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Aiming at the miniaturization requirement of shifted excitation Raman spectroscopy test system, a portable grating-coupled external cavity (EC) tunable semiconductor laser in Littrow configuration is designed and fabricated with a commercial 785 nm high-power laser diode as the gain device. By using a new wavelength tuning method, aiming to change the position of gain device relative to the collimating lens in the horizontal direction, a miniaturized device with the size of 140 mm×65 mm×50 mm is designed. Compared to the traditional wavelength tuning method which is to change the light incident angle by rotating the diffraction grating, this new tuning method reduces the translational distance of semiconductor gain device effectively, thus it is conductive to the fast and broad wavelength tuning of portable EC laser. The experimental results show that the EC laser has a wide wavelength tuning range. Under any injection current from 340 to 900 mA, a wavelength tuning range of more than 10 nm can be realized. Especially at 900 mA, good performance including a 11.67 nm-wavelength tuning range from 779.40 to 791.07 nm, a less than 0.2 nm-spectral linewidth, an up to 280 mW-output power, and a more than 25 dB-amplified spontaneous emission suppression ratio is presented, which fully meets the basic testing requirements of shifted excitation Raman spectroscopy. Moreover, 1.35 nm-electric wavelength tuning range is achieved by applying a mini-piezoelectric actuator. This indicates that the home-made 785 nm portable grating-coupled EC tunable semiconductor laser is suitable as the light source of portable shifted excitation Raman spectroscopy testing system to eliminate the fluorescence background of Raman spectrum.

We demonstrate a dual-wavelength continuous-wave (CW) Nd:YVO4 laser working at 1064.3 and 1066.7 nm. At a pump power of 7.25 W, the maximum total output power is 1140 mW and the optical conversion efficiency is 15.7%. The spectral line-widths of the dual-wavelength line are 1.1 nm and 1.2 nm, respectively. This laser system is very simple, compact and efficient.

We obtain a continuous-wave (CW) Nd:YVO4/PPMgLN intracavity singly resonant optical parametric oscillator (ISRO). The threshold value of the CW-ISRO system is only 2.8 W at 808 nm. When the pump power is 5.5 W, an idle laser output power of 410 mW, and a signal laser output power of 345 mW have been achieved. By changing the grating periods of the domain structure on the PPMgLN wafer, we enable a wide-tunable mid-infrared spectrum of 2.95–4.16 μm and near-infrared spectrum of 1.43–1.66 μm.

National High Technology Research and Development Program of China [2006AA03Z409]; National Science Foundation of China [60876007, 10974165]; Xiamen Municipal Science and Technology Bureau [2006AA03Z110]

A metallization scheme of Ni/Ag/Ti/Au has been developed for obtaining high reflective contacts on p-type GaN. In order to find optimal conditions to get a high reflectivity, we studied samples with various Ni thicknesses, annealing temperatures and annealing times. By annealing at 500 degrees C for 5 min in an O-2 ambient, a reflectivity as high as 94% was obtained from Ni/Ag/Ti/Au (1/120/120/50 nm). The effects of Ti layers on the suppression of Ag agglomeration were investigated by using Auger electron spectroscopy (AES). From AES depth profiles, it is clear that Ti acts as a diffusion barrier to prevent Au atoms from diffusing into the Ag layer, which is important in the formation of high reflectivity.

Optically pumped GaN-based vertical cavity surface-emitting laser (VCSEL) with two Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs) was fabricated via a simplified procedure: direct deposition of the top DBR onto the GaN surface exposed after substrate removal and no use of etching and polishing processes. Blue-violet lasing action was observed at a wavelength of 397.3 nm under optical pumping at room temperature with a threshold pumping energy density of about 71.5 mJ/cm2. The laser action was further confirmed by a narrow emission linewidth of 0.13 nm and a degree of polarization of about 65%. The result suggests that practical blue-violet GaN-based VCSEL can be realized by optimizing the laser lift-off technique for substrate removal.

project of High Technology Research and Development of China [2006AA03Z409]; National Natural Science Foundation of China [10974165, 91023048]

InGaN based light emitting devices (LEDs) with asymmetric coupled quantum wells (AS-QWs) and conventional symmetric coupled quantum wells (CS-QWs) active structures were grown by metal-organic chemical vapor deposition technique. The LEDs with AS-QWs active region show improved light emission intensity and reduced forward voltage compared with LEDs with CS-QWs active region. Based on the electroluminescence measurements and the devices structure analysis, it can be concluded that these improvements are mainly attributed to the efficient hole tunneling through barriers and consequently the uniform distribution of carriers in the AS-QWs. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3254232]

We have fabricated and characterized GaN-based vertical cavity surface emitting lasers (VCSELs) with a unique active region structure, in which three sets of InGaN asymmetric coupled quantum wells are placed in a half-wavelength (0.5 lambda) length. Lasing action was achieved under optical pumping at room temperature with a threshold pumping energy density of about 6.5 mJ/cm(2). The laser emitted a blue light at 449.5 nm with a narrow linewidth below 0.1 nm and had a high spontaneous emission factor of about 3.0x10(-2). The results indicate that this active region structure is useful in reducing the process difficulties and improving the threshold characteristics of GaN-based VCSELs.

Blue-green GaN-based vertical cavity surface emitting lasers (VCSELs) were fabricated with two dielectric Ta 2 O 5 / SiO 2 distributed Bragg reflectors. Lasing action was observed at a wavelength of 498.8 nm at room temperature under optical pumping. Threshold energy density and emission linewidth were 189 mJ/cm 2 and 0.15 nm, respectively. The result demonstrates that blue-green VCSELs can be realised using III-nitride semiconductors.