Development Of Coherent Light Sources Research Articles

Room temperature exciton\u2013polariton Bose\u2013Einstein condensation in organic single-crystal microribbon cavities

Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices.

Enhancing and controlling single-atom high-harmonic generation spectra: a time-dependent density-functional scheme

High harmonic generation (HHG) provides a flexible framework for the development of coherent light sources in the extreme-ultraviolet and soft X-ray regimes. However it suffers from low conversion efficiencies as the control of the HHG spectral and temporal characteristics requires manipulating electron trajectories on attosecond time scale. The phase matching mechanism has been employed to selectively enhance specific quantum paths leading to HHG. A few important fundamental questions remain open, among those how much of the enhancement can be achieved by the single-emitter and what is the role of correlations (or the electronic structure) in the selectivity and control of HHG generation. Here we address those questions by examining computationally the possibility of optimizing the HHG spectrum of isolated hydrogen and helium atoms by shaping the slowly varying envelope of a 800 nm, 200-cycles long laser pulse. The spectra are computed with a fully quantum mechanical description, by explicitly computing the time-dependent dipole moment of the systems using a time-dependent density-functional approach (or the single-electron Schrodinger equation for the case of H), on top of a one-dimensional model. The sought optimization corresponds to the selective enhancement of single harmonics, which we find to be significant. This selectivity is entirely due to the single atom response, and not to any propagation or phase-matching effect. Moreover, we see that the electronic correlation plays a role in the determining the degree of optimization that can be obtained.

A scannable detector of microwave-modulated light

The development of coherent light sources has made possible new optical radar systems in which target information should be determined with a far greater accuracy than would be possible with a conventional microwave radar system. However, the same factors which make the improved resolution possible impose difficult requirements on the optical receiver. Presently available image detectors have very limited frequency response and are not suitable for use in a Doppler or ranging system. This paper describes the design and experimental evaluation of an image detector with an instantaneous bandwidth of 4 Gc/s. This photodetector is capable of providing simultaneous target velocity and target position information when the Doppler shifted frequency is in the range of 0 to 4 Gc/s. The device consists of an image dissector electron gun and a traveling-wave output coupler. The scanning of an optical field of view for microwave-modulated light signals was demonstrated experimentally by a direct modulation-demodulation experiment with a modulation frequency of 10.7 Gc/s.