Virtual Journal of Laser

We have reported on the development of the 1.34-μ.m high-power mode-locked Nd:GdVO₄ laser with a semiconductor saturable absorber mirror. Based on optimum resonator design, average output power of 2.2 W was produced, corresponding to a slope efficiency of 17%. The laser operated at five spectral bands around 1.34 μ.m with long-time stability. 3.3 ps of pulse duration was obtained, which is the best performance among 1.3-μ.m mode-locked neodymium-doped lasers.

An electroplated copper substrate was evaluated for heat dissipation in 1.55-μ.m optically pumped vertical extended cavity surface emitting lasers (OP-VECSELs). It is a cost-effective and flexible solution compared with the previously proposed chemical vapor deposition diamond substrate assembled by metallic bonding. Continuous-wave (CW) lasing operation was demonstrated from a device (with copper electroplated substrate) under optical pumping with pump spot diameter of 100 μm and a maximum output power of 260 mW at 0°C; heatsink temperature was achieved. Room-temperature CW operation with an output power of 75 mW and an external quantum efficiency of 35% was achieved in an optimized plane-concave cavity. The thermal resistance and the maximum output power of VECSEL chips assembled with bonded bulk copper and electroplated copper substrates were measured and compared. A value of ~50 K/W was estimated for both devices, and a similar rollover point was observed, which indicates that the electroplated copper solution leads to similar thermal properties as a bonded bulk copper substrate.

Extremely large epitaxial waveguides with thickness t_WG = 8.6 μm enable diode lasers with very narrow vertical divergence angle. We demonstrate that when such designs are processed in ridge waveguide laser format, there is substantial interaction between the vertical and lateral waveguiding mechanisms. For very narrow stripes with width w ≪ t_WG, such interaction leads to lasing operation in the second-order mode in the vertical direction. For the case of an optimal stripe width w~t_WG single fundamental mode operation is achieved, with peak kink-free optical output power of 1.3 W and beam divergence angles (vertical, lateral) of 9° × 6° at full-width at half-maximum and 17° × 13° with 95% power content. The maximum brightness is 90 MW × cm^-2 sr^-1 for 95% power content.

A rate-equation-based model is established to describe the behavior of an intracavity optical parametric oscillator (OPO) pumped in an actively -switched Raman laser system. The intracavity photon densities and the initial population inversion density are assumed to be Gaussian distribution. These coupled rate equations are solved numerically. In the experiment, a laser diode end-pumped acousto-optically -switched KTP-OPO pumped by a Nd:YAG/ Raman laser is demonstrated. The output characteristics are studied carefully. And the experimental results about the average output power agree with the numerical solutions.

An all-optical inverter using polarization switching (PS) of a long-wavelength single-mode vertical-cavity surface-emitting laser (VCSEL) is experimentally demonstrated. PS appears when linearly polarized light is injected orthogonally to the linear polarization of the solitary VCSEL. The dynamic behavior of an all-optical inverter under different pulsed optical inputs is analyzed. Time traces, rise and fall times of the linearly polarized output signals are reported. The dependence of these quantities on the bias current and injected optical power is investigated. This analysis permits us to identify proper operation conditions for the all-optical inversion. The PS-based all-optical inverter is demonstrated with a 2.5-Gb/s non-return-to-zero input signal.

We combine all the known experimental demonstrations and spectroscopic parameters into a numerical model of the Ho³⁺-doped fluoride glass fiber laser system. Core-pumped and cladding-pumped arrangements were simulated for all the population-bottlenecking mitigation schemes that have been tested, and good agreement between the model and the previously reported experimental results was achieved in most but not in all cases. In a similar way to Er³⁺-doped fluoride glass fiber lasers, we found that the best match with measurements required scaled-down rate parameters for the energy transfer processes that operate in moderate to highly concentrated systems. The model isolated the dominant processes affecting the performance of each of the bottlenecking mitigation schemes and pump arrangements. It was established that pump excited-state absorption is the main factor affecting the performance of the core-pumped demonstrations of the laser, while energy transfer between rare earth ions is the main factor controlling the performance in cladding-pumped systems.

The effect of the active region inhomogeneity on the spectral characteristics of InAs/InP quantum-dash (Qdash) lasers is examined theoretically by solving the coupled set of carrier-photon rate equations. The inhomogeneity due to dash size or composition fluctuation is included in the model by considering dispersive energy states and characterized by a Gaussian envelope. In addition, the technique incorporates multilongitudinal photon modes and homogeneous broadening of the optical gain. The results predict a red shift in the central lasing wavelength of Qdash lasers on increasing the inhomogeneous broadening either explicitly or implicitly, which supports various experimental observations. The threshold current density and the lasing bandwidth are also found to increase.

Laser oscillations except for 1560 nm were suppressed and efficient acousto-optic Q-switched pulse lasers at a single wavelength of 1560 nm were realized in Er:Yb:RAl₃(BO₃)₄ (R=Y and Lu) crystals by a special design of the cavity mirror transmissions, when a 970-nm diode laser with a 2% duty cycle was used as the pump source. At an absorbed pump power of 13.5 W and a pulse repetition frequency of 1 kHz, 400-μJ pulse energy with a width of 155 ns and 580-μJ pulse energy with a width of 110 ns were achieved in Er:Yb:YAl₃(BO₃)₄ and Er:Yb:LuAl₃(BO₃)₄ crystals, respectively. Furthermore, intracavity frequency doubling 780-nm Q-switched pulse lasers were realized by using a KTP nonlinear optical crystal. The pulse energy and width were 30 μJ and 80 ns for Er:Yb:YAl₃(BO₃)₄ crystal and 50 μJ and 68 ns for Er:Yb:LuAl₃(BO₃)₄ crystal, respectively.

An electroplated copper substrate was evaluated for heat dissipation in 1.55-
$mu{rm m}$ optically pumped vertical extended cavity surface emitting lasers (OP-VECSELs). It is a cost-effective and flexible solution compared with the previously proposed chemical vapor deposition diamond substrate assembled by metallic bonding. Continuous-wave (CW) lasing operation was demonstrated from a device (with copper electroplated substrate) under optical pumping with pump spot diameter of 100
$mu{rm m}$ and a maximum output power of 260 mW at 0
$^{circ}{rm C}$; heatsink temperature was achieved. Room-temperature CW operation with an output power of 75 mW and an external quantum efficiency of 35% was achieved in an optimized plane-concave cavity. The thermal resistance and the maximum output power of VECSEL chips assembled with bonded bulk copper and electroplated copper substrates were measured and compared.

We have reported on the development of the 1.34-
$mu{rm m}$ high-power mode-locked
${rm Nd}{:}{rm GdVO}_{4}$ laser with a semiconductor saturable absorber mirror. Based on optimum resonator design, average output power of 2.2 W was produced, corresponding to a slope efficiency of 17%. The laser operated at five spectral bands around 1.34
$mu{rm m}$ with long-time stability. 3.3 ps of pulse duration was obtained, which is the best performance among 1.3-
$mu{rm m}$ mode-locked neodymium-doped lasers.