Discovery of Bragg confined hybrid modes with high Q-factor in a hollow dielectric resonator

The authors report on observation of Bragg confined mode in a hollow cylindrical dielectric cavity. A resonance was observed at 13.4 $GHz$ with an unloaded Q-factor of order $2\times10^5$, which is more than a factor of 6 above the dielectric loss limit. Previously such modes have only been realized from pure Transverse Electric modes with no azimuthal variations and only the $E_{\phi}$ component. From rigorous numeric simulations it is shown that the mode is a hybrid mode with non-zero azimuthal variations and with dominant $E_r$ and $E_{\phi}$ electric field components and $H_z$ magnetic field component.Comment: Accepted to be published in Applied Physics Letter

Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relaxation times have been evaluated from comparison with measured data.Comment: 7 pages, 6 figure

Precise phase synchronisationof a cryogenic microwave oscillator

International audienc

Characterization of materials and mode structure of high-Q resonators using Bragg confined modes

International audienc

Discovery of Bragg confined hybrid modes with high Q factor in a hollow dielectric resonator

International audienc

Accurate phase synchronisation of a microwave oscillator

International audienceWe developed an effective technique for phase synchronization of a cryogenic microwave oscillator. The achieved quality of phase synchronization is a few milliradians. It enables accurate measurements of extremely weak phase fluctuations expected from the next generation of frequency stabilized microwave oscillators based on the cryogenically cooled sapphire dielectric resonators

Modification de la permittivité de l'Arséniure de Gallium et du Phosphure de Gallium sous l'effet de la lumière à 50K

National audienc

Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

International audienc