A knock-on deuteron imager for measurements of fuel and hotspot asymmetry in direct-drive inertial confinement fusion implosions (invited).

A knock-on deuteron imager (KoDI) has been implemented to measure the fuel and hotspot asymmetry of cryogenic inertial confinement fusion implosions on OMEGA. Energetic neutrons produced by D-T fusion elastically scatter ("knock on") deuterons from the fuel layer with a probability that depends on ρR. Deuterons above 10 MeV are produced by near-forward scattering, and imaging them is equivalent to time-integrated neutron imaging of the hotspot. Deuterons below 6 MeV are produced by a combination of side scattering and ranging in the fuel, and encode information about the spatial distribution of the dense fuel. The KoDI instrument consists of a multi-penumbral aperture positioned 10-20 cm from the implosion using a ten-inch manipulator and a detector pack at 350 cm from the implosion to record penumbral images with magnification of up to 35×. Range filters and the intrinsic properties of CR-39 are used to distinguish different charged-particle images by energy along the same line of sight. Image plates fielded behind the CR-39 record a 10 keV x-ray image using the same aperture. A maximum-likelihood reconstruction algorithm has been implemented to infer the source from the projected penumbral images. The effects of scattering and aperture charging on the instrument point-spread function are assessed. Synthetic data are used to validate the reconstruction algorithm and assess an appropriate termination criterion. Significant aperture charging has been observed in the initial experimental dataset, and increases with aperture distance from the implosion, consistent with a simple model of charging by laser-driven EMP.

Fast pulse shaping for a novel gated electron mirror.

We present the design and prototype of a switchable electron mirror, along with a technique for driving it with an arbitrary pulse shape. We employ a general technique for electronic pulse-shaping, where high fidelity of the pulse shape is required, but the characteristics of the system, which are possibly nonlinear, are not known. This driving technique uses an arbitrary waveform generator to pre-compensate the pulse, with a simple iterative algorithm used to generate the input waveform. This is a broadly applicable, general method for arbitrary pulse shaping. Driving our switchable electron mirror with a flat-top pulse, we demonstrate an improvement in rms error of roughly two orders of magnitude compared to an uncompensated waveform. Our results demonstrate the feasibility of high fidelity waveform reproduction in the presence of nonidealities, with immediate applications in the realization of novel electron optical components.

Electro-optic imaging enables efficient wide-field fluorescence lifetime microscopy.

Nanosecond temporal resolution enables new methods for wide-field imaging like time-of-flight, gated detection, and fluorescence lifetime. The optical efficiency of existing approaches, however, presents challenges for low-light applications common to fluorescence microscopy and single-molecule imaging. We demonstrate the use of Pockels cells for wide-field image gating with nanosecond temporal resolution and high photon collection efficiency. Two temporal frames are obtained by combining a Pockels cell with a pair of polarizing beam-splitters. We show multi-label fluorescence lifetime imaging microscopy (FLIM), single-molecule lifetime spectroscopy, and fast single-frame FLIM at the camera frame rate with 103-105 times higher throughput than single photon counting. Finally, we demonstrate a space-to-time image multiplexer using a re-imaging optical cavity with a tilted mirror to extend the Pockels cell technique to multiple temporal frames. These methods enable nanosecond imaging with standard optical systems and sensors, opening a new temporal dimension for wide-field low-light microscopy.

Design for a 10 keV multi-pass transmission electron microscope.

Multi-pass transmission electron microscopy (MPTEM) has been proposed as a way to reduce damage to radiation-sensitive materials. For the field of cryo-electron microscopy (cryo-EM), this would significantly reduce the number of projections needed to create a 3D model and would allow the imaging of lower-contrast, more heterogeneous samples. We have designed a 10 keV proof-of-concept MPTEM. The column features fast-switching gated electron mirrors which cause each electron to interrogate the sample multiple times. A linear approximation for the multi-pass contrast transfer function (CTF) is developed to explain how the resolution depends on the number of passes through the sample.

Multi-pass transmission electron microscopy.

Feynman once asked physicists to build better electron microscopes to be able to watch biology at work. While electron microscopes can now provide atomic resolution, electron beam induced specimen damage precludes high resolution imaging of sensitive materials, such as single proteins or polymers. Here, we use simulations to show that an electron microscope based on a multi-pass measurement protocol enables imaging of single proteins, without averaging structures over multiple images. While we demonstrate the method for particular imaging targets, the approach is broadly applicable and is expected to improve resolution and sensitivity for a range of electron microscopy imaging modalities, including, for example, scanning and spectroscopic techniques. The approach implements a quantum mechanically optimal strategy which under idealized conditions can be considered interaction-free.

Iterative creation and sensing of twisted light.

The iterative interaction of a photon with a sample can lead to increased sensitivity in measuring the properties of the samples, such as its refractive index or birefringence. Here we show that this principle can also be used to generate and sense states of light. In particular, we demonstrate a technique to generate states with high orbital angular momentum using a single-vortex phase plate (VPP). This is accomplished by placing the phase plate in a self-imaging cavity such that light interacts with it multiple times; for an ideal phase plate, this is equivalent to iterative applications of the angular momentum operator. Using a discrete VPP, we show that our setup realizes a high-dimensional generalization of the Pauli matrix σx, and that the created states show sub-diffraction limited features that might find applications in structured illumination microscopy.

Multi-pass microscopy.

Microscopy of biological specimens often requires low light levels to avoid damage. This yields images impaired by shot noise. An improved measurement accuracy at the Heisenberg limit can be achieved exploiting quantum correlations. If sample damage is the limiting resource, an equivalent limit can be reached by passing photons through a specimen multiple times sequentially. Here we use self-imaging cavities and employ a temporal post-selection scheme to present full-field multi-pass polarization and transmission micrographs with variance reductions of 4.4±0.8 dB (11.6±0.8 dB in a lossless setup) and 4.8±0.8 dB, respectively, compared with the single-pass shot-noise limit. If the accuracy is limited by the number of detected probe particles, our measurements show a variance reduction of 25.9±0.9 dB. The contrast enhancement capabilities in imaging and in diffraction studies are demonstrated with nanostructured samples and with embryonic kidney 293T cells. This approach to Heisenberg-limited microscopy does not rely on quantum state engineering.

Ultrafast oscilloscope based on laser-triggered field emitters.

Laser-triggered electron emission from sharp metal tips has been demonstrated in recent years as a high brightness, ultrafast electron source. Its possible applications range from ultrafast electron microscopy to laser-based particle accelerators to electron interferometry. The ultrafast nature of the emission process allows for the sampling of an instantaneous radio frequency (RF) voltage that has been applied to a field emitter. For proof-of-concept, we use an RF signal derived from our laser's repetition rate, mapping a 9.28 GHz signal in 22.4 fs steps with 28 mv accuracy.

Ultrafast Time-Resolved Photoelectric Emission.

The emission times of laser-triggered electrons from a sharp tungsten tip are directly characterized under ultrafast, near-infrared laser excitation at Keldysh parameters of 6.6<γ<19.1. Emission delays up to 10 fs are observed, which are inferred from the energy gain of photoelectrons emitted into a synchronously driven microwave cavity. Few femtosecond timing resolution is achieved in a configuration capable of measuring timing shifts up to 55 ps. The technique can also be used to measure the microwave phase inside the cavity with a precision below 70 fs upon the energy resolved detection of a single electron.

Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures.

In LaAlO(3)/SrTiO(3) heterointerfaces, charge carriers migrate from the LaAlO(3) to the interface in an electronic reconstruction. Magnetism has been observed in LaAlO(3)/SrTiO(3), but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. Using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlO(3) thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

The television, school, and family smoking prevention and cessation project. VIII. Student outcomes and mediating variables.

BACKGROUND: This paper presents the student outcomes of a large-scale, social-influences-based, school and media-based tobacco use prevention and cessation project in Southern California. METHODS: The study provided an experimental comparison of classroom delivery with television delivery and the combination of the two in a 2 x 2 plus 1 design. Schools were randomly assigned to conditions. Control groups included "treatment as usual" and an "attention control" with the same outcome expectancies as the treatment conditions. Students were surveyed twice in grade 7 and once in each of grades 8 and 9. The interventions occurred during grade 7. RESULTS: We observed significant effects on mediating variables such as knowledge and prevalence estimates, and coping effort. The knowledge and prevalence estimates effects decayed partially but remained significant up to a 2-year follow-up. The coping effort effect did not persist at follow-ups. There were significant main effects of both classroom training and TV programming on knowledge and prevalence estimates and significant interactions of classroom and TV programming on knowledge (negative), disapproval of parental smoking, and coping effort. There were no consistent program effects on refusal/self-efficacy, smoking intentions, or behavior. CONCLUSIONS: Previous reports demonstrated successful development and pilot testing of program components and measures and high acceptance of the program by students and parents. The lack of behavioral effects may have been the result of imperfect program implementation or low base rates of intentions and behavior.

Relations of coping effort, coping strategies, perceived stress, and cigarette smoking among adolescents.

Coping strategies may influence adolescent smoking behaviour because they provide alternative behavioral and cognitive outlets which facilitate or inhibit smoking, or because they are expressions of general coping effort to smoke or not smoke. The present investigation examined three possibilities regarding how coping strategies versus coping effort compare as predictors of adolescent smoking: (1) general coping effort to not smoke may be a better predictor of adolescent smoking behaviors than are specific coping strategies; (2) coping strategies may be relatively better predictors of smoking behaviors; or (3) these two constructs may be relatively better predictors of different parameters of smoking behavior. Analytic strategies included calculation of a series of multiple regression models, involving (a) 11 coping strategies previously studied in adolescent smoking research, (b) a new simple measure of coping effort to not smoke, and (c) perceived stress, as concurrent predictors of four smoking-related items. Of the 11 coping strategies, partying, relaxation, seeking spiritual guidance, and getting revenge were related to at least one of the four cigarette smoking items. Only coping effort was directly related to recent smoking behavior, whereas only the coping strategies were related to cumulative smoking. Both types of items predicted refusal self-efficacy and intention to smoke in the future. Apparently, these two types of items show unique as well as common predictive variance. These results suggest that coping strategies are related to cumulative smoking for reasons other than motivation to not smoke.

Characteristics of eighth-grade students who initiate self-care in elementary and junior high school.

The purpose of this paper is to examine whether children who care for themselves for longer periods of time are at increased risk of poor grades, truancy, anger, family conflict, stress, risk-taking, and peer influences (in addition to the increased risk of substance use previously reported). Demographic characteristics of eighth-grade students who initiate self-care in junior high school are compared with those initiating self-care in elementary school. Further, increased risks for those initiating self-care in elementary school are examined. Over two thirds of the respondents (67.8%) cared for themselves after school without adult supervision at some time during the week; 23.5% for 1 to 4 hours per week, 15.7% for 5 to 10 hours per week, and 28.6% for 11 or more hours per week. Of those in self-care, 48.5% initiated self-care during elementary school and 51.5% during junior high school. Students who were in the highest category of self-care (greater than or equal to 11 hours per week) vs those in self-care zero hours per week were 1.5 to 2 times as likely to score high on risk-taking, anger, family conflict, and stress, to be more likely to see their friends as their major source of influence, and to attend more parties. The self-reports of academic grades did not differ. The grade of initiation of self-care (elementary vs junior high school) conferred additional risk for drinking alcohol (odds ratio = 1.4), risk-taking tendencies (odds ratio = 1.5), and attending parties (odds ratio = 1.6).

Substance use among eighth-grade students who take care of themselves after school.

This investigation focused on substance use among children who regularly care for themselves after school (latchkey children). The data, collected from 4932 eighth-grade students, indicated that self-care is an important risk factor for alcohol, tobacco, and marijuana use. Data collected from 2185 parents validated these findings. Eighth-grade students, who took care of themselves for 11 or more hours a week, were at twice the risk of substance use as those who did not take care of themselves at all. This relationship held at all levels of sociodemographic status, extracurricular activities, sources of social influence, and stress. Of the 186 stratified tests of the relationship, 90% were significant; even those not found to be significant were in the direction expected. Path analyses suggest that risk-taking, having friends who smoke, and being offered cigarettes may partially explain the relationship between self-care and substance use. Those eighth-grade students who select friends who smoke and place themselves in situations in which they are offered cigarettes may be manifesting a desire to display their sense of maturity and independence. The fact that the increase in substance use occurred among almost all strata tested and the fact that mediation was not complete suggest that more than one mechanism may account for the associated increase in substance use. It is also possible that more time in self-care results in more unnoticed solitary trials of substances, as well as trials motivated by peer offers or peer pressure to use substances.

The power of policy: the relationship of smoking policy to adolescent smoking.

This study examined the effects of smoking policy on 4,807 adolescents in 23 schools over a two-county area in California. Amounts and prevalence rates of adolescent smoking were measured with a self-report survey and a biochemical measure; school smoking policy was measured with two independent surveys of school staff. Policy effects were evaluated with multiple and logistic regression analyses controlling for school-level socioeconomic status and environmental support for teaching and administration. Of the 23 schools, 100 percent had a formal written and regularly enforced policy component restricting student smoking on school grounds, 94 percent restricted students leaving school grounds, 65 percent restricted smoking near school grounds, and 57 percent had a smoking prevention education plan. Schools with policies having all four versus less than four components, high versus low emphasis on prevention, and a low versus high emphasis on cessation reported lower amounts of smoking in the last week and in the last 24 hours. Punitive consequences of policy violation had no effect. Results were compared to school staff observations of adolescent smoking, and school archival records of student smoking violations in the last year. Results suggest that school smoking policy is associated with decreased amounts of smoking in adolescents.

The television, school, and family project. V. The impact of curriculum delivery format on program acceptance.

Social psychological interventions have been successful in preventing drug and tobacco use in adolescents, but target audience involvement has not been well documented. Examination of program acceptance is necessary to avoid ambiguity when interpreting findings within and across studies. This report presents results from a program acceptance study of a seventh-grade smoking/drug-use prevention and cessation field trial. The research design is an assessment of two experimentally manipulated variations in program delivery on the program acceptance of all provider and target groups involved. Experimental manipulations included classroom and mass broadcast television demonstrations of social resistance skills against pressures to smoke and use drugs. Three aspects of target audience program acceptance were assessed: participation, satisfaction, and perceived program efficacy. Respondents included the target audience (seventh-grade students and parents), instructors, classroom observers, and school administrative staff. Strong main effects of television delivery on student and parent participation were observed. The findings suggest the usefulness of student homework assignment to view television segments with parents at home as a strategy to achieve family involvement in school-based programs. Both television and classroom delivery separately demonstrated significant positive effects on overall program acceptance with moderate interactive effects on perceived program efficacy. While classroom teacher/observers and school administrators reported strong preferences for the experimental (social resistance) classroom curriculum, acceptance of experimental and comparison (information-based) curricula by the student/parent target audience was equivalent.

Joiners and non-joiners in worksite smoking treatment: pretreatment smoking, smoking by significant others, and expectation to quit as predictors.

Treatment joiners were differentiated from non-joiners when examined across six worksite clinic locations in the Los Angeles area. Predictors examined included preprogram smoking, demographic variables, smoking by significant others, behavioral expectations to quit, and self-efficacy regarding completing treatment and resisting urges to smoke. Non-joiners reported higher preprogram smoking levels and more friends and children who smoked.

The television, school and family smoking prevention/cessation project. IV. Controlling for program success expectancies across experimental and control conditions.

A major issue in smoking prevention research is that no study has tried to equate program success expectancies across experimental and placebo control conditions. Equivalent overall program success expectancies should be established to help rule out the effects of extra-theoretical variables which influence program outcomes. The present study tested whether an attention-placebo (information based) smoking prevention program would produce equivalent expectancies about the likelihood of program success in comparison to an experimental social influences program. To try to equate program success expectancies, the design of the two programs differed in content but was similar in procedure. Fourteen middle schools were randomly assigned to the two conditions. As hypothesized, baseline expectancies were found to predict outcome measures, even after controlling for baseline smoking intentions, ethnic group, and gender. Second, the equivalence of program expectancies at posttest was tested. Youths held equivalent overall expectancies for success across conditions. This study suggested the need to control for program expectancies in prevention research, and showed that program expectancies could be controlled for by equating process of program delivery.