Tel Aviv University (TAU) develops a groundbreaking nano-laser (called a SPASER) for medicine and electronics “Spaser” is an acronym for “surface plasmon amplification by stimulated emission of radiation”
Spasers are considered a critical component for future technologies based on nanophotonics — technologies that could lead to radical innovations in medicine and science, such as a sensor and microscope 10 times more powerful than anything used today. A Spaser-based microscope might be so sensitive that it could see genetic base pairs in DNA.
It could also lead to computers and electronics that operate at speeds 100 times greater than today’s devices, using light instead of electrons to communicate and compute. More efficient solar energy collectors in renewable energy are another proposed application.
Nanoplasmonics has recently experienced explosive development with many novel ideas and dramatic achievements in both fundamentals and applications. The spaser has been predicted and observed experimentally as an active element — generator of coherent local fields. Even greater progress will be achieved if the spaser could function as a ultrafast nanoamplifier — an optical counterpart of the MOSFET (metal-oxide-semiconductor field-effect transistor). A formidable problem with this is that the spaser has the inherent feedback causing quantum generation of nanolocalized surface plasmons and saturation and consequent elimination of the net gain, making it unsuitable for amplification. We have overcome this inherent problem and shown that the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable. On the basis of quantum density matrix (optical Bloch) equations we have shown that the spaser amplifies with gain greater than 50, the switching time less or on the order of 100 fs (potentially, 10 fs). This prospective spaser technology will further broaden both fundamental and applied horizons of nanoscience, in particular, enabling ultrafast microprocessors working at 10 to 100 THz clock speed. Other prospective applications are in ultrasensing, ultradense and ultrafast information storage, and biomedicine. The spasers are based on metals and, in contrast to semiconductors, are highly resistive to ionizing radiation, high temperatures, microwave radiation, and other adverse environments.
We demonstrate that the conditions of spaser generation and the full loss compensation in a resonant plasmonic-gain medium (metamaterial) are identical. Consequently, attempting the full compensation or overcompensation of losses by gain will lead to instability and a transition to a spaser state. This will limit (clamp) the inversion and lead to the limitation on the maximum loss compensation achievable. The criterion of the loss overcompensation, leading to the instability and spasing, is given in a analytical and universal (independent from system’s geometry) form.
Loss is a crucial problem in plasmonic integrated optical circuits and metamaterials. The Er, Yb codoped gain material is introduced into a magnetic plasmon waveguide composed of a chain of nanosandwiches in order to solve the loss problem in such subwavelength waveguide. The magnetic plasmon mode and a higher order mode are chosen as the signal and pump light to enhance the radiation and pump efficiencies. The signal light propagating in the waveguide is investigated with different Er3+ doping concentration and signal decay time. It is shown that the gain effect can not only compensate the loss but also is able to amplify the signal, when exceeding certain threshold values of doping concentration and signal decay time.
The demonstration of enhanced spontaneous emission of nanoscaled optical emitters near metallic nanoparticles and the recent realization of a nanolaser based on surface plasmon amplification by stimulated emission of radiation (spaser) encourage the search for strong coupling regime at the nanoscale. Here we propose the concept of nanopolaritons. We demonstrate with accurate scattering calculations that the strong coupling regime of a single quantum emitter (a semiconductor quantum dot) placed in the gap between two metallic nanoparticles can be achieved. The largest dimension of the investigated system is only 36 nm. Nanopolaritons will advance our fundamental understanding of surface plasmon enhanced optical interactions and could be used as ultra-compact elements in quantum-information technology.
Simultaneously enhanced reflectance and transmittance greater than 35 dB are demonstrated for the lasing spaser (or spasing) behavior in an active fishnet metamaterial. In mimicking a lasing cavity, an equivalent active slab with Lorentz dispersion for the index of refraction is established to model the spasing metamaterial through the Fabry-Perot effect. Numerical and theoretical results show good agreement in the equal enhancement of reflectance and transmittance, as well as the non-monotonic dependence of the spasing intensity on the gain coefficient. In addition, directed emission of the spasing beam is verified numerically
The paper contains a theory of laser action in a so called SPASER, a laser with a surface plasmon. The goal of the theory development is an ascertainment of physical nature of SPASER lasers that were successfully put into action by M. A. Noginov et al, announced in the paper entitled Demonstration of a spaser-based nanolaser, and by Xiang Zhang et al, the paper Plasmon lasers at deep subwavelength scale, both papers in Nature Advance online publication, August 2009. Plasmonic modes have huge losses but simultaneously the probabilities of radiative processes in atoms (molecules) with emission of radiation into such modes are increased thousandfold as compared with probabilities to radiate in free space. This makes clear how the losses are compensated by amplification. It is made apparent the kinship of physical nature of the phenomenon with that of of the SERS.
The Spaser uses surface plasma waves, whose wavelength can be much smaller than that of the light it produces. That’s why a Spaser can be less than 100 nanometers, or one-tenth of a micron, long. This is much less than the wavelength of visible light, explains Prof. Bergman.
With the development of surface plasma waves — electromagnetic waves combined with an electron fluid wave in a metal — future nano-devices will operate photonic circuitry on the surface of a metal. But a source of those waves will be needed. That’s where the Spaser comes in.
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