Radiation-loss management in modulated waveguides

In this work, we discuss the management of radiation loss in photonic waveguides. As an experimental basis, we introduce a new technique of fabricating waveguides with tunable loss, which is particularly useful when implementing non-Hermitian (PT-symmetric) systems. To this end, we employ laser-written waveguides with a transverse sinusoidal modulation, which causes well-controllable radiation losses of almost arbitrary amount. Numerical simulations support our experimental findings. Our study shows that the radiation loss not only depends on the local waveguide curvature but also is influenced by interference effects. As a consequence, the loss is a nonmonotonous function of the bending parameters, such as period length.

Laser-generated broadband antireflection structures for freeform silicon lenses at terahertz frequencies

We present a flexible technology to generate broadband antireflection (AR) structures for the terahertz (THz) frequency range on planar and curved surfaces of silicon optics. Ultrashort laser pulses are used to ablate the surface to form a pattern of conical pillars with a period of 30 μm. These subwavelength structures act as an effective medium with gradual transition of the refractive index from air to silicon, which reduces the Fresnel reflection losses. The characterization with the THz time-domain spectroscopy system shows an AR effect for a frequency range of 0.1-1.5 THz with a maximum enhancement of the spectral amplitude by ca. 32% at 0.4 THz for planar surfaces. In addition, we demonstrate laser-generated AR structures on convex silicon lenses of both photoconductive emitter and detector devices. Here, the THz pulse amplitude can be increased by about 28%, and single frequencies even show an improvement of the spectral amplitude up to 58%.

Measurement of stable changes of self-management skills after rehabilitation: a latent state-trait analysis of the Health Education Impact Questionnaire (heiQ™)

PURPOSE

To assess stable effects of self-management programs, measurement instruments should primarily capture the attributes of interest, for example, the self-management skills of the measured persons. However, measurements of psychological constructs are always influenced by both aspects of the situation (states) and aspects of the person (traits). This study tests whether the Health Education Impact Questionnaire (heiQ™), an instrument assessing a wide range of proximal outcomes of self-management programs, is primarily influenced by person factors instead of situational factors. Furthermore, measurement invariance over time, changes in traits and predictors of change for each heiQ™ scale were examined.

METHODS

Subjects were N = 580 patients with rheumatism, asthma, orthopedic conditions or inflammatory bowel disease, who filled out the heiQ™ at the beginning, the end of and 3 months after a disease-specific inpatient rehabilitation program in Germany. Structural equation modeling techniques were used to estimate latent trait-change models and test for measurement invariance in each heiQ™ scale. Coefficients of consistency, occasion specificity and reliability were computed.

RESULTS

All scales showed scalar invariance over time. Reliability coefficients were high (0.80-0.94), and consistency coefficients (0.49-0.79) were always substantially higher than occasion specificity coefficients (0.14-0.38), indicating that the heiQ™ scales primarily capture person factors. Trait-changes with small to medium effect sizes were shown in five scales and were affected by sex, age and diagnostic group.

CONCLUSION

The heiQ™ can be used to assess stable effects in important outcomes of self-management programs over time, e.g., changes in self-management skills or emotional well-being.

Nursing research in the Gynecologic Oncology Group

OBJECTIVES

To review nursing science history within the Gynecology Oncology Group (GOG); to discuss challenges of nursing science in the cooperative group (CG) using a current nurse-led protocol (GOG-0259) as an exemplar; and to propose recommendations to advance nursing science in the CG setting.

DATA SOURCES

Indexed citations and personal experience.

CONCLUSION

Benefits of CG research include opportunities for inter-disciplinary collaboration and ability to rapidly accrue large national samples. Challenges include limited resources to support non-treatment trials, a burdensome protocol approval process, and lack of experience with nursing/quality-of-life intervention studies. Formal GOG structures need to evolve to encourage nurse scientists to become active members; promote collaboration between experienced GOG advanced practice nurses and nurse scientists to identify nursing research priorities; and consider new funding sources to support pilot intervention studies.

IMPLICATIONS FOR NURSING PRACTICE

Understanding the CG research process is critical for nurse scientists. A multi-disciplinary team of CG leaders can help investigators navigate a complex research environment and increase awareness of the value of nursing research.

Photonic coherent state transfer with Hamiltonian dynamics

We report the observation of near-perfect light wave transfer by emulating quantum state transfer on a lattice with Hamiltonian dynamics, i.e., time-dependent intersite couplings. The structure transferring a single waveguide excitation over 11 sites with a fidelity of 0.93 works for classical light as well as single photons. As our implementation of perfect quantum state transfer uses a photonic setting, we introduce polarization as a new degree of freedom to the transport protocol. We demonstrate rotation operations of up to 40° on polarization during state transfer.

Superballistic growth of the variance of optical wave packets

We experimentally demonstrate that hybrid ordered-disordered photonic lattices can generate faster than the ballistic growth of the second moment of a spreading wave packet for parametrically large time intervals.

[Collection and processing of personal data to evaluate cancer screening programmes - results of a survey of the German population in light of the bill 'early detection of cancer and cancer registries']

In a representative German sample, 62.1% of participants of cancer screening interventions indicated willingness to provide personal data for data-linkage with cancer registries. An agreement of over 90% is deemed necessary to conduct a meaningful population-based evaluation. The 'early detection of cancer and cancer regis-tries' bill proposed a procedure based on the use of pseudonyms only. This way personal consent is not required but participants are granted the right to object.

Probing timescales during back side ablation of Molybdenum thin films with optical and electrical measurement techniques

In this study we present a new measurement technique to investigate the timescales of back side ablation of conductive films, using Molybdenum as an application example from photovoltaics. With ultrashort laser pulses at fluences below 0.6 J/cm(2), we ablate the Mo film in the shape of a fully intact Mo 'disc' from a transparent substrate. By monitoring the time-dependent current flow across a specifically developed test structure, we determine the time required for the lift-off of the disc. This value decreases with increasing laser fluence down to a minimum of 21 ± 2 ns. Furthermore, we record trajectories of the discs using a shadowgraphic setup. Ablated discs escape with a maximum velocity of 150 ± 5 m/s whereas droplets of Mo forming at the center of the disc can reach velocities up to 710 ± 11 m/s.

Self-trapping threshold in disordered nonlinear photonic lattices

We investigate numerically and experimentally the influence of coupling disorder on the self-trapping dynamics in nonlinear one-dimensional optical waveguide arrays. The existence of a lower and upper bound of the effective average propagation constant allows for a generalized definition of the threshold power for the onset of soliton localization. When compared to perfectly ordered systems, this threshold is found to decrease in the presence of coupling disorder.

Einstein-Podolsky-Rosen spatial entanglement in ordered and anderson photonic lattices

We demonstrate quantum walks of a photon pair in a spatially extended Einstein-Podolsky-Rosen state coupled into an on-chip multiport photonic lattice. By varying the degree of entanglement we observe Anderson localization for pairs in a separable state and Anderson colocalization for pairs in an Einstein-Podolsky-Rosen entangled state. In the former case, each photon localizes independently, while in the latter neither photon localizes, but the pair colocalizes--revealing unexpected survival of the spatial correlations through strong disorder.

Vacuum instability and pair production in an optical setting

In the Dirac-sea picture, the physics of pair production and instability of the quantum electrodynamics vacuum in presence of an oscillating electric field resembles the phenomenon of interband transition of light waves in photonic superlattices induced by a geometric curvature. We realize a binary wave guide superlattice with a curved optical axis mimicking dynamical pair production induced by two counterpropagating ultrastrong laser pulses. Our optical analogue enables visualization of formation of electron-positron pair in physical space as splitting of a wave packet, originally representing an electron in the Dirac sea.

Biphoton generation in quadratic waveguide arrays: a classical optical simulation

Quantum entanglement became essential in understanding the non-locality of quantum mechanics. In optics, this non-locality can be demonstrated on impressively large length scales, as photons travel with the speed of light and interact only weakly with their environment. Spontaneous parametric down-conversion (SPDC) in nonlinear crystals provides an efficient source for entangled photon pairs, so-called biphotons. However, SPDC can also be implemented in nonlinear arrays of evanescently coupled waveguides which allows the generation and the investigation of correlated quantum walks of such biphotons in an integrated device. Here, we analytically and experimentally demonstrate that the biphoton degrees of freedom are entailed in an additional dimension, therefore the SPDC and the subsequent quantum random walk in one-dimensional arrays can be simulated through classical optical beam propagation in a two-dimensional photonic lattice. Thereby, the output intensity images directly represent the biphoton correlations and exhibit a clear violation of a Bell-like inequality.

Optical analogues for massless dirac particles and conical diffraction in one dimension

We demonstrate that light propagating in an appropriately designed lattice can exhibit dynamics akin to that expected from massless relativistic particles as governed by the one-dimensional Dirac equation. This is accomplished by employing a waveguide array with alternating positive and negative effective coupling coefficients, having a band structure with two intersecting minibands. Through this approach optical analogues of massless particle-antiparticle pairs are experimentally realized. One-dimensional conical diffraction is also observed for the first time in this work.

Anderson cross-localization

We report Anderson localization in two-dimensional optical waveguide arrays with disorder in waveguide separation introduced along one axis of the array, in an uncorrelated fashion for each waveguide row. We show that the anisotropic nature of such disorder induces a strong localization along both array axes. The degree of localization in the cross-axis remains weaker than that in the direction in which disorder is introduced. This effect is illustrated both theoretically and experimentally.

Observation of the gradual transition from one-dimensional to two-dimensional Anderson localization

We study the gradual transition from one-dimensional (1D) to two-dimensional (2D) Anderson localization upon transformation of the dimensionality of disordered waveguide arrays. An effective transition from a 1D to a 2D system is achieved by increasing the number of rows forming the arrays. We observe that, for a given disorder level, Anderson localization becomes weaker with increasing numbers of rows-hence the effective dimension.

Negative coupling between defects in waveguide arrays

We report on the experimental demonstration of negative coupling constants between defect guides in a waveguide lattice. We find that coupling can only be negative if the defects are negative and an odd number of lattice sites is between the defect guides.

Anderson localization in a periodic photonic lattice with a disordered boundary

We investigate experimentally the light evolution inside a two-dimensional finite periodic array of weakly coupled optical waveguides with a disordered boundary. For a completely localized initial condition away from the surface, we find that the disordered boundary induces an asymptotic localization in the bulk, centered around the initial position of the input beam.

Skin cancer screening participation and impact on melanoma incidence in Germany--an observational study on incidence trends in regions with and without population-based screening

BACKGROUND

The SCREEN (Skin Cancer Research to provide Evidence for Effectiveness of Screening in Northern Germany) project involved population-wide skin cancer screening with whole-body examination by general physicians and dermatologists. It was conducted in the German state of Schleswig-Holstein (July 2003-June 2004), but not in the German state of Saarland.

METHODS

The population-based registries of Schleswig-Holstein and Saarland provided data on melanoma incidence before, during, and after SCREEN to assess the association of skin cancer screening with incidence.

RESULTS

Approximately 19% of the Schleswig-Holstein population participated in SCREEN (women: 27%, men: 10%). A total of 52% of all melanomas diagnosed during SCREEN in Schleswig-Holstein were detected as part of the project. Melanoma incidence increased during SCREEN (invasive melanoma in women: +8.9 per 100,000 (95% confidence intervals (CI): 6.1; 11.7); men: +4.0 per 100,000 (95% CI: 1.6; 6.4)) and decreased afterwards (women: -10.6 per 100,000 (95% CI: -13.3; -7.9); men: -4.1 per 100,000 (95% CI: -6.5; -1.7)). Similar changes were not observed in Saarland that had no such project. The differences between the two states were greatest among women, the group with the greater SCREEN participation.

CONCLUSION

The SCREEN project had a substantial impact on melanoma incidence. This is consistent with the impact of effective screening for other cancers.

Three-dimensional light bullets in arrays of waveguides

We report the first experimental observation of three-dimensional light bullets, excited by femtosecond pulses in a system featuring quasi-instantaneous cubic nonlinearity and a periodic, transversally modulated refractive index. Stringent evidence of the excitation of light bullets is based on time-gated images and spectra which perfectly match our numerical simulations. Furthermore, we reveal a novel evolution mechanism forcing the light bullets to follow varying dispersion or diffraction conditions, until they leave their existence range and decay.