Periodic adjustment of the position of a laser beam spot on a semiconductor saturable absorber mirror in a passively mode-locked solid-state laser

A laser diode end-pumped passively mode-locked Nd：YVO4 solid-state laser with a semiconductor saturable ab- sorber mirror （SESAM）, in which the intracavity laser beam spot on the SESAM can be adjusted periodically, is investigated. Inserting a rectangular prism （RP） into the laser cavity is a promising approach towards the goal of periodically moving the position of the focus spot of the intracavity pulse on the SESAM surface to avoid the long-time irradiation of the laser beam on the same position, thereby solving a series of problems caused by damage to the SESAM and greatly prolonging its usage life. The adjustment of the rectangular prism in the laser cavity does not break the stable continuous wave （CW） mode-locked condition. The laser generates a stable picosecond pulse sequence at 1064 nm with an output power of 3.6 W and a pulse width of 14 ps. The instabilities of the output power and the pulse width are 1.77% and 4.5%, respectively.