A simple, compact, and efficient diode-side-pumped linear intracavity frequency doubled Nd:YAG rod laser with 50 ns pulse width and 124 W green output power Rev. Sci. Instrum. 81, 073104 (2010); 10.1063/1.3457000Self-mode locking in a diode-pumped self-Q -switched green laser A rate equation model with spatial hole-burning effect is built to calculate the Q-switch Nd:YAlO 3 ͑Nd:YAP͒ simultaneous dual wavelength laser. We find that 1341.4 and 1079.5 nm lasers can be simultaneously generated in a linear cavity by controlling the output coupling rates of the two coherent radiations. In contrast, a Y cavity and devices to control relative Q-switch delay were necessary for the dual wavelength Nd:YAG laser in previous work. Also with this model, some optimum parameters' relationships to pump energy are investigated.

In consideration of the hole-burning effects, based on the single longitudinal mode rate equation, the operating condition of continuous wave simultaneous dual wavelength laser (SDWL) in neodymium host crystals is studied. The relationship between the operating threshold of SDWL and thresholds of the single wavelength laser for both wavelengths is ascertained. The effect of multilongitudinal modes on the operation result has been discussed qualitatively. Taking Nd:YAlO3 crystal as an example, the experimental results agree well with our theoretical analysis.

The competition between amplified spontaneous emission (ASE) and main laser in solid-state laser resonators is investigated both theoretically and experimentally. A coupled model using the spatial volume integral instead of the Monte Carlo type raytrace technique is proposed to depict ASE in the laser resonators. This model is able to evaluate all possible reflections at both the polishing surface and the diffusive side, to calculate ASE for an inhomogeneous gain distribution, and to include the spectral correction. An experiment is carefully designed to verify the theoretical model and to investigate the distinct physical properties caused by the coupling between ASE and the laser oscillations. The experimental data exhibit an excellent agreement with the theoretical predictions. According to that model, we confirm that ASE in thin-disk lasers can be characterized approximately by the product of the threshold gain of the resonator and the diameter of the disks, as laser modes are highly overlapped with the pumping beam. Theoretical evaluation shows that the scattering characteristic of the disk side impacts on ASE significantly. Furthermore, we point out that ASE decreases output laser power by affecting threshold pumping power, while slope efficiency is not changed by ASE. This observation provides us with a simple way to estimate the decrease of the optical efficiency by ASE.

Considering grid requirements of high Reynolds flow, wall-modeled large eddy simulation (WMLES) and detached eddy simulation (DES) have become the main methods to deal with near-wall turbulence. However, the flow separation phenomenon is a challenge. Three typical separated flows, including flow over a cylinder at ReD = 3900 based on the cylinder diameter, flow over a wall-mounted hump at Rec = 9.36e5 based on the hump length, and transonic flow over an axisymmetric bump with shock-induced separation at Rec = 2.763e6 based on the bump length, are used to verify WMLES, shear stress transport k-ω DES (SST-DES), and Spalart–Allmaras DES (SA-DES) methods in OpenFOAM. The three flows are increasingly challenging, namely laminar boundary layer separation, turbulent boundary layer separation, and turbulent boundary layer separation under shock interference. The results show that WMLES, SST-DES, and SA-DES methods in OpenFOAM can easily predict the separation position and wake characteristics in the flow around the cylinder, but they rely on the grid scale and turbulent inflow to accurately simulate the latter two flows. The grid requirements of Larsson et al. (δ/Δx,δ/Δy,δ/Δz≈(12,50,20)) are the basis for simulating turbulent boundary layers upstream of flow separation. A finer mesh (δ/Δx,δ/Δy,δ/Δz≈(40,75,40)) is required to accurately predict the separation and reattachment. The WMLES method is more sensitive to grid scales than the SA-DES method and fails to obtain flow separation under a coarser grid, while SST-DES method can only describe the vortices generated by the separating shear layer, but not within the turbulent boundary layer, and overestimates the separation-reattachment zone based on the grid system in this paper.

We demonstrate a high-efficiency, high-average-power, CW master oscillator power amplifier based on a conduction-cooled, end-pumped Yb:YAG slab architecture at room temperature (RT). Firstly, the CW amplification property is theoretically analyzed based on the kinetics model for Yb:YAG. To realize high-efficiency laser amplification extraction for RT Yb:YAG, not only intense pump but also a high-power seed laser is of great importance. Experimentally, a composite Yb:YAG crystal slab with three doped and two un-doped segments symmetrically is employed as the gain medium, which is end-pumped by two high-power, 940-nm diode lasers. A high-power, narrow-spectral-width, 1030-nm fiber seed laser then double passes the composite slab to realize efficient power amplification. For 0.8-kW seed input, maximum output power of 3.54 kW is obtained at 6.7 kW of pump power, with the optical conversion efficiency of 41% and the highest slope efficiency of 59%. To the best of our knowledge, this is the highest power and efficiency reported for Yb:YAG lasing at RT except thin-disk lasers.

A direct-liquid-cooled side-pumped Nd:YAG multi-disk QCW laser resonator is presented, in which the oscillating laser propagates through multiple thin disks and cooling flow layers in Brewster angle. Twenty Nd:YAG thin disks side-pumped by LD arrays are directly cooled by flowing deuteroxide at the end surfaces. A laser output with the highest pulse energy of 17.04 J is obtained at the pulse width of 250 μs and repetition rate of 25 Hz, corresponding to an optical-optical efficiency of 34.1% and a slope efficiency of 44.5%. The maximum average output power of 7.48 kW is achieved at the repetition rate of 500 Hz. Due to thermal effects, the corresponding optical-optical efficiency decreases to 30%. Under the 12.5 kW pumping condition while not oscillating, the wavefront of a He-Ne probe passing through the gain module is as low as 0.256 μm (RMS) with the defocus and tetrafoil subtracted.

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We investigated the dynamics of coherent backscattering cone and random laser in a disordered gain medium of ZnO powder. Theoretical fit to the coherent backscattering cone yields a transport mean free path l approximately equal to the probe wavelength , indicating that the scattering process is in the strong scattering regime. Supernarrow emissions from the laser are accompanied by enhancement and sharpening of the coherent backscattering cone. This enhanced and sharpened backscattering cone returns to a normal profile within 10-20 ps, indicating an ultrafast gain lifetime in the medium, which is in good agreement with the time-resolved measurement of the random laser emissions.