Enhanced four-wave mixing in P T-symmetric optomechanical systems.

We investigate the enhanced four-wave mixing (FWM) process in a parity-time (P T)-symmetric optomechanical system, where an active cavity is coupled to a passive cavity supporting a mechanical mode. The passive cavity is optically driven by a strong control field and a weak probe field, and the mechanical mode is excited by a weak coherent driving field. By tuning the coupling strength between the two cavities with balanced gain and loss, we find that the FWM intensity can be significantly enhanced near the exceptional points (EPs) at low control power, which is about 12 orders of magnitude higher than that of the single-cavity case. Due to the interference effect induced by the optical and mechanical driving field, it is shown that the FWM intensity can be further enhanced or suppressed by tuning the amplitude and phase of the mechanical driving field. Moreover, the dependence of the FWM intensity on the frequency and power of the control field is also discussed. Our work provides a route to enhance the four-wave mixing process in a flexible way.

Ce3+/Mn2+-activated Ca7(PO4)2(SiO4)2: efficient luminescent materials for multifunctional applications.

To develop new efficient phosphors for LEDs based on multifunctional applications, a series of Ce3+/Mn2+ activated Ca7(PO4)2(SiO4)2 (CPS) samples were prepared by solid-state reaction method. Upon 365 nm excitation, a broad emission band around 439 nm in the Ce3+-single-doped CPS was observed. The optimal Ce3+ concentration was determined to be 3%, for which the quantum efficiency was obtained to be 90.4%, higher than that of the commercial BAM phosphor. By monitoring 458 nm, an intense and broad excitation band was found from 240 to 400 nm, which can match well with the near-ultraviolet (NUV) LED chip. For Ce3+-Mn2+ codoped CPS, a new red emission band belonging to Mn2+ appeared and an energy transfer from Ce3+ to Mn2+ was confirmed. It was also found that the emission spectra of Ce3+/Mn2+ could well cover the optical absorption bands of plants. The fabrication of the phosphors on NUV LED chip indicates that the present phosphors could be promising in solid lighting and plants growth.

Photoluminescence properties, Judd-Ofelt analysis, and optical temperature sensing of Eu3+-doped Ca3La7(SiO4)5(PO4)O2 luminescent materials.

A series of Eu3+-doped Ca3La7(SiO4)5(PO4)O2 (CLSPO) multifunctional phosphors were synthesized by a high-temperature solid-state reaction method. The crystal structure of the CLSPO host was explored using Rietveld refinement. The photoluminescence properties of CLSPO: Eu3+ phosphors were investigated systematically. Upon 392 nm near-ultraviolet light excitation, the phosphor exhibited strong characteristic emissions of Eu3+ ions with a dominant red emission peak around 613 nm, indicating its potential use in solid-state lighting. Calculations of Ω2 and Ω4 Judde-Ofelt intensity parameters provided insight into the structure-luminescence correlation in the CLSPO: Eu3+ system. By exploring the temperature sensitivity of photoluminescence intensity, the application potential of the sample to optical thermometry was studied.

Fourier transform profilometry based on a projecting-imaging model.

In order to obtain the correct height reconstruction of a measured object, a projection lens and a camera lens must be placed at equal heights above the reference plane in the traditional Fourier transform profilometry (FTP) method. We propose an improved phase-height mapping formula based on an improved description of the reference fringe and the deformed fringe in FTP when the projection lens and the camera lens are not placed at equal height. With our method, it is easier to obtain the full-field fringe by moving either the projector or the imaging device. In some cases, where the required parallel condition cannot be met, the proposed method offers a flexible way to calculate the height distribution.