In the thesis, various laser emissions in Nd-doped crystals and wavelength conversion with nonlinear optics are the main goal. Besides, high-pulse-energy lasers generation is an additional goal. Therefore two pump source, including CW fiber-coupled laser diode and QCW two dimensional laser diode stacks, are used in laser experiments. The main text of this thesis is organized as following.
Laser operation on the transition 4F3/2 →4F9/2 of Nd3+ ions generates wavelengths of 910 to 950 nm and allows for SHG into the blue spectrum region. End pumping is especially good for quasi-three-level operation, because of the high pump intensity in laser crystal. In chapter 2, we realize a quasi-three-level 946 nm Nd:YAG laser and blue light generation at 473 nm by intracavity frequency doubling. For the low gain Nd:YAG laser at 946 nm, we develop a semiconductor quantum-wells saturable absorber with low nonsaturable losses. Furthermore, we make a thorough comparison for the 946-nm passively Q-switched performance between the saturable absorbers of the semiconductor quantum-wells saturable absorber and the Cr4+:YAG crystal. In order to generate a higher-power 946 nm Nd:YAG laser and a blue light at 473 nm, a high-power quasi-continuous-wave (QCW) diode stack is used as a pump source.
SESAM is not only used to be an absorber element for passively Q-switched laser, but also to be a novel intracavity selective absorber (ISA) used for suppressing high-gain lines. In chapter 3, we report an ISA with an AlGaInAs QW–barrier structure grown on a Fe-doped InP transparent substrate. With the novel ISA, an efficient high-power Nd:YAG laser at 1.44 μm is successfully realized.
Nd3+-doped lasers operating at 1.0 μm have been maturely developed for many years and possess superior performances. In chapter 4, eye-safe wavelength is obtained from Nd3+-doped lasers that are wavelength-shifted with an optical parametric oscillator (OPO). Efficient eye-safe lasers with mJ pulse energy are studied for military requirement. We theoretically and experimentally study the output performance of an intracavity OPO in a shared cavity configuration. Besides, we present an analytical design model to investigate the dynamics of simultaneous
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emission of fundamental and signal waves. Furthermore, we design an AlGaInAs QW material with a low nonsaturable loss and large modulation strength to be a saturable absorber used in an intracavity Nd:YVO4/KTP optical parametric oscillator.
In the previous chapter, a plane-parallel configuration generates a high-energy laser but leads to a large beam divergence and poor beam quality. In chapter 5, to improve the beam quality and accomplish efficient energy extraction, we design an unstable convex-concave resonator stabilized by thermal-lensing effect to generate a large fundamental mode volume in a passively Q-switched laser. By using ABCD law and the complex beam parameter q, the laser mode size is analyzed. Based on the unstable cavity, a passively Q-switched Nd:YAG/ Cr4+:YAG laser with a large fundamental mode volume and good beam quality is experimentally confirmed.
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