Huomu Yang

Simulations of Temperature in Disk-Type Laser With Fluid–Solid Interaction

Temperature field in high average power disk-type laser is investigated with fluid-solid interaction (FSI). The coolant flow, heat diffusion, heat convection, and heat conduction in the pumping and cooling processes are analyzed without the arbitrary values of thermal boundary conditions, including boundary temperature, heat flux, or heat exchange coefficient at the cooling faces, which are in turn the simulation results. The velocity field and temperature field of coolant are explored as well as the temperature field of gain medium. Moreover, the influences of coolant flow velocity, deposited heat power and gain medium thickness on temperature field are discussed. Experimental results reveal that simulation of temperature in gain medium with the FSI can get a more accurate temperature filed.

Generation of wavelength- and OAM-tunable vortex beam at low threshold

Wavelength- and OAM- tunable laser with large tunable range is the key source for the application in large capacity optical communications. In this paper, we demonstrate a wavelength- and OAM-tunable vortex laser in a 1.2 W single mode fiber coupled LD pumped Yb:phosphate laser. A z-type cavity has been used to precisely control the laser mode diameter. A thin film polarizer (TFP) is inserted to finely control the intra-cavity loss and tune the wavelength. Corresponding laser fundamental mode to pump beam ratio has been optimized to decrease the pump threshold for high order HG mode running. A pair of cylindrical lenses has been used to convert the HG mode to vortex output. The vortex beam with OAM-tunable range from 1ħ to 14 ħ with wavelength tuning range of ~36.2 nm for LG0,1 vortex beam, and ~14.5 nm for LG0,14 vortex beam at pump power of only 1.2 W have been realized, which is the largest tuning range of both OAM and wavelength at ~1 W pump power range to the best of our knowledge.

Direct emission of chirality controllable femtosecond LG01 vortex beam

Direct emission of a chirality controllable ultrafast LG01 mode vortex optical beam from a conventional z-type cavity design SESAM (SEmiconductor Saturable Absorber Mirror) mode locked LD pumped Yb:Phosphate laser has been demonstrated. A clean 360 fs vortex beam of ∼45.7 mW output power has been achieved. A radial shear interferometer has been built to determine the phase singularity and the wavefront helicity of the ultrafast output laser. Theoretically, it is found that the LG01 vortex beam is obtained via the combination effect of diagonal HG10 mode generation by off-axis pumping and the controllable Gouy phase difference between HG10 and HG01 modes in the sagittal and tangential planes. The chirality of the LG01 mode can be manipulated by the pump position to the original point of the laser cavity optical axis.Direct emission of a chirality controllable ultrafast LG01 mode vortex optical beam from a conventional z-type cavity design SESAM (SEmiconductor Saturable Absorber Mirror) mode locked LD pumped Yb:Phosphate laser has been demonstrated. A clean 360 fs vortex beam of ∼45.7 mW output power has been achieved. A radial shear interferometer has been built to determine the phase singularity and the wavefront helicity of the ultrafast output laser. Theoretically, it is found that the LG01 vortex beam is obtained via the combination effect of diagonal HG10 mode generation by off-axis pumping and the controllable Gouy phase difference between HG10 and HG01 modes in the sagittal and tangential planes. The chirality of the LG01 mode can be manipulated by the pump position to the original point of the laser cavity optical axis.

Research on multiannular channel liquid cooling method for thin disk laser

Abstract. For the nonuniform distribution of pump and temperature in the large-aperture, high-power, thin-disk laser medium, a cooling method of multiannular channel liquid cooling was proposed and examined both experimentally and theoretically. The temperature distribution in the gain medium becomes uniform utilizing the method of multiannular channel liquid cooling, which is proved by a numerical model using Ansys software. In the modeling, the distribution of temperature in the medium varies with the changes of the flow rate and temperature of the coolant in each annular channel. An excellent uniform temperature distribution could be obtained in the gain medium with arbitrary power and profile of pump light by setting a tailored parameter of the coolant in each annular channel. The highest temperature difference in the gain medium with multiannular channel liquid cooling reduces about 88% compared with evenly cooling. Also, the thermal effect has been suppressed; the experimental result is consistent with numerical modeling. This method could be a new idea for designing the thin-disk laser’s cooling system.

Thermal management of liquid direct cooled split disk laser

The thermal effects of a liquid direct cooled split disk laser are modeled and analytically solved. The analytical solutions with the consideration of longitudinal cooling liquid temperature rise have been given to describe the temperature distribution in the split disk and cooling liquid based on the hydrodynamics and heat transfer. The influence of cooling liquid, liquid flowing velocity, thickness of cooling channel and of disk gain medium can also be got from the analytical solutions.

Multi-annular channel liquid cooled Nd:YAG thin disk laser medium

For the non-uniform distribution of pump and temperature in the large aperture, high-power thin disk laser medium, a novel cooling method of multi-annular channel liquid cooling is proposed and examined both experimentally and theoretically. The temperature distribution in the gain medium is getting into uniform utilizing the method of multi-annular channel liquid cooling, which is proved by a numerical model using ANSYS software. In the modeling, the distribution of temperature in the medium varies with the changes of the flow rate and temperature of the coolant in each annular channel. A wonderful uniform temperature distribution could be obtained in the gain medium with arbitrary power and profile of pump light by setting a tailored parameter of the coolant in each annular channel. The highest temperature difference in the gain medium with multi-annular channel liquid cooling reduces about 88% compared with an evenly cooling. And the thermal effect has been suppressed, the experimental result is consistent well with numerical modeling. This method could be a new idea for designing the thin disk laser’s cooling system.

Thermal Effects in kW Nd:YAG Thin Disk Laser

We report the Thermal lensing characterization of face cooled Nd:YAG disk laser by considering the influence of heat sink, the simulating results are compared with the results without considering the influence of substrate. according to the pump energy distribution, thermal lensing of disk under Gaussian pump, super-Gaussian pump and uniform pump are simulated. Result revealed that depolarization loss due thermal stress is very low compare to rod-shape laser, the loss could be neglected in disk worked in fundamental mode, disk deformation is the mainly component to the thermal lensing.