Broadband high-gain Yb: YAG crystal-derived silica fiber for low noise tunable single-frequency fiber laser.

An over 75 nm broadband spectrum with a gain per unit length of >2 dB/cm was obtained from a homemade Yb: YAG crystal-derived silica fiber (YCDSF) with Yb-doping concertation of 6.57 wt.%. Using a 13-cm-long YCDSF, a low-noise wavelength-tunable single-frequency fiber laser has been constructed, enabling a single longitudinal mode oscillation from 1009 to 1070 nm. In particular, in the 1023-1056 nm waveband, the laser operating at any wavelength exhibited a maximum output power over 37 mW with power fluctuations below 0.38%, a slope efficiency >8%, and an optical signal-to-noise ratio higher than 60 dB. A linewidth of less than 2.8 kHz was also observed at the maximum pump powers, and relative intensity noise was as low as -155 dB/Hz at frequencies above 1.0 MHz. These results indicate that the YCDSFs with broadband high-gain characteristics are promising for wavelength-tunable fiber lasers in applications such as optical coherence tomography, precision metrology, nonlinear frequency conversion, and so on.

Near and mid-infrared optical vortex parametric oscillator based on KTA.

We investigated high energy, near and mid-infrared optical vortex lasers formed by a 1 µm optical vortex-pumped KTiOAsO4 (KTA) optical parametric oscillator. The orbital angular momentum (OAM) of the pump beam can be selectively transferred to the signal or idler output by changing the reflectivity of the output coupler. With this system, 1.535 µm vortex signal output with an energy of 2.04 mJ and 3.468 µm vortex idler output with an energy of 1.75 mJ were obtained with a maximum pump energy of 21 mJ, corresponding to slope efficiencies of 14% and 10%, respectively. The spectral bandwidth (full width at half maximum, FWHM) of the signal and idler vortex outputs were measured to be Δλs ~ 1.3 nm (~ 5.5 cm-1) and Δλi ~ 1.7 nm (~ 1.4 cm-1), respectively.

Effect of Li+ doping on the luminescence performance of a novel KAlSiO4:Tb3+ green-emitting phosphor.

A new green-emitting phosphor, KAlSiO4:1.5 mol% Tb3+, x mol% Li+, was prepared via a high-temperature solid-phase method, and its crystal structure, diffuse reflectance spectrum, and luminescence were studied. The results show that the Li+ doping shifts the strongest diffraction peak to a high angle direction, reducing grain size by 11.4%. The entry of Li2CO3 improves the luminescence performance of KAlSiO4:1.5 mol% Tb3+. At a Li+ concentration of 1.5 mol%, the sample has strong absorption in the ultraviolet light range from 250 to 400 nm. The luminous intensity of the sample at 550 nm approximately quadruples after Li+ doping. Additionally, the colour purity of the sample and the internal quantum yield increase to 83.3% and 42%, respectively. The sample changes colour with time when exposed to air without an obvious fading phenomenon. The emission intensity at 200 °C is 95.1% of its value at room temperature, indicating that the phosphor has excellent thermal stability when x = 1.5. These results show the feasibility of using the silicate phosphor for generating the green light component of white light-emitting diodes for solid-state lighting.

Rare earth ion Tb3+ doped natural sodium feldspar (NaAlSi3O8) Luminescent properties and energy transfer.

In this study, Tb3+-doped natural sodium feldspar (NaAlSi3O8) phosphors have been successfully prepared using high-temperature solid-state method with natural sodium feldspar as a substrate. Energy-dispersive X-ray spectrometry analysis (EDX) of NaAlSi3O8 showed that 0.03 wt% of Eu element was present, and elemental distribution mapping analysis showed that the distribution of trace Eu in minerals was aggregated. The crystal structure and luminescence properties of the natural sodium Eu-containing feldspar and synthetic sodium feldspar NaAlSi3O8:Eu3+, Tb3+ phosphors are discussed in detail. The crystal structure analysis of the samples showed that the Na+ in the natural matrix was partly replaced by the doped Tb3+. Studies on the photoluminescence properties of the samples indicate that Eu does not form a luminescent center in the natural mineral, however, the strong characteristic peak of Eu3+ at 615 nm appears after doping with Tb3+ and the peak at 615 nm increases with the increase of Tb3+ concentration. According to the above spectral results, the energy transfer from Tb3+ to Eu3+ is obtained. Through the measurement and analysis of color coordinates, it is found that with the increase of Tb3+ concentration, the luminescence color of the samples can be regulated in the green to red region. NaAlSi3O8:Eu3+ Tb3+ phosphors has potential application value.

Beam propagation of efficient frequency-doubled optical vortices.

Frequency doubling of optical vortices is demonstrated with an optical-optical efficiency exceeding 70%, using a spiral phase plate at a fundamental vortex energy of 10.6 mJ. Beam propagation of the doubled vortex output is also investigated both experimentally and theoretically. Spatial transforms in the output during propagation are observed.

Octave-band tunable optical vortex parametric oscillator.

We developed an octave-band tunable optical vortex laser based on a 532 nm optical vortex pumped optical parametric oscillator with a simple linear-cavity configuration by employing cascaded non-critical phase-matching LiB3O5 crystals. The optical vortex output was tunable from 735 to 1903 nm. For a pump energy of 9 mJ, an optical vortex pulse energy of 0.24-2.36 mJ was obtained, corresponding to an optical-optical efficiency of 0.3-26%.

Widely-tunable vortex output from a singly resonant optical parametric oscillator.

We demonstrated a widely tunable 1-µm optical vortex laser formed from a 0.532-µm optical vortex pumpedoptical parametric oscillator with a singly-resonant cavity configuration employing cascaded non-critical phase-matching LiB3O5 crystals. With this system, the topological charge of the pump beam can be selectively transferred to the signal or idler output, and a vortex output in the wavelength range of 850-990 nmor 1130-1300 nm could be obtained.A maximum signal vortex output energy of 0.9 mJ was achieved, corresponding to an optical efficiency of 10%.

Handedness control in a 2-µm optical vortex parametric oscillator.

We present the first handedness control of an optical vortex output from a vortex-pumped optical parametric oscillator. The handedness of the optical vortex was identical to that of the pump vortex beam. Over 2 mJ, 2-µm optical vortex with a topological charge of ± 1 was achieved. We found that the handedness of a fractional vortex with a half integer topological charge can also be selectively controlled.

Tunable 2-µm optical vortex parametric oscillator.

We generated tunable 2-µm optical vortex pulses with a topological charge of 1 or 2 in the wavelength range 1.953-2.158 µm by realizing anisotropic transfer of the topological charge from the pump beam to the signal output in a vortex-pumped half-symmetric optical parametric oscillator. A maximum vortex output energy of 2.1 mJ was obtained at a pump energy of 22.8 mJ, which corresponds to a slope efficiency of 15%. The topological charges of the signal and idler output were investigated using a shearing interferometric technique employing a low-spatial-frequency transmission grating.

[Luminescence properties of thenardite activated with Cu].

Na2SO4:Cu phosphors were prepared by heating pure natural thenardite with Cu at 1100 degrees C for 20 min in air. Their photoluminescence spectra were investigated at room temperature. The shapes of emission spectra depend on the excitation wavelengths, The emission spectrum under 260 nm excitation consists of a broad band with a peak at 430 nm, which can be attributed to the 3d 94s --> 3d10 transition within Cu+. The emission spectrum under 300 nm excitation consists of two broad bands with peaks at 430 and 550 nm respectively, which can be attributed to the 3d 94s --> 3d10 transition within Cu+ and transition from the conduction band of Na2 SO4 to the level of excited Cu2+ (d9) in the Na2SO4 band gap, respectively. With the increase in Cu contents, concentration quenching did not occur in the luminescence at 430 nm, but occured at 550 nm.

[Luminescence properties of thenardite activated with Tm3+ under vacuum ultraviolet excitation].

The Na2 SO4 : Tm3+ phosphor was synthesized by the high temperature solid state reaction method in air. The crystalline structure was examined by X-ray diffraction (XRD). Narrow bands observed in emission spectra were well identified with the electronic transitions within the 4f12 configurations of Tm3+, and the excitation spectrum is consisted of strong bands assigned to the 4f12 --> 4f11 5d transition at 183 nm, the O(2-)-Tm3+ charge transfer band at 170 nm and weak bands assigned to host absorption (130, 223 and 258 nm). In addition, the authors also found that the content of Tm3+ in the 8-16 mg concentration range caused quenching.