Femtosecond laser induced low propagation loss waveguides in a lead-germanate glass for efficient lasing in near to mid-IR

To support the growing landscape of near to mid-IR laser applications we demonstrate a range of low propagation loss femtosecond laser (FSL) written waveguides (WGs) that have achieved guided-mode laser operation in a rare earth (RE) doped lead-germanate glass. The WGs are fabricated in both the athermal and thermal FSL writing regimes using three different pulse repetition frequencies (PRF): 100 kHz (athermal); 1 MHz; and 5 MHz (thermal). The lasing capability of Yb3+ doped lead-germanate waveguides is verified in the near-IR. The refractive index contrast (∆n) for 100 kHz WGs is ~ 1 × 10–4, while for 5 MHz, ∆n increases to ~ 5 × 10–4. The WGs in the thermal regime are less effected by self-focusing and are larger in dimensions with reduced propagation losses. For the 1 MHz repetition rate thermal writing regime we report a low propagation loss WG (0.2 dB/cm) and demonstrate laser operation with slope efficiencies of up to ~ 28%.

Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser

The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75–300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.

Electrical control of single-photon emission in highly charged individual colloidal quantum dots

Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons with only one or two extra charges have been observed and exploited for very efficient lasing or single–quantum dot light-emitting diodes. Here, by room-temperature time-resolved experiments on individual giant-shell CdSe/CdS quantum dots, we show the electrochemical formation of highly charged excitons containing more than 12 electrons and 1 hole. We report the control over intensity blinking, along with a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase in the decay rate, accompanied by 12-fold decrease in the emission intensity, while preserving single-photon emission characteristics. These results pave the way for deterministic control over the charge state, and room-temperature decay rate engineering for colloidal quantum dot–based classical and quantum communication technologies.

Broadening the Photoluminescence Excitation Spectral Bandwidth of YVO4:Eu3+ Nanoparticles via a Novel Core-Shell and Hybridization Approach

For many optoelectronic applications, it is desirable for the lanthanide-doped phosphors to have broad excitation spectrum. The excitation mechanism of the lanthanide-doped YVO4, a high quantum efficient lasing material, primarily originates from the energy transfer process from the host VO43− complexes to the lanthanide ions, which has an excitation spectral bandwidth range of 230–330 nm. For applications in silicon solar cells, such phosphors can convert ultraviolet light to visible light for more efficient power generation, but this spectral range is still not broad enough to cover the entire ultraviolet spectrum of solar light. In this work, a novel core-shell and inorganic–organic hybridization strategy has been employed to fabricate Eu3+-doped YVO4 nanoparticles to broaden their photoluminescence excitation spectral bandwidth to the range of 230–415 nm, covering the entire ultraviolet spectrum of solar light and enabling their potential applications in silicon solar cells.