Dual-output kilohertz pump laser for high-energy picosecond OPCPA.

A dual-output thin-disk picosecond laser operating at 100 W with 1 kHz repetition rate is reported in this Letter. By electronically adjusting the amplitude of the optical seed pulses that are injected into the laser cavity, the energy extracted from the gain medium can be shared between two pulses. Amplified double pulses are subsequently spatially separated into two independent beams by a fast Pockels cell, compressed in one common compressor, and frequency-doubled with ∼70% efficiency. This approach significantly decreases strain on the optics, as well as nonlinear effects, and is advantageous for power scaling.

120 mJ, 1 kHz, picosecond laser at 515 nm.

We report on a 1 kHz, 515 nm laser system, based on a commercially available 230 W average power Yb:YAG thin-disk regenerative amplifier, developed for pumping one of the last optical parametric chirped pulse amplification (OPCPA) stages of the Allegra laser system at ELI Beamlines. To avoid problems with self-focusing of picosecond pulses, the 1030 nm output pulses are compressed and frequency doubled with an LBO crystal in vacuum. Additionally, development of a thermal management system was needed to ensure stable phase matching conditions at high average power. The resulting 515 nm pulses have an energy of more than 120 mJ with SHG efficiency of 60% and an average RMS stability of 1.1% for more than 8 h.

Optical properties of lithium terbium fluoride and implications for performance in high power lasers.

LiTbF4 has the potential to replace traditional magneto-optic garnet materials as a Faraday rotator in high power laser systems due to its high Verdet constant. New measurements are reported of the ordinary and extraordinary refractive indices of LiTbF4 as functions of wavelength and temperature, respectively, as well as their corresponding Sellmeier expressions. Consequently, the Verdet coefficient was calculated and plotted as a function of wavelength and temperature. These measurements will aid in further development of LiTbF4 as an optical isolator.

Error-related functional connectivity of the thalamus in cocaine dependence.

Error processing is a critical component of cognitive control, an executive function that has been widely implicated in substance misuse. In previous studies we showed that error related activations of the thalamus predicted relapse to drug use in cocaine addicted individuals (Luo et al., 2013). Here, we investigated whether the error-related functional connectivity of the thalamus is altered in cocaine dependent patients (PCD, n = 54) as compared to demographically matched healthy individuals (HC, n = 54). The results of a generalized psychophysiological interaction analysis showed negative thalamic connectivity with the ventral medial prefrontal cortex (vmPFC), in the area of perigenual and subgenual anterior cingulate cortex, in HC but not PCD (p < 0.05, corrected, two-sample t test). This difference in functional connectivity was not observed for task-residual signals, suggesting that it is specific to task-related processes during cognitive control. Further, the thalamic-vmPFC connectivity is positively correlated with the amount of cocaine use in the prior month for female but not for male PCD. These findings add to recent literature and provide additional evidence for circuit-level biomarkers of cocaine dependence.

Gray matter volume correlates of global positive alcohol expectancy in non-dependent adult drinkers.

Alcohol use and misuse is known to involve structural brain changes. Numerous imaging studies have examined changes in gray matter (GM) volumes in dependent drinkers, but there is little information on whether non-dependent drinking is associated with structural changes and whether these changes are related to psychological factors-such as alcohol expectancy-that influence drinking behavior. We used voxel-based morphometry (VBM) to examine whether the global positive scale of alcohol expectancy, as measured by the Alcohol Expectancy Questionnaire-3, is associated with specific structural markers and whether such markers are associated with drinking behavior in 113 adult non-dependent drinkers (66 women). Alcohol expectancy is positively correlated with GM volume of left precentral gyrus (PCG) in men and women combined and bilateral superior frontal gyri (SFG) in women, and negatively correlated with GM volume of the right ventral putamen in men. Furthermore, mediation analyses showed that the GM volume of PCG mediate the correlation of alcohol expectancy and the average number of drinks consumed per occasion and monthly total number of drinks in the past year. When recent drinking was directly accounted for in multiple regressions, GM volume of bilateral dorsolateral prefrontal cortices correlated positively with alcohol expectancy in the combined sample. To our knowledge, these results are the first to identify the structural brain correlates of alcohol expectancy and its mediation of drinking behaviors. These findings suggest that more studies are needed to investigate increased GM volume in the frontal cortices as a neural correlate of alcohol expectancy.

Error processing and gender-shared and -specific neural predictors of relapse in cocaine dependence.

Deficits in cognitive control are implicated in cocaine dependence. Previously, combining functional magnetic resonance imaging and a stop signal task, we demonstrated altered cognitive control in cocaine-dependent individuals. However, the clinical implications of these cross-sectional findings and, in particular, whether the changes were associated with relapse to drug use, were not clear. In a prospective study, we recruited 97 treatment-seeking individuals with cocaine dependence to perform the stop signal task during functional magnetic resonance imaging and participate in follow-up assessments for 3 months, during which time cocaine use was evaluated with timeline follow back and ascertained by urine toxicology tests. Functional magnetic resonance imaging data were analysed using general linear models as implemented in Statistical Parametric Mapping 8, with the contrast 'stop error greater than stop success trials' to index error processing. Using voxelwise analysis with logistic and Cox regressions, we identified brain activations of error processing that predict relapse and time to relapse. In females, decreased error-related activations of the thalamus and dorsal anterior cingulate cortex predicted relapse and an earlier time to relapse. In males, decreased error-related activations of the dorsal anterior cingulate cortex and left insula predicted relapse and an earlier time to relapse. These regional activations were validated with data resampling and predicted relapse with an average area under the curve of 0.849 in receiver operating characteristic analyses. These findings provide direct evidence linking deficits in cognitive control to clinical outcome in a moderate-sized cohort of cocaine-dependent individuals. These results may provide a useful basis for future studies to examine how psychosocial factors interact with cognitive control to determine drug use and to evaluate the efficacy of pharmacological or behavioural treatment in remediating deficits of cognitive control in cocaine addicts.

Neural processes of an indirect analog of risk taking in young nondependent adult alcohol drinkers-an FMRI study of the stop signal task.

BACKGROUND: Alcohol abuse and dependence are common problems in the United States that stem from a variety of factors, one of which may be a period of high level social drinking during college and early adulthood. Extant study implicates risk taking as a cognitive factor that contributes to habitual and heavy drinking. We sought to examine the neural processes of risk taking in young, nondependent drinkers. METHODS: We compared 20 young adult social drinkers with a high level of alcohol use (AH), as defined by number of drinks per month, and 21 demographically matched drinkers with low to moderate alcohol use (ALM) in a functional magnetic resonance imaging study of the stop signal task. By contrasting risk taking (speeded) to risk aversion (slowed) trials, we examined the neural correlates of risk taking. Brain imaging data were analyzed with Statistical Parametric Mapping. Regions of interest were identified and corresponding effect sizes were examined for correlations with self-reported alcohol use. RESULTS: The results showed that, compared with ALM, AH demonstrated decreased activation in right superior frontal gyrus and left caudate nucleus when contrasting risk taking and risk aversion trials at p < 0.001, uncorrected. Furthermore, examination of the effect size data showed that the extent of these decreased regional activations correlated with frequency of drinking in women, but not men. CONCLUSIONS: These findings suggest a neural analog of nondependent, high level drinking. Specifically, high level social drinking is associated with altered activation of the caudate and superior frontal cortex, an association that appears to be stronger in women than in men and is strongly tied to the frequency of drinking. These results are relevant in understanding risk taking behavior in social drinking as well as in examining the potential path from high level social use in young adults to dangerous alcohol consumption later in life.