Ultrashort optical pulse generation from a chromium(4)-doped yttrium aluminium garnet tunable solid-state laser

In this thesis, experimental results of ultrashort pulse generation from Cr4+-doped yttrium aluminium garnet (YAG) laser system are presented. The Cr4+:YAG crystal is a vibronically broadened solid state laser gain medium, which lases at room temperature from 1.34 to 1.58 μm and can be pumped by a Nd:YAG laser at 1.06 μm. Ultrashort pulses from this coherent light source are potentially important in technology applications such as ultrafast fiber-optic communications and time-resolved spectroscopy of narrow-bandgap, semiconductors. It is a practical alternative to more conventional cryogenic colour center lasers at this wavelength such as NaCl:OH– or complex optical parametric oscillators synchronously pumped by a Ti:sapphire laser.; The cw power performance of a Cr4+:YAG laser was characterized and several unique properties were identified. A broad tuning range of 210 nm, i.e., from 1345 to 1557 nm, was demonstrated by means of one set of mirrors with useful cw output power of as high as 730 mW at 1.46 μm (with a Nd:YAG pump power of 6.5 W). The lasing action was found to be strongly influenced by the temperature of the crystal and the combined effects of thermal lensing and saturable absorption of the pump beam. The excited-state absorption (ESA) at the pump and lasing wavelengths were investigated both experimentally and theoretically. ESA at the lasing wavelength occurs for the transition from the state 3B₂(3T₂) to 3E(3T₁(F)), while the pump ESA comes from the transition from 3A₂(3T₂ ) to 3E(3T₁(P)). The emission ESA cross sections for the free-running modes were estimated from the laser efficiency data by taking into account the pump and cavity parameters.; Ultrashort pulse generation with a Cr4+:YAG laser was investigated using passive mode-locking with a semiconductor quantum well saturable absorber. Self-starting of the laser system was demonstrated using a strained GaInAs/InAlAs saturable Bragg reflector (SBR) with a single prism for dispersion compensation instead of the standard prism pair. Near transform-limited 390 fs long pulses were produced from 1420 to 1510 nm with as high as 240 mW of useful output power. In order to understand the mode-locking mechanism, the SBR sample was investigated by high resolution x-ray diffraction and photoluminescence measurements. The fast recovery of the SBR nonlinear response was explained by misfit dislocations which act as non-radiative recombination centers.