249,337 research outputs found
Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method
Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium
Phosphide samples have been examined both in darkness and under white light at
50 K. In both samples we observed change in permittivity under light and dark
conditions. This results from a change in the polarization state of the
semiconductor, which is consistent with a free electron-hole
creation/recombination process. The permittivity of the semiconductor is
modified by free photocarriers in the surface layers of the sample which is the
region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure
Continuous-wave Cascaded-Harmonic Generation and Multi-Photon Raman Lasing in Lithium Niobate Whispering-Gallery Resonators
We report experimental demonstration of continuous-wave cascaded-harmonic
generation and Raman lasing in a millimeter-scale lithium niobate
whispering-gallery resonator pumped at a telecommunication-compatible infrared
wavelength. Intensity enhancement through multiple recirculations in the
whispering-gallery resonator and quasi phase-matching through a nonuniform
crystal poling enable simultaneous cascaded-harmonic generation up to the
fourth-harmonic accompanied by stimulated Raman, two-photon, three-photon, and
four-photon Raman scattering corresponding the molecular vibrational
wavenumbers 632 cm-1 and 255 cm-1 in z-cut lithium niobate at pump power levels
as low as 200mW. We demonstrate simultaneous cascaded-harmonic generation and
Raman lasing by observing the spectrum of the scattered light from the
resonator and by capturing the image of the decoupled light from the resonator
on a color CCD camera
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
Controlled tuning of whispering gallery modes of GaN/InGaN microdisk cavities
Controlled tuning of the whispering gallery modes of GaN/InGaN {\mu}-disk
cavities is demonstrated. The whispering gallery mode (WGM) tuning is achieved
at room temperature by immersing the {\mu}-disks in water and irradiating with
ultraviolet (UV) laser. The tuning rate can be controlled by varying the laser
excitation power, with a nanometer precision accessible at low excitation power
(~ several {\mu}W). The selective oxidation mechanism is proposed to explain
the results and supported by theoretical analysis. The tuning of WGMs in
GaN/InGaN {\mu}-disk cavities may have important implication in cavity quantum
electrodynamics and the development of efficient light emitting devices
Naturally-phasematched second harmonic generation in a whispering gallery mode resonator
We demonstrate for the first time natural phase matching for optical
frequency doubling in a high-Q whispering gallery mode resonator made of
Lithium Niobate. A conversion efficiency of 9% is achieved at 30 micro Watt
in-coupled continuous wave pump power. The observed saturation pump power of
3.2 mW is almost two orders of magnitude lower than the state-of-the-art. This
suggests an application of our frequency doubler as a source of non-classical
light requiring only a low-power pump, which easily can be quantum noise
limited. Our theoretical analysis of the three-wave mixing in a whispering
gallery mode resonator provides the relative conversion efficiencies for
frequency doubling in various modes
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