Lasing Characteristics And Quantum State Manipulation Of Exciton-Polaritons In Wide Band-gap Semiconductors At Room Temperature

Polariton is an element excitation of light-matter strong-coupled interaction regime.In semiconductor strong-coupling microcavity,the reversible energy exchange between exciton state of semiconductor and photon state of cavity mode lets the hybrid exciton-polariton state become the eigenstate of the system.As a bosonic quasiparticle,exciton-polariton features the large interaction strength inherited from excitonic fraction and the low effective mass inherited from photonic fraction,which ensures a much higher transition temperature of Bose-Einstein condensation in excitonpolaritonic system compared to ultracold atom.Such characteristics provide a feasible method for exploring the macroscopic condensates and related physics in solid-state system,such as superfluidity,quantum vortices,soliton states and nonlinear effect of exciton-polariton.In driven-dissipative system,the external radiation of excitonpolariton condensates will create coherent photon signal,namely the exiction-plariton lasing.Exciton-polariton lasing can occur in the absense of electronic inversion population,and exhibits lower lasing threshold compared to general photon lasing,thus substantially reduces the energy consumption of laser device.However,the exciton binding energy in traditional Ga As/Cd Te materials is relatively small,limiting the operation temperature of excition-polariton device to liquid helium temperature,which significantly impedes the practical application of such device.Recently,the wide bandgap semiconductors with large exciton binding energy and oscillator strength are employed as active materials of strong-coupling microcavity system,which succesfully increases the operation temperature of exciton-polariton device to room temperature.Indeed,several problems that are not distinct at low temperatures will emerge at raised temperatures: 1.The enhanced disordered collisions of particles and the decoherent processes result from impurities and defectes severely affect the output performance and lasing coherence of exciton-polariton device;2.The increase in incoherent scattering relaxation channels makes it difficult to manipulate the quantum state of exciton-polariton.Based on the strong-coupled wide-band gap semiconductor microcavity system,this dissertation focuses on the two problems of room temperature exciton-polariton system mentioned above.Firstly,the spin degeneracy of exciton-polariton is lifted in Zn O chiral planar microcavity,which leads to the emergence of relaxation channel from the high-energy anti-spin state to the low-energy spin state.The effective manipulation of spin orientation of exciton-polariton is realized by spontaneous spin polarization of the system.Experiments certify that even if the pump beam is fully left-circularly polarized,the output lasing signal still feature a certain degree of right-circular polarization,which indicates the robust spin selectivity of such system.Secondly,the nonlinear interaction of exciton-polariton is investigated in Zn O one-/two-dimentional microcavities,wherein a pair of signal and idler exciton-polariton is created through parametric scattering process,realizing the quantum manipulation of scattering states.The non-degenerate parametric scattering of exciton-polariton is demostrated in both experiment and theory,and the condensed laing of exciton-polariton in signal state is also obseved.In the last part of our work,the excitation beam is modulated to introduce a horizontal ring-shaped optical potential trap in Zn O and In Ga N planer microcavities.Due to the extra quantum confinement provided by the ring-shaped trap,the continuous dispersion of exciton-polariton will transform into quantized energy levels,the energy spacing of which exhibits reducing tendency with increasing trap size.The transverse distribution of wavefunction in Zn O microcavity is inspected for various trap radii.In In Ga N microcavity,exciton-polariton will condense in the ground state of quantized levels when excitation power is raised beyond threshold.Since the condensed region is spatially separated from the pump region under ring-shaped excitation,the incoherent reservoir-condensate scattering should be substantially suppressed,which results in ultra-narrow polariton lasing with extremely high coherence.Such trapped excitonpolariton-based room temperature laser device is much superior to current room temperature devices in monochromaticity,directionality,quantum coherence and other related performance.