Growth and spectral properties of Yb : FAP single crystal

In this paper, single crystal of ytterbium (Yb) doped Ca-5(PO4)(3)F (FAP) has been grown along the c-axis by using the Czochralski method. The segregation coefficients of Yb3+ in the Yb:FAP crystal has been determined by ICP-AES method. The absorption spectrum, fluorescence spectrum and fluorescence lifetime of the Yb:FAP crystal has been also measured at room temperature. In the absorption spectra, there are two absorption bands at 904 and 982 nm, respectively, which are suitable for InGaAs diode laser pumping. The absorption cross-section (sigma(abs)) is 5.117 x 10(-20) cm(2) with an FWHM of 4 nm at 982 nm. The emission cross-section is (sigma(em)) 3.678 x 10(-20) cm(2) at 1042 nm. Favorable values of the absorption cross-section at about 982 nm are promising candidates for laser diode (LD) pumping. (c) 2005 Elsevier B.V. All rights reserved.

Room-temperature cw and pulsed operation of a diode-end-pumped Tm:YAP laser

We report the continuous-wave and acousto-optical Q-switched operation of a diode-end-pumped Tm:YAP laser. Continuous-wave output power of 3.5 W at 1.99 mu m was obtained under the absorbed pump power of 14 W. Under Q-switched laser operation, the average output power increased from 1.57 W to 2.0 W, with an absorbed pump power of 12.6 W, as the repetition rate increased from 1 kHz to 10 kHz. The maximum Q-switched pulse energy was 1.57 mJ with a repetition rate of 1 kHz. The minimum pulse width was measured to be about 80 ns, corresponding to a peak power of 19.6 kW.

Bulk crystal growth and efficient diode-pumped laser performance of Yb 3+:Sc2SiO5

A bulk crystal of Yb:Sc2SiO5 (Yb:SSO) with favorable thermal properties was successfully obtained by the Czochralski method. The energy level diagrams for Yb:SSO crystal were determined by optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. The full width at half maximum of the absorption band centering at 976 nm was calculated to be 24 nm with a peak absorption cross-section of 9.2x10(-21) cm(2). The largest ground-state splitting of Yb3+ ions is up to 1027 cm(-1) in a SSO crystal host. Efficient diode-pumped laser performance of Yb:SSO was primarily demonstrated with a slope efficiency of 45% and output power of 3.55 W.

Continuous-wave and passively mode-locked Yb : GYSO lasers pumped by diode lasers

We report both continuous-wave and passively mode-locked laser actions in a Yb3+-doped gadolinium yttrium oxyorthosilicate Yb:GdySiO(5) (Yb:GYSO) crystal. Continuous-wave (CW) laser operations were compared under different pump conditions with high-power diodes of different wavelengths and fiber cores. CW mode-locking was obtained with a semiconductor saturable absorber mirror.

Diode-pumped Q-switched Tm:YAP laser with a pump recycling scheme

We reported on a diode end-pumped AO Q-switched Tm:YAP laser at 1937 nm. The average output power was 3.9 W, with a slope efficiency of 29.4% and optical-optical conversion efficiency of 21.6% at a 5-kHz repetition rate. The temperature dependency of the output power and the pulse width at different repetition rates were investigated in details.

Diode-pumped continuous wave and Q-switched operation of a c-cut Tm,Ho:YAlO3 laser

We report on a diode-pumped, cryogenic and room temperature operation of a Tm,Ho:YAlO3 (c-cut) laser. In a temperature of 77 K, an optical-optical conversion efficiency of 27% and a slope efficiency of 29% were achieved with the maximum continuous-wave (CW) output power of 5.0 W at 2.13 mu m. Acousto-optic switched operation was performed at pulse repetition frequency (PRF) from 1 kHz to 10 kHz, the highest pulse energy of 3.3 mJ in a pulse duration of 40 ns was obtained. In room temperature (RT), the maximum CW power of Tm,Ho:YAlO3 laser was 160 mW with a slope efficiency of 11% corresponding to the absorbed pump power. (C) 2008 Optical Society of America.

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5 nm/5 nm) film deposition. The surface morphology of wafers and the current-voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes

Single-photon-emitting diode at liquid nitrogen temperature

We report on the study of a single-photon-emitting diode at 77 K. The device is composed of InAs/GaAs quantum dots embedded in the i-region of a p-i-n diode structure. The high signal to noise ratio of the electroluminescence, as well as the small second order correlation function at zero-delay g((2))(0), implies that the device has a low multiphoton emission probability. By comparing the device performances under different excitation conditions, we have, in detail, discussed the basic parameters, such as signal to noise ratio and g((2))(0), and provided some useful information for the future application. (c) 2008 American Institute of Physics.

Effect of CO on characteristics of AlGaN/GaN Schottky diode

Pt Schottky diode gas sensors for CO are fabricated using AlGaN/ GaN high electron mobility transistor ( HEMTs) structure. The diodes show a remarkable sensor signal (3 mA, in N-2; 2mA in air ambient) biased 2V after 1% CO is introduced at 50 degrees C. The Schottky barrier heights decrease for 36meV and 27meV in the two cases respectively. The devices exhibit a slow recovery characteristic in air ambient but almost none in the background of pure N2, which reveals that oxygen molecules could accelerate the desorption of CO and offer restrictions to CO detection.

The performance enhancement in organic light-emitting diode using a semicrystalline composite for hole injection

A semicrystalline composite, 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) doped N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), has been fabricated and characterized. An organic light-emitting diode using such a composite in hole injection exhibits the improved performance as compared with the reference device using neat NPB in hole injection. For example, at a luminance of 2000 cd/m(2), the former device gives a current efficiency of 2.0cd/A, higher than 1.6cd/A obtained from the latter device. Furthermore, the semicrystalline composite has been shown thermally to be more stable than the neat NPB thin film, which is useful for making organic light emitting diodes with a prolonged lifetime.

Experimental study on a diode-pumped passively mode-locking Nd : GdVO4/SESAM laser

We demonstrate a low-threshold and efficient diode-pumped passively continuous wave (CW) mode-locked Nd:GdVO4 laser with a reflective semiconductor saturable absorber mirror (SESAM). The threshold for the continuous wave was 0.36 W, and it is the lowest threshold for a continuous wave in a passively mode-locked Nd:GdVO4 laser to our knowledge. The maximum average output power of 1.82 W was obtained at a pump power of 6.65 W with a slope efficiency of about 29%. The CW mode-locked pulse duration was measured to be about 10.5 ps with a 116-MHz repetition rate.

Diode-pumped passively mode-locked YVO4/Nd : YVO4 composite crystal laser with LT-In0.25Ga0.75As saturable absorber

A passively mode-locked all-solid-state YVO4/Nd:YVO4 composite crystal laser was realized with a low temperature (LT) In0.25Ga0.75As semiconductor saturable absorber mirror. The saturable absorber was used as nonlinear absorber and output coupler simultaneously. Both the Q-switch and continous-wave mode locking operation were experimentally realized. At a pump power of 4 W, the Q-switched mode locking changed to continuous wave mode locking. An average output power of 4.1 W with 5 ps pulse width was achieved at the pump power of 12 W, corresponding to an optical-optical conversion efficiency of 34.2%.

Continuous-wave operation of GaN based multi-quantum-well laser diode at room temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

High performance 1689-nm quantum well diode lasers

1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers. Stripe width and cavity length of the laser were 1.8 and 300 pm, respectively. After being cavity coated. and transistor outline (TO) packaged, the lasers showed high performance in practice. The threshold current was about 13 +/- 4 mA, the operation current and the lasing spectrum were about 58 6 mA and 1689 +/- 6 nm at 6-mW output power, respectively. Moreover, the maximum output power of the lasers was above 20 mW.