Explore the vast range of titles available.

Currently spin waves are considered for computation and data processing as an alternative to charge currents. Generation of spin waves by ultrashort laser pulses provides several important advances with respect to conventional approaches using microwaves. In particular, focused laser spot works as a point source for spin waves and allows for directional control of spin waves and switching between their different types. For further progress in this direction it is important to manipulate with the spectrum of the optically generated spin waves. Here we tackle this problem by launching spin waves by a sequence of femtosecond laser pulses with pulse interval much shorter than the relaxation time of the magnetization oscillations. This leads to the cumulative phenomenon and allows us to generate magnons in a specific narrow range of wavenumbers. The wavelength of spin waves can be tuned from 15 μm to hundreds of microns by sweeping the external magnetic field by only 10 Oe or by slight variation of the pulse repetition rate. Our findings expand the capabilities of the optical spin pump-probe technique and provide a new method for the spin wave generation and control.

Optical tools are promising for spin-wave generation because of the possibilities of ultrafast manipulation and local excitation. However, a single laser pulse can inject spin waves (SWs) only with a broad frequency spectrum, resulting in short propagation distances and low wave amplitudes. Here, we excite a magnetic garnet film by a train of fs-laser pulses with a 1-GHz repetition rate so that the pulse separation is shorter than the decay time of magnetic modes, which allows us to achieve a collective impact on the magnetization and establish a quasistationary source of spin waves, namely, a coherent accumulation of magnons (“magnon cloud”). This approach has several appealing features: (i) The magnon source is tunable, (ii) the SW amplitude can be significantly enhanced, (iii) the SW spectrum is quite narrow, providing long-distance propagation, (iv) the periodic pumping results in an almost constant-in-time SW amplitude for the distances larger than 20μm away from the source, and (v) the SW emission shows pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave the way for applications in data processing, including the quantum regime. The quasistationary magnon accumulation might also be of interest for applications in magnon Bose-Einstein condensates.

Amidst ongoing efforts to reduce the nation’s prison population, as well as calls to defund the police and invest in civilianized public safety strategies following the murder of George Floyd, community-based violence intervention (CVI) strategies have been increasingly recognized as a critical means by which to ameliorate the United States’ enduring gun violence problem without exacerbating the harms of over policing and mass incarceration. However, most contemporary CVI research has assessed program impacts on neighborhood rates of gun violence and has produced conflicting findings, leading scholars to call for the need to examine a wider range of program-related functions and outcomes. Drawing inspiration from the reentry literature, this dissertation explores the impact of CVI on the social integration outcomes of individuals returning to society after release from incarceration. Specifically, I sought to better understand 1) how employment as a violence interventionist impacts the reintegration trajectories of workers, most of whom are formerly incarcerated, and 2) how workers provide resources and services to their clients, who are often returning from incarceration. To do so, I used two data sources: survey data collected from the city-wide population of CVI workers in Boston (N=63) as part of the Violence Intervention Worker Study (VIeWS), and semi-structured interviews with a subset of formerly incarcerated Boston workers (n=15). Regarding the first research question, I found that CVI employment serves several socially integrative functions, including fostering a sense of empowerment, promoting and/or reinforcing desistance, encouraging new and strengthened connections to individuals and institutions, reducing stigma and enabling deeper community integration, and allowing workers to actively engage in a process of accountability. However, I also found that the job has the capacity to hinder reintegration, due to low wages, regular and ongoing proximity to crime, violence, and trauma, and insufficient mental health support for workers. Regarding the second question, I found that formerly incarcerated streetworkers rely heavily on their past and present credibility, which is enhanced by a deep sense of personal responsibility, to form sustained and trusting relationships with their clients. I then found that, to provide and/or connect their clients to prosocial opportunities and resources, workers adopt one of five unique “roles,” each of which helps clients overcome barriers to service access. I conclude that CVI workers function as key actors within the reentry service field, connecting some of society’s most marginalized young people to crucial forms of support that increase the likelihood of a successful reentry. By contributing to and integrating the CVI and reentry literatures to establish CVI as a case study of “reintegration in action,” this dissertation has offered a lens by which to see the field in a new way that enables a deeper understanding of the processes underlying post-incarceration social integration. Moving forward, I suggest that reentry scholars regard CVI as a form of restorative reentry and take seriously its position within the reentry service field, and that those studying CVI consider it just as much a project of social integration as it is a program of violence reduction.

Optical tools are of great promise for generation of spin waves due to the possibility to manipulate on ultrashort time scales and to provide local excitation. However, a single laser pulse can inject spin waves only with a broad frequency spectrum, resulting in a short propagation distance and low amplitude. Here we excite a magnetic garnet film by a train of fs-laser pulses with 1 GHz repetition rate so that pulse separation is smaller than decay time of the magnetic modes which allows to achieve collective photonic impact on magnetization. It establishes a quasi-stationary source of SWs, namely a coherent magnon accumulation (\"magnon cloud\"). This approach has several appealing features: (i) the source is tunable; (ii) the SW amplitude can be significantly enhanced; (iii) the spectrum of the generated SWs is quite narrow that provides longer propagation distance; (iv) the periodic pumping results in almost constant in time SW amplitude up to 100 um away from the source; and (v) the SW emission shows a pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave a way for applications in data processing, including the quantum regime. The quasi-stationary magnon accumulation might be also of interest for the problem of magnon Bose-Einstein condensate.