Study On High-order Transverse Modes' Generation And Evolution In LD Pumped Nd:YVO₄ Lasers

Transverse multimodes(high-order transverse modes or combination of severalhigh-order transverse modes) frequently appear in laser output, with two primaryformations, Hermit-Gaussian (HG) and Laguerre-Gaussian (LG).The generation oftransverse multimodes, especially high-order Laguerre-Gaussian has important physicsand technological applications. Recently, their value in chaos study, laser cooling,optical trapping, and fluid physics is appreciated. So, either ways to restrain or togenerate transverse multimodes are valuable to investigate. Ample transversemultimodes were obtained and the their dynamic evolution was recorded in a shortcavity LD pumped all-solid-state Nd:YVO₄ laser in this thesis. We found that thenumber of the petals in the periphery part of the pattern increased by 4 every time. Ahexagonal pattern and rotating pattern were observed experimentally. The thesis alsointroduced the theoretical study and experimental progress in chaos and complicatedpattern formation in LD pumped all-solid-state Nd:YVO₄ lasers which are connectedwith the transverse multimodes' generation and evolution.The main contents of thethesis are as follows:1: introduced the Maxwell Equations describing a light wave's propagating and theHelmholtz equation which depicts the electric filed of a light wave. Illustrated typicaldegenerate laser output modes.Described the cooperative frequency locking law,cooperative frequency shift law which the amplitudes and frequencies of each modemust satisfies when a laser operates with multimodes. The physics and technologicalvalue of high-order transverse modes were also pointed out.2: Compared the Maxwell-Bloch equation and the Lorentz model. Recentexperimental Observation of periodic oscillation, frequency locking, chaotic output,vortex lattices, and the coexisting state of vortex lattices and Laguerre-Gaussian werealso described.3: Studied the output characteristics of a LD pumped all-solid-state Nd:YVO₄ laser,attained CW output of 1064nm with threshold pump power being 0.5W and slopeefficiency being 50%;Using Cr4+:YAG as saturable absorber, gained 1064 quasi-CWoutput;Utilizing KTP as birefringent phase match crystal, 532nm quasi-CW output wasobtained. Studied the output characteristics of a LD end pumped short cavity(cavitylength being 18 or 30mm) Nd:YVO4 laser, compared the output of 1064nm and532nm in different cavity lengths. With cavity length being 30 mm, Cr4+:YAG asQ-switcher, ample transverse multimodes were observed and their dynamic evolutionwas recorded when pump power was increased gradually.Notably, the number of thepetals in the periphery part of the pattern was found to increase by 4 every time.Ahexagonal pattern and a rotating pattern were observed.Using the method ofLaguerre-Gaussian modes'superposition, we simulated the observed pattern with thesofeware Mathematica, and the result was satisfying.The correspondingqualitativeexplanation was put forward.