Papers by Author: Guang Hua Cheng

Abstract: We demonstrate a Yb:YAG thin disk laser with multi-pass diode-pumped structure and direct water cooling device. In the pump system, four passes of the pump radiation are focused on the thin disk using a center-punched spherical lens. The thin disk serves as the window of a copper tank and is directly cooled with recycle water-contacted method. The thin disk laser has a low pump at the threshold of operation. We obtained 450 mW output power around 1030 nm in a simple F-P resonant cavity.

Abstract: A femtosecond laser machine consisting of femtosecond fiber laser, trepanning head, linear motor stages system and Siemens 840D system has been integrated for industry application. The femtosecond laser source is all fiber system which contains a fiber mode-lock laser at 1053 nm with a repetition rate of 3.9 MHz, a double-cladding gain fiber amplifiers and a PCF amplifier. An acoustical modulator has employed to tune repetition rate from 3.9 MHz to 100 KHz. An in-line fiber chirped grating is used to stretch the pulse duration to 700 ps. After the PCF amplifier pulse is compressed to sub-ps with 50% efficiency based two grating compressor. The system outputs an average power of 15 W at 100 KHz and 800 fs. Using four wedges trepanning head, cylinder hole is drilled in 1mm thickness SiC ceramics in 30 s.

Abstract: This paper reports a novel micro extrinsic fiber-optic F-P interferometric (MEFPI) sensor micromachined on a conventional optical fiber (Corning SMF-28) by using a near-infrared femtosecond laser, for the first time to the best of our knowledge. The strain and temperature characteristics of such a sensor were investigated and the experimental results show that the strain and temperature sensitivities are 0.006nm/με and -0.0017nm/°C, respectively. This type of MEFPI sensors has a number of advantages when compared with conventional EFPI sensors, such as easy fabrication, high integration degree, good reliability, low temperature cross-sensitivity, low cost, and capability for mass-production, offering great potential for a wide range of sensing applications.

Abstract: The femtosecond laser ablation has been investigated on second generation single crystal superalloy CMSX-4 using a commercial titanium:sapphire laser system (λ = 780nm, τ = 120 fs). The ablation thresholds of bulk alloy CMSX-4 have been determined as a function of the pulse number (1, 10, 100, 1000) in air, argon gas and vacuum. The results indicate that the multiple-pulse threshold of this material decreased with increasing the pulse number in all the cases. For the same pulse number, the threshold changed in the descending order: air, vacuum and argon gas. The incubation coefficient in air has been determined: ξ = 0.86 ± 0.03. The preliminary results showed the better quality of femtosecond laser machining of CMSX-4 in vacuum and argon gas than in air.