Manipulating the electron dynamics in the non-sequential double ionization process of Ar atoms by an orthogonal two-color laser field

Electron dynamics during non-sequential double ionization(NSDI) is one of the most attractive areas of research in the field of laser–atom or laser–molecule interaction. Based on the classic two-dimensional model, we study the process of NSDI of argon atoms driven by a few-cycle orthogonal two-color laser field composed of 800 nm and 400 nm laser pulses. By changing the relative phase of the two laser pulses, a localized enhancement of NSDI yield is observed at 0.5πand 1.5π, which could be attributed to a rapid and substantial increase in the number of electrons returning to the parent ion within extremely short time intervals at these specific phases. Through the analysis of the electron–electron momentum correlations within different time windows of NSDI events and the angular distributions of emitted electrons in different channels, we observe a more pronounced electron–electron correlation phenomenon in the recollision-induced ionization(RII) channel. This is attributed to the shorter delay time in the RII channel.

Non-sequential narrow band imaging for targeted biopsy and monitoring of gastric intestinal metaplasia

AIM： To evaluate the efficacy of non-sequential narrow band imaging （NBI） for a better recognition of gastric intestinal metaplasia （GIM）. METHODS： Previously diagnosed GIM patients underwent targeted biopsy from areas with and without GIM, as indicated by NBI, twice at an interval of 1 year. The authors compared the endoscopic criteria such as light blue crest （LBC）, villous pattern （VP）, and large long crest （LLC） with standard histology. The results from two surveillance endoscopies were compared with histology results for sensitivity, specificity, positive predic-tive value （PPV）, negative predictive value （NPV）, and likelihood ratio of positive test （LR＋）. The number of early gastric cancer cases detected was also reported. RESULTS： NBI targeted biopsy was performed in 38 and 26 patients during the first and second surveillance endoscopies, respectively. There were 2 early gastric cancers detected in the first endoscopy. No cancer was detected from the second study. Surgical and endoscopic resections were successfully performed in each patient. Sensitivity, specificity, PPV, NPV, and LR＋ of all 3 endoscopic criteria during the first/second surveillances were 78.8%/91.3%, 82.5%/89.1%, 72.8%/77.8%, 86.8%/96.1, and 4.51/8.4, respectively. LBC provided the highest LR＋ over VP and LLC. CONCLUSION： Nonequential NBI is useful for GIM targeted biopsy. LBC provides the most sensitive reading. However, the optimal duration between two surveillances requires further study.

The effect of electron initial longitudinal velocity on the non-sequential double ionization process in an elliptically polarized laser field

The effect of initial longitudinal velocity of the tunnelled electron on the non-sequential double ionization （NSDI） process in an elliptically polarized laser field is studied by a semiclassical model. We find that the non-zero initial longitudinal velocity has a suppressing effect on single-return collision （SRC） events in the double ionization process, more specifically, it results in an obvious reduction in the center part of the correlation momentum distributions in the direction of the major polarization axis （z axis） and makes the distribution of single-return collision in the minor polarization axis （x axis） become narrower.

Theoretical study on non-sequential double ionization of carbon disulfide with different bond lengths in linearly polarizedlaser fields

By using a two-dimensional Monte-Carlo classical ensemble method, we investigate the double ionization（DI） process of the CS_2 molecule with different bond lengths in an 800-nm intense laser field. The double ionization probability presents a ＂knee＂ structure with equilibrium internuclear distance R = 2.9245 a.u.（a.u. is short for atomic unit）. As the bond length of CS increases, the DI probability is enhanced and the ＂knee＂ structure becomes less obvious. In addition,the momentum distribution of double ionized electrons is also investigated, which shows the momentum mostly distributed in the first and third quadrants with equilibrium internuclear distance R = 2.9245 a.u. As the bond length of CS increases,the electron momentum becomes evenly distributed in the four quadrants. Furthermore, the energy distributions and the corresponding trajectories of the double-ionized electrons versus time are also demonstrated, which show that the bond length of CS in the CS_2 molecule plays a key role in the DI process.

Internal collision double ionization of molecules driven by co-rotating two-color circularly polarized laser pulses

The double ionization process of molecules driven by co-rotating two-color circularly polarized fields is investigated with a three-dimensional classical ensemble model. Numerical results indicate that a considerable part of the sequential double ionization(DI) events of molecules occur through internal collision double ionization(ICD), and the ICD recollision mechanism is significantly different from that in non-sequential double ionization(NSDI). By analyzing the results of internuclear distances R = 5 a.u. and 2 a.u., these two recollision mechanisms are studied in depth. It is found that the dynamic behaviors of the recollision mechanisms of NSDI and ICD are similar. For NSDI, the motion range of electrons after the ionization is relatively large, and the electrons will return to the core after a period of time. In the ICD process,electrons will rotate around the parent ion before ionization, and the distance of the electron motion is relatively small. After a period of time, the electrons will come back to the core and collide with another electron. Furthermore, the molecular internuclear distance has a significant effect on the electron dynamic behavior of the two ionization mechanisms. This study will help to understand the multi-electron ionization process of complex systems.

Narrow-band imaging optical chromocolonoscopy: Advantages and limitations

Narrow-band imaging （NBI） is an innovative optical technology that modifies the center wavelength and bandwidth of an endoscope＇s light into narrow-band illumination of 415 ：1： 30 nm. NBI markedly improves capillary pattern contrast and is an in vivo method for visualizing microvessel morphological changes in superficial neoplastic lesions. The scientific basis for NBI is that short wavelength light falls within the hemoglobin absorption band, thereby facilitating clearer visualization of vascular structures. Several studies have reported advantages and limitations of NBI colonoscopy in the colorectum. One difficulty in evaluating results, however, has been nonstandardization of NBI systems （Sequential and nonsequential）. Utilization of NBI technology has been increasing worldwide, but accurate pit pattern analysis and sufficient skill in magnifying colonoscopy are basic fundamentals required for proficiency in NBI diagnosis of colorectal lesions. Modern optical technology without proper image interpretation wastes resources, confuses untrained endoscopists and delays interinstitutional validation studies. Training in the principles of ＂optical image-enhanced endoscopy＂ is needed to close the gap between technological advancements and their clinical usefulness. Currently available evidence indicates that NBI constitutes an effective and reliable alternative to chromocolonoscopy for in vivo visualization of vascular structures, but further study assessing reproducibility and effectiveness in the colorectum is ongoing at various medical centers.

Exploration of strong-field double ionization of C_(3)H_(6) with the structures of propene and cyclopropane in intense laser fields

By using classical ensemble method,we investigate the double ionization of C_(3)H_(6) molecule with different structures(propene and cyclopropane)in intense laser fields.The numerical results show that the non-sequential double ionization occurs in propene molecule rather than cyclopropane molecule in 1200 nm laser field.To further explain this interesting phenomenon,the momentum distribution of double ionized electrons is presented and the result presents the"finger-like"structure at about 30 TW/cm^(2) of propene molecule,and this structure is more obvious than that in cyclopropane molecule.The above phenomena are also demonstrated by analysing the energy distributions of double-ionized electrons versus time.Moreover,we also investigated the angular distribution at the end of pulse,which is different between propene and cyclopropane.

Component importance assessment of power systems for improving resilience under wind storms

Increasingly natural disasters and man-made malicious attacks threaten the power systems.Improving the resilience has become an inevitable requirement for the development of power systems.The importance assessment of components is of significance for resilience improvement,since it plays a crucial role in strengthening grid structure,designing restoration strategy,and improving resource allocation efficiency for disaster prevention and mitigation.This paper proposes a component importance assessment approach of power systems for improving resilience under wind storms.Firstly,the component failure rate model under wind storms is established.According to the model,system states under wind storms can be sampled by the non-sequential Monte Carlo simulation method.For each system state,an optimal restoration model is then figured out by solving a component repair sequence optimization model considering crew dispatching.The distribution functions of component repair moment can be obtained after a sufficient system state sampling.And Copeland ranking method is adopted to rank the component importance.Finally,the feasibility of the proposed approach is validated by extensive case studies.