Abstract
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.
Highlights
Recent research on spin waves (SWs) is increasingly driven by their unique linear and nonlinear properties as well as anticipated applications in telecommunication, image processing, and even quantum computation [1,2,3,4,5]
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”)
Summarizing the experimental data and their analysis, we have demonstrated that a train of optical pump pulses can drive the magnetization within the illuminated area, thereby exciting magnons
Summary
Recent research on spin waves (SWs) is increasingly driven by their unique linear and nonlinear properties as well as anticipated applications in telecommunication, image processing, and even quantum computation [1,2,3,4,5]. SWs are launched if, in a magnetically ordered material, the magnetization is pushed out of equilibrium. Quantum information processing necessitates addressing a qubit by a magnetic field with a submicron gradient [5]. This challenge might be solved if the magnetic system is disturbed by ultrashort laser pulses that can be focused microscopically [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24].
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