Staffan Tjörnhammar

Thermal limitations of volume Bragg gratings used in lasers for spectral control

We investigated the effect of absorption in volume Bragg gratings (VBGs) and the associated temperature effects that appear when they are used as mirrors in diode pumped solid-state lasers. The primary result is an uneven longitudinal temperature distribution that causes a reduction in the reflectivity and the spectral selectivity.

Infrared absorption in KTP isomorphs induced with blue picosecond pulses

Picosecond blue-light induced infrared absorption (BLIIRA) was investigated in periodically poled KTiOPO4, Rb:KTiOPO4, RbTiOPO4, KTiOAsO4 and RbTiOAsO4. The dependence of BLIIRA on blue light average power and intensity as well as on crystal temperature was studied. The results show the presence of at least two different types of color centers. A higher level of remnant absorption was observed in the phosphates compared to the arsenates. We attribute the largest portion of the induced absorption to photo-generated electrons and holes self-trapped in the proximity to Ti4+ and O2- ions, respectively, forming polaron color centers. Stabilization of these centers is aided by the presence of mobile alkali metal vacancies in the crystal. The lower level of remnant absorption in arsenates is related to higher population of thermal phonons related to TiO6 group vibrations in arsenates.

Numerical modeling and determination of limiting powers for volume Bragg gratings used in lasers for spectral control

In this paper we present a model to investigate the thermal limitations of volume Bragg gratings (VBGs) used in lasers for spectral control. Also presented are the limiting optical powers, to which intracavity VBGs of different length could be subjected, before the laser operation rapidly deteriorates. The results revealed that the power limit of a VBG-locked laser is highly dependent on the length of the employed VBG. Furthermore, the power limit expressed in incident power related linearly to the radius of the laser beam irradiating the VBG.