Magnetron sputtered Al-doped ZnO thin film as saturable absorber for passively Q-switched Er/Yb double clad fiber laser

Abstract

Abstract The passive Q-switched operation of a ring cavity Er/Yb-doped double clad fiber laser by using an Al-doped ZnO (AZO) thin film as saturable absorber is experimentally demonstrated. In order to improve the absorbance in the C-band wavelength region, a thin film of AZO containing Zn and Al metal precursors in a proportion of 98:2 wt% was developed by an radio-frequency (RF) magnetron sputtering process. Then the AZO film was used as a saturable absorber (SA) in a ring cavity Er/Yb double clad fiber laser. The AZO-SA exhibits a modulation depth of 11.3% and a saturation intensity of 0.057 MW cm −2 in the 1.55 µ m waveband. In a pump power range from 0.475 to 1.356 W, stable Q-switched pulse trains with repetition rates of 70.1–161.3 kHz were observed. With a maximum pump power of 1.356 W, a minimum pulse width of 1.12 µ s and a maximum pulse energy of 1.32 µ J are obtained. To the best of our knowledge, we present the first demonstration of a passive Q-switching laser operation using an RF sputtered AZO thin film as a saturable absorber. The reliability of the RF magnetron sputtered AZO thin films used as an SA for 1.55 µ m Q-switched laser applications is experimentally demonstrated.