Yuen Hong Tsang,
The Hong Kong Polytechnic University, Hong Kong
Dr. Yuen Hong Tsang has completed BSc and PhD study in the School of Physics and Astronomy, The University of Manchester, UK in 2004. He is now Assistant Professor in Applied Physics Department, The Hong Kong Polytechnic University. He has published >100 SCI international journals with H-index >20 and total citation >1400. His current research interests include development of novel 2D materials, e.g. MoS2, WS2, etc. for laser photonics, photo-catalysis, solar energy conversion applications, e.g. photo-catalyst, solar heat absorber, saturable absorber, optical limiter, photodetection, Q-switched and mode locked lasers, etc
To understand and modify the nonlinear optical properties of transition metal dichalcogenides, TMDs, two-dimensional layered materials are very important research topics nowadays as they can serve as building block for developing next generation high performance micro optics and photonic devices. These materials are very compact with atomic thick layer and have natural bandgap so they can provides strong interaction with light and other favorable features e.g. broadband absorption, transparent and high carrier mobility etc. WS2, which is a typical TMDs material, has layer number depending bandgap energy. The WS2 bandgap energy and optical properties can be modified by varying their size, layer number and structures. The WS2 nano materials and film in various size, layer number or film thickness are fabricated by two methods – ultrasound and sputtering. The nonlinear optical properties of different samples are then studied by using z-scan technique. We have successfully demonstrated some viable methods to tune the nonlinear absorption properties of WS2. We also use the fabricated WS2 film within the diode pumped solid state Nd:YVO4 crystal laser to generate pulsed laser output. A stable pulsed laser operation is achieved by using the fabricated WS2 saturable absorber. The average output power obtained is 19.6 mW (135 kHz). These research findings indicate strong nonlinear optical proporties of WS2 and high potential for nonlinear optical devices.