Kerr-odaklamalı kip-kilitli Cr:LiSAF lazerinden kazanç-anahtarlamalı çıkış aynası yardımıyla 15 femtosaniye altı darbe üretimi

Generation of ultrashort laser pulses with long?term stability and robustness is very important for many applications such as material processing, biomedical imaging, and spectroscopy. Kerr?lens mode?locking (KLM) is one of the well?known techniques used to generate ultrashort pulses. One drawback of the KLM method is that the modulation depth resulting from the Kerr nonlinearities is typically weak especially in lasers with low nonlinear refractive index. This makes it very difficult to apply the KLM technique to colquiriite type gain media such as Cr:LiCAF and Cr:LiSAF which have low nonlinear refractive indices. Recently, a novel approach has been proposed to overcome this drawback by using what can be referred to as gain?matched output couplers (GMOC). The spectral transmission characteristics of a GMOC are designed in such a way as to provide a higher effective gain for a broadband pulse as opposed to a continuous wave beam, which favors the mode?locked operation of a laser oscillator with much higher temporal stability. In this thesis work, this approach which utilizes the GMOC technology has been applied to a low?cost, directly diode pumped Cr:LiSAF laser around 850 nm. In the experiments, we used a low?cost red diode around 660 nm which could pump the Cr:LiSAF laser without any cooling requirement. An astigmatically compensated x?fold cavity was constructed to house a 6 mm long, 1.5 % Cr doped LiSAF crystal. The GMOC mirror used in the experiments had a transmission of 0.7 % near the center wavelength of the emission band. To obtain the shortest pulses, dispersion compensation was used with chirped mirrors and fused silica prism pairs. In this case, the net cavity dispersion was around ~?50fs2. When KLM operation was initiated with the GMOC mirror, this configuration resulted in the generation of nearly transform?limited pulses as short as 13 fs, with 25 mW of average output power, at a repetition rate of 126 MHz near 855 nm. Other cases with different levels of cavity dispersion and the tunability of the femtosecond laser were also investigated. The experimental results clearly demonstrated that the use of a GMOC mirror enables a very robust and stable operation of a Cr:LiSAF laser despite the fact that the nonlinear refractive index of the medium is low.