Xingsheng Xu

Femtosecond and continuous-wave laser performance of a diode-pumped Yb3+:CaYAlO4 laser.

The cw and femtosecond laser operations of Yb(3+):CaYAlO(4) (Yb:CYA) are demonstrated. The laser emitted a maximum cw power of 1.94 W with a slope efficiency (η(slope)) of 71% and an optical-to-optical efficiency (η(opt)) of 51%. Under mode-locking operation, the laser emitted near transform-limited pulses with 156 fs pulse width, 8.1 nJ pulse energy and 0.74 W average power. The η(slope) and η(opt) of the mode-locked laser were 37% and 20%, respectively.

Crystal growth, spectroscopic and laser properties of Tm:LuAG crystal

Tm:Lu3Al5O12 (Tm:LuAG) crystal was grown by the Czochralski method. The segregation coefficient was measured by Inductively Coupled Plasma Atomic Emission Spectrometer. The cell parameters were analyzed with X-ray powder diffraction experiments. The absorption and fluorescence spectra of Tm:LuAG crystal at room temperature were investigated. With a 20 W fiber-coupled diode laser as pump source, the continuous-wave (CW) laser action of Tm:LuAG crystal was demonstrated. The maximum output power at 2020 nm was obtained to be 3.04 W, and the slope efficiency was 25.3%.

Crystal growth, optical properties, and laser operation of Yb3+-doped NYW single crystal

Laser crystal Yb3+-doped NaY(WO4)2 (Yb:NYW) with excellent quality has been grown by Czochralski technique. The rocking curves from (400) plane of as-grown Yb:NYW crystal was measured and the full-width value at half-maximum was 19.92″. The effective segregation coefficients were measured by the X-ray fluorescence method. The polarized absorption spectra and the fluorescence spectra of Yb:NYW crystal were measured at room temperature. The fluorescence decay lifetime of Yb3+ ion in NYW crystal has been investigated. The spectroscopic parameters of Yb:NYW crystal are calculated and compared with those of Yb:YAG crystal. A continuous wave output power of 3.06 W at 1031 nm was obtained with a slope efficiency of 42% by use of diode pumping.

Two-photon excited fluorescence from CdSe quantum dots on SiN photonic crystals

Two-photon excited fluorescence from CdSe quantum dots on a two-dimensional SiN photonic crystal surface is investigated by using a femtosecond laser. By using a photonic crystal, a 90-fold enhancement in the two-photon excited fluorescence in the vertical direction is achieved. This is the highest enhancement achieved so far in the two-photon excited fluorescence in the vertical direction. The mechanism of the enhancement for two-photon excited fluorescence from quantum dots on photonic crystals is analyzed.

Diode-pumped femtosecond Yb:CaNb2O6 laser

We report to our knowledge a diode-pumped passively mode-locked Yb:CaNb(2)O(6) (Yb:CN) laser for the first time. Both CW and passive mode-locking operation of the laser are experimentally investigated. A maximum CW output power of 1.4 W with a slope efficiency of 20% is obtained on a 7 mm long 1.5 at.% Yb:CN crystal, while stable passive mode-locking with a commercial semiconductor saturable absorption mirror (SESAM) was achieved on a 3 mm long 3 at.% Yb:CN crystal. The mode-locked pulses have pulse width of 251 fs and an average output power of 44 mW at 1038 nm.

Crystal growth, spectral and laser properties of Yb3+:NaGd(WO4)(2) crystal

Yb3+-doped NaGd(WO4)2 (Yb:NGW) crystal has been successfully grown by Czochralski method. The rocking curves from (400) plane of as-grown Yb:NGW crystal was measured and the full-width values at half-maximum was 21″. The polarized absorption spectra, the fluorescence spectra and the fluorescence decay lifetime of Yb:NGW crystal were measured at room temperature. The spectroscopic parameters of Yb:NGW crystal are calculated and compared, with those of Yb:YAG crystal. A continuous wave output power of 3.01 W at 1048 nm was obtained with a slope efficiency of 71% by use of diode pumping.

Dynamics of spontaneous emission from SiN with two-dimensional photonic crystals

We investigated the dynamics of spontaneous emission from a photonic crystal etched into a SiN slab. After fitting the decay curves of the emission to double exponential functions, we divided the dynamic process of the spontaneous emission into a fast process and a slow process. It was observed that the presence of the photonic crystal increased the proportion of the fast decay component, and consequently, the emission rate and time-integrated emission intensity were also enhanced. These enhancements were a result of the coupling of the guide modes to the leaky modes of the photonic crystal slab waveguide.

Fabrication of two-dimensional Ta2O5 photonic crystal slabs with ultra-low background emission toward highly sensitive fluorescence spectroscopy

A two-dimensional tantalum pentoxide (Ta2O5) photonic crystal (PC) slab with low-background emission was fabricated and a 12-fold enhancement of fluorescence from the organic dyes of perylene diimide adsorbed on the surface of the PCs was observed. The background emissions of the Ta2O5 substrates with and without the PCs after thermal annealing at 600°C with oxygen gas were comparable to that of a well-cleaned cover glass. This is to date the lowest level of background emissions of two-dimensional PCs using materials with a high refractive index (>2). The results reported here provide new insights into the fabrication of the photonic devices that enable highly sensitive fluorescence microscopy or optical detections.

Surface recombination in GaAs thin films with two-dimensional photonic crystals

The dynamics of spontaneous emission from GaAs slabs with photonic crystals etched into them are investigated both theoretically and experimentally. It is found that the intensity of spontaneous emission decreases significantly and that photonic crystals significantly shorten the lifetime of emission. The mechanics of enhancement and the reduction of emission from photonic crystals are analyzed by considering the surface recombination of GaAs. The measured and calculated lifetimes agree at a surface recombination velocity of 1.88×105cm∕s.

Electro-optic modulator based on a photonic crystal slab with electro-optic polymer cladding.

A type of modulator based on a shallow-etched photonic crystal (PC) slab of silicon-on-insulator material with electro-optic (EO) polymer cladding is designed and investigated. The transmission spectra of the PC slab with the EO polymer are calculated using a finite-difference time-domain method. The band structure and the field distribution of the guided mode resonance are calculated and analyzed. The modulation voltage and bandwidth of the hybrid modulator are simulated. It is shown that flexible designs of low-voltage modulation (0.2 V) or high-bandwidth modulation (62 GHz) can be obtained with the hybrid modulator.