Abstract

Efficient and high power mode locking operation of lasers operating around 1.3 m, is interesting for applications in semiconductor industry, telecommunications and medicine. Passive mode-locking of Nd-lasers operating on the ⁴F_3/2 → ⁴I_13/2 transition is problematic for semiconductor saturable absorber mirrors (SESAMs) not only because of difficulties in their fabrication process but also in relation to the achievable parameters and damage resistivity [1]. Moreover each SESAM is designed and fabricated to operate only at specific wavelength. Recently an alternative passive mode-locking technique based on second-order nonlinearity inside the Nd-laser cavity, which utilizes χ⁽²⁾-lens formation in a second-harmonic generation (SHG) crystal, was successfully used for generation of pulses with a duration of few picoseconds at 1.06 m [2] as well as at 1.34 m [3]. Although passive mode-locking operation around 1.3 m is in principle similar to the same regime near 1 m, when Nd-vanadate lasers are pumped by 808 nm laser diodes, the scaling of the output power is quite limited due to the lower emission cross-section and higher thermal load, compared with the case of 1 m emission. These major drawbacks restrict also the achievable laser efficiency. On the other hand, direct in-band pumping around 880 nm enables minimization of the thermal load by reducing the quantum defect by ~14%, while the absorption cross section remains high enough for efficient CW and mode locked operation.

© 2011 Optical Society of America