| Abstract [eng] |
As two-photon microscopy global market gets bigger and bigger, there has been a need for simpler, specialized lasers that generate ultra-short pulses of wavelengths region from 900nm to 920nm. Since most of these commercial systems are expensive and complex (titanium-sapphire oscillator, optical parametric oscillator), the idea arose to try to implement a passive mode synchronization in a Nd : YVO4 laser. Because the crystal has an absorption at a wavelength of 880nm and can generate a wavelength of 914nm, a small amount of heat is released in the crystal due to a small quantum defect, which has a number of advantages such as a small thermo-lens in the crystal. The aim of this work was to investigate the operation of a 880nm wavelength diode-pumped Nd : YVO4 laser in passive mode-locked regime generating 914nm wavelength radiation. In this work, four different laser resonators were constructed. For the first time 914nm laser operation was realised with 880nm diode-pumping. The generation efficiency of 914nm in the Nd : YVO4 crystal was found to be affected by the crystal length and concentration. The cooling temperature of the crystal also influences laser efficiency, because of the 914nm wavelength reabsorption and high thermal filling of the lower laser level, which reduces the efficiency of the laser. The lower the temperature of the crystal, the more efficient the laser. As the diode module was used for pumping, and as the pumping power increased, the central wavelength of the diode changed, which significantly changed the efficiency of the laser. Modelocked regime was realised in four different laser resonators. Stable 72MHz repetition rate pulse train without q-switching was observed. The duration of stable 270mW average power Gaussian pulses was measured 8.1ps. Pulse spectrum width - 1.4nm. The product of Δν ∗ Δτ is 4.1 - generated pulses are not transform-limited. Better optimised SESAM for 914nm is needed to reach shorter pulse durations. |
