Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE

We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30 μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.

Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy

Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ~ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability.

[National data set "emergency department": development, structure and approval by the Deutsche Interdisziplinäre Vereinigung für Intensivmedizin und Notfallmedizin]

BACKGROUND

The Deutsche Interdisziplinäre Vereinigung für Intensivmedizin und Notfallmedizin (DIVI) is divided into sections one of which is the "Sektion Notaufnahmeprotokoll" (emergency department protocol section) founded in 2007. The main task was to create a national data set for the documentation of patients in emergency departments (ED).

MATERIAL AND METHODS

In order to create such a data set a careful look was taken at the current state of documentation in many different hospitals throughout Germany. In addition, existing registries and international requirements were also taken into consideration. The content of the dataset "ED documentation" was developed in interdisciplinary and interprofessional expert rounds.

RESULTS

The dataset "ED documentation" forms the first basis for documentation in German EDs. The modular data set contains 676 fields and covers all relevant information of the whole clinical process in the ED. Legal issues as well as several aspects for internal and external quality management are also included. For this reason the data of several German quality registries (e.g. TraumaRegister DGU® of the German Society of Trauma Surgery) are part of the data set. Furthermore, the data set forms the basis for several financial and billing aspects. A set of six forms was created in accordance with the developed modular data set. In 2010 the data set was approved by the executive committee of the DIVI. Several German medical associations (e.g. German Association for Emergency Medicine/Deutsche Gesellschaft Interdisziplinäre Notfall- und Akutmedizin, DGINA) recommend its use. Currently 80 hospitals are using the data set.

CONCLUSION

Beside the ability to exchange information the presented data set is the basis for internal and external quality assessment in the ED even if most of the available scoring and benchmarking tools are not validated for the German medical system. Implementing an ED register in Germany which is planned in the future, could close this gap.

Microscopic description of intraband absorption in graphene: the occurrence of transient negative differential transmission

We present a microscopic explanation of the controversially discussed transient negative differential transmission observed in degenerate optical pump-probe measurements in graphene. Our approach is based on the density matrix formalism allowing a time- and momentum-resolved study of carrier-light, carrier-carrier, and carrier-phonon interaction on microscopic footing. We show that phonon-assisted optical intraband transitions give rise to transient absorption in the optically excited hot carrier system counteracting pure absorption bleaching of interband transitions. While interband transition bleaching is relevant in the first hundreds of fs after the excitation, intraband absorption sets in at later times. In particular, in the low excitation regime, these intraband absorption processes prevail over the absorption bleaching resulting in a zero crossing of the differential transmission. Our findings are in good qualitative agreement with recent experimental pump-probe studies.

[The concept of small volume resuscitation for preclinical trauma management. Experiences in the Air Rescue Service]

BACKGROUND

Prompt hemorrhage control and adequate fluid resuscitation are the key components of early trauma care. However, the optimal resuscitation strategy remains controversial. In this context the small volume resuscitation (SVR) concept with hypertonic-hyperoncotic solutions is a new strategy.

PATIENTS AND METHODS

This was a retrospective study in the Helicopter Emergency Medical Service over a 5-year period. Included were all major trauma victims if they were candidates for SVR (initially 4 ml HyperHaes/kg body weight, followed by conventional fluid resuscitation with crystalloids and colloids). Demographic data, type and cause of injury and injury severity score (ISS) were recorded and the amount of fluid volume and the hemodynamic profile were analyzed. Negative side-effects as well as sodium chloride serum levels on hospital admission were recorded.

RESULTS

A total of 342 trauma victims (male 70.2%, mean age 39.0 ± 18.8 years, ISS 31.6 ± 16.9, ISS>16, 81.6%) underwent prehospital SVR. A blunt trauma mechanism was predominant (96.8%) and the leading cause of injury was motor vehicle accidents (61.5%) and motorcycle accidents (22.3%). Multiple trauma and polytrauma were noted in 87.4% of the cases. Predominant was traumatic brain injury (73.1%) as well as chest injury (73.1%) followed by limb injury (69.9%) and abdominal/pelvic trauma (45.0%). Within the whole study group in addition to 250 ml HyperHaes, mean volumes of 1214 ± 679 ml lactated Ringers and 1288 ± 954 ml hydroxethylstarch were infused during the prehospital treatment phase. There were no statistically significant differences in the amount of crystalloids and colloids infused regarding the subgroups multisystem trauma (ISS>16), severe traumatic brain injury (GCS<9) and entrapment trauma compared to the total study group. In patients with an initial systolic blood pressure (SBP) >80 mmHg significantly less colloids (1035 ± 659 ml vs. 1288 ± 954 ml, p<0.006) were infused, whereas in patients with an initial SBP ≤ 80 mmHg significantly more colloids were infused (1609 ± 1159 ml vs. 1288 ± 954 ml, p<0.002). There was a statistically significant increase in systolic as well as diastolic blood pressure at all times of blood pressure measurement during prehospital treatment after bolus infusion of HyperHaes within the whole study group. The same applies to the subgroups multisystem trauma, severe traumatic brain injury and entrapment trauma. Minor negative side-effects were observed in 4 cases (1.2%). The mean serum sodium chloride profile on hospital admission was 146.9 ± 5.0 mmol/l, the base excess (BE) was -5.7 ± 5.3 mmol/l) and the pH was 7.3 ± 0.1.

CONCLUSION

The concept of small volume resuscitation provides early and effective hemodynamic control. Clinical side-effects associated with bolus infusion of hypertonic-hyperoncotic solutions are rare.

Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses

Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Δ/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.

Observation of forbidden exciton transitions mediated by Coulomb interactions in photoexcited semiconductor quantum wells

We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.

Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior

We present the results of pump–probe experiments on multilayer graphene samples performed in a wide spectral range, namely from the near infrared (photon energy 1.5 eV) to the terahertz (photon energy 8 meV) spectral range. In the near infrared, exciting carriers and probing at higher photon energies provides direct evidence for a hot carrier distribution. Furthermore, spectroscopic signatures of the highly doped graphene layers at the interface to SiC are observed in the near-infrared range. In the mid-infrared range, the various relaxation mechanisms, in particular scattering via optical phonons and Auger-type processes, are identified by comparing the experimental results to microscopic modeling. Changes from induced transmission to induced absorption are attributed to probing above or below the Fermi edge of the graphene layers. This effect occurs for certain photon energies in the near-infrared range, where it is related to highly doped graphene layers at the interface to SiC, and in the far-infrared range for the quasi-intrinsic graphene layers. In addition to the relaxation dynamics, the saturation of pump-induced bleaching of graphene is studied. Here a quadratic dependence of the saturation fluence on the pump photon energy in the infrared spectral range is revealed.

[The TraumaRegister DGU® as the basis of medical quality management. Ten years experience of a national trauma centre exemplified by emergency room treatment]

BACKGROUND

The trauma register of the German Society of Trauma Surgery (TraumaRegister DGU®/TR-DGU) has been proven to be a valuable tool for external assessment of quality in the treatment of patients with major trauma. This publication shows for the first time how the quality of trauma treatment in a level I trauma centre could be improved over a period of almost ten years with the help of continuous quality management, i.e. recognizing a problem, developing a solution and evaluating its effect.

MATERIALS AND METHODS

Tracer parameters and indicators of quality are presented in four periods over a total study period from 1st January 1989 to 31st March 2007. The division into four periods is due to major changes in the trauma treatment algorithms or structural changes in the trauma room. The results are displayed for all patients treated in the trauma room and for those patients with an injury severity score (ISS)≥16.

RESULTS

Over all four periods a total number of n=2,239 patients were admitted to the trauma room. Based on the results of the trauma register a number of changes were made, not only structural changes, such as the introduction of point-of-care diagnostics, initially conventional X-ray, then digital X-ray and finally multislice computed tomography (CT) scanning in the trauma room but also changes in the way personnel participating in the trauma treatment are trained. Advanced trauma life support (ATLS®) has become the standard training for doctors and prehospital trauma life support (PHTLS®) for nurses. Time efficient treatment algorithms were introduced. All measures led to changes in several parameters which are chosen as indicators for good treatment quality. It was for instance possible to reduce the average total trauma treatment time for patients with an ISS≥16 from initially 90.9±48.6 min to 37.4±18.  min in the final study period.

CONCLUSIONS

The external quality management performed by the TR-DGU has proved to be a constant source of inspiration. The effects of the changes made can be scientifically proven. It is to be discussed to what extent a sole external quality management can be useful.

[Special aspects of the emergency medical care of head and neck injuries]

The overall incidence of severe head, face and neck injuries as seen from the German Trauma Registry of the National Association of German Trauma Surgeons is 81.3%. The leading causes of death among these patients are hemorrhage and severe traumatic brain injury. The aim of prehospital emergency medical care is to stabilize vital functions in order to ensure primary survival and to reduce morbidity with appropriate prehospital treatment of the individual injuries within the overall injury pattern. In this review, special aspects as well as pitfalls of the prehospital management of patients with head, face and neck injuries are demonstrated. Prehospital airway management concepts as well as concepts for stopping bleeding in the head, face and neck region are discussed in detail.

Carrier relaxation in epitaxial graphene photoexcited near the Dirac point

We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 to 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical-phonon frequency; however, owing to the presence of hot carriers, optical-phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.

Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation

Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect.