Microwave electrometry with Rydberg atoms in a vapor cell using microwave amplitude modulation

We have theoretically and experimentally studied the dispersive signal of the Rydberg atomic electromagneticallyinduced transparency(EIT)Autler–Townes(AT)splitting spectra obtained using amplitude modulation of the microwave(MW)electric field.In addition to the two zero-crossing points interval△f_(zeros),the dispersion signal has two positive maxima with an interval defined as the shoulder interval△f_(sho),which is theoretically expected to be used to measure a much weaker MW electric field.The relationship of the MW field strength E_(MW)and△f_(sho)is experimentally studied at the MW frequencies of 31.6 GHz and 9.2 GHz respectively.The results show that△f_(sho)can be used to characterize the much weaker E_(MW)than that of△f_(zeros)and the traditional EIT–AT splitting interval△f_(m);the minimum E_(MW)measured by△f_(sho)is about 30 times smaller than that by△f_(m).As an example,the minimum E_(MW)at 9.2 GHz that can be characterized by△f_(sho)is 0.056 mV/cm,which is the minimum value characterized by the frequency interval using a vapor cell without adding any auxiliary fields.The proposed method can improve the weak limit and sensitivity of E_(MW)measured by the spectral frequency interval,which is important in the direct measurement of weak E_(MW).

Enhancing redshift phenomenon in time-resolved photoluminescence spectra of AlGaN epilayer

AlGaN epitaxial layer has been studied by means of temperature-dependent time-integrated photoluminescence（PL）and time-resolved photoluminescence（TRPL）. An enhancing redshift phenomenon in TRPL spectra with increasing temperature was observed, and the localized excitons behaved like quasi two-dimensional excitons between 6 K and 90 K. We demonstrated that these behaviors are caused by a change in the carrier dynamics with increasing temperature due to the competition of carriers＇ localization and delocalization in the AlGaN alloy.

Broadband Acoustic Vibration Sensor Based on Cladding-Mode Resonance of Double-Cladding Fiber

We have proposed and demonstrated a double-cladding fiber (DCF) with cladding?mode resonance property for broadband acoustic vibration sensing. Since the fundamental mode in the core waveguide is able to be coupled to LP05 mode in the tube waveguide once the phase-matching condition is fulfilled, the transmission spectrum can exhibit a dip with a large extinction ratio. An acoustic vibration could induce the wavelength shift of such transmission spectrum, so that the intensity variation at a wavelength near the dip is coded with the information of the acoustic vibration signal. By demodulating the response of intensity variation, the frequency of the applied acoustic vibration signal can be recovered. Such a DCF-based sensor with an intensity modulation could measure the acoustic vibration with a broadband frequency range from 1 Hz to 400 kHz and exhibits the maximum signal-to-noise ratio (SNR) of ?80.79 dB when the vibration frequency is 20 kHz. The obtained results show that the proposed DCF-based acoustic vibration sensor has a potential application in environmental assessment, structural damage detection, and health monitoring.