Progress in the development of efficient and reliable diode-pumped ytterbium femtosecond laser systems based on Kerr-lens
mode locking effect is reported. Average output power of up to 1 W is demonstrated in a Kerr-lens mode locked
Yb:YVO<sub>4</sub> laser with pulse durations as short as 80 fs at a pulse repetition frequency of 79 MHz. Measurements of the
nonlinear refractive indexes of the Yb<sup>3+</sup>:YVO<sub>4</sub> crystal, n<sub>2</sub>, were performed and were determined to be 39×10<sup>-16 </sup>cm<sup>2</sup>/W
and 49×10<sup>-16 </sup>cm<sup>2</sup>/W for E||c and E⊥c polarizations, respectively. These results were found to be in a good agreement
with those calculated using both the Kramers-Krönig relation and Boling, Glass and Owyoung formula.
Keywords: Mode-locked lasers, diode-pumped lasers
Progress in the development of efficient and reliable diode-pumped femtosecond laser systems based on both Kerr-lens
and saturable-absorber mode locking is reported. Efficient Kerr-lens mode locking in diode pumped ytterbium-doped
lasers, namely Yb:KY(WO<sub>4</sub>)<sub>2</sub> (Yb:KYW) and Yb:YVO<sub>4</sub>, is demonstrated with average output powers in excess of 1W, pulse durations around 100fs and electrical-to-optical efficiencies that exceed 15%. Novel semiconductor saturable
absorbers based on InAs/InGaAs quantum dots are described and their applicability for efficient femtosecond pulse
generation from near-infrared solid-state lasers is discussed. Efficient passive mode locking in the spectral regions
around 1.3&mgr;m and 1.55&mgr;m in Cr:forsterite and the more recently developed Er, Yb:YAl<sub>3</sub>(BO<sub>4</sub>)<sub>3</sub> crystalline lasers has been demonstrated using low-loss InGaNAs saturable absorbers. A few examples of applications for this category of robust and efficient femtosecond lasers have been included. Specifically, the characteristics of a femtosecond visible
light source producing pulses as short as 200fs at 520nm are outlined.
SU8 is a commercial negative photoresist, which is highly transparent in the visible and near-infrared and extremely resistant to many organic solvents. Here we show that sub-micron period diffraction gratings, and 2D photonic crystal structures, can be readily formed holographically over extended areas. By coating the SU8 layer with a suitable gain medium, such structures may be used as feedback and output-coupling gratings for organic waveguide lasers. Thin films of SU8, were initially deposited by spin casting onto glass substrates. These films were then mounted in one arm of a Lloyd's mirror interferometer and exposed with the expanded beam of a HeCd laser, operating at 325 nm. Subsequent baking and developing steps lead to both volume gratings with index contrast of 0.014, and surface gratings with corrugation depths of up to 140 nm. By varying the incidence angle of the HeCd laser beam to the SU8 film we have tuned the microstructure period from 500 nm down to 200 nm. Using multiple exposures, both doubly-periodic diffraction gratings and square-lattice crystal structures have been produced.