The Size of a Localized Electron at a Metal/Adsorbate Interface
Authors: Bezel I. , Gaffney K. , Garrett-Roe S. , Liu S. , Miller A. , Szymanski P. , Harris C. B.
Published: February 2020

Electron localization in different systems has been a topic of study for over a half of a century; polaron formation in the solid state and electron solvation by liquids are just two examples. Structureless by itself but interacting strongly with the condensed phase environment, an electron is often utilized as a probe of its local microscopic structure. Despite that, there are few attempts to access the shape of a localized electronic wave function directly from an experiment. Here, we report an elegant way of estimating the electron localization size parallel to a two-dimensional metal/adsorbate interface by using time and angle resolved two-photon photoemission (TAR TPPE).
Inversionless amplification of coherent THz radiation
Authors: Janke C. , Bolivar P. Haring , Bartels A. , Kurz H. , Künzel H.
Published: February 2020

A surface field THz emitter placed inside a high repetition-rate THz resonator is synchronously pumped by a femtosecond laser. The emitter efficiency is increased by more than one order of magnitude via amplification without inversion.
Dynamics of peptide structures by multiple pulse 2D IR spectroscopy
Authors: Hochstrasser R.M. , Chang J. , Chen J.-X. , Ge N.-H. , Kim Y.S. , Park J. , Rubtsov I. , Zanni M. T.
Published: February 2020

An ideal approach to visualizing chemical and biological processes would come from snapshots of atomic positions of participating molecules throughout the course of chemical reactions or conformational changes. Although unlikely to be obtained from a single experimental technique, a combination of methods may well achieve this goal. Exciting new experiments have demonstrated that the idea of using 2D IR spectroscopy to obtain molecular structures with sufficient time resolution to resolve barrier crossing processes, chemical reactions and conformational dynamics, now appears to have exceptional promise. The advantage [1] of the technique is its intrinsically high time resolution, which is on the order of picoseconds. Thus 2D IR spectroscopy naturally accesses the time scales that are hard to reach by 2D NMR and X-ray diffraction methods in solutions. Exciting biological applications include structural dynamics of nucleotides, peptides [2], and perhaps small proteins. Other application in photochemistry, polymer dynamics, and liquids will be possible.
Coherent Two-Dimensional Fourier Transform Infrared Spectroscopy
Authors: Khalil M. , Demirdöven N. , Tokmakoff A.
Published: February 2020

Purely absorptive two-dimensional (2D) infrared vibrational spectra are obtained by adding together rephasing and non-rephasing 2D spectra. The modulation of cross-peaks and emergence of new peaks are demonstrated as a function of the mixing period.
Generation and characterization of few-cycle mid-infrared pulses from 2800 to 4600 nm
Authors: Gruetzmacher Julie A. , Scherer Norbert F.
Published: February 2020

Sub-five-cycle pulses in the spectral region from 2800 to 4600 nm are generated using a potassium niobate optical parametric amplifier employing a germanium pulse compression scheme. The sub-65-fs mid-infrared pulses are fully characterized by XFROG.
1-GHz repetition-rate femtosecond optical parametric oscillator
Authors: Kuhl J. , Zhang X. P. , Hebling J. , Bartels A. , Nau D. , Rühle W. W. , Giessen H.
Published: February 2020

We achieved 1-GHz-repetition-rate and low-pump-threshold operation of a femtosecond optical parametric oscillator (OPO) based on periodically poled LiNbO3 (PPLN) using higher-order synchronous pumping.
Watching bare charges get dressed in an ultrabroadband THz experiment
Authors: Huber R. , Tauser F. , Brodschelm A. , Leitenstorfer A.
Published: February 2020

The concept of quasiparticles is an essential tool to describe interacting many-body systems. A dense electron-hole plasma in a semiconductor constitutes a prime example: Detailing the ensemble in terms of isolated charge carriers which interact with all individual particles via the bare Coulomb potential would be far too complex. An intuitive description accounts for the fact that each charge attracts a polarization cloud of opposite sign forming a dressed quasiparticle. These new units interact via a dynamically screened potential. However, the model is justified only if the carrier distributions in momentum space are slowly changing. Over the last decade, there has been an intense discussion on how to treat Coulomb interactions during ultrafast relaxation of a many-body ensemble in the extreme nonequilibrium regime. Hot carriers excited in a semiconductor by a femtosecond light pulse are an important model system for these questions. It has been supposed that immediately after generation of an electron-hole plasma no screening of the Coulomb interaction should exist. Quantum kinetic calculations predict that many-body correlations dressing up bare charges develop on an ultrashort time scale of the order of the inverse plasma frequency [1,2].
Amplitude and phase measurements of femtosecond pulses shaped using spectral hole burning in free-base naphthalocyanine-doped films
Authors: Fraigne S. , Galaup J.-P. , Le Gouet J.-L. , Joffre M. , Canioni L. , Bousquet B. , Likforman J.-P.
Published: February 2020

Spatio-temporal holography using persistent spectral hole-burning in dye molecules embedded in plastic films is promising for applications such as femtosecond pulse shaping, data storage or phase conjugation. In addition to the common 2 spatial dimensions of classical holograms, each point in the sample plane can be used to store spectral informations such as the shape of a femtosecond pulse. On each point of the sample, spectral interferences between a reference pulse and an object pulse (for example chirped) are recorded via spectral hole-burning in the absorption band of the dye molecule. As early as 1983, photon echo and time-reversal experiments using persistent spectral hole-burning were performed in porphyrazine styrol solutions at 630 nm [1]. Then several developments, like the reconstruction of the polarization state of object pulses [2], time and space holography [3,4], image holograms using a single pair of femtosecond pulses [5] were demonstrated in different photosensitive media.
The control of optical damage threshold by the chirp of ultraviolet femtosecond pulses
Authors: Ono Shingo , Suzuki Yuji , Murakami Hidetoshi , Kozeki Toshimasa , Ohtake Hideyuki , Koshihara Shin-ya , Sarukura Nobuhiko
Published: February 2020

The damage process of the aluminum coating for the ultraviolet-femtosecond pulses is investigated. It is found that the damage threshold becomes lower for the positively-chirped pulse irradiation case even the pulse duration becomes longer.
Observation of a hysteretic pseudogap behavior via coherent phonons in high temperature superconductors
Authors: Dekorsy T. , Georgiev N. , Helm M. , Misochko O.V.
Published: February 2020

We investigate ultrafast reflectivity changes of a near-optimally doped YBCO (123) superconductor. Coherently excited phonons reveal a pseudogap regime above Tc with two crossover temperatures which exhibit a clear hysteretic behavior as a function of temperature.
Ultrafast laser-induced structural changes in anisotropic solids
Authors: Sokolowski-Tinten K. , Temnov V.V. , Zhou P. , von der Linde D. , Ashitkov S.I. , Agranat M.B. , Fortov V.E.
Published: February 2020

Time-resolved polarization microscopy was used to study laser-induced structural changes in anisotropic materials. For graphite the transition from an optically anisotropic to an isotropic state, indicating the loss of crystalline order, occurs on a subpicosecond time scale.
Laser spectroscopic visualization of molecular rotations in liquid water
Authors: Pommeret S. , Bratos S. , Leicknam J.-Cl. , Gallot G. , Lascoux N. , Gale G.M. , Amir W.
Published: February 2020

An infrared laser spectroscopic experiment is described permitting a visualization of molecular rotations in liquid water. One first selects hydrogen bonds of a given OH..O length by pumping the system with an appropriate infrared frequency; the rotational dynamics are analyzed next by measuring its rotational anisotropy. The procedure requires a careful theoretical analysis, realized by adopting the correlation function approach. This experiment also permits to visualize the passage from the inertial rotation to the rotational diffusion. The lifetime of OH..O bonds in water is rotation-limited.
Femtosecond pump-probe spectroscopy using a two-dimensional smart pixel detector array
Authors: Bourquin S. , Prasankumar R. P. , Morgner U. , Kaertner F. , Fujimoto J. G. , Lasser T. , Salathé R. P.
Published: February 2020

Femtosecond pump-probe spectroscopy is a well-known method used to investigate ultrafast excited state dynamics in condensed matter, chemical, and biological systems. The standard technique uses a narrowband pump and continuum probe to excite the sample, and employs a spectrometer to acquire the wavelength dependent absorption saturation dynamics. This technique often requires the use of a femtosecond amplifier to achieve sufficient intensities for continuum generation and sufficient pump-probe signal magnitudes. With the development of 5 fs lasers, which can generate spectra spanning one octave, spectrally resolved pump-probe measurements can be performed without the need for amplifiers [1,2,3]. Although the pulse repetition rate from a laser oscillator is extremely high, pulse energies are low and signal levels are small. Standard CCD detectors cannot detect modulated signals and thus it is not possible to take advantage of high signal to noise measurements that are possible with high repetition rate laser sources. Here, we present a new technique that enables the parallel acquisition of pump-probe measurements for multiple wavelengths. This is made possible using a novel, two-dimensional smart pixel detector array, which was originally developed for high speed optical coherence tomography (OCT) [4,5]. Each pixel performs amplitude demodulation, and in combination with a diffraction grating, probe transmission signals can be acquired in parallel for multiple wavelengths. The smart pixel array can achieve sensitivities comparable to lock-in amplification but can perform demodulation of probe transmission signals at multiple wavelengths simultaneously, enabling time and wavelength resolved femtosecond pump-probe spectroscopy.
Electronic coupling and coherence effects in ultrafast heterogeneous electron transfer
Authors: Zimmermann C. , Willig F. , Ramakrishna S. , Eichberger R. , Biswas N. , Storck W.
Published: February 2020

Single exponential behavior with time constant 35fs and 75fs, respectively, was measured for electron injection from a molecule into a semiconductor with two different spacer-cum-anchor groups. Modulation of electron transfer by a vibrational wavepacket was found.