Solid state saturable absorbers for Q-switching at 1 and 1.3μm: investigation and modeling

Yttrium and Lutecium garnets (YAG and LuAG) doped by Chromium or Vanadium ions (Cr 4+ or V 3+ ) were investigated as saturable absorbers potentially useful for passive Q-switching at wavelengths 1 μm and/or 1.3 μm. For comparison also color center saturable absorber LiF:F - 2 and Cobalt doped spinel (Co:MALO) were studied. Firstly, low power absorption spectra were recorded for all samples. Next, absorbers transmission in dependence on incident energy/power density was measured using the z -scan method. Crystals Cr:YAG, Cr:LuAG, V:YAG, and LiF:F - 2 were tested at wavelength 1064 nm. Therefore Alexandrite laser pumped Q-switched Nd:YAG laser was used as a radiation source (pulse length 6.9 ns, energy up to 1.5 mJ). Crystals V:YAG, V:LuAG, and Co:MALO were tested at wavelength 1338 nm. So diode pumped Nd:YAG/V:YAG microchip laser was used as a radiation source (pulse length 6.2 ns, energy up to 0.1 mJ). Using measured data fitting, and by their comparison with numerical model of a "thick" saturable absorber transmission for Q-switched Gaussian laser beam, following parameters were estimated: saturable absorber initial transmission T 0 , saturation energy density w s , ground state absorption cross-section σ GSA , saturated absorber transmission T s , excited state absorption cross-section σ ESA , ratio γ = σ GSA /σ ESA , and absorbing ions density. For V:YAG crystal, a polarization dependence of T s was also investigated. With the help of rate equation numerical solution, an impact of saturable absorber parameters on generated Q-switched pulse properties was studied in plane wave approximation. Selected saturable absorbers were also investigated as a Q-switch and results were compared with the model.