The Research On Characteristics Of Crystal And Performance Of Diode-pumped Nd: YLF Lasers

In the last few years, major advances in solid-state lasers have become possible due to the fast progress in the field of high-power diode lasers. This thesis is about the basic research and experiments on Nd:YLF crystal and laser performance of diode-pumped Nd:YLF. This thesis is organized as follows:The Nd:YLF spectrum of absorption, stimulated emission spectrum and Raman spectrum are measured. We analyzed the characters of spectrum and computed the parameters using J-O theory. According to couple equation and threshold condition, we obtained the equation to calculate the crystal loss coefficient. The experiment was established based on the equation, and the Nd:YLF loss was measured. The coefficient is measured to be 0.019%cm-1. The result was equal to Findlay-Clay. The power scaling end-pumped Nd:YLF laser is hindered by the crystal's inherent rather low stress fracture limitation 26⁵2GPa, which is ⁵ times lower than that of Nd:YAG. In this thesis, we applied the plane stress approximation, Gaussian pump profile and TEMoo oscillation to obtain the formula of thermal stress and fracture-limitation pump power. The characteristics of stress and output as the function of concentration and pump beam spot size are analyzed. For Nd:YLF, the maximum end-pumped power is 19W and the maximum output on 1053nm is 5W.For the upper-level lifetime of Nd:YLF is 500μs, we took active Q-switched and passive Q-switched experiments to analyse the crystal characteristics. The pulse energy was 2 times higher in A-O Q-switched operation and 5 times higher in Cr⁴⁺:YAG passive Q-switched operation than that of Nd:YVO4. The output power was 320mW of 527nm laser, and 430mW of 524nm. The pulse width of Cr⁴⁺:YAG passively Q-switched laser was 19ns, and the pulse energy was 210μJ. We designed a V-shaped cavity to match the mode size in Nd:YLF and focus the beam on GaAs absorber. Q-switched mode-locking pulses with 100% modulation depth were obtained. The high mode-locked pulses were suppressed under the Q-switched envelope. The pulse width near the maximum Q-switched envelope is 21ps, and the pulse energy was 1.6μJ. The slop-efficiency was 20% and the Q-switched mode-locking laser is of interest in practice.Stable CW mode-locking operation was achieved on benefits of the crystal`s wide gain band and an output-coupling LT- In0.25Ga0.75As absorber. Stable pulse duration of 3-ps was achieved at the repetition rate of 98MHz. The average output power was 530mW at 1053nm under the incident pump power of 10W, corresponding to the peak power of 1.8kW and pulse energy of 5.4nJ.We designed an intracavity OPO laser to obtain the eye-safe wavelength 1.5μm. At the incident pump power of 8W and repetition rate of 20kHz, the minimum signal pulse width of 4ns was obtained with the average output of 368mW. Average output power and slop efficiency on function of repetition rate was also investigated.