Generation and characterization of self-starting titanium sapphire laser

Abstract

A Kerr lens mode-locking (KLM) technique is well recognized as the modelocking process to generate ultrashort pulses to the few femtosecond regimes. However, KLM is typically not self-starting i.e. the pulse formation does not start on its own and requires additional perturbation. By introducing a semiconductor saturable absorber mirror (SESAM) in the laser system, it is possible to obtain selfstart femtosecond laser system with wide tuning range and which is also independent of the cavity design. In this work, an experimental study is carried out on the selfstarting KLM Ti: sapphire laser. The laser is aligned in asymmetric Z-folded cavity comprising of four mirrors with the SESAM as one of the end mirror of the cavity. The Ti: sapphire crystal is employed as the gain medium and is positioned between the two concave mirrors inside a linear cavity portion. The crystal is optically pumped by a Diode Pump Solid State (DPSS) laser at 532 nm which is focused on the Ti: sapphire laser crystal to produce a fundamental wavelength of 808 nm. The dispersion compensation is achieved by introducing the intracavity pair of prism. The mode-locked pulse trains signal is detected via a fast photodiode coupled to an oscilloscope. The femtosecond pulse is measured using interferometric autocorrelation (IAC) technique via an Autocorrelator device. Pulse duration as short as 55 fs and average output powers up to 138 mW at the pump power of 5.5 W is obtained from the self-starting laser. The signal shows that SESAM can provide close to the theoretical transform-limit even at a higher region of the pumping power compared to a non self-starting laser. The maximum tuning range is observed about 93 nm within the cavity length of 767 nm to 860.28 nm. The laser pulse with maximum power and the shortest pulse duration is observed atwavelength of 813 nm. Dual-wavelength emission is randomly observed as the pump power increases.